Maximum distance with a yagi? / Scantenna radiation pattern

[kinsey6]

Hey everyone,

I'm going to be putting up a Scantenna pretty soon and am thinking of putting up a yagi with it too and I was just wondering what type of range could be expected with a good yagi? I would like to pick up Springfield's 800 mhz system but live 70 miles from their tower. My mast is going to be about 30 feet, and it's pretty flat between here and there. So is there a particular yagi I could get that would have a good chance of getting Springfield, especially if I used LMR 400 coax and got a rotator and played around with pointing it..... or is this more like a lost cause at that distance?

I've read where several people have said they can get 90-100 miles out of their discones and Scantennas (hard to believe but I've read that several times), so I'm thinking with a good yagi with high dB gain it should be possible.

Also does anyone know where I can see an illustration of what the radiation pattern of a Scantenna looks like?

Thanks

 

[zz0468]

I'm going to be putting up a Scantenna pretty soon and am thinking of putting up a yagi with it too and I was just wondering what type of range could be expected with a good yagi?

Unanswerable. There are too many unknown variables. Yagi gain, elevation above ground, ground height above average terrain, geography, foliage, frequency, transmitter power, receiver sensitivity, receiver IF bandwidth, modulation type, etc. etc. etc.

Figure it'll pull more signal in the direction it's pointed than the Scantenna.

I would like to pick up Springfield's 800 mhz system but live 70 miles from their tower... ...or is this more like a lost cause at that distance?

Can you hear anything at all from that system? If there's a bit of signal, a Yagi might bring in enough to be usable. If there's no signal at all, then no amount of antenna gain will put signal there, where there is none. Keeo in mind, many systems are specifically designed to NOT talk too far outside their intended coverage area. This is usually due to a need to share frequencies with other agencies.

I've read where several people have said they can get 90-100 miles out of their discones and Scantennas (hard to believe but I've read that several times), so I'm thinking with a good yagi with high dB gain it should be possible.

Again, it's impossible to tell from here. I've talked 200 miles with an HT with a stubby antenna. But then, I was on a high mountain top talking to a very high performance repeater on a high mountain top. In that case, the unknown variables worked in my favor. It doesn't always work that way.

Also does anyone know where I can see an illustration of what the radiation pattern of a Scantenna looks like?

Here's Antennacraft's spec sheet on it:

http://www.antennacraft.net/pdfs/ST2.pdf

There's a lot they don't say about it, including a pattern. That would vary wildly with frequency, and I suspect that they've never put it on an antenna range to measure it.

The don't give any gain figures, beam widths, or any other performance characteristics. This is because they either...

a. have no idea.
b. have an idea and don't want you to know.
c. what are performance characteristics?

 

[kinsey6]

Thanks for all the info... that helps. To answer your question as to whether I can receive any signal at all, I don't know. That's because I only have handheld antennas right now and I wouldn't expect to be able to pick up a signal at that distance with a short handheld antenna (especially in the 800mhz range). I'm going to be putting up a Scantenna, but I'd like to put up some type of high-gain directional antenna at the same time too so I wouldn't have to bother with trying to get up on the roof and put up something else at a later time. Ideally, this would be broadband, directional, high-gain, and cheap. I'm going to change the focus of this question a little though and rather than post more in my reply here then post a new thread too I'm just going to start a new question.

 

[zz0468]

Thanks for all the info... that helps. To answer your question as to whether I can receive any signal at all, I don't know.

Is it possible to take your scanner up on the roof and see if you can hear that 70 mile distant system at all? If you can hear even a glimmer of it while standing on the roof, chances are pretty fair that a yagi would help a lot.

If you hear nothing, then don't bother. If, with a scantenna you hear something, then going back up for the second antenna would be the thing to do.

Your choice sounds like two trips up the roof, or the possibility of wasted money on a yagi that turns out to be useless. Your call.