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Transmitting on both radios

R

RandyRMc

I'm New Here
I have a Bob Archer T/R switch and a single Comant 122 antenna for both a Garmin 430 and KX 125 radio in my RV7A
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When I key the MiC it now transmits on both radios, whether I am on Com1 or Com2 on my Garmin 340 audio panel.

I am thinking the easiest solution is to just add a second Comant 122 antenna so each radio has its own antenna, removing the Archer switch.

Questions: How far apart do they need to be mounted, either across from each other or front to back to prevent any interference from each other?

Thx for any help with this.
Randy McFarland
San Jose Ca
RV7A 778hrs
 
Just a usage comment

This probably does not apply to your situation at all but I thought I would pass it along just in case.

I have two of the bent whip Comant antennas on the bottom of the fuselage approximately 4 inches inboard of the outboard side of the fuselage under the seat of the RV-6A. When I installed them sometime before March 2004 I researched the the separation requirements and satisfied myself that they were satisfied. I have a Terra Com panel and everything works fine and I can receive on both tranceivers and all of the nav and marker beacon receivers at the same time with no problem. I can transmit with either transeiver (SL-30 and SL-60) on their individual antennas but when I transmit on the SL-60 I have to put the com panel "speaker-off-headset" switch for the SL-30 in the off position or the feedback drops com quality in my headset to about 5x1. I only noticed this when I happened to have my #2 on headset. I only use the number 2 com for getting weather or as a backup com unit in addition to its nav function. Number 2 com works fine as well and I assume it has the same feedback problem if I have both units on headset and transmit on number 2 but I can't remember if I have actually done that or not. If this is the kind of "problem" you are experiencing, you may be disappointed after making the antenna change. RF is a funny thing.

We went to the Garlic Festival had a very good time and even ate the garlic ice cream. We landed at the South County Airport. Also went to the Flying Lady Restaurant where they had the world class large scale models moving by overhead suspended from a conveyor or track of some kind. SAY! Are you the fine Scotsman I met at Reno on on June 7?

IMG_0001-19_zpscc58331f.jpg

taken in 1987

Bob Axsom
 
Last edited:
Stop!

Do not proceed until you fix this. Having one transmitter on but not connected to anything is hard on the output circuitry, even though modern designs have some protection built in.

It sounds like there is something wrong with your audio panel, its settings, or its wiring. Or the PTT wiring going to the T/R switch. Only one transmitter should be on at any one time.

If you install a second antenna you still need to fix this problem.

If you were asking if it is possible to listen to one radio while transmitting on the other, the answer is maybe, if the antennas are far enough apart and the frequencies are also far apart. But on most RVs you cannot get the antennas far enough apart.
 
Belly antenna, turtle deck antenna

BobTurner said:
.... if the antennas are far enough apart and the frequencies are also far apart. But on most RVs you cannot get the antennas far enough apart.
Click to expand...

Just my experience but I have one antenna on the belly, and another on the turtle deck of our RV9A for maximum separation. I can transmit on one while simultaneously receiving on the other, and so far we have not found any problematic frequencies in real life situations.

This feature is quite handy at times. Once I had to speak to the Flight Service Station while I was on flight following. As I modified my flight plan with FSS, I could hear the controller calling me on the other frequency. Pretty cool.
 
Garmin stuff

BobTurner said:
Good receiver! What brand/model is it?
Click to expand...

Garmin GNS-480 and an SL30. Basically the GNS-480 (nee CNX80) has the guts of an SL30. Funny thing is, I can now listen to a cacophony of frequencies, as each radio can monitor a standby frequency. In reality, I use mainly one radio, and the other for monitoring 121.5.

Another nifty feature is the split com (audio panel feature), which could come in handy when two pilots are flying.
 
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