[Drake] Problem on 20 meters.

[Paul Blumhardt]

Carlos

Based on what you say below, it sounds like you are getting RF into the mic
lead.

Listen to your signal using another receiver and see how it sounds. This may
give you some insight into the problem.

If you hear lots of squealing/scratching, you are probably getting RF into
the mic.  If you suspect RF issues, try moving the radio, try removing any
ground leads, try changing the length of the ground lead (you do have the
radio grounded don't you?). You may try adjusting the PA tuning or PA
loading to see if the problem changes or goes away. Does the problem go away
at lower output power levels?

How far is the radio from the antennas? If the radio is very close to the
antenna, this would point to getting RF into the microphone lead.

Try a Radio Shack Ferrite on the mic lead.

Also, it's possible that you have a problem with the mic cord itself.
Grounding the Mic audio lead will put a hum on the audio lead and this would
cause the radio to be "hum modulated". (There are 3 leads, Ground, Audio,
PTT on a mic cord).

Good Luck with your problem

Vy 73
Paul K5RT

-----Original Message-----
From: drake-bounces at mailman.qth.net [mailto:drake-bounces at mailman.qth.net]
On Behalf Of Carlos A. Archilla
Sent: Sunday, June 03, 2007 2:59 PM
To: drake at mailman.QTH.net
Subject: [Drake] Problem on 20 meters.

Hello all:

My otherwise fine TR4cw has developed a curious behavior; it won't transmit
on 20 meters. Works on other bands, receives OK on 20, it seems to loads ok
on 20 but modulation at the mic just won't produce the normal plate current
deviations on the meter, instead, it jumps to 250 ma or so and stays there
while you are speaking into the mic.  While this is happening, nothing is
heard on the air.  VOX will kick right back to receive when you stop
talking.

For a while, I solved this problem by putting the antenna through the
MN-2000 tuner.  Switching the tuner in and out would "fix" or produce the
malfunction.  The antenna is a TH6DXX with fine SWR as it works with all my
other radios.  Now I just cannot work 20 meters with or without the tuner.
Any of you folks out there have any idea what's happening before I venture
into the "inner sanctum" of this classic?

Carlos / KP4GL
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