On Tuesday, December 31, 2019 at 4:43:49 PM UTC-8, wrote:
On Sunday, February 6, 2011 at 7:55:37 PM UTC-8, Paul Remde wrote:
Hi,

The Trig TT21 and TT22 manual is also quite fussy about transponder antenna
cable. But it important to note that many of the "long run" antenna cables
they recommend are extremely expensive.

I recommend mounting the transponder unit (it is separate from the control
head) as close to the antenna as possible. When that is done I have
received customer feedback that RG-58 cable works fine - with all required
tests passed with flying colors.

Paul Remde

"Eric Greenwell" wrote in message
...
On 2/6/2011 11:18 AM, JJ Sinclair wrote:
On Feb 6, 11:12 am, wrote:
I understand your point - I saw those suggestions on my L2
instructions, laughed, and pitched it. Why should you pay for
transponder output just to heat up the antenna cable with outdated
RG-58, when low loss LM240 is only $0.70 more per foot? And if RG-58
is bad, RG-174 is 4 times worse...



The instructions from Advanced Aircraft Electronics call for RG-58A/U
unless wire bundle size is critical where the smaller RG-174/U may be
used if length is held to 20 feet or less.
JJ- Hide quoted text -

- Show quoted text -

You're right John.................I'll disregard the manufactures
instructions and go with something I heard on ras.............
Yeah, right!

JJ, call AAE and ask about the LM240 cable. It might be their
recommendation was aimed at airplanes carrying 200+ watt transponders and
using shorter cable runs, compared to gliders that might using units with
150 watts or less and long cable runs. Also, looking at the transponder
manufacturer's recommendation is probably a better indication of what's
needed than the antenna manufacturer. My Becker instructions made quite a
fuss about which cable to use.

Generally, I like to go the "good stuff" for transponders, as attenuation
per foot is much higher at transponder frequencies than our communication
radios frequencies (factor of 8).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email
me)

I installed an antenna as recommended by SH on my Ventus 2c, down by the wheel. Drilling the hole was traumatic. SH recommended carefully drilling a small hole then using a fine file to gently enlarge it, and that worked well. I installed an aluminum sheet ground plane inside the fuselage, since I could find no clear advice on whether carbon fiber is or is not an adequate ground plane. Even though I only had about a 5ft cable run to the antenna, I used low-loss coax cable recommended by Trig, and got the cable custom cut to length with the proper connectors attached. Its important that the coax connectors are properly fitted, and I didn't have the proper crimper. I also looked up the coax cable specs and found that there was a limitation on the radius that the cable should be bent, and I kept within that bend spec. Its not only that cable and connectors and bends can cause attenuation, they can cause reflections back to the transponder which can upset it's operation.

Trig specifies that the cable loss must be no more than 1.5 dB. They have a table of acceptable cables in their installation manual. RG304 is ok for runs up to 3.8 m (12.5 ft).

Tom