"don" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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I think a lot of people do not realize how important it is for the ALC
to be set correctly, or even on the conservative side. While a scope will
show flat topping, they don't show bandspread very well, and few of us can
afford a good spectrum analyzer to really see what's going on. With that
being the case I have seen many hams brag about how strong their rig is,
when in fact the ALC is set too far and that extra 50watts is just going
towards splatter. I would rather operate at 90-95 watts and know that I have
a good clean understandable signal, than be at 100-120 and have to repeat
everything I say. If I really need the extra power, 10 or 20 watts probably
will not make difference, that's when the amp comes into play!!
This just shows how very important it is to have good quality,
calibrated, test equipment on hand when performing repairs or alignments.
and even then, double check! does the reading on the watt meter match with
your scope?, is that old dummy load still 50 ohms?, how about the coax
jumpers? just how old are they anyway?? so often there is thousands of
dollars in radios, and yet the $5 jumper is garbage. or the 100 watt dummy
load has regular been subjected to 150+ watts for extended time. or we
expect accurate readings from the 30-40 year old meter we bought off
e-bay!!!
Having recently had similar issues, I have been aggressively
"remodeling" my radio/work bench. all new jumpers made, fresh coax and
connectors to the antennas, new and better quality antenna switches, new
transmatch(currently homebrewing), oscope, dvm, cap meter, and new wattmeter
next month, and even reworking the shack's ground system.
Thanks for the update !!
73 Don Ke7ffm
----- Original Message -----
From: "Craig Roberts" <[EMAIL PROTECTED]>
To: "drake" <[email protected]>
Sent: Monday, December 12, 2005 8:58 AM
Subject: [drakelist] TR-7 transmit audio saga
Craig Roberts <[EMAIL PROTECTED]> made an utterance to the drakelist
gang
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As you may recall, I was complaining recently of RF contamination of my
TR-7's transmitted audio. The problem was traced to my "aftermarket" PTT
footswitch with unshielded leads. Removal of the footswitch cleaned up
the audio considerably -- but not entirely. I was still getting reports
of minor distortion. Some said I still had a little RF in my signal.
Others described a quality that sounded like clipping.
Then I remembered that I had installed a one-resistor mod on the ALC board
that tightened up the decay time. Could this be the problem?
I clipped out the added resistor.
I also re-aligned the transmitter section using a newly calibrated Bird 43
wattmeter and learned -- to my surprise -- that the old military surplus
wattmeter I had used to align the transmitter a few weeks ago was reading
almost 30 watts low. Therefore, my original transmitter power output and
ALC settings were based on a real power output of over 150 watts on 20
meters, rather than the recommended 120 watts or so. (My TR-7 had arrived
at my door tweaked to put out over 200 watts and exhibited all kinds of
weirdnesses, so even my first, faulty re-alignment had been an
improvement).
Anyway, re-aligning the transmitter with the correct, lower power output
and appropriate ALC setting cleaned up the audio completely and I'm now
getting reports of excellent, "broadcast quality" transmissions with a
Heil Classic mike.
I really don't know if the now-removed ALC mod was contributing to the
problem or not -- but I think I'll just leave well enough alone.
Apparently it is my mission in life to screw up so you don't have to.
73,
Craig
W3CRR
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