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mike_beresford(at)yahoo.c
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 Posted: Sat Oct 07, 2006 11:39 pm Post subject: Radio Troubleshooting |
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Hi all
I'm trying to sort out a radio problem, would
appreciate any advice from the experts.
When the aircraft was with its previous owner, the
Baklan-5 failed. The owner fitted a Bendix King, and
simply stopped using the original set-up. As far as I
know the PTT button on the fron throttle is the only
part of the system that has any connection to the old
radio.
I've been trying to get the old system working again,
as I preferred the PTT intercom / radio setup. First
had some local radio boffins look at the old Baklan-5,
but they couldn;t do anything with it. They put
another Baklan-5 in there, but couldn't get it to
transmit properly. At that point they gave up.
I've now obtained a replacement radio and selector
from Mark, which I fitted yesterday. I am finding
that:
- The intercoms work fine, just a little soft.
- The radio receives, again a little soft
- When transmitting there is an odd wave-like noise in
the headset
- Tower report "carrier wave only" (tried from both
cockpits)
I went through all the aerial connections, but
couldn't see anything out of place. Since the
intercoms work, I suspect it's not microphone wiring
related. The Bendix King is "off", so it shouldn't be
interfering with the Baklan. As far as I can see, the
Bendix-King has its own antenna.
Does anyone have any suggestions on where to look
next?
Thanks
Mike
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Rob Rowe
Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK
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| Posted: Mon Oct 09, 2006 5:21 am Post subject: Re: Radio Troubleshooting |
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Hi Mike,
You might try adjusting the two slotted pots on the front panel of the Baklan 5 transceiver ... sounds like you have a -52 so just pop the tray lid off in the rear cockpit to access the avionics bay & you'll be able to see them (transceiver is the left most box, looking rearward).
They're labelled (in Cyrillic, so nearest chars shown) "Cn" & "MOA".
"Cn" is receive audio level control.
"MOA" is transmit audio level control.
Your transmit carrier wave only problem might be over or under modulation ... so try adjusting "MOA" down as well as up to see if this improves the quality.
There are some other headset impedance mismatch issues on the receive side that might impact intercom longevity, but lets try & get the basics sorted first.
I'm off-line for a few days so will catch up with you later in the week to see how you've got on.
Cheers, Rob Rowe
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mike_beresford(at)yahoo.c
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| Posted: Tue Oct 10, 2006 12:20 pm Post subject: Radio Troubleshooting |
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Hi all
No great success with adjusting the pots.
I have an idea that the problem is aerial related. Two
radios have given similar problems, so I'm of the
opinion that the fault is outside the actual radio
unit.
Since the intercom is working, I'm assuming that the
problem is not related to the microphone set-up.
Pushing the radio PTT causes a squeeling noise in the
headset, which can only be eliminated by turning the
left hand (looking back) pot on the Baklan radio right
down. Turning the right hand pot alters the pitch of
the sound. (NB radio pots, not the panel controls) Is
this perhaps some form of feedback through the system?
A previous owner had some VHF equipment fitted that is
no longer in the aircraft, save for an American VHF
antenna. If I make a cable with the correct fittings,
is there any reason that I can't connect this antenna
to the BAKLAN-5? This may help determine if the
Russian aerial system is the cause of the problems.
Blue skies
Mike
--- Rob Rowe <yak-list(at)robrowe.plus.com> wrote:
| Quote: |
<yak-list(at)robrowe.plus.com>
Hi Mike,
You might try adjusting the two slotted pots on the
front panel of the Baklan 5 transceiver ... sounds
like you have a -52 so just pop the tray lid off in
the rear cockpit to access the avionics bay & you'll
be able to see them (transceiver is the left most
box, looking rearward).
They're labelled (in Cyrillic, so nearest chars
shown) "Cn" & "MOA".
"Cn" is receive audio level control.
"MOA" is transmit audio level control.
Your transmit carrier wave only problem might be
over or under modulation ... so try adjusting "MOA"
down as well as up to see if this improves the
quality.
There are some other headset impedance mismatch
issues on the receive side that might impact
intercom longevity, but lets try & get the basics
sorted first.
I'm off-line for a few days so will catch up with
you later in the week to see how you've got on.
Cheers, Rob Rowe
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=66714#66714
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mark.bitterlich(at)navy.m
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| Posted: Wed Oct 11, 2006 1:38 pm Post subject: Radio Troubleshooting |
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Troubleshooting antenna problems is really not best approached by the
premise of just changing parts and then see what happens.
Never-the-less, it is possible that the radio squealing when you
transmit is indeed caused by a high VSWR issue. That issue can be
caused by a bad antenna, OR bad coax, OR bad connectors. Any one of the
three can cause an impedance mismatch. The proper troubleshooting
method is to either install a directional wattmeter inline and measure
forward and reverse power, or... Use an antenna analyzer such as the MFJ
series. The latter are wonderful devices and every group of airplane
owners at a local airport should spring for one so that it can be
available for just these kind of issues.
To answer your question:
All of the Russian VHF radios use the world wide standard of 50 ohm
systems. Thus our coax and our antennas will work just fine with their
radios, assuming you can the proper connectors to hook things together
with.
The best way to troubleshoot your problem is to connect a 50 ohm dummy
load to your Balkan 5, and then test it. If the squeal goes away and
you have good side-tone, then you indeed have a coax/antenna issue. If
the problem remains when using a dummy load, and it does it with
multiple radios, then look for bad wiring from the mike connector to the
radio itself.
Make sure you put those pots back where they were when you are done.
The TRANSMIT AUDIO LEVEL (MOA) adjustment actually adjusts percentage of
modulation for the Amplitude Modulated transmitter (AM). If set too
high, this will cause bad splatter and adjacent channel interference and
that is a bad thing. Since you have already messed with it without the
proper test equipment available, the best "fix" you can do there is to
listen to your radio from ANOTHER AIRPLANE and then listen to say the
"tower" transmitting. Adjust the MOA in your Balkan 5 so that it does
not sound any "louder" then anyone else's radio. This is crude, but
better than nothing. Avoid turning the MOA pot around if possible.
Mark Bitterlich
N50YK
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mark.bitterlich(at)navy.m
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| Posted: Wed Oct 11, 2006 1:50 pm Post subject: Radio Troubleshooting |
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Ring out the microphone wiring to the radio. I suspect that it was
tapped and fed to the new radio and never properly disconnected since
they pulled the Balkan 5 R/T and it would have just led to a dead end.
Make sure the Balkan 5 you are testing with works good in another known
good aircraft. Lastly, suspect antenna coax problems as a bad "Z"
mismatch could cause this problem.
My money is that the wiring is messed up, regardless of whether the ICS
works or not.
Mark Bitterlich
N50YK
P.s. I've repaired a number of Balkan 5's, so I do have a little
experience anyway.
--
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