Hello folks,
This is an off topic question, but I post here because of the
wealth of technical knowledge you folks have:
I have recently "infected" my Collins station with a beautiful
Drake TR-4CW/RIT. After repairing a small problem (lo B+
resistor, soft finals) it works great. Gave it a careful
alignment, as per manual.
Here's my question: Unlike Collins, older Tentec, and others,
the Drake uses two SB filters (upper and lower) with a single
BFO Xtal.....after CAREFULLY centering the osc frequency (SEVERAL
times) I notice that the usb/lsb positions have different
audio characteristics and slightly different gain on receive.
They are WELL within tolerance for the radio to permit it to
meet spec, transmit and receive, but the difference is there.
With the filter matching networks carefully aligned and the
9mhz osc CAREFULLY centered, the "shape" of the sound and the
gain thru the filters is slightly different, when switching
back and forth from USB-LSB.....on all bands, of course, BUT
the USB/LSB "position" changes when going from 40 to 20, for
example (due to the mixing scheme of the radio)....
Am I just being anal retentive? I hear a difference, and see
it on a constant carrier (calibrator, for example).....seems
to be a difference in shape/gain of the two filters, or some
by-product of the radio's odd conversion scheme. Again, both
sidebands sound nice, and the radio has easily enough excess
gain to meet spec (~175-195 watts out XMIT, peaks up the RX
noise with no ant connected) but it "bothers" me!!
If you have a Drake TR-4* (any suffix), does yours exhibit
this tendency? I know it was a "budget" radio compared to
Collins, are the filters just not that tightly controlled
in manufacture, or is it that the "sides" of the bandpass
of the filters is different depending on the position of the
carrier osc?
Thanks for your input on my "non-problem",
Thanks Walt
WB5LJW
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