Alternatives To Log Periodics - Need An Inexpensive, Directional, Broadband Antenna

[kinsey6]

I'm wondering what type of cheap alternative there is to a log periodic antenna... something that's broadband, directional, high-gain, but low-cost too? It occurred to me in looking at log periodics how much they resemble regular 'ol TV antennas. I'm not so naive to think I could put a TV antenna up and have it work just as good as a log periodic just because they look nearly identical in many cases. But what I'm not sure about is what I'd be giving up or just how good one might perform by putting up a TV antenna instead of a log periodic for a scanner.

So what would be a good substitution that's low-cost, directional, and broadband -- even if it's second-hand? I'd be open to other types of antennas too if they'd work. I *think* a horn might, and that might even be preferable to a log periodic or TV antenna because of the high wind and icing potential we have here sometimes, but that's a secondary concern to the other considerations right now. If I can't find an alternative then I'm thinking my only option right now may be to just get a high-gain yagi and hope for the best but with a limited frequency range.

P.S. Unless it required limited tools I doubt I'd be too good with building my own.

 

[zz0468]

... I'm not so naive to think I could put a TV antenna up and have it work just as good as a log periodic just because they look nearly identical in many cases.

Why not? The typical TV antenna IS a log periodic antenna. Lots of guys are turning the elements vertical and hooking them up to their scanners.

Now, there IS a bit of a difference, though. The TV broadcast spectrum is adjacent to land mobile spectrum, and TV antennas are designed to be optimal at in the TV spectrum. There may or may not be sufficient overlap for a TV antenna to work well in the frequency ranges you want.

But what I'm not sure about is what I'd be giving up or just how good one might perform by putting up a TV antenna instead of a log periodic for a scanner.

What you get for the price of a TV antenna is relatively low cost. Unless you can dig out some real specs or make some real measurements, performance will be unknown.

I *think* a horn might, and that might even be preferable to a log periodic or TV antenna because of the high wind and icing potential we have here sometimes, but that's a secondary concern to the other considerations right now.

For what frequency range? Horns are generally considered microwave antennas and are quite large compared to a wavelength. They are quite broadbanded, maybe approaching an octave or more.

You might consider a corner reflector.

If I can't find an alternative then I'm thinking my only option right now may be to just get a high-gain yagi and hope for the best but with a limited frequency range.

Knowing what your frequency and gain requirements are would be helpful. Log periodic antennas are not efficient, in terms of gain vs. physical size. You could have a LP antenna with a 10 foot boom that has 8 db of gain from 150 to 800 MHz, and that same boom length on 800 MHz only might have 18 db gain... not actual figures but they illustrate the point. Yagi gain is quite dependent on boom length and a long boom yagi with wide spaced directors will have more gain than a shorter boom with closer director spacing. In a log periodic antenna, because of the broadband design, only a few elements come into actual use for any given frequency, which is what limits their gain.

Edit:

Looking back at your other antenna thread, it would appear that you're interested primarily in 800 MHz. In that case, disregard the "broadband" requirement, and concentrate on finding an 800 MHz yagi.

 

[n5ims]

I'm wondering what type of cheap alternative there is to a log periodic antenna... something that's broadband, directional, high-gain, but low-cost too? It occurred to me in looking at log periodics how much they resemble regular 'ol TV antennas. I'm not so naive to think I could put a TV antenna up and have it work just as good as a log periodic just because they look nearly identical in many cases. But what I'm not sure about is what I'd be giving up or just how good one might perform by putting up a TV antenna instead of a log periodic for a scanner.

So what would be a good substitution that's low-cost, directional, and broadband -- even if it's second-hand? I'd be open to other types of antennas too if they'd work. I *think* a horn might, and that might even be preferable to a log periodic or TV antenna because of the high wind and icing potential we have here sometimes, but that's a secondary concern to the other considerations right now. If I can't find an alternative then I'm thinking my only option right now may be to just get a high-gain yagi and hope for the best but with a limited frequency range.

P.S. Unless it required limited tools I doubt I'd be too good with building my own.

A few main comments on what you're proposing.

First, in general, what you're asking about should work, but you'll need to make a few adjustments. Most important, a TV antenna is horizontally polarized while scanner antennas should be vertically polarized. This may be easy to handle by modifying how your antenna is mounted. You could swap the polarity by changing the mounting if the design will let you. You may also need to offset it using a short piece of pipe to do the rotation for you (which will also move the elements away from the mast and help performance a bit).

Second, check the frequencies for your specific TV antenna to see how they align with where you scan. Since the TV frequencies are fairly spread out with the scanner frequencies generally between channels this may be fairly easy to find coverage. Don't forget to check the FM frequencies since often a TV antenna will also be designed to include them as well.

Third, and probably most important, is to first see what frequencies you really need coverage for. That is a pretty specific question and totally different from what frequencies does your scanner cover. This can be best answered using the RadioReference database, not the scanner's manual.

If your scanner goes (as most do) from about 30 MHz to about 1 GHz (skipping a few small ranges in between) but you only listen to systems on the 800 MHz band, your answer will be 800 - 900 MHz, not 30 MHz to 1 GHz. By restricting the antenna specs to at least the fairly small range you actually need you'll find much better performance (and generally lower cost) than trying to find one that covers everywhere.

The reason for this is similar to finding the specs for a truck to tow a boat to and from the lake. Since boats can be found in all lengths and weights, say easily from 6 foot aluminum rowboat to 40+ feet boats weighing a couple of tons the necessary truck will differ based on where along that range the boat you have is. The 6' aluminum rowboat will probably work with nearly any kind of truck (or even a small compact car) while that large 36' inboard cruiser may require a large F350 dual-wheel monster to haul it. To relate, an 800 MHz band only antenna will be high gain, small, and cheap while one that covers DC to Daylight will give you minimal gain, be quite large, and cost quite a bit.

 

[jack103]

Try looking at the Grove Scannerbeam antenna with a Radio Shack TV rotator.

 

[kinsey6]

That Scannerbeam III looks like it should do the trick. Thanks for suggesting it.