High Def Forum - Your High Definition Community & High Definition Resource

Go Back   High Def Forum - Your High Definition Community & High Definition Resource >
Rules HDTV Forum Gallery LINK TO US! RSS - High Def Forum AddThis Feed Button AddThis Social Bookmark Button Groups

Local HDTV Info and Reception Learn about your local HDTV stations, availability, reception issues, OTA antennas and any other local issues.

Question about CM 7777

Reply
AddThis Social Bookmark Button
 
Thread Tools
Old 10-09-2009, 07:48 PM   #1  
Direct TV Fresh Meat
Thread Starter
 

Join Date: Feb 2007
Posts: 2,464
Default 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.
DoctorCAD is offline   Reply With Quote
Old 10-09-2009, 09:39 PM   #2  
Antennas by Committee
 

Join Date: Jan 2006
Location: Clay, New York
Posts: 1,564
Default

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_...oducts_id=6736

http://www.crutchfield.com/p_6597777...7.html?tp=6341

http://www.google.com/products?q=CM+...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
Rick0725 is offline   Reply With Quote
Old 10-10-2009, 12:42 AM   #3  
Go to a movie tonight
 

Join Date: Sep 2008
Location: Gettysburg, PA
Posts: 161
Default

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.
Pamajestic is offline   Reply With Quote
Old 10-10-2009, 07:30 AM   #4  
High Definition is the definition of life.
 
JB Antennaman's Avatar
 

Join Date: Jun 2009
Location: Pennsylvania
Posts: 1,409
Default

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.
JB Antennaman is offline   Reply With Quote
Old 10-10-2009, 01:01 PM   #5  
High Definition is the definition of life.
 

Join Date: Sep 2009
Posts: 193
Default

Quote:
Originally Posted by DoctorCAD View Post
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?
jdemaris is offline   Reply With Quote
Old 10-10-2009, 01:17 PM   #6  
High Definition is the definition of life.
 
JB Antennaman's Avatar
 

Join Date: Jun 2009
Location: Pennsylvania
Posts: 1,409
Default

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.
JB Antennaman is offline   Reply With Quote
Old 10-10-2009, 03:09 PM   #7  
Sony KD34XS955
 

Join Date: Jul 2005
Location: Pointe-Claire QC
Posts: 2,865
Default

Quote:
Originally Posted by JB Antennaman View Post

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?
BrianO is offline   Reply With Quote
Old 10-10-2009, 04:58 PM   #8  
High Definition is the definition of life.
 

Join Date: Sep 2009
Posts: 193
Default

Quote:
Originally Posted by BrianO View Post
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.
jdemaris is offline   Reply With Quote
Old 10-10-2009, 05:08 PM   #9  
High Definition is the definition of life.
 

Join Date: Sep 2009
Posts: 193
Default

Quote:
Originally Posted by JB Antennaman View Post
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."
jdemaris is offline   Reply With Quote
Old 10-10-2009, 06:22 PM   #10  
High Definition is the definition of life.
 

Join Date: Sep 2009
Posts: 193
Default

Quote:
Originally Posted by JB Antennaman View Post
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.
Attached Images
File Type: jpg Viking redio.jpg (37.5 KB, 27 views)
File Type: jpg Viking redio2.jpg (50.7 KB, 24 views)
jdemaris is offline   Reply With Quote
Old 10-10-2009, 06:46 PM   #11  
Direct TV Fresh Meat
Thread Starter
 

Join Date: Feb 2007
Posts: 2,464
Default

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?
DoctorCAD is offline   Reply With Quote
Old 10-10-2009, 11:31 PM   #12  
Sony KD34XS955
 

Join Date: Jul 2005
Location: Pointe-Claire QC
Posts: 2,865
Default

Quote:
Originally Posted by jdemaris View Post
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.
BrianO is offline   Reply With Quote
Old 10-11-2009, 07:00 AM   #13  
High Definition is the definition of life.
 
JB Antennaman's Avatar
 

Join Date: Jun 2009
Location: Pennsylvania
Posts: 1,409
Default

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.

Last edited by JB Antennaman; 10-11-2009 at 07:12 AM..
JB Antennaman is offline   Reply With Quote
Old 10-11-2009, 07:59 AM   #14  
High Definition is the definition of life.
 

Join Date: Sep 2009
Posts: 193
Default I absolutely disagree

Quote:
Originally Posted by JB Antennaman View Post
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.
jdemaris is offline   Reply With Quote
Old 10-11-2009, 08:32 AM   #15  
High Definition is the definition of life.
 

Join Date: Sep 2009
Posts: 193
Default

Quote:
Originally Posted by DoctorCAD View Post
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.
jdemaris is offline   Reply With Quote
Sponsored Links
Go Back   High Def Forum - Your High Definition Community & High Definition Resource >
AddThis Social Bookmark Button
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


to Question about CM 7777
Thread Thread Starter Forum Replies Last Post
Another antenna question DocCasualty Local HDTV Info and Reception 8 10-13-2007 09:04 AM
Antenna Question. realnerd Local HDTV Info and Reception 20 07-01-2006 09:29 AM
Okay, a question about pre-amps.... Huey Local HDTV Info and Reception 21 06-25-2006 06:10 PM
Winegard AP 8275 in place of CM 7777? Amerikes Local HDTV Info and Reception 49 06-07-2006 03:02 PM
Antenna / HDTV question from a newbie... Steve Goss Local HDTV Info and Reception 17 01-26-2006 05:36 PM
Question for Antenna Gurus Lurf Local HDTV Info and Reception 14 01-06-2006 05:02 PM


All times are GMT -6. The time now is 04:41 PM.



Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright 2004 - 2018, MH Sub I, LLC dba Internet Brands