Today's Message Index:
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1. 12:30 AM - Re: Dual Comm Transmitter Problem (John Rippengal)
2. 09:04 PM - Re: Dual Comm Transmitter Problem (KD4ZHA@aol.com)
3. 09:37 PM - Re: Dual Comm Transmitter Problem (KD4ZHA@aol.com)
4. 09:37 PM - Re: Dual Comm Transmitter Problem (ECLarsen81@aol.com)
5. 10:49 PM - Re: Dual Comm Transmitter Problem (John Rippengal)
6. 11:12 PM - Re: Dual Comm Transmitter Problem (KD4ZHA@aol.com)
Message 1
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| Subject: | Re: Dual Comm Transmitter Problem |
Well just using logic and no special knowledge the closeness of the
antennas cannot be the problem.
You have been using them for 7 years with no problem so there is no
reason for the closeness to be causing weak transmission now. It is not
ideal to have them so close and although it is not the major problem it
would be worthwhile reviewing your options. On top of the fuselage would
be a good place to move one of the antennas.
The closeness can cause feedback into the non transmitting receiver
though which could cause your 'tinny noises' and I would be a bit
concerned about protecting the receive chips in the non transmitting
unit since they will get a belt of power which cannot do them much good.
All that is peripheral to your main problem of weak transmissions. Get a
'Ham' to check your VSWR on each feeder antenna system which will check
the coax, its connectors and the antennas. Funny though that BOTH
feeders and antenna connections seem to be acting up all of a sudden.
Anyway the VSWR check will also reconfirm that the power output from the
transmitters is normal.
John
From: John
I just now subscribed to the Avionics list in hopes that I can get
some experts advice. I know absolutely nothing about radio equipment so
please understand that you are talking to a dummy. <grin>
7 years ago I bought a Harmon Rocket which is equipped with a KLX135A
Gps/Comm and a KY97A Transceiver. I also have a KT76A Transponder, A
Rocky Mountain Encoder, and a SPA-400 Sigtronics Intercom with a Music
Switcher (I believe it is a STEREOCOM-400 ). The audio panel consists
of three separate toggle switches. One switch selects the radio to
transmit from. The other two turn the respective receivers ON or OFF
This system has worked well for me until just recently when I started
having transmitter problems. Both of my receivers are excellent under
all conditions. I sent my radios to Aurora for a bench check but they
didn't find any problems with them.
I'm not sure how good my transmissions have been over the years but I
didn't get any complaints. Lately though I am being advised that my
transmissions are weak, scratch and barely readable when I am only a few
miles away from a station. Also, I have been getting an annoying, kind
of hollow tinny background noise in my headset when I transmit from my
KLX135A while the KY97A is also turned ON. The noise becomes less
troublesome if I turn the volume down on the KY97A. When I transmit
from the KY97A with the KLX135A turned ON, I don't hear the noise in my
head set, but it too is reported to be weak and scratchy. Transmitting
from either radio with the other completely turned off does not solve
the problem either. I still send out weak and scratchy transmissions.
I guess I must have some deteriorating wire or possibly some other
kind of interference that is cutting down the signal strength before it
reaches the antennas. Medford Jet Center Avionics techs tell me a big
part of my problem is caused by the close proximity of the 45 degree
whip antennas between the gear legs. The antennas are only 18 inches
apart. They say the minimum recommended is 36 inches. I really don't
have an option to relocate the antennas. I suppose if all else fails I
can yank the KY97A out and use the KLX135A as my single flip-flop. I
think most Rockets and RVs have only one comm anyway. I wonder what
would happen if I disconnect the coax cable from the KY97A antenna.
Would that have the same affect as removing the radio completely, or
will the dead antenna still interfer with the KLX135A transmissions?
The Jet Center Avionics shop looked at my aircraft and determined that
I have poorer quality coax cable and unshielded wiring. They estimate 6
hours labor plus parts which probably shouldn't run much over $600.
That is probably the best way to go.
I just though I would toss this problem out there and see if any of
you have had experience with something similar.
John
Message 2
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| Subject: | Re: Dual Comm Transmitter Problem |
John, it all worked fine before, so adding $600 worth of shielding is
probably just throwing away good money! I'd check both coax connections to
the antennas for broken center conductors and corrosion, and check the base of
each antenna for good grounding (corrosion can prevent that). Don't forget to
check any coax spices or extensions for corrosion, also. If you've enough
coax, swap antennas, and see if the problem changes in some way or goes away.
If
there is absolutely no change after swapping the coax leads, the problem is
likely in one of the radios (overmod or bad finals on the transmitter, loss of
selectivity on the receiver). Have an SWR check done on both systems before
you spend good money to fix a problem that could just be a bad antenna or
connection!
Message 3
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| Subject: | Re: Dual Comm Transmitter Problem |
I am a ham, and the closest thing a ham would have to check SWR on VHF air
frequencies would be a 2 meter SWR meter (144-148mhz). It just doesn't have the
range to check aircraft VHF systems.
Carl
Message 4
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| Subject: | Re: Dual Comm Transmitter Problem |
Since both antennas are on the bottom, I say it's a good bet that the
interface has some corrosion.
Message 5
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| Subject: | Re: Dual Comm Transmitter Problem |
Carl,
The 2 metre band meters work perfectly well in the VHF airband and are
useful even in the nav band down to 108 Mhz.
John
From: KD4ZHA@aol.com
I am a ham, and the closest thing a ham would have to check SWR on VHF
air frequencies would be a 2 meter SWR meter (144-148mhz). It just
doesn't have the range to check aircraft VHF systems.
Carl
Message 6
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| Subject: | Re: Dual Comm Transmitter Problem |
Cool! Mine won't even twitch on VHF air! I guess the bandwidth is too
narrow on mine! Good luck!
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