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TM-221 PL tone output level adjustment

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June 17th 07, 09:24 PM posted to rec.radio.amateur.equipment

Fred McKenzie Fred McKenzie is offline

Fred McKenzie is offline

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TM-221 PL tone output level adjustment

In article ,
(Dave Platt) wrote:

The alignment instructions say to adjust VR1 so that the transmitted
signal deviation level (tone, but no other audio) is around .65 kHz
(650 Hz). This is consistent with recommendations I've read for other
radios and seems to be good practice.

Bonus question: I have the same problem with an Alinco DR-590; if you
can help me with that too, that would be nice.

I've been told that in at least some Alinco radios, the CTCSS tone
level is set by a fixed resistor on the PC board (it's not intended to
be adjustable via a pot), and that it's set too high.

Dave & KA1IOR-

I've seen alignment procedures on older commercial radios, where there
was no adjustment. The procedure was to merely verify that the CTCSS
tone's deviation was between 0.5 and 1.0 KHz. I don't know the official
spec, but 0.65 KHz would be a good choice if it is adjustable.

The key is to measure the actual tone deviation, not just rely on hum
reports. Any given repeater may not be filtering out the tone as it is
supposed to. (That same filter should reduce 60 or 120 Hz hum as well.)
A repeater that transmits tone, should be regenerating it, not repeating
the input tone.

It may be difficult to measure the exact frequency of a CTCSS tone, but
you should be able to sync your oscilloscope to 60 Hz line frequency,
and observe whether the received "hum" is drifting or not. (You could
sync the scope to a CTCSS tone generator if you had one.)

Fred
K4DII

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