Transmitter frequency?

Question

I want to build a small on/off 5 watt transmitter and receiver so i can have a remote trigger. I know how to accomplish this but i am stuck on what frequency to use. I would like it to go as far as possible and not be severely effected by hills or buildings.

I was thinking of around 30mhz in the citizen band because it would be completely fcc friendly, but around 500mhz would be good because a quarter wave antenna is only a few inches long and i will get help from the ionosphere.

p.s. this will not be operated for no more then a second very rarely so is not a problem fcc wise

Answer 1

why build? this would require FCC certification.

use surplus commercial radios.

27Mhz AM is legal, as is 154.57, 154.60 and 2 other MURS channels.

I cannot think of any legal UHF channels for A1/F1 emission.

27MHz limits you to 4W output, MURs allows more, I am not a MURS user so I cannot quote a maximum power.

Other than that, get a ham license, no-code Tech will get you VHF and UHF non-commerical channels.

Answer 2

As a ham, I would agree that this is the way to go.

However, there many things to take into consideration.

Mode, for instance. I would go for a 1.3 GHz system.

The antenna array is smaller and you can have a lot of gain in a pencil beam, with good lobe attenuation, and little interference from other users (stay clear of bleed over from the TV portion, though, as the sidebands are 27 MHz wide).

The RX can have a simple switch using an emitter follower to turn on  a power relay, etc.

Good luck

Dr Antony

Answer 3

Bob's got a pretty good point about 2 things here.

1) get a ham lic...It's so easy to do a monkey could get a tech lic. Study the answers, and your lic to do what you want. The cost...almost nothing

2) use a commercial radio to do this...you can get some surplus for next to nothing, and most will have a "data" input. This way you don't have to worry about building a transmitter that will splatter all over the spectrum and possibly get you a big fine from the FCC. Save yourself some heart ache and some grief. I know it's sounds fun to build a transmitter, but the outcome could be bad. Your still gonna have to do the interface and that's kinda fun..