If it's not too much trouble, try a coax cable length of 21 11/16 inches
which would be 2 wavelengths at 1090 MHz (assuming my arithmetic is
correct).Â* You may have reflected power in your coax which will reduce
performance.

On 12/31/2017 2:22 PM, Scott Williams wrote:
On Sunday, December 31, 2017 at 2:08:17 PM UTC-6, Darryl Ramm wrote:
On Sunday, December 31, 2017 at 11:25:42 AM UTC-8, Scott Williams wrote:
On Sunday, December 31, 2017 at 12:58:25 PM UTC-6, Darryl Ramm wrote:
On Sunday, December 31, 2017 at 10:03:37 AM UTC-8, Scott Williams wrote:
On Sunday, December 31, 2017 at 7:33:39 AM UTC-6, wrote:
AC 43.13B 308d says you need a backing ground plane.
But I didn't see any special details for CF versus other composites?

Following the instructions from the glider manufacturer seems smart.
My std Cirrus has a schempp-Hirth TN that clearly spells out the installation
of the blade antenna. but it allows either aluminum or copper for a ground plane.
I chose a copper plate 0f .043 thick.
Trigg 22 has good output, but the 'sensitivity' was right on the low tolerance.
Any thoughts or insights?
thanks,
Scott
What did the technician doing the test recommend? If there was a doubt why did they not direct connect test the transponder?

These measurements are not highly precise. If its within tolerance then go fly. If not then get a different avionics technician to repeat the test if possible and if its bad then direct connect test the transponder to see it is likely the transponder or cable/antenna..
in short,
New trig tt22, new only 14 inch antenna coax, new antenna, copper ground plane, trig authorized shop doing test, fresh battery with good voltage.
Tech reports using two different 'test rigs' , also report "sensitivity is on the low tolerance, but I'll pass it" with no other suggestions.
I followed up with Trig factory tech line, maybe have to send it in for a factory check. Factory rep had on suggestions.
I have no idea just what 'sensitivity is. factory was helpful, but I think maybe "sensitivity" may be outside of the influence of installation variables.
I was hoping for someone to have an insight.

Thanks,
Scott
Did they direct connect test the transponder?

Sensitivity is the transponder sensitivity to interrogation. A poor antenna or coax install will affect that the same as it will affect the transmitted power. You can compare the radiated power measurements and guess the loss, but you don't know with much precision what that is if measured by a radiated test. The radiated tests are pretty imprecise, they are not done in free space, they have reflections and lots of stuff going on. If a direct connect test to the transponder with a different coax shows a marginal result then the Trig agent/test shop would hopefully be discussing that for you with mid-century.

The proper thing to do here if in doubt was just direct connect the transponder to a test kit. Did the technician do that? If not was the test kit not capable?? (I can't recall one that isn't but could be wrong)? He didn't have a coax or adapters with him? He really though it was just not an issue to waste time on? The shop/technician should have been able to answer all the questions you seem to have here questions and do more troubleshooting (maybe for a fee) especially after discussion if you still had concern.
the tech did not directly connect, he also admitted that the steel hangar door and wall 18 feet away "could influence" the tests, he had never done a glider and was really friendly, but only did tests with a tripod mounted radiated device. The first device only reported "failed" the second device reported the Sensitivity as a number, 68 or 69 I believe. all other aspects passed.
Initially he was willing to do a "benchtop"? but said he did not have the correct harness.

This is my first experience with transponders and I am just learning.
Scott

--
Dan, 5J