 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
Rowland_Carson
Joined: 04 Jul 2008
Posts: 155
Location: Cheltenham, England
|
 Posted: Mon Sep 07, 2009 2:52 pm Post subject: radio noise on xmit & xponder interrogation |
 |
|
My friend Tim (who does not inhabit this list) has had a problem
arise with his comm radio that seems to have arisen suddenly, without
any changes to the installation.
He has a MicroAir 760 comm radio, with a FlightTech ITC402P intercom,
installed in a Europa.
Symptoms: intercom works fine, other stations' transmissions heard fine.
When either (P1 or P2) of the PTT buttons is pressed, a loud
distorted noise immediately occurs in both (noise-cancelling)
headsets. The words of the person speaking are barely discernable
through this. However, anyone listening to the transmission on
another comm radio hears the voice OK with no distortion (well, no
more than usual on any airband R/T!). So, the bad stuff is only
happening on the sidetone circuit, not on the signal going out to the
transmitter.
A noise also occurs when the transponder is interrogated. It's
usually not quite so loud as that heard with the PTT, and sounds like
white noise in character. This does seem to come and go - on a recent
trip we got so fed up with TSST, TSST, TSST at irregular intervals in
the headphones that we turned off the xponder on the outbound leg
because we couldn't concentrate. On the return leg we tried it to see
if it was still happening - it seemed considerably quieter and then
after some time ceased to occur at all (we were still getting
interrogated).
However, the distorted sidetone problem remained unabated.
These may be 2 separate things but it's suspicious they have
materialised at the same time.
I'm a bit puzzled as to why this should have suddenly sprung up. My
feeling is that it may be some poor earthing or poor screening in the
microphone leads. But it would need to be somewhere common to both
headset circuits as it is affecting each equally.
We are planning a longer trip this weekend (3 hours each way) and
will need to do much more talking this time. If there was a simple
fix to try before then I'd love to hear about it!
regards
Rowland
--
| Rowland Carson http://home.clara.net/rowil/
| <rowil(at)clara.net> ... that's Rowland with a 'w' ...
| | - The Matronics Avionics-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Avionics-List |
|
|
|
| Back to top |
|
 |
jetboy
Joined: 22 Jul 2006
Posts: 233
|
| Posted: Thu Sep 10, 2009 2:56 pm Post subject: Re: radio noise on xmit & xponder interrogation |
|
|
Likely problem is RF getting into the intercom, so check earth braids there first. Ferrite beads placed over certain cables may help, but this cure is reserved for dealing with improper equipment or installations.
The Microair radios do, as part of their "normal" function, transmit noise coming from both mics regardless of which ptt was pressed, but this noise is minor (with a correctly adjusted mic gain) and not the type of RF feedthrough noise you describe.
I'm not quite sure whether his radio has also its own built in intercom, which should be disabled, or used instead of the external intercom.
Ralph
| | - The Matronics Avionics-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Avionics-List |
|
_________________
Ralph - CH701 / 2200a |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
