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Rule of thumb for antenna placing?

swisseagle

swisseagle

Well Known Member
Hello

I do not have all instruments and avionics yet, but planing where to route the cables for Com 1 +2 and transponder.

It is really difficult to find a place where all meets the requirements others are telling, especially in an RV-XA.

Are there rules of thumb for antenna placment?

Lets say something like this?

- Between two com antennas, min distance X ft
- Between com and transponder antenna, min. X ft
- Between com unit and antenna min. distance in a straight line min X ft
- Min, max antenna cable length on a com / transponder
- min. distance to a steel object (like gearleg, flaps, exhaust)
- Do not route com 1+2 antena cable together
- Do not route com and transponder antenna cable together
- Do not place an antenna closer to a human body than X ft (or does it not mather because it is outside of the aircraftshell?)

Maybe Stein or someone else who is working with things like this can help.


Thanks alot and kind regards,

Dominik
RV-7A
Switzerland
 
Last edited:
I can answer some questions. Cable with braided shield, even with double shields such as RG400, will have some coupling when tied close together. Cable with a solid outer conductor, such as Andrew FSJ1-50A has no coupling or leakage which can be measured, so it can be tightly tied to another. FSJ1-50A Weighs 0.045 lb/ft, costs $1.20/ft. and has a loss of 1.81 dB/100' at 100 MHz (VHF COMM) and 6dB/100' at 1000 MHz (Transponder and DME). Its F1TMB-C BNC connector costs $17.41 each. RG400 weighs slightly more at 0.05 lb/ft, costs $2.75/ft, and has 3.9 dB/100' at 100 MHz and 13dB/100' at 1000 MHz, and its BNC connector costs $2.95 each. A 10' length of FSJ1-50A with a BNC connector at each end will cost $46.82, and a 10' length of RG400 will cost $33.40, so $13.42 more for a cable that's lighter, much lower loss, with less mutual coupling and leakage. At 19' length the cost is the same. Tally Comm for FSJ1-50A and ACS for RG400.
 
Hello

Thanks @ elippse for all this information and resurch! Need to read it a few times until I can follow, but that looks like a good way to go.

@ Ron, here in switzerland are not so many RV's, so not so easy to find one that has a good setup.

I had a few setups made on paper, but was not happy with it. There is so much to fullfill like: structurally ok, cable routing ok, away from steel parts, not to close to each other and so on. I skiped the trials, but now the decissions has to bean made.

Regards, Dominik
 
Just read Garmin Install Manuals Looking For This Info

From Garmin install manuals:

Garmin 430W
Locate unit as far as possible from all COM antennas

GPS Antenna
RG-142B or RG-400 coax if length is less than 35 feet.
Cable loss should be 3-7 dB
No closer than 2' from COM antenna
As far as possible from ELT antenna

Com Antenna
50 ohm vertically polarized antenna
Mounted on 18? x 18? metal surface
Minimum of 6? from any other COM antenna
Minimum of 2? from 430W GPS antenna
Mounted as far as practical from ELT antenna
RG-142B or RG-400 coax

Garmin 327 Transponder
Antenna mounted vertically on the bottom of the aircraft
Minimum of 3? from any COM antenna
Minimum of 3? from 327 unit its self
Max length of RG-400 is 6?

Garmin SL-40
50 ohm vertically polarized antenna
Mounted on 18? x 18? metal surface
Minimum of 2? from above GPS antenna
Mounted as far as practical from ELT antenna (prefer one on top and other on bottom of aircraft)

Not sure it is possible to meet all these on an RV, but this is what Garmin requests.

Alan Jackson
Hartselle, AL
 
Note, that if Garmin has a maximum length of ONLY 6' for RG400 on the transponder, you could use up to 13' of FSJ1-50A.
 
Hello Allen and Elippse

That's what really helps! The definition from Allen and the info to enhance the cable lenght from Elippse.

Garmin dont wanted to send me this information! They told that I should work (and pay) with a local dealer to let the system install! No thanks!

Thanks alot, I appreciate that!

Regards Dominik :)
 
Do search for install manuals

Dominik
Use the search here or try google. You can find a link to get you to any of the Garmin install manuals.
Alan
 
Hello

I have seen the canadian regulation, but then you can not nearly place two com, one transponder and one ELT onto an RV ... these planes are small!

Maybe I should put Com2 into a wingtip, but there is the strobe unit in the front corner ant it will need a long cable.

Will see, maybe I reduce the minimum dimensions a little bit 3' is a bit difficult, but from 2.3-2.6' there are more possibilities.

Thanks, Dominik
 
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