Radio X83 transmission/reception problem.

[MarcF]

Hello,
My full carbon FK14 Le Mans ULM is equipped with 2 HDX-700 screens with integrated SV-COM-X83 radio and SV-INTERCOM-2S intercom. When I just got this airplane, I had quite some problems with poor reception and transmitting range. These problems were partly solved by adding a decent ground plane in the carbon fuselage.
Unfortunately I still experience a malfunction of the radio. The start-up of the HDX is normal: the connection between the HDX screens and the radio is made correctly and the radio can be controlled via the screens and via the control panel.
Most of the time, I have no reception and no transmitting of the radio. I’ve put an SWR meter just before the antenna: the SWR is OK, so a transmitting signal arrives at the antenne. Max transmitting/reception range is hardly 10 meters. At best, you have some unreadable noise.
Sometimes the radio starts working after a few minutes. In the exceptional case that this happens the radio works fine, the transmitting/reception signal has an acceptable range, until it is switched off. But no warranty it will work next time if you start it up again.
I use a comant CI122 antenna connected to the radio with a RG58 coax.
The complete HDX system is in use since May 2018.

Any suggestions?

 

[jakej]

Which side of the carbon fibre is the ground plane ?
FWIW only use RG 400 or similar coax - this is the industry standard as it has really low loss due to the excellent shielding.

 

[MarcF]

The groundplane is on the inside of the fuselage.

 

[Garrett]

I think Jake is correct about using RG400 cable. There is a lot of rf energy/noise near the Dynon screens that could leak thru your RG58 cable. My Icom A6 handheld will not work in my cockpit without a remote antenna to get it away from the Dynon screen rf interference. I have a Remos GX with RG400 cable with the antennas located behind the pilot seats top and bottom of aircraft with ground planes inside plane using SL30 and a GTN650 for radios and they work fine al the time.

 

[kellym]

I think Jake is correct about using RG400 cable. There is a lot of rf energy/noise near the Dynon screens that could leak thru your RG58 cable. My Icom A6 handheld will not work in my cockpit without a remote antenna to get it away from the Dynon screen rf interference. I have a Remos GX with RG400 cable with the antennas located behind the pilot seats top and bottom of aircraft with ground planes inside plane using SL30 and a GTN650 for radios and they work fine al the time.

RG400 is only needed for high frequencies like transponder, GPS  and DME. It is overkill for com frequencies. RG58 is fine for com and nav frequencies, UNLESS you have an extreme RF noise situation. RG58 was the industry standard until GPS came along. That would be for at least 50 years. I am using Syview 10" screens with GTN650 and SL30. Only the 18" pigtail at the panel for wiring convenience is RG400. The rest of the cable to the antennas for both coms and both wingtip nav antennas is RG58, and works fine in my RV-10. Yes, have RG400 for GPS antenna and transponder antenna, because of the frequency they operate at, and the very low signal strength of the GPS satellites, as well as the TSO calling for that cable. You can spend the money for RG400 for your com and nav radios if you wish, but very unlikely you will notice a significant difference unless you have an improper noise source like unshielded ignition lines and unshielded strobes.
More likely to have problems with poor connection of BNC or TNC connectors than with the cable itself. I would try some wiggling of the connections while trying to transmit, to find the villain.

 

[jakej]

Quote -“UNLESS you have an extreme RF noise situation.”
Yes that is one situation however I don’t want to have ANY possibility of that happening as ‘noise’ (in audio or electrical terms) can take a serious amount of time to troubleshoot. I have found that by using low loss coax, eg RG400, & making sure grounding ( bonding) is of good quality, I can run the coax with other elecrical & audio cables (not battery) without any issues - with RG 58 you’re in no mans land IMO & experience.
A question for those who have had the experience - is it much better to have the ground plane on carbon fibre to be on the outside of the skin ?
MarcF
Can you post pictures of the inside end of the coax connectors ?- what I’m trying to determine is if the pins are in the correct position or retracted.  Using a DMM only confirms if the pins are actually connected.

 

[Garrett]

Yeah, maybe the coax connectors were not installed correctly. Also if the connector gets wet and with dis similar metals you can get corrosion under the crimped part of the coax connector which can short out the center conductor to the shield.

 

[Raymo]

is it much better to have the ground plane on carbon fibre to be on the outside of the skin ?

It doesn't matter, which is why it is typically on the inside and hidden from site.

I'm with Jake, install RG-400 and KNOW that it is not the problem.

 

[MarcF]

Since my first post, we sended the radio to Trig in order to update the radio to version 1.10. This update reduces background noise from electrically noisy installations and changes the scaling of the receiver volume control (radio volume now increases more quickly with clockwise rotation).
We checked the cable: no problem with it, also checked if there wasn’t a connection to the mass .everything ok.
We set the radio on 136,000 Mhz. Permanently broadcast and scanned with a portable radio. The scan has been stopped on the frequencies 127.260 and 134.425 where we could briefly hear our radio transmission. After 3 seconds it was gone again.
All of a sudden the scanning stopped at 136,000 and we could send and receive. It has been since one month that we once again managed to get the radio up and running. And now suddenly without doing anything the radio worked perfectly on all possible frequencies. It seems that by warming up the radio through the long broadcast, it suddenly started to function.
Personally, I think the problem can come from the Dynon screen or remote head: one of them sends wrong frequency information to the radio.
Shortly we will change the remote head and check if the problem has finally gone.