Question about CM 7777

What is the difference between a CM 7777 and a CM 7778?

7777 is hard to find, but I've read many reviews here and elsewhere that say it is one of the best pre-amps available.

The CM7778 is a CM spartan series (a step down) amp in a Titan series box. The CM7778 has less gain and slightly higher noise figure than the cm7777. The cm 7777 is typically suggested for use about 30+ miles from towers.

Summit source currently has the Cm7777 in stock as does crutchfield and others.

http://www.summitsource.com/product_info.php?ref=1&products_id=6736

http://www.crutchfield.com/p_6597777/Channel-Master-7777.html?tp=6341

http://www.google.com/products?q=CM+7777&oe=UTF-8&scoring=r&sa=N&start=0

cm 7777
Number of Inputs: 1/2 (VHF & UHF)
Input and Output Impedance: 75 Ohms
Input and Output Connectors: F Type Connectors
VHF Gain: 23 dB
VHF Noise Figure: 2.8 dB
VHF Output Capability: 57 dBmV
Switchable FM Trap
UHF Gain: 26 dB
UHF Noise Figure: 2.0 dB
UHF Output Capability: 51 dBmV

CM7778
Number of Inputs: 1/2 (VHF & UHF)
Input and Output Impedance: 75 Ohms
Input and Output Connectors: F Type Connectors
VHF Gain: 16 dB
VHF Noise Figure: 3.0 dB
VHF Output Capability: 56 dBmV
Switchable FM Trap
UHF Gain: 23 dB
UHF Noise Figure: 2.2 dB
UHF Output Capability: 50 dBmV

Currently $51.99 at Warren Electronic and you pay actual shipping.

http://www.warrenelectronics.com/antennas/7777.htm

Edit: I just noticed it is currently listed as out of stock.

The 7778 is used in a application where you have a local VHF and more distant UHF stations.

Usually, the UHF needs more amplification then the VHF - due to the fact that there is more loss in the wire for the UHF frequency's then for the VHF at the same distance.

Some markets only have one VHF station and other markets has NO VHF stations.

The pre amp does not physically amplify the signal - make it stronger, all it really does is changes it into a more powerful signal which is stepped up at the antenna and then stepped back down again at the power injector - before you connect it to your television.

VHF is more susceptible to noise - ignition noise from lawnmowers and motorcycles and automobiles, electric fences, electric motors inside of the house, the microwave oven, lightning - just about everything that runs on electric causes some kind of noise.

UHF is a higher frequency then VHF and is not as affected by the noise, but since the wire looses more of the signal, the UHF benefits more from amplification then does the VHF.

IN the analog days, the VHF was transmitted with a lot more power and so the picture you received on your television was not as affected by electrical noise as it is with digital.

What is the difference between a CM 7777 and a CM 7778?

7777 is hard to find, but I've read many reviews here and elsewhere that say it is one of the best pre-amps available.


The CM 7777 can't be very hard to find. I bought six of them in the past few months, all from SolidSignal.com. Never been back-ordered. Every time I order from them, the stuff is here in two days.

So far, I'm not overly impressed with the CM7777 - especially for the price. I've done two installs where an AntennaCraft amp pulled in a slightly stonger signal that the CM7777 with UHF signals. So did a Winegard AP-8275. In one case, it made the difference of getting a consistent signal.

Only advantage that I know of, for sure, with the CM7777 is the dual input mode for separate VHF and UHF antennas. The other possible advantage is, if it is actually more durable. If the CM7777 units last 10 years and others only 5, then maybe I'll agree it's somewhat better.
So far, I have no way of telling. I do know I've tested several installs and swapped amps. On all, the CM777 came in #3, the AP-8275 second, and the Antenna Craft 10G202 #1 - even though it by far, the cheapest. I just bought two at $27 each.

On paper, after factoring in gain - minus- noise- you get this:

Antenna Craft 10G212 (or 10G202) has a net gain on UHF - 26.5 dB
Winegard AP-8275 has a net gain on UHF - 25.2 dB
Channel Master CM777 has a net gain on UHF - 24 dB

With VHF?
Antenna Craft 10G202 has a net gain on VHF - 26 dB
Winegard AP-8275 has a net gain on VHF - 27.1 dB
Channel Master CM777 has a net gain on VHF - 20.2 dB

So far, the Antenna Craft is by far, the best bang for the buck. The 10G202 has adjustable gain which might be nice for some people if suburban. And, if you doubled the price, it's still better unless it's going to burn out in a year. Since all the amps have short warranties, I wonder?
I had what I believe was an Antenna Craft running for 10 years before it stopped working. It was bought from a local Radio Shack. And, we get a lot of severe cold, wind, rain, and snow. So, I think 10 years is pretty good. Truth is, I'm not even sure the amp went bad. We had a bad storm, lost the signal, and I installed a satellite dish without attempting to repair. I didn't care at that time.

Also, one note about the CM 7777 amps and quality control in China. I've gotten two so far that were not set up properly, out of the box. They come with internal dip switches. They are supposed to come with a factory default setting of "FM trap on" and "combined input." I got two that came set as "FM trap off" and "separate antenna input." Not a big deal as long as you pull it apart and check before using. My point is, if they screwed that part up, I wonder how quality control is with the rest?

That is why the instructions tells you to take them apart and check the position of the switches.

I also put a small dab of anti seize on the threads of all the screws before I put it back together. Better safe then sorry.

I believe somewhere down the road, if the FCC figures out some way to fit all the channels up in the UHF that they will do away with the VHF and sell off those frequency's also.

So somewhere down the road, you might not need a VHF antenna for anything more then FM radio - which by the way is being switched to all digital - with no mandated date set for the switch.

They tried AM Stereo -= and it didn't work.

They tried AM digital -= and it didn't work.

They tried FM digital -= and so far with only dismal results.

If Comcast buys up NBC and the radio stations goes digital, it won't be long before you will need some sort of license to receive radio and television signals and you will pay for your reception - just like with cable television and Dish type packages.

The pre amp does not physically amplify the signal - make it stronger, all it really does is changes it into a more powerful signal which is stepped up at the antenna and then stepped back down again at the power injector - before you connect it to your television.


What utter self-contradictory nonsense! Care to rephrase?

What utter self-contradictory nonsense! Care to rephrase?

I suspect he did not mean exactly what his words did, when put into that sentence. Connotation versus denotation.

All that counts is what works, and what does not. A preamp at the antenna certainly does provide a way to get a picture on your TV screen where no-amp might yield zero picture. That certainly is making a stronger signal - if we are to define "signal" as the stuff coming through the air that we are trying to get onto our TV screen.
Rate it by millivolts, or rate it by dBs, it doesn't really matter. In many cases, a preamp virtually makes your antenna a higher-gain unit, whereas a line-amp will only preserve signal strength. I.e., the preamp makes the incoming signal stronger (like a bigger/better antenna), and the lineamp compensates for delivery loss (like better or bigger wire might do). I guess there is no perfect way to say it. The amp and antenna companies use the old Bell Telephone "dB" to rate things. The old "1/10th Bell Unit", created by Bell Telehpone labs, was originally only a measure of signal loss on wire-runs, not of incoming signal strength. Yet, at times, they can mean almost the same thing.

That is why the instructions tells you to take them apart and check the position of the switches.


To be technical, that's not exactly what the installation manual states. It reads as thus: " FM trap is factory set IN." In regard to inputs, manual reads "It is factory set to single UHF/VHF input." Also, in another part of the manual, it reads "ensure correct setting."
What is does not say, is "hey, we might of screwed up so don't believe us when we tell you how this thing came shipped. Please take it apart and check for our possible mistakes."

I believe somewhere down the road, if the FCC figures out some way to fit all the channels up in the UHF that they will do away with the VHF and sell off those frequency's also.

If Comcast buys up NBC and the radio stations goes digital, it won't be long before you will need some sort of license to receive radio and television signals and you will pay for your reception - just like with cable television and Dish type packages.

God knows what the FCC might do in the future. VHF works better in many hilly rural areas. There's still a lot of VHF around now, analog and digital. And, even more yet in Canada. I have two properties where half my TV reception is from Canada. I have no idea what their version of the USA FCC is doing now or in the future.
There was a time however, in Canada, when you had to buy a license to listen to radio. Not sure when or why. I've got a old, maybe 1930-1940s Canadian radio here. Just a broadcast-band receiver. Operates on 120 VAC, 50 cycle current (as opposed to our 60 cycle). Has a warning sticker on it about using it without a license. I attached an image of it.

I have 2 high VHF's, 7 and 13.

Channel 7's antenna crashed and burned during a microburst and they JUST got their new one up and running. I could get them when they were on UHF (pre digital switch-over) digital. I doubt that with all the money to erect the new tower, they have any left to get a UHF remap.

13 is way up in the mountains and I have heard rumblings of them considering a UHF switch, but not quickly.

When I scan, the TV hangs on both 7 and 13 with a cheap RS pre-amp, so I figured a better pre-amp would help.

Is that Antennacraft really that much better?

I suspect he did not mean exactly what his words did, when put into that sentence. Connotation versus denotation.


Actually, JB has no idea what a pre-amp does or how it works. He has made the claim that they don't actually amplify the signal before, but his explanation was different and even more off the mark than this one.

Sorry BrianO - but I don't think that YOU understand how a pre amp works.

Does it work - as if to make a small antenna appear larger - nope.

The only thing that a pre amp does is compensate for line loss.

If there is no signal present, the pre amp cannot amplify what is not there.

The correct way to receive a signal is by using the proper antenna for the job. If you had a 10 ton load, you wouldn't use a 1/2 ton pick up truck and make 10 trips. You would get a 10 ton truck and haul it all in one trip.

The same is true with antenna's. We know from technology developed in the late 40's that your antenna has to be a certain shape and a certain size in order to receive well for a fringe station that is available.

When purchasing a antenna, you need to remember that we always use some sort of safety factor - a certain amount of loss that we figure you will experience - once the antenna deteriorates.

Let's use 15% as a example.

Back in the day when I was a kid, late 60's - early 70's. For Christmas a family would go out and buy a color television set and a cheap antenna. When I say cheap, a color console television was somewhere around $500 - $600,( like $3000 today) and the antenna would be around $40!

The owner would go outside on the main roof and mount the antenna and attach the twin lead cable and point the antenna in a general direction of where the reception was best for all stations. You had to compromise some on the quality of some signals for the sake of receiving them all.

Life was good!

Then around about April, when the leaves returned on the trees and a little bit of corrosion started to develop on the antenna, the signal would weaken and you would loose some stations all together.

If you lived in a city, you could call up the local cable company and have them install cable TV to your house, which only delivered what ever local stations were available.

There was no TNT, there was no FOX Movie Channel, there was no HBO, there was no Cinemax or Showtime and there was no ESPN or MTV.

If you lived in a rural area with no available TV cable, you went to a television store and you bought the largest antenna you could afford and a antenna rotor and you put your antenna as high as you could put it and you aimed it properly.

I just threw away several rotor boxes that were good internally, but were wore out mechanically from the owners turning it to three positions on the dial. 4 times a day, 7 days a week, 365 days a year they turned it ESE in the morning to watch The Price is Right, then at lunch time they turned it SW to watch the Channel 4 news and at 1 oclock they turned it South to watch Days of our Lives and at 6 Pm they turned it West again to watch the evening news.

At the same time, the only available station UHF was Channel 53 out of Pittsburgh. Only one homeowner in my area could receive it well, and he had 4 Channel Master, 4221 antenna's tied together.

At one time, Channel 53 carried the Penguins games - so you could compare it to our modern day ESPN - because it let us watch sports when the Steelers or the Pirates were not playing.

UHF is line of sight, and he lived around the side of a mountain from a direct signal to the South West. But the signal diffracted over the horizon and was a 2 edge signal - which could be received as long as the weather permitted and he had enough surface area to receive the signal. Again, with a pre amplifier - which was crude by today's standards, some RG 6 coax and a proper aim, he could watch UHF as well as or better then the VHF coming from the same hill in the same area of Pittsburgh.

The best signal you have is right at the antenna, everything after that is loss. The only way to compensate for that loss is by making the signal received at the antenna into a stronger signal, which is like increasing the pressure in a water hose to get it to squirt further. Once the signal has traveled as far as it needs to go, we just drop the pressure back down to something that the television tuner can accept and you are back in business.

Although we amplified the signal physically to get it down the wire, we never changed how much signal is present at the antenna.

Unfortunately amplifiers amplifies everything. The good signal we are trying to use and the bad - noise both from the surrounding area, the atmosphere and internally from the amplifier it's self.

It has been found that a maximum amount of gain in db for a fringe area for a cheap pre amp is about 26 for a UHF signal.

We can calculate how much loss there is going to be on the line, once the signal gets to the power injector and is then split several times and diverted to different rooms in the house.

We know that there is a safety factor in the tuner of the television / converter box of about 10 db that can be absorbed without affecting the ability of the tuner to use it - over load.

Let's say that the wiring in the house absorbs 5 db, that still gives you a gain factor of about 11 db - if you have a pre amp with 2.7 db of noise, you have to subtract the 2.7 - which would leave you with a gain of about 8 db..

So physically the signal appears to be as strong as if we were sitting on the roof with our television right there beside our antenna. But at the same time, if no signal is present, we still can't watch that station, no matter how many times we try to amplify it.

Once the signal reaches the digital cliff and there is no signal to amplify and our receiver tells us - NO SIGNAL!

So buying the wrong size antenna and then trying to use some sort of amplifier to compensate for the lack of ability of the antenna to properly receive it is just the wrong way to do it.

Sorry BrianO - but I don't think that YOU understand how a pre amp works.

Does it work - as if to make a small antenna appear larger - nope.




I totally and absolutely disagree.

I'm will avoid a long list of technical jargon that will make any reply confusing, and off point. The reality is, much of what is associated with electricity and communciations is still theory based, and not 100% predicitable science. That's why the Electron Theory, and the Hole Theory, are still just that . . . theories that have never been proven. "Modern science" still does not know, for sure, what a flow of electricty actually is. We've been guessing for years, and still are.

True, a preamp cannot make signal "out of nothing." Neither can any antenna. If a signal is there though, a good preamp certainly CAN make a small antenna behave as if it's larger and/or better tuned.

On the other hand, an amp used in a transmission line generally will not do that. What it will do is offset line-loss, i.e., preserve what you've got coming from the antenna and/if the preamp.

You, we, et. al. could argue until the cows come home and prove absolutely nothing. I've been farting around with electronics, TV signals, radio signals, satellite signals, etc. for over 40 years and all in fringe areas.
That does not mean I gained any great amount of highly technical expertise from the hands-on work. It does mean that I've been in many situtations where I actually tried using different compents to test, in identical situations. I also have technical training, but that sometimes contraticts what happens in the real world.

So, call it, or call things, or call situations whatever you like. I have many times made small antennas act large by using a good preamp. And, I have many times offset lineloss on long runs with line-amps.
When we read specs published by Winegard, Antenna Craft, Channel Master, etc. , those specs are basically predictions based on past behavior - not guarantees. But, often, they are reliable predictions.
As I assume most here know, if past behavior was a perfect predictor of future behavior, we would not have the study (and use) of Quantum Pysics, that defy the so-called Laws of Newtonian Gravity.

So, for my own predictions? Considering that in every fringe situation I've ever worked on, a preamp made a night-and-day difference on an enhanced signal and a watchable TV screen, I will continue to believe what I see with my own eyes, along with what has been written by many communication's engineers.

Is that Antennacraft really that much better?

I'm not claiming the Antennacraft is universally better. What I am claiming that it HAS worked better for me, in several situations - when compared to the Channel Master 7777.

I'm a little mad at myself for not trying it earlier. The thing is, since Radio Shack sells Antenna Craft with the Radio Shack brand-name on it, I steered away from it. Radio Shack sells an awful lot of crap, and "one bad apple" can spoil a whole "bunch" of repuation. Radio Shack has sold many bad and high-noise preamps - but not this one.

I am also claiming, that on published data-sheets, the CM 7777 comes in third place for gain - as compared to the Antenna Craft and the Winegard. Also, the highest gain-rated amp is half the price of the CM 7777.

Maybe I'm missing something here, but I have to ask. Since the CM 7777 is the lowest rated gain, and one of the highest prices - why is it mentioned so much as # 1? I admit, that I have a certain fondness in my heart for the brandname of "Channel Master" simply because it what I grew up with. But, it's all made in China now, as most else is.

My installations are not scientifically controlled experiments. I DO spends a lot of time trying to compare. I do that since so much I read on forums, and specs datasheets do not always reflect reality.

When I swap amps on the same antenna, pointing at the same direction, I still have certain variables I cannot control.

#1, Is it possible one amp works better on certain antennas than others? Maybe. I don't have the time or budget to test them all.
It has been proven that preamps work differently on differing frequencies. But, how about on different style antennas, or in different types of reception areas, or in different weather conditions?

#2 The signal in most fringe and hilly areas that I've worked in, changes constantly, every minute, every hour, every day can vary. So, I check signal strength on one setup, tear it down, and try another. Meanwhile, regardless if ten minutes have passed, or ten hours, the signal in the air might of changed. So, when I test signal strength at the receiver/tuner, I don't really know what has caused any change I perceive. Best guess is to check an average signal over time.

#3 Even a reading of signal strength is not perfect; at least not with my equipment. I can hook up one antenna system and get a "70" strength reading on a 1 - 100 scale, yet get pixelization and drop-outs. Hook up to another and get a reading of only "40" yet, get a perfect picture with no pixelization and no drop-outs. This is all in weak fringe areas where a large antenna and no preamp gets NO signal reading at all.
I suspect much of this is caused by the signal strength meter not being "real time." There is a second or two of time-lag and also buffering - like the fuel gauge in a car works. So, short spikes of very low readings do not even show on the meter.

I'm not purposely confusing the issue. I'm just stating that I'm not always sure what is going on. If I make a change and it works well consistently for many days, during stable weather and not during big season changes - then yeah, I assume it is a true gain.

UHF is NOT only line-of-sight, like some many info places, and people on this forum claim. That is PURE BS. I have no line-of-sight to any transmitters and I get many UHF channels. Several are not coming from the direction of those transmitters, not even close. My kid's favorite channel - QUBO on channel 50, has my antenna pointed at some woods below a mountain top, and at 210 magnetic degrees. The transmitter is 60 miles away, way below that mountaintop, and at 60 magnetic degrees. So, I point at 210 degrees and get signals from a transmitter at 60 degrees. Not exactly what I call line-of-sight.

Again, I did not intend to give a convolued answere, but I am trying to give an accurate report of my experiences on this issue. I have tried the Antenna Craft at my in-laws home in northern Michigan, at my cabin in the NY Adirondcacks, and at my farm here in central New York. All fringe-reception areas. In all cases, the Antenna Craft and the Winegard amps outperformed the CM 7777. In one case, the Antenna Craft provided a consistent picture, whereas the CM 7777 did not. That's in Alpena, Michigan. We ran for a week with the CM7777, and then a week with the Antenna Craft. Then, put the CM 7777 on again, and then the Antenna Craft again. Results were the same, over and over. I'll add, I also tried installing a second CM 7777, just in case the first was somehow defective.

And an amplifier is an amplifier...

Firstly let us acknowledge that gravity does in fact exist - despite whatever some whack-job scientists/theorists, or what have you may want you to believe...

A dB is nothing more than a unit of measure, period.
dB = 10* Log (Pwr In / Pwr Out)
So for example if you feed a signal worth 10w into an amplifier that has a gain of 10dB you then have 100w out the other side. If you then feed this down a line that has a 10dB loss, at some given frequency, you are back to 10w at the end of that line, at that freq.

This is not theory, this is calculated and measurable science!

If you set up a transmitter, antenna and a receiver with "X" amount of air between them you will have some given signal strength in the air at that antenna location above/below the ambient noise floor - lets call it the Noise Margin.;)

Enter the antenna...
Your antenna has, at any given frequency, some given gain value - the ability of the antenna to gather electrical energy from the air, and magnify it. And again, this is not theory but is calculated (nowadays by computer modeling) and confirmed in the real world with testing. It is variable only to production tolerances, which I'm sure are taken into account when publishing mfgr specs.

So now say you have 0.1w of signal in the air at that antenna location, and this level of power is equal to a +10dB NM. (The noise present at that frequency being at 0.01w) Your antenna is gathering enough energy at that given freq to achieve a gain of 10dB, so you now have 1.0w at the output of the antenna, or a +20dB NM value.

But now you have to transport that signal to the tuner, and the cable & distribution system incurs loss.

Enter the amplifier...
An amplifier will amplify what ever it has been given at it's input by whatever its rated gain is. So an amp does NOT raise the signal above the noise floor, (or increase the NM figure) because it has also amplified the noise along with the signal it receives.

It furthermore actually lowers the NM by introducing its own noise into the line. Insert an amp with a 12dB gain and a noise factor of 3dB in the example above and your result is an incident signal of 15.85w with a noise floor that is now 0.317w (Not including balun loss) or a 17dB S/N or NM.

What's in a name?
An amp is an amp, regardless of what you call it it is doing the same thing. The only difference is where you put it in the system, and why. A pre-amp is designed to withstand the elements and is located at the antenna to amplify the signal before it is attenuated by the line loss incurred in the cable run. A distribution amp is used where the signal is sufficient for one tuner, but subsequent losses incurred by splitting will drop the signal below the noise floor. They are also used when the signal present at the antenna is overly strong on some channels and may overload the amp, and attenuation in the primary cable run drops these to acceptable levels, while still leaving sufficient signal on other channels to be amplified to overcome subsequent losses.

An amp has a minimum gain spec, and a maximum noise spec. Once again this is calculated & measured, and variable to production tolerances. Because they are given as min/max over wide bands (UHF/VHF) the actual performance may be considerably different at some given frequency. It is certainly reasonable to assume the actual gain of a production unit to exceed the min gain at some freq by several dB while also achieving a lower noise contribution. In other words real world performance will vary. But you can at least design a system by the numbers and know what you will have in the end, as a worst case - or can you?

Enter SWR...
Often overlooked, this is the measure of reflected power occurring/caused by impedance mismatch, and is virtually impossible to calculate in any given system. Each connector on a piece of coax cable has some mismatch at some given frequency, and will reflect some of the power its fed instead of transmitting it. Luckily these losses as well as the losses incurred in the cable run itself, and also the noise introduced by the tuner, are all compensated for by the amp.

So where does all this "black magic" come in?

As you change frequency Rf transmissions will behave differently, given the same circumstances. Signals of different frequencies will diffract or reflect dependent on not only their environment but the wavelength of the transmission. TVFool givs us a starting point of how strong a given channel is going to be based on transmitted power, our distance from the transmitter and the general topography between. What it doesn't take into account is your local, or actual situation - trees, buildings, etc that will radically effect the actual signal available to you in the air. A surface that is transparent to a VHF signal may be absorptive to a Low freq UHF, while becoming reflective to a High freq UHF signal. It also doesn't take into account local circumstances that may raise the noise floor, which will determine your ability to receive a signal.

And you thought JB could ramble!:D

JB
The problem that makes you wrong is that most tuners are designed for Cable TV level signals now. In the past well designed tuners had low noise preamps built in. They were designed for OTA.

Now we need preamps to get the good antenna signal up to the Cable TV levels.

Also the power injector DOES NOT lower the signal back down. The gain is spec'd thru from input to output. Cable loss will of course reduce the available gain.

So if cable level is 10 dbm and the tuner is good for -20 dbm then you need one hellatious big antenna to pickup a -70 dbm signal OTA and expect the tuner to see it.

Now I know my tuners are a little better than that but I need every bit of the CM7775 to get my channel 18 with the PR8800 and 80 ft of cable.

The little 20" LG cannot see this signal at the antenna!
The Samsung DTB260F could at least get PSIP but no picture at the antenna. One bar part time.

With preamps and filtering (also minus the mixing loss tho it is made up prior to the mixer) and distribution amp all the TVs in the house can view this channel.

I think what we're missing here is the fundamental of what level, or amplitude of signal can be detected by a given tuner. Obviously different tuners have different sensitivity thresholds, and thus different tuners will pull channels in at different rates.

I'm not so sure TV tuners had built-in amplifiers in the past, but they certainly had better sensitivity thresholds. As do the D/A converter box tuners produced today.

Say you have a tuner with a sensitivity threshold of 0.1w and a noise factor of 3dB. Now say you have a signal at that tuner of say 0.2w after all line and distribution losses. Let's also say that signal is even 10dB above the noise floor. (NM) With this situation you still won't be able to receive that signal reliably, since the tuner's noise is dropping the signal by 50% to 0.1w, and you are on the cliff...

So you add an amp to the equation and this solves the problem. Adding an amp with 10dB gain & 3dB noise factor reduces the S/N, or NM to 7dB, but boosts the amplitude of the desired signal to 2.0w, thus more than compensating for the tuner's noise and you are able to receive the signal reliably.

And I do would hope someone will correct me if I've stated anything incorrectly.

Sorry BrianO - but I don't think that YOU understand how a pre amp works.


Actually I do. OTOH, you have shown in multiple posts with erroneous statements with long winded, laughable explanations that you do not. And there are a few knowledgable posters on this site who agree with me.

Firstly let us acknowledge that gravity does in fact exist - despite whatever some whack-job scientists/theorists, or what have you may want you to believe...

My comment were on Newtonian Gravity (from Isaac Newton) that was the accepted rule for most of written history. And, it has been disproven, over and over. That's why, if you believe test data from noted scientists, that many types of sub-atomic particles have NO gravity, and many huge masses have NO gravity.
Much of this came about with the study of Quantum Physics.
On the other hand, you don't believe info fed to us by some of the world's leading scientists/researchers, or what is currently taught in college phsyics classes, that is fine with me. But, if so, then don't pick and choose and claim a knowledge of other findings in other fields of science.


A dB is nothing more than a unit of measure, period.


Yeah, and so is a quart or a gallon. The "dB" originated for use by researchers at Bell Telephone to calculate line-loss in telephone lines, not signal strengh with over-the-air communications. But yes, it has been adopted and used as a general reference for other things.

Enter the antenna...
Your antenna has, at any given frequency, some given gain value - the ability of the antenna to gather electrical energy from the air, and magnify it. And again, this is not theory but is calculated (nowadays by computer modeling) and confirmed in the real world with testing. It is variable only to production tolerances, which I'm sure are taken into account when publishing mfgr specs.


It is calculated, for the most part, in controlled environments. That's why published figures are general ones, meant for general comparison. No amount of antenna test data, along with published figures, is going to apply equally to all situations.


What's in a name?
An amp is an amp, regardless of what you call it it is doing the same thing. The only difference is where you put it in the system, and why. A pre-amp is designed to withstand the elements and is located at the antenna to amplify the signal

No, not universally true, unless you want to play semantics. There are different types of amps, so subsequently, they get different names. Are you watching TV hooked to your old Fender tube-based guitar amp? I suspect not. With TV reception, a preamp, or LNA, if worth a damn, uses the best transistors possible to prevent from amplifying noise excessively along with signal. Line amps often have cheaper circuitry. Also, since an amp used to enhance a signal needs to be as close to the antenna as possible, the power supply usually has to be located quite some distance. That, because many if not most antennas don't have a power-outlet attached to them. Like I said, if an "amp is an amp", find me someone watcting TV hooked to their guitar amp. Funny thing though . . . the old tube amps if used in suburban areas will indeed pick up radio signals on an ad hoc basis.

What a bunch of shit....

Cant you even give it up for one simple question.

Bunch of fuckin windbags, DID i ASK FOR A DISERTATION?

JB
The problem that makes you wrong is that most tuners are designed for Cable TV level signals now. In the past well designed tuners had low noise preamps built in. They were designed for OTA.


Yes, and the same can be said for radios. Besides living in a fringe area for TV reception, radio is also a problem. I have many old radios (some from the 1920s) that work much better than most new ones bought at the consumer/el cheapo level. Radios and TVs, historically, were built to work on weak signals, and built repuations on it. Now ?? Not so easy. In fact, last year I did a little searching in an effort to buy an AM radio that was actually built for good reception. I bought two of the highest rated models. One was the GE Supertuner, and I forget what the other was. Grundig, I think. Both were a total waste of money. My 1930s Zenith easily beats them all.

Going by what JB and few others have stated, my first satellite dish that I built 25 years ago, could not have worked. It was 14 feet in diameter, and the parabolic curve of the chicken wire I used focused signals from almost-outer space, onto the center area of the dish. There, a low-noise-amp HAD to be used, or I would get NO reception. The signal was there, but not useable without the amp.

And yes, TV reception is not quite to that extreme, but we are still talking along the same principle.

I spent the past two days swapping antennas and amps. I just did a test on . . . a Winegard 9032, XG91 and Terrestial DB8. Tested all on the same mast in the same spot, with no amps, with CM Winegard, and Antenna Craft amps, and also . . . with a tiny 18" wide RV antenna.
No pubished data dictating outcomes here. Just hooking stuff up and seeing what works.

To be a little briefer, the DB8 outdid all the other antennas. I was very suprised. On a few channels, it reads a slightly lower signal strength, but the picture is more consistent. No more pixelization. On the weakest channel with the 9032 and XG91 - the DB8 did MUCH better. And, what really blew me away is . . . I found one channel I'd never gotten before (RF 43). The 9032 and XG91 does not sense it, and the DB8 does. I don't know why, and don't really care at this point.

Keep in mind that I am in a extreme-fringe area and have no line-of-sight to any TV transmitters anywere.

Here is an example of what a preamp did, as tested today. All testing was at the antenna, not downstream. I scanned channels at various compass points. The DB8 with no amp got a signal strength on these channels of - 5 bars on RF 29, NO signal on RF 26, and 1 bar on RF 50 (not watchable). I did a complete scan and it only locked into these three channels.

I then hooked in a CM 7777 amp. Then, I got 9 bars on RF 29, 8 bars on RF26, and 8 bars on RF 50. All came in perfect. Also got four more channels.

I then hooked up a little 18" wide RV antenna with no amp. Got no signal at all. Then, hooked the CM 777 amp to it. I scanned and got five channels. It did almost as well as the DB8 did with no amp on the original three channels, and got two more. A little less signal strength, but not by much.

Now, that is what I am going to call . . . an amp making a small antenna behave like a bigger one.

When I started out working on my system here, AntennaWeb told me I might get one channel. I've got over 30 now. I've got three antennas setup at two locations. At one is a Winegard 8200 with a Antennacraft amp, and the other a DB8 and an ancient 18 foot long VHF antenna. I bought it new from Radio Shack in 1979. Subsequently, I used the CM 7777 amp due to its dual UHF and VHF inputs. The furthest is 520 feet from my house. That being said, my signal strenght at the TV in the house is just as strong as measure at the antenna. All antennas have preamps, and I also have an $8 line amp at the half-way mark that works great. And, please excuse my use of the terms "amp" and "preamp" for those that state an "amp is an amp."

What a bunch of shit....

Cant you even give it up for one simple question.

Bunch of fuckin windbags, DID i ASK FOR A DISERTATION?

Did anyone ask YOU to read the posts?

Looks to me like a poster named Rick, answered your question before anyone else posted anything.

As to the rest, who forced you to read on, if you find it all so painful?

Maybe I'm missing something here, but I have to ask. Since the CM 7777 is the lowest rated gain, and one of the highest prices - why is it mentioned so much as # 1? I admit, that I have a certain fondness in my heart for the brandname of "Channel Master" simply because it what I grew up with. But, it's all made in China now, as most else is.


You are missing something. The main thing to look for in a pre-amp is low noise figure. That is what cost all the money to design. It is cheap to design a noisy high-gain pre-amp.

The AntennaCraft 10G212 Noise Figure is listed at <3.5dB UHF. The CM 7777 is listed at 2.0dB for UHF. For UHF this means everything in trying to receive deep fringe signals. For noise figures 0.2dB can make a big difference. The CM 7777 is lowest noise UHF amp sold domestically. The Pre-Amp UHF noise figure should be 2.0dB or less. 4.0dB or more noise figure is considered a high noise amplifier.

The other thing you are missing is that a good pre-amp has a very high maximum possible output. If your cheap amp has a lot of gain but will clip when a strong signal is received, it is useless. Any amp that doesn't advertise it max possible output level can be assumed to be inferior. The CM 7777 is advertised at UHF Output Capability: 51 dBmV. I have had a cheap amp that worked great until the neighbor started up is lawn mower and then started to pixelating all of the networks (the RF noise from the mower was over driving the amp.) Some people have a combination distant stations and local stations, so they need a amp that can handle a wide variety of signal levels.

You are missing something. The main thing to look for in a pre-amp is low noise figure. .

The other thing you are missing is that a good pre-amp has a very high maximum possible output.

Yes, I'm aware of the published specs. I have also seen many posts by people who say they have equipment to test amps for noise, and have stated figures that don't always coincide with the manf. datasheets. I have no way to test myself other then install and observe the results. I can see where the rated max. output can be a factor in areas with a mix of strong and weak signals. I've never been in that situation though, and have always been in extreme fringe areas. That's why I've made a point of mentioning my fringe area when reporting on my personal observations.

As to the amps, regardless of the noise figures, I've gotten an improvement at two separate installs when I pulled CM 7777 amps and replaced with the Antenna Craft 10G202 or 10G212. Not really sure which since the amps are Radio Shack branded, # 150-2507. Radio Shack rates them at 30 dB average gain with noise specs.
Main thing is, in these two situations, and with one specific channel, they worked better enough to make the difference of a channel pixelating and freezing, to a channel NOT pixelating or freezing. RF channel 24, WCML. I don't know why, and am not saying they give an overall gain or work better in other situations. Also, these have adjustable gain controls, which I have no use for. If I turn them down, the signal degrades and the pixelization comes back. But, I assume it would help in areas that DO have strong signals around - as you mentioned as a potential problem.

If I had money to burn, I'd like to try the Research Communications # 9253 amp that's rated at 23 dB gain and 6/10ths dB noise. But, I could buy 5-8 cheaper amps for the price of that one, so I'm not willing to buy on posted specs alone.

What a bunch of shit....

Cant you even give it up for one simple question.

Bunch of fuckin windbags, DID i ASK FOR A DISERTATION?

Basically we are trying to correct ONE windbag who isn't smart enough to know he doesn't know everything yet gives a disertation with EVERY reply. If I hadn't been sick at home I could have avoided this too!

"Those who can, do. Those who can't, teach" quote from my Dad a lifelong teacher. I don't know his source.

PS I have played a radio thru a Fender amp.;)

Did anyone ask YOU to read the posts?

Looks to me like a poster named Rick, answered your question before anyone else posted anything.

As to the rest, who forced you to read on, if you find it all so painful?

Its MY post. What do you mean who forced me to read it?

I asked a question and got an answer that required another question. I was expecting an answer to that second question. Not a bunch of people bickering about shit THAT HAD NOTHING TO DO WITH THE TOPIC.

So fuck off...

...

Is that Antennacraft really that much better?

jdemaris thinks it is better. But I would go with the CM7777 because thats what I'm experienced with and it works well for me.

Sorry for the excess but we bit into JB's bait again.

Firstly let us acknowledge that gravity does in fact exist - despite whatever some whack-job scientists/theorists, or what have you may want you to believe...

I was making that statement in the context of our lives here on earth. I couldn't give a rats ass about quantum physics, the origin of black holes, nor the scientific explanation for the existence of the universe - as far as I'm concerned it has no bearing on this discussion.

On the other hand, you don't believe info fed to us by some of the world's leading scientists/researchers, or what is currently taught in college phsyics classes, that is fine with me. But, if so, then don't pick and choose and claim a knowledge of other findings in other fields of science.

Are you saying I must believe anything and everything that "science" claims to be so, in order to accept anything science has proven? That seems a bit narrow minded, don't you think?

And yes, a quart or a gallon is a measure of liquid volume, as is a dB a relative measure of power. How the unit came to be is of little consequence to this discussion. But fear not, it may come in handy when you play your next round of Trivial Pursuit... My point was that it is a universally accepted measurement; whether we are measuring sound waves, microwaves, etc. - it is simply a relative measurement of power.

It is calculated, for the most part, in controlled environments. That's why published figures are general ones, meant for general comparison. No amount of antenna test data, along with published figures, is going to apply equally to all situations.

I disagree, but will take that statement one step further and say they may not apply to any situation - insofar as mileage ratings are concerned. (Due to the many factors beyond our control, as I thought I eluded to in the last paragraph of my first post.) Point is, if the signal is in the air at some given level an antenna will gather and magnify that signal - and this is called the gain of the antenna. It has been calculated and tested, is measured in dB, and is a fair prediction of how much energy will come out of the antenna. Now when we consider multipath reflections and phase-canceling of the incident signal all the tests go out the window...

As far as my statement "An amp is an amp" is concerned I was referring to amplifiers used in the context of TV reception, as is the context of this thread - I really didn't think I needed to post a disclaimer. And I stand by my assertion that "An amp is an amp" insofar as it pertains to what an amp is doing to the signal, for the purposes of this discussion. Are you going to tell me if you call it a pre-amp, a line amp, or a distribution amp these are actually doing anything different, when it comes right down to it? Of course not. Are these differently named components produced with varying quality & construction? Surely they are. Are their intended uses and locations in a system different? Naturally. But that changes not the fundamentals of what is happing, how it's measured, or the effect on the outcome - you have a min gain & a max noise... If you had an extra HDP-269 amp lying around and you needed to suddenly add an 8-way splitter to your system to accommodate your wife's unemployed cousin and his whole family who were moving in and each had to have their own TV, would you just put the 269 amp ahead of your 8-way or would you go out and buy a "Distribution Amplifier"???

I just did a test on . . . a Winegard 9032, XG91 and Terrestial DB8. Tested all on the same mast in the same spot...

And also at the same aim?

On the weakest channel with the 9032 and XG91 - the DB8 did MUCH better. And, what really blew me away is . . . I found one channel I'd never gotten before (RF 43). The 9032 and XG91 does not sense it, and the DB8 does. I don't know why, and don't really care at this point.

Keep in mind that I am in a extreme-fringe area and have no line-of-sight to any TV transmitters anywere.

If you had all the antennas at the same aim I would venture a guess that you were picking up a reflected signal with the wider beamwidth of the DB8 as compared to the 9032 or 91XG. I would say tune the aim of the DB8 to maximize the signal and then retest the 9032 & 91XG. But like you said, you don't really care at this point...

Now, that is what I am going to call . . . an amp making a small antenna behave like a bigger one.

I'll drink to that. And this is why you see mfgr's putting amps in little shitbox antennas you stick on the windowsill... And this technique even sometimes offers results.


To DoctorCAD:
I apologize if I seemed to go on, I do usually try not to do that.
I was trying to clarify a few points.
But this seems like a classic case of expecting a simple answer to a complex question...

jdemaris thinks it is better. But I would go with the CM7777 because thats what I'm experienced with and it works well for me.

Sorry for the excess but we bit into JB's bait again.

Thank you. I will order one today and report back.

jdemaris thinks it is better. But I would go with the CM7777 because thats what I'm experienced with and it works well for me.


No, I don't claim the Antenna Craft amp is better in general. Better is a relative term. What I stated was, it WAS better in two specific installs that I did, as compared to the CM 7777 that I pulled. As to why it worked better, I do not know. It worked better and cost much less.

I don't tend to believe all published spec, not do I believe that science can accurately predict results for us, all the time. If I did believe all, I'd just spend 13 British Pounds (21 US dollars) for a Triax-Wolsey preamp rated at 34 dB gain on UHF and only 1.8 dB noise. On paper it greatly beats the CM 7777 and is less then half the price.

I read these forums to gain some knowledge of real world results by people doing actual installs.

If you had all the antennas at the same aim I would venture a guess that you were picking up a reflected signal with the wider beamwidth of the DB8 as compared to the 9032 or 91XG. I would say tune the aim of the DB8 to maximize the signal and then retest the 9032 & 91XG. But like you said, you don't really care at this point...


Every swap was done first with the antenna on the same mast, same height, and same direction. I then did many tests at approx every 20 degrees of compass points. The DB8 had a much wider reception area for each channel, whereas the Winegard 9032 was the most narrow needing to be pointed dead-on.

Variables include the fringe signals that constantly change. So, even if I pulled down an antenna and then put the same antenna back up, I might get a very different reading. So, all results needed to be taken as an average over time.

One other variable was when I added the huge VHF antenna. The UHF antenna sits on top of the mast, around 30 feet up, hooked to a rotator. When I installed the huge VHF antenna 10 feet down, several UHF channels (from the top DB8 antenna) got stronger. I tested several times. I could watch the signal meter go up every time I moved that VHF antenna up on the mast near the UHF antenna. So, there's an effect I probably would not find in the datasheets.
I don't know if it would have the same synergetic effect with the XG91 or 9032. Too much work to find out. That VHF antenna is huge and it was windy out.

Note, I have a similarly odd effect in my workshop with AM radio. After 8 PM at night, when the ionospheric bounce starts, I lose my only AM radio station that comes from 60 miles away. But, if I turn on 2/3 of my shop lights, it comes back strong. If I put on only 1/3, or all of them, the signal drops and I lose reception. Been like that for 10 years. I have three wall switches. Each one turns on six dual-neon shop-lights. If I turn on the first two switches, I get good radio. No other combo works.

TV reception, especially digital TV reception is more of an art than a science.

Calculations and number will only take you so far, after that everything is experimental and highly variable.

Here is an older essay about UHF & pre-amps. Interesting read.
http://www.geocities.com/toddemslie/UHF-TV-DX.html

Here is an older essay about UHF & pre-amps. Interesting read.
http://www.geocities.com/toddemslie/UHF-TV-DX.html

Yea, but I need it for High VHF more than UHF.

Here is an older essay about UHF & pre-amps. Interesting read.
http://www.geocities.com/toddemslie/UHF-TV-DX.html

It's a good article. Too bad, that it lists some components (I've been trying to buy) that seem to be no longer available in the USA.
Mainly the "stacking combiners" he mentions from Lindsay.

I'm in the process of ordering some from Triax in England. I haven't been able to find any here in the US, except for the high-loss junk I got from Winegard. Installing the Winegard ends up with more loss then gain.

I stacked two Winegard 9032 UHF antennas, using the Winegard CC7870 antenna coupler. Possible gain I was hoping for was an extra 3 dB. Ends up the Winegard coupler has a 3.5 dB insertion loss, and yes, I got less signal with the dual antennas.

I'm going to stack four antennas and see what happens. A company in England sells the antenna-combiner for four, with an insertion loss of only 3/10 ths dB. Gain is reported to be 5.7 dB with four antennas, or 2.8 dB with two antennas. Guess I'll find out when I get the parts. They also sell high gain (34 dB), low noise (1.8 dB) mast preamps for 1/2 the cost of US amps. Not sure why so cheap, unless the specs are BS.

I stacked two Winegard 9032 UHF antennas, using the Winegard CC7870 antenna coupler. Possible gain I was hoping for was an extra 3 dB. Ends up the Winegard coupler has a 3.5 dB insertion loss, and yes, I got less signal with the dual antennas.

I was of the understanding that you can combine two identical antennas on the same aim with just a regular 2-way splitter used in reverse. As long as the signals are in phase you cancel the 3dB loss and get a 3dB gain - well less 0.5dB for the insertion loss of the splitter, so a net of ~2.5dB. If they're out of phase the two cancel each other and you're screwed. Usually flipping one balun solves this.

Am I misinformed?

I was of the understanding that you can combine two identical antennas on the same aim with just a regular 2-way splitter used in reverse. As long as the signals are in phase you cancel the 3dB loss and get a 3dB gain - well less 0.5dB for the insertion loss of the splitter, so a net of ~2.5dB. If they're out of phase the two cancel each other and you're screwed. Usually flipping one balun solves this.

Am I misinformed?

Well . . . if you are misinformed, so am I. I often discover things don't work quite like some tech tutorial claims.

I read the same info; that's why I went though the work of installing dual antennas with the Winegard coupler. At first, I had one antenna mounted and was testing with my worst fringe channel. It was working, but pixelating and freezing a bit. Then installed the dual antennas and did it pretty carefully. Stacked vertically, and pointed, tilted exactly the same. All coax leads the same length. And, the height makes no difference here. I can go up 15 feet or 60 feet and the signal is exactly the same. TV Fool verifies that, although I've already tried it.

Got all done, and no picture at all. It was weakened enough to not be viewable by the TV. Same with the reading on the signal-strength meter. I checked all the leads, reverserd on balun, etc. No change. So, I quickly unhooked the coupler and hooked one antenna up direct (eliminating the other) and the picture came back. One antenna - signal meter had four bars (scale of 1 to 10 bars). Two antennas, signal meter was 2 bars with no picture on the TV.

There is some good info on stacking, and using low-loss combiners here:

http://www.triax.com/upload/gb-stackning_of_antennas.pdf

I tend to believe what I see, over what I read. Sometimes . . . yes . . . I discover that I've missed something. But, also many times I find tech writeups to be just plain wrong.

Guess I won't know for sure until I get a low-loss coupler and see if it makes a difference. Triax sells one rated at .6 dB loss. The Winegard I bought is rated at 3.5 dB.

I stacked two Winegard 9032 UHF antennas, using the Winegard CC7870 antenna coupler. Possible gain I was hoping for was an extra 3 dB. Ends up the Winegard coupler has a 3.5 dB insertion loss, and yes, I got less signal with the dual antennas.


Something is wrong. The phasing of the baluns may be backwards. The antenna locations may be less optimum.

Read some more ideas here: http://www.hdtvprimer.com/ANTENNAS/16bay.html

Something is wrong. The phasing of the baluns may be backwards. The antenna locations may be less optimum.

Read some more ideas here: http://www.hdtvprimer.com/ANTENNAS/16bay.html

I agree that something is wrong, but I don't know what the "something" is. I don't believe phasing is the issue.
It was very windy and starting to rain, during my last attempt. Not a great feeling when you're 25-30 feet in the air, on a ladder clamped to a backhoe bucket. I'm 60 years old, and not as brave as I once was.

Inverting one balun made no difference. I also tried each antenna by itself, and each worked fine. Also tried a regular splitter in place of the Winegard antenna coupler, and no change. Also tried antenna adjustments with no change. In fact, this setup with identical antennas in the same location, worked worse - then when I hooked two totally different antennas together, that were in two different locations. At one time, I tried joining the single 9032 UHF only antenna, to my VHF/UHF 8200 antenna that is 250 feet away and was pointed in a different direction. Sometimes it worked well, and sometimes, channels canceled each other out. I wasn't expecting it to work, but was just jerking around to see what would happen. When the 9032 and the 8200 (at different locations) were pointing the same direction, it sometimes worked very well. But at other times of the day, it worked worse than just one antenna, and that obviously WAS a phasing issue.

I've read that "16 bay" article along with many others, here in the USA, and also many done in Great Britian. One common theme I keep finding is people who had problems until they used a low-loss antenna combiner. If it truly exists, it's hard to find. Lindsay Electronics (USAJ) no longer sells its "low loss stripline combiner."

Presently, I'm waiting on a Triax unit from England. I read many articles on antennas, amps, etc. Many claims and reported results conflict. So, in situations like this one, I willing to spend some money on odd-ball components, hook them up, and see what happens.

If I always believe posted specs, I'd never hooked up any antennas here.

At present, I'm very pleased with the single DB8. For channel 50, it beats all the others I've tried. But, I'm always looking for the best possible setup, so I keep fooling around. If I had money to burn, I'd try dual DB8s instead of dual 9032s - but I already have the two 9032s here. They only cost $35 each, but still hate to see them go to waste.

Presently, I'm waiting on a Triax unit from England. I read many articles on antennas, amps, etc. Many claims and reported results conflict. So, in situations like this one, I willing to spend some money on odd-ball components, hook them up, and see what happens.

Here's another combiner, but you'll need BNC to F cables or adapters.

http://minicircuits.com/pdfs/ZAPD-2-252-75+.pdf

There are many things involved in a reception system, and many different signal interactions, the workings of which can be perceived as art or black magic - however this is not one of them.

Call it a power divider/combiner, splitter whatever - so long as the signals being fed into the ports are of the same amplitude and in phase they should combine and you will get a resultant gain of 3dB - less the insertion loss of the unit itself.

So lets face it, jerking around with tenths of a dB difference in insertion loss isn't going to make much difference, or solve the problem.

jdemaris checked all the usual causes; using identical antennas on an identical aim, identical cable lengths, flipping one balun, and I assume distance from the roof to the lower antenna was ruled out, as reflections could cause such an upset.

UHF has a short enough wavelength that a couple of feet in any direction can make the difference between being in a strong signal position or being in a null, especially when ground reflections are present. Due to reflective/diffractive signals if one of the antenna positions was receiving the signal differently, this would cause them to cancel.

I would try a wider spread vertically and see if you can get better results.
And maybe choose a nicer day!:D