troubleshooting com's transmission

[jan olieslagers[_2_]]

On my first cross-country solo, I observed everybody was clearly
readable by everybody - except nobody could understand ME clearly.
The radio on the club plane is an Icom A200, quite common I believe and
not too bad quality though it is on the cheap side. But I can't imagine
my poor transmission was due to the radio so next suspect is the
antenna, in comes the buzzword "SWR" . Is there a published procedure
for checking SWR on an existing installation?
Any other possible causes? Antenna location perhaps, or lack of ground
plane? But that should show on SWR-verification too, shouldn't it?
TIA,
KA

[Edwin Johnson]

On 2009-04-12, jan olieslagers > wrote:
> On my first cross-country solo, I observed everybody was clearly
> readable by everybody - except nobody could understand ME clearly.
> The radio on the club plane is an Icom A200, quite common I believe and
> not too bad quality though it is on the cheap side. But I can't imagine
> my poor transmission was due to the radio so next suspect is the
> antenna, in comes the buzzword "SWR" . Is there a published procedure

When you say 'couldn't understand', do you mean they could hear you but
it was unintelligible? If that's the case, the audio portion is probably at
fault - microphone (try another microphone or headset) itself or loose
connections, if an audio panel in the plane, problems in that, audio
problems in the radio itself, wiring associated with any of the above.

Avionics antennas are built to interface at 50 ohms to the radio, so no
tuning or anything needs to be done if installed correctly. Loose cables or
ground in the cables (shielding) would cause SWR (standing wave ratio)
problems, but if a contact was intermittent you would probably hear static.
SWR problems would degrade slightly the received audio and definitely effect
transmitted, but the effect would be reduced output, not unintelligibility.

Probably first thing to check is microphone (headset) and connections,
trying another to see if that one works fine.

....Edwin
--
------------------------------------------------------------
"Once you have flown, you will walk the earth with your eyes
turned skyward, for there you have been, there you long to
return."-da Vinci http://bellsouthpwp2.net/e/d/edwinljohnson

[Brian Whatcott]

jan olieslagers wrote:
> On my first cross-country solo, I observed everybody was clearly
> readable by everybody - except nobody could understand ME clearly.
> The radio on the club plane is an Icom A200, quite common I believe and
> not too bad quality though it is on the cheap side. But I can't imagine
> my poor transmission was due to the radio so next suspect is the
> antenna, in comes the buzzword "SWR" . Is there a published procedure
> for checking SWR on an existing installation?
> Any other possible causes? Antenna location perhaps, or lack of ground
> plane? But that should show on SWR-verification too, shouldn't it?
> TIA,
> KA

Standing Wave ratio is a concern for radio amateurs who wish to operate
transceivers on widely different frequencies. They use a box with a
directional transmission line section, and compare the power going in
the transmitter-wards direction with the amount coming back.
Their SWR measuring boxes are not expensive but are typically set up for
the use of UHF connectors which are those screw in coax connectors about
twice the diameter of the BNC connectors you may see on some scopes and
hand-helds. Perhaps a simpler approach would be substituting the
installed antenna by a test antenna and feed cable as a test.
One of RST's tape antennas intended for glass fuselages would make a
cheap test antenna for instance.

Brian W