Antenna Placement

[drone_pilot]

Hello All,

This is actually my first post in the forum. I am in the process of purchasing the antennas for my 7A. I am going with the complete Dynon Skyview system including their new SV-COM-C25 COM radios. I am going with two coms, transponder, ADS-B antennas. I have been talking with Don Pansier of DeltaPop Aviation. I have asked him if I could add two side-by-side com antennas to the bottom my RV-7A and use both at the same time. His response was....

"The ability to use two transmitters at once is a function of the radios, transmit frequency difference, and antenna spacing, some radios have an inhibit function which reduces the receiver sensitivity while the other is transmitting. I can not confirm the Dynon?s ability to do this, it may be best to pose that question on VAF and field some responses."

I am not well versed in this at all, so is there anyone out there who can tell me if the Dynon radios will function as mentioned above? I am not an IFR pilot at this time and currently fly using one com to listen/communicate to ATC and the other to monitor ATIS, etc. I do intend to get IFR rated in the future. If my worries are a non-issue, let me know that as well.

Any advice is greatly appreciated!

Thanks!

Ben

 

[bret]

Welcome to VAF! The only thing I know is that the transponder and com antennas need at least 36 inch separation. But I am no expert, I'm sure some more qualified folks will chime in

 

[Joe]

Ben,

There is no "magic" minimum spacing distance, either in inches or in wavelength. More is better. And "more" may still not be enough.

The answer to your specific question with regard to the Dynon radios is the same one that Sen. Bob Dole gave Barbara Walters when she asked whether he wore boxers or briefs: "Depends"

<g>. People who don't watch American TV ads may not understand that.

Get as much distance between your antennas as practical while still maintaining an adequate ground plane under each. (An adequate ground plane is at least a quarter wavelength -- about the length of the antenna -- in all directions.) Give priority to increasing the distance between your comm antennas. If you can mount one on the top of the fuselage (I cannot in my RV-8A), that would be excellent (with regard to spacing).

I do not know of an aerodynamic reason why nearly everyone is resistant to putting antennas on the bottom of the wings; perhaps there is one. I put my 3rd VHF comm antenna (used for APRS) on a wing inspection panel. Another one will be used to mount my ADS-B antenna if I ever get around to installing it.

Just do the best you can and you'll be fine.

--
Joe

 

[N941WR]

Welcome to the VAF forums!

Your question comes up from time-to-time and there are a lot of options available to you. Try using the Search (or Advance Search) feature and I'm sure you will find lots of pictures and suggestions!

Best of luck with your build!

 

[RVDan]

The OP states "2 transmitters at once" If you are really looking to transmit on 2 radios at once (pilot and co-pilot?) most audio panels won't allow this and I doubt (but do not know) if Dynon will do this. It is possible to do but takes some special arrangements.

If you are looking to transmit on one radio while recieving on the other- you can do that on most all audio panels, most likely with Dynon.

With regards to antennas, I have a -6A with deltapop com antennas mounted on the belly side by side as far apart as I could get them and they work fine with SL30/40 radios.

I have mounted antennas under wings in military applications where we did flight test to validate potential aerodynamic effects, but this is not commonly done in the commercial world because of potential aerodynamic effects.

 

[Dbro172]

heres some pics

I fretted over the same considerations at one point and spent a great deal of time researching. Here is what I ended up with. I am not flying yet , but i can verify that in the garage the Comm1, Comm2, Transponder and ADS-B all work, with no known transmit or receive interference to speak of. The ELT is mounted per the Far's and the Nav antenna per the instructions so I have no reason to believe those will not work. My GPS antennas for the G3X system will be mounted on the glare shield inside the cockpit. All antennas have flush riveted doubler plates.

Here is my array of Deltapop antennas:

Front Left - Comm1
Front Right - Comm2
Right Rear - Transponder
Left Rear - ADS-B
Top Rear - ACK E-04 ELT
Wing Tip - Bob Archer Nav1
Not Pictured - G3X GPS Antenna, Garmin 400W GPS Antenna

 

[drone_pilot]

Thanks

Thanks for all of the good info, advice, and pics! As usual, I have probably been making this decision more difficult than it really is.

 

[Dbro172]

Thanks for all of the good info, advice, and pics! As usual, I have probably been making this decision more difficult than it really is.

Not really! This is a big decision and no instructions in the plans. So a pretty tough nut to crack really. This is also so much based in your equipment (that's not shown in the plans) and all future wiring runs (also not shown in plans)..... So thank goodness for VAF

 

[flightlogic]

Without a copilot qualified to make transmissions on the radio, it is a moot point.
If one is in an aircraft needing simultaneous transmissions, then freq.. Probably Need to be a few meg apart. Otherwise the radios will be swamped and not on their best behavior. Go with a radio that can listen to ATIS on scan and another freq. on primary and save some money.

 

[Walt]

ADS-B receivers/UAT devices generally recommend 5 ft minimum spacing from a Xpd antenna.

 

[Scott Hersha]

Ben,
I've had two COM antennas mounted on the belly of my RV6 & my RV8 parallel to each other, and have had no problems with either. I can listen on either or both at the same time. I've never tried to transmit on both at the same time - not sure how you would do that without two parallel audio panels, but they work fine In any normal mode. Listening on both ( ATC on one, ATIS on the other) no problem; transmitting on both at the same time, not possible for me, but why would anyone (outside of a 2 crew cockpit) want to do that? Make sure the coax is wired correctly and don't worry about it.

 

[rvmills]

Ben,

I've played with various antenna placement schemes on my -6, and previously had two CI-122 bent whips on the belly. Because I have the Dynon roll servo under the cockpit floor, I had those two whips in the second bays in, instead of the outer bays. That put them closer together than recommended, and I did find that when I transmitted on comm 2 while monitoring comm 1, it broke squelch on comm 1. Comm 1 is an SL-40, and comm 2 (then) was a SAR radio (137-174 MHz).

The roll servo in a -7 typically goes in the wing, so you should be able to put your antennas in the outer bays, have them farther apart, and avoid that issue. As Scott and others said, many have had good success with that.

There's also the Archer option, or some DIY options too. I now have a slightly modified bent whip inside each wingtip, each attached to a 9"x9" ground plane, and a Pete Howell Enterprises j-pole down each gear leg. My current comm 2 (another SL-40) and my APRS are switchable between the right wingtip ant and the right gear leg ant. The tip has better range for comm, and better coverage for APRS, but the j-pole does pretty well, even next to gear leg. It's a short range solution though (< 25nm). The j-pole works better out in the tip too (to be fair to Pete!).

Two whips on the belly, and a j-pole or whip in the tip would do very well for 2 comms and an APRS. One on the belly and one in each tip would do well too. Just depends on what you want hangin'.

If you are concerned about needing to transmit on two radios at once for operating In the IFR system, it should not be a concern. The Garmin 340 actually has a mode where that is possible (the Comm 1/2 button). I thought I might need that for a SAR observer to use my old SAR radio while I talked to ATC, but the situation never came up. It should not come up in typical IFR ops. Having a backup comm for IFR ops, listening to ATIS and a few other auxiliary uses make a comm 2 useful, but with good antenna placement, no worries on interference in normal ops.

Cheers,
Bob