How important is antenna size?

Aaron62

Contributor
Staff member
#1
Speaking in terms of outdoor antennas, how important is antenna size? This is just a guess on my part, but I would think that mounting height would play a far more important role than size of antenna based on whether the antenna is even in a position to receive DTV signals. True?
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#2
Aaron wrote:

Speaking in terms of outdoor antennas, how important is antenna size? This is just a guess on my part, but I would think that mounting height would play a far more important role than size of antenna based on whether the antenna is even in a position to receive DTV signals. True?

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Aaron,
If you're suggesting the bigger an antenna is, the better it is, that's wrong. 50 feet of chain-link fencing with coax attached to it might be an antenna for something but probably not for TV reception, nor would be an 80 meter dipole for ham radio. Also, many older commercially built UHF antennas were designed to receive up to channel 83 and are not 'maximized' for 14-51.

Regarding height, two examples: for me to receive KVOS-12 (35) 75 miles away, I am using my home-brew 15 element cut-to-35 Yagi and the signal level I receive is a function of its height. A proper antenna and the higher the better.

On the other hand, I am catching a bounced signal from a downtown skyscraper to receive KING-5 (48) and their (useable) signal is present between 18 and 20 feet above my roofline -- NO higher and NO lower. This is on my home-brew eleven element cut-to-48 Yagi. A proper antenna at a specific height.

So using an appropriate antenna, try different locations on your roof and different heights. I discovered the 'bounce' mentioned above completely by accident in the process of lowering the antenna. I accidently rotated it about 45 degrees and when it passed thru the 20-18 foot level --- BINGO! :thumb:

I consider HDTV reception to be a bit of a black art and trial and error testing really pays off.
Jim :D
 

Piggie

Super Moderator
#3
I always found antenna placement a bit of black art. I had an dipole on 40 meters I used to have up about 20 meters off the ground. It worked great. Then I moved and I could not get more than about 10 meters. It couldn't receive 1KW next door. Then I read about the "Inverted L" and how they work great close to the ground. So I dropped the hot let (no balun) down toward the ground and bingo. It wasn't a super DX but it heard DX on low angle that while it was a dipole it would not.

WESH on CH 11 comes in here in my yard as good (maybe better) at 10 ft than at 25 feet. It's at 83 miles yet to pick up Jax, FL at 61 miles the higher the better all the way. WNBW doesn't work any better at 30 ft than it does at 10ft (both heights LOS).

VHF is crazy, because you can't as easily predict knife edge or reflections (takes something big) as you can on UHF. Tilting an antenna from my experiments in the yard only makes VHF worse.

Back to the original question. I am going to say yes bigger is better, but only in some cases. The reason I want to say this is so many antennas are made too small to provide aesthetic appeal, yet don't work worth a duck dodo. The more directors on a yagi, up to about 4 wavelengths always add gain if done correctly. The larger the dish or parabolic reflector almost always means more gain.

Your point is well taken. The antenna HAS to be designed correctly if bigger is going to help.

Another good example of what won't help that a lot of people fell into was using an older model 2-69 for DTV when they didn't even have any low band because "it was bigger".

Another way higher sometimes hurts is co-channel. If you have a bad co-channel problem often hiding down low or behind a wall will block the other station. There is a long boom UHF up on a hotel in Orlando that was put behind the top of the elevator shaft building (protrudes from the rest of the roof) to pick up a station actually farther away from a full power station and the elevator shaft blocks a LP on the same channel.

Another example of higher not needed. Back in the day when most cable head ends relied on OTA for locals (not microwave or satellite reception) other tricks besides high on a tower. High Springs/Alaucha FL cable head end had a 12 to 18 ft high chain link fence (saw it once 30 years ago) that was strung on a field in an arc of a circle (not parabolic). This gave different foci for the different stations from Orlando at 80 miles away. Since it was north of Orlando, the fence created a huge front to back for the system. The antennas where then mounted about 6 to 8 ft high off the ground pointed back at the fence arc. It was a HUGE dish antenna for VHF. It was much more reliable for picking up Orlando than the single cut yagis on their tower. It was really immune to co-channel from Georgia.

One cable company lowered their Ch 4 receive array on a tower owned by a company I worked for because up higher than got nailed by another ch4. They had 2 single channel yagis stacked horz up about 150 ft pointed at Jax FL from McCleney FL about 45 miles away. Worked great until frequent tropo set in at night. So they stacked 4 in a quad pattern (2 over 2) and lowered the array down about 100 ft. It didn't solve all the tropo but it greatly improved their reception. The 2 extra antennas and being lower on the tower gave them a tighter beam width besides being lower on the tower, did stop most of the tropo.

I have watched and seen (including my own) best engineered antenna projects be out performed once in the real world, often found as Jim did by accident.

I found and it's no where on TVFool or the books, that if I put an antenna up 20 plus ft to pick up WUFT-DT on ch36, I have a lot less fading than at 10 ft, even though they are LOS down to about 3 ft off the ground where I live. Probably trees moving or cars, etc.

First every antenna install itself is at least a minor engineering survey project and then often there are so many factors that you just can't take into account experimenting often yields results you would not expect. Thank goodness for most people within suburban range of towers about anything tends to work. But once you are in the fringe zone, anything goes. It's best to try a various heights and various styles of antennas.

Another example I found in my yard. I had up 4221A (old version) up about 18 ft. It was plagued with multipath from WOGX, that is only 25 miles way and powerful. Had me very confused. I was going to build a very high gain directional antenna with another 4221A and put up a very old Radio Shack U-75R (even with an reflector element gone) for a temp antenna to watch TV while I experimented with the 4221As. Low behold, even though my signal quality meter dropped about 10 points, the mulitpath was gone! Analog was still on the air from the same tower and antenna on 51 and there was no degradation of the analog signal noticeable even though their digital on 31 dropped 10 points of quality. It was pure luck I found that old corroded thing worked better than a huge fancy antenna. But that won't work everywhere. It just happened to solve some multipath I was having in my particular situation.

Experiment............ and don't buy small "pretty" antennas if you live in fringe zone.
 

Piggie

Super Moderator
#5
You guys never cease to amaze me with your answers and details. Thanks!
Jim and I have been playing with some kind of antenna since the 1960's.

And as I keep saying and repeat and EV's old finds from magazines and stuff prove out, there really aren't any new "antennas" around these days. You will see new designs that take this or that from another design, but basically there is a dipole, the loop, then probably have to add yagi (and all it's kin, quads, traveling wave, log). And also the Marconi vertical 1/4 wave.

The one part of the digital transition that didn't go digital were the carrier waves of the TV stations. They are still analog. So all those decades of knowledge still apply to antennas.
 

FOX TV

Contributor
#6
Antenna Height VS Size !!

Speaking in terms of outdoor antennas, how important is antenna size? This is just a guess on my part, but I would think that mounting height would play a far more important role than size of antenna based on whether the antenna is even in a position to receive DTV signals. True?
Any "Conventional" antenna is nothing but a piece of metal wire, a metal rod, or other electrically conductive material that is cut to a certain dimension that is directly related to the frequency that you are trying to receive. In other words, its total length matches the physical wavelength of the signal you are tying to receive to a fractional or mathematical degree.

Any type of "Conventional" antenna will only be most efficient at that one given frequency, and that frequency is in direct relation to the physical dimensions of the antenna, and the frequency of radio signal itself. Any signals above or below this frequency are not received as efficiently as that one certain frequency that the antenna was designed for.

That is basic theory regarding "Conventional" antennas, but there are two other situations that come to mind where these rules don't exactly apply. At low frequencies such as shortwave, or AM broadcasting, the length of antennas at these wavelengths are extremely large, and not practical for general use, so there are "Matching Devices" that fool the transmitter or receiver into thinking that they are coupled to a properly cut antenna.

In this situation, an antenna that is physically larger without using a "Matching Device" would improve reception quite a bit, and especially if a 1/4 wavelength or better could be achieved at these frequencies, but you would need several acres of land to achieve this.

The next and most "Non Conventional" antenna design is known as a "Fractal" antenna. A fractal antenna is "a rough or fragmented geometric shape that can be split into parts, each of which is approximately a reduced-size copy of the whole". By repeating this process many times, a fractal antenna becomes many more "Fractal Antennas".

This repeating process known as "iteration". "Iteration is the act of repeating a process, (In this case, it means reproducing multiple miniature copies of the antenna). Each repetition of the process is also called an "iteration", and the results of one iteration are used as the starting point for the next iteration." Definitions loosely taken from Wikipedia, the free encyclopedia

As the "iteration" process continues for hundreds or thousands of times, many more "Fractal Antennas" are produced, thus the theoretical gain, and the physical size of the antenna increases also. This fractal antenna array can then become capable of receiving multiple bands and frequencies now as its physical size grows.

I normally relate this to the harmonic frequency phenomenon to give it an example for comparison, or to the process of looking into two mirrors placed directly in front and behind you. It looks as if you can see infinity by doing this, and fractal antennas can be compared to these known concepts for clarity.

We do know that stacking or ganging conventional antennas increases gain, and the fractal antenna concept takes this aspect of stacking or ganging antennas to a whole new dimension, and they are the antennas of the future, and that future is here now, as most Cell Phones now use this new computer age antenna technology.

On the topic of antenna height, you are correct that antenna height is the most important aspect in most cases. It is one of the most efficient ways to improve your signal strength, if low signal is the issue. This may also help in some cases, with multi path, and signal quality issues as well, and in some cases could also let exact aiming of the antenna become a little less critical.

Since an antenna mounted higher is sometimes mounted above the "Ground Clutter Zone" that contributes to the multi path phenomenon, this could solve a lot of reception issues, especially when compared to indoor antennas that are always mounted in the "Ground Clutter Zone". (My term for all of the possible reflection points that an indoor antenna may "See")

But, we all have different opinions on this as can be seen in Piggies post above, and there are always situations where one theory will apply where another one that worked in the past will not apply now. Every receive location is different, and different situations call for different approaches.
 
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