In article ,
Dan Yemiola AI8O wrote:

Can anybody give me an idea of what is causing this problem with my IC27A?
(I know its 25 years old,but don't laugh, it's paid for).

I am trying to use the radio through several repeaters that require a CTCSS
(PL) tone to access the repeater.
I do not have this problem with repeaters that do not require a PL.

When I am far away from the repeater I use high power (25W) and the PL.
As I get closer to the machine using Hi power, I get to a point where I
cannot access the repeater using PL and Hi power.
If I cut back to low power ( 5w ) and PL the radio will access the rptr.
If I move farther away from the repeater at some point I can again access
the rptr on high power.

I think the fastest way to diagnose the actual cause of the problem
will be to use a service monitor and/or spectrum analyzer, to look at
several aspects of the rig's transmitted signal: RF frequency
accuracy, signal deviation level (with PL only, and with PL plus
voice), and the cleanliness and frequency accuracy of the PL signal.

I'd tend to suspect one of several problems:

- PL tone is off-frequency, or it's being injected at too high or too
low a level (typically, around 700 Hz of carrier deviation is
considered optimal).

- PL waveform is distorted.

- RF feedback or some other sort of audio-level stability problem
(e.g. parasitic oscillation) is injecting an unwanted audio signal
into the modulator, and is swamping out the PL tone.

- RF carrier is off-frequency, causing your signal to fall partway
outside the passband of the repeater's receiver, and the resulting
noise and distortion is causing the PL detector to drop out.

I'm not sure why your signal problems are worse when the repeater's
receiver gets a strong signal - the receiver squelch behavior may
change with strong signals (I've seen some which behave this way).

Your rig may need nothing more than a recalibration, or it may have
components going bad (e.g. electrolytic filter caps drying out with
age, and losing capacity).

In any case, finding somebody who has an accurately-calibrated service
monitor is probably the first best thing for you to do.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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