Van's Air Force
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Dual Antennas/ Single Comm
- Thread starter ivanjr
- Start date
Sam Buchanan
been here awhile
Just curious, why would you want to do this?
azcloudflyer
Active Member
What you are referring to is an antenna diversity system. On the transmit side it is pretty easy as you split transmit power between the two antennas using a splitter.
On the receive side it is more complicated because the received wave has different phase on the two antennas and simply combining the signals produces constructive and destructive interference at your receiver. That produces fading of the signal that would not normally be there in the over-the-air link. Receivers designed to resolve signals from multiple antennas are diversity reception receivers and are much more complicated than the SL-40.
Mike
On the receive side it is more complicated because the received wave has different phase on the two antennas and simply combining the signals produces constructive and destructive interference at your receiver. That produces fading of the signal that would not normally be there in the over-the-air link. Receivers designed to resolve signals from multiple antennas are diversity reception receivers and are much more complicated than the SL-40.
Mike
Kilo Charlie
Active Member
How about a switch
The plane I fly for work (C-130) has a switch for Top-Auto-Bottom antenna. I don't know how it's wired but it works great. Auto works most of the time, but on the ground Top is MUCH better and when overhead a station Bottom works great. Might take a fancy radio as said before or maybe you could just wire a Top-Bottom switch if you wanted.
I don?t know why but this is only on our UHF radios so maybe VHF does not benefit as much from selecting antennas? Our #1 VHF has it?s antenna on top and #2 on the bottom. But then again my POH says the C-130 has 35 antennas
so maybe they are just spacing them out?
KC
The plane I fly for work (C-130) has a switch for Top-Auto-Bottom antenna. I don't know how it's wired but it works great. Auto works most of the time, but on the ground Top is MUCH better and when overhead a station Bottom works great. Might take a fancy radio as said before or maybe you could just wire a Top-Bottom switch if you wanted.
I don?t know why but this is only on our UHF radios so maybe VHF does not benefit as much from selecting antennas? Our #1 VHF has it?s antenna on top and #2 on the bottom. But then again my POH says the C-130 has 35 antennas
so maybe they are just spacing them out?KC
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There is a box out there that will automatically switch between radios to transmist on one antenna based on the PTT (downstread of the audio panel). It works well, but - and here's the big but - it costs about $1,000. It has a coax lead for each radio, then one lead for the antennas, a power/ground and then the PTT leads.
So, it's a lot cheaper, easier and better to just install a second antenna.
My 2 cents!
Cheers,
Stein
So, it's a lot cheaper, easier and better to just install a second antenna.
My 2 cents!
Cheers,
Stein
One Antenna - Two Comm Switcher
Bob Archer sells a box that permits you to use one external comm antenna with 2 transceivers. It gets wired to the PTT switch on the back of your radios so that whatever transceiver is in use gets the path to the antenna during transmit. During receive, both use the antenna. It's pretty inexpensive - maybe $150? I can't recall exactly. (I have one in my RV9A). Bob is listed on the Kitplanes list of antenna vendors - call him to order. - Robert
Bob Archer sells a box that permits you to use one external comm antenna with 2 transceivers. It gets wired to the PTT switch on the back of your radios so that whatever transceiver is in use gets the path to the antenna during transmit. During receive, both use the antenna. It's pretty inexpensive - maybe $150? I can't recall exactly. (I have one in my RV9A). Bob is listed on the Kitplanes list of antenna vendors - call him to order. - Robert
Norman CYYJ
Well Known Member
Be real careful of inexpensive RF relays they could cost you a bundle in the end.
