Location of Second Comm Antenna

[sbateman7799]

'morning,
I have an RV-12 with Skyview D1000 and Garmin SL40 comm radio. I want to add a second comm radio (considering the PS Engineering PAR200B audio panel with the Trig TY91L remote mounted radio). The existing comm antenna is as per KAI 42M-07: mounted underneath, offset from centerline.
Any suggestions for locating a second comm antenna?
Has anyone been successful (lack of interference) mounting it underneath, offset to the other side?

 

[Eriselle]

I would consider putting the second one on top instead of the bottom.

 

[12vaitor]

I added my second comm antenna on top. Based on the antenna drag number I ended up with a doubler under the skin along with two J-channels between the frames to stiffen the thin skin. Adding another COAX from the front panel was another problem to be solved due to the limited space in the tunnel snap bushings. Issue with the bottom is I already have IFF, ADS-B and COMM antennas there, plus switching from bottom to top helps in some situations where I have poor comms.

 

[sbateman7799]

Thanks for your reply and for the photo. Yes - same issue with lack of room in the existing snap bushings and the cable clamps in the tunnel.
I'm taking a long look at the RAMI AV-590 smart coax switch which in theory avoids the need for the second antenna and coax run.
What did you use for the second radio and where did you mount it in the panel?

 

[12vaitor]

Thanks for your reply and for the photo. Yes - same issue with lack of room in the existing snap bushings and the cable clamps in the tunnel.
I'm taking a long look at the RAMI AV-590 smart coax switch which in theory avoids the need for the second antenna and coax run.
What did you use for the second radio and where did you mount it in the panel?

I am running an Avidyne IFD540 as COMM/NAV 1 and a Garmin GTR-200 as COMM 2. I built a custom one-piece panel with redesigned radio support brackets. I ended up adding another set of 3/4" snap bushings to accommodate the added COAX (NAV/ILS antenna, GA35 GPS, and COMM 1) in the tunnel. I use the Garmin mainly for AWOS/ASOS with voice comms on the IFD540 (better comm quality).

 

[sbateman7799]

Interesting. Again, many thanks for the info!

 

[CTCole]

I added my second comm antenna on top. Based on the antenna drag number I ended up with a doubler under the skin along with two J-channels between the frames to stiffen the thin skin. Adding another COAX from the front panel was another problem to be solved due to the limited space in the tunnel snap bushings. Issue with the bottom is I already have IFF, ADS-B and COMM antennas there, plus switching from bottom to top helps in some situations where I have poor comms.

Do you have a magnetometer anywhere near that top antenna? I've wondered if there would be any interference, especially during transmission.

 

[bjdecker]

Do you have a magnetometer anywhere near that top antenna? I've wondered if there would be any interference, especially during transmission.

Got a handheld radio and a compass? Put the compass near the antenna, transmit and see if the needle swings...

 

[12vaitor]

Do you have a magnetometer anywhere near that top antenna? I've wondered if there would be any interference, especially during transmission.

The Dynon Skyview installation manual for the SV-ADAHRS-200/201indicates a 2-foot minimum distance from dynamic magnetic fields. My -200 is located about 2-ft forward of the antenna. I have never seen the mag heading indicator change during a radio transmission.

 

[rcarsey]

I put a HAM radio antenna (144-148Mhz) on the co-pilot side's access panel on the belly. I'm not sure what the distance is from the airband VHF antenna (maybe 2 feet?), but I can tell you that it is too close.. even with the two radios operating 20Mhz apart. Depending on the frequencies, its about a 50/50 shot whether I overpower the airband VHF's receiver when I transmit on the HAM radio. I'm not too concerned about blowing out the airband VHF (GTN 650)'s receiver because its rated to accept some amount of power (i think it was 5 watts).. and I limit my HAM radio to 5 watts output.. so whatever gets coupled to the GTN650's antenna is much less than 5w. But, I'd 100% suggest mounting it on top of the aircraft.. The proper thing to do though is to wire up the Inhibit wires - so one radio turns its receiver off while the other is transmitting..

 

[CTCole]

I wondered about that Ham/shortwave radio in your photo of the panel....