Raised antenna 8 feet; little gain

I raised my antenna from 24 to 32 feet but there wasn't much of a gain--maybe 1%. My Zip Code is 34949, and all of my UHF stations are coming in around 88-94%, but the VHF stations are anywhere from 4% to 98%, averaging around 81% during the middle of the day.

Do you think this map may have the answer?

www.mountainlake.k12.mn.us/ham/aprs/path.cgi?map=na

In a word no, that map is of little use to YOU. I might be wrong, but the map better describes the probability of DX-ing conditions, lucky atmospheric anomalies where high clouds reflect televisions signals back down to the ground instead of allowing them to simply pass through meaning they are lost to outer space. And even in yellow areas, they simply are nor reliable.

If you are getting good performance on UHF at your present location,, but poor performance from VHF signals, its far more probable your problem is in antenna selection.

But posting an exact address TV fool report would be the better alternative. A generic zip code address is not as useful.

And giving this forum some data about your present antenna would also help a bunch.

Once that data is in, we will all be in a better situation in terms of answering questions and making quality suggestions.

Weather conditions, or tropospheric ducting, can improve a signal temporarily, but it can also cause signal failure when a distant station interferes with your local station....I would agree his antenna should be questioned.

Moving the antenna (along the roof peak) vs raising the antenna, usually provides better results. ;)

I noticed on Monday and Tuesday morning around 5:00 a.m., that the NBC stations broadcasting on Channel 12 wasn't coming in well--signal around 51% but a Tampa station was coming in on Channel 29 (28-1) around 65%. Obviously a signal bounce since Tampa is 130 miles away.

Before the digital transition, VHF stations had to be 200 miles away ore more, and now we're allowing them to be much closer. Looks like that is causing a problem for this consumer.

I have been designing communications systems for over 30 years and here is an old "rule of thumb." You will get 6dB of system gain everytime you double the antenna height, minus the loss of the additional transmission line. Therefore, moving your antenna from 24 to 32 feet would not have any affect at all unless you are moving your antenna up to get over a very near field obstruction (for example, your roof).

I have been designing communications systems for over 30 years and here is an old "rule of thumb." You will get 6dB of system gain everytime you double the antenna height, minus the loss of the additional transmission line. Therefore, moving your antenna from 24 to 32 feet would not have any affect at all unless you are moving your antenna up to get over a very near field obstruction (for example, your roof).

That info actually helps quite a bit - in other words, don't kill yourself trying to get more height...

My first post!

jdv

That info actually helps quite a bit - in other words, don't kill yourself trying to get more height...

My first post!

jdv

Exactly! When I was designing commications systems, the question I always had to answer was it worth the cost to a customer to increase antenna height from say 400' to 500', or how about 500' vs. 1000'? The answer was almost always no because what little was gained in coverage was offset by the huge increase of tower costs, either to buy and construct or rent space.

BTW - - Welcome to the Board!

I have been designing communications systems for over 30 years and here is an old "rule of thumb." You will get 6dB of system gain everytime you double the antenna height, minus the loss of the additional transmission line. Therefore, moving your antenna from 24 to 32 feet would not have any affect at all unless you are moving your antenna up to get over a very near field obstruction (for example, your roof).

I usually do not quote me, but whatever.......

Just to add to my previous post, if your are correctly using a pre-amp ("correctly" meaning mounted right next to the antenna) then increasing the antenna height is more beneficial since there will not be any additional transmission line loss to deduct. A good pre-amp system will totally overcome any transmission line, or downstream splitter, losses.

BTW - - Welcome to the Board!

Thanks a lot - what a cool forum. Gave up on Comcast 3 months ago and haven't looked back.

john

Going from 24 to 36 feet can be huge if it gains you Line Of Sight to the transmitting tower.

Furthermore if 24 feet is siting on top of you roof, then an extra 8 feet also gives you gains from "ground" interference....clearing the obstacle or especially the Earth ground level) for .5 to 1 wavelength at VHF Low frequencies and greater at UHF.

At UHF frequencies also hot spots or sweet spots where the antenna is better illuminated by the signal can give you great gains.

From what I understand...

Good information! Thanks for the posts!

Going from 24 to 36 feet can be huge if it gains you Line Of Sight to the transmitting tower.

Furthermore if 24 feet is siting on top of you roof, then an extra 8 feet also gives you gains from "ground" interference....clearing the obstacle or especially the Earth ground level) for .5 to 1 wavelength at VHF Low frequencies and greater at UHF.

At UHF frequencies also hot spots or sweet spots where the antenna is better illuminated by the signal can give you great gains.

From what I understand...

As I mentioned earlier, it has been proven over many, many years of designing communications systems that you have to double the antenna height to get approximately 6bB of additional system gain minus the additional transmission line loss.

That is a general rule that although very old, has turned-out to be fairly accurate after complicated computer software programs were developed in more recent years to show very accurate coverage (not to mention actual field results). (The kind of accuracy required when a company's executive officer's signature is required on a multi-million dollar contract, which I have desiged many BTW.)

The only real exceptions are if you have near-field obstructions (antenna below roof line, or very nearby trees, buildings, or hills). Such obstructions can severely hamper signal reception. If any of these types of problems exists at a specific house, then many times the only fix is to go up.

Another real world example: You know those small portable radios that nearly all public safety people carry? Some users like to mount the radio on their belt and use a speaker/microphone to listen/talk. Other users will just pickup their radio and talking directly into the microphone. The difference in antenna height between the two users; about 3 feet. The first user's radio is 3' off the ground (at waist level), the second user's antenna is about 5-6 feet. No big difference? Think again; double the antenna height = 6dB more gain for user #2. (Actually, much more than that since the body of user #1 is also shielding the antenna adding even more loss.) BTW - - Everything I just said applies to cell phone users also, so keep that in mind if you are having cell phone problems.)

Back to the OP's original question; going from 24 to 32 feet. Eight feet would provide little, or no, measurable signal increase. The only exception is if this increase gets the antenna over a roof line of his house or the house next door, or a tree/building that is very close by.

Maybe some of these general rules people are mumbling about might apply over some still ocean, but after you add in difficult land terrain,
trees, hills, and building, there are probably few if any general rules that
can be relied on.

Maybe some of these general rules people are mumbling about might apply over some still ocean, but after you add in difficult land terrain,
trees, hills, and building, there are probably few if any general rules that
can be relied on.

I assume that you are referring to my comments, but I can promise you that the general rule-of-thumb rules that I have writtern are correct and have nothing to do with surrounding terrain or water. There are many multi-million dollar contracts that are based on what I have written. Not to mention the lives of many police, fire, and other public safety officers.

The only wingle room in this thread is that we are dealing with a point-to-point path (TV transmitter antenna to a TV receive antenna that is at a fixed location). However, every rule that I have written about still applies.

Sprout, Im not refuting your rule.

You are missing other parts of the picture, is all Im saying.

The difference between 500ft and 1000ft, your rule applies....the only consideration is LOS to distant antennas. At 20 miles that doesnt apply, at 55 miles that extra 500ft becomes very beneficial....for reasons having nothing to do with gain increases at height....and everything to do with LOS to the towers from the transmitting location....or vice versa the recieve antenna location and height.

Furthermore, 500ft and 1000ft both clear any considerations about ground interference with the antenna field....at that height all you are worried about is the tower itselfs interference with the field.

I just brough other considerations into the mix.

Then again, Im no expert. Just a hobbyist, and one still learning the ropes at this stage...just getting into ham and antennas.

I went to www.tvfool.com and found out this information

Our local NBC station, WPTV is broadcasting on Channel 12 at 50,000 watts and is 61 miles away.

With an antenna 15 feet in the air, the station comes in at -79.3
With an antenna 32' in the air, the station comes in at -75.5
With an antenna 100' in the air, the station comes in at -68.9
With an antenna 500' in the air, the station comes in at -53.5

I went to www.tvfool.com and found out this information

Our local NBC station, WPTV is broadcasting on Channel 12 at 50,000 watts and is 61 miles away.

With an antenna 15 feet in the air, the station comes in at -79.3
With an antenna 32' in the air, the station comes in at -75.5
With an antenna 100' in the air, the station comes in at -68.9
With an antenna 500' in the air, the station comes in at -53.5

Looks familiar;). BTW, I never have used tvfool; does it allow the user to take into account transmission line & splitter losses (which would be considerable in the 100/500' example), and very important in most all installations?

Sorry OP for dragging your thread thought hell.......

Thanks EscapeVelocity for your comments and thoughts on this subject. (BTW - - My experience is based on nearly 40 years of; land-based microwave and two-way radio system design and implementation, and limited TV broadcasting engineering many, many years ago. My only reason for mentioning this is that most all of my experience is not in TV broadcasting.)

The 6dB Rule that I mentioned has been known to Communications Systems Engineers for years, long before there was much to back it up other than field experience. Now large communication companies, like the one I retired from a couple years ago, have complex and propriety computer software that they use to predict coverage and then design systems based on these predictions. Literally, millions of dollars (not to mention lives) are at stake when designing systems to meet customer desired, and usually contract required, coverage. After the fact field testing usually backs-up the predicted coverage. It is amazing how close the computer studies usually are compared to actual. (Good thing, there is usually a lot of money at risk for the vendor).

I cannot even image how many thousands of such computer studies that I have ran. During this time we have discovered that the old 6dB Rule is very accurate for almost any combination of transmit and/or receive antenna combinations. This is very helpful when first starting the design process where we have to quickly decide what towers are appropriate for our customers. For example, is it worth the extra money, and usually other issues, to sell (or rent space on) a 500' vs. a 400' tower? The answer is almost always no. The main exception is if that very, very small increase in coverage is just enough to cover some small area that the customer requires. The extra 100' may save the costs of developing a second site. Even huge, 1000' towers, are not considered because of the high costs and very little coverage gain because of all the transmission line losses. I did have one exception to this here in Houston, but it was unusual, it had a small radio building at the top of the tower; no transmission line losses! Tall buildings is the other exception, you get all the benefits of extra antenna height, but with very little transmission line loss.

For the readers that do not think this applies to you, reread my earlier post that included a discussion about portable radios and cell phones. Do you like your Bluetooth Headset? Most have the cell phone clipped to their belt (on in a purse), and to make matters even worse are sitting in their car with the cell phone between their body and the car door. Your cell coverage will suck big-time! Assume at least 20-30 dB of loss vs. just standing outside with the cell phone at your ear.

Predicting radio coverage (of any kind) is always part science and part wild a** guess (I am not even sure which is the most important). However, the comments that I have made in this thread are very accurate and time-tested.