Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Bob -
The first thing to do is get the Carrier Oscillator at least "near" the
correct frequency. If you have a "modern" receiver with digital
readout, put it's antenna near the Carrier oscillator of the T-4X and
look for the Carrier signal at 5645 kHz. You'll need to put the T-4XC
in SSB mode, with the GAIN control full CCW, and key the PTT line either
by pressing the PTT on the mike or by grounding the PTT line of the mike
jack. Adjust C6 to set the frequency. C6 should be fairly close to the
center of it's adjustment. If you can't set it to exactly 5645 MHz, you
may have a bad crystal.
Now listen to the output frequency of the transmitter on the external
receiver and adjust R21 and C17 alternately for minimum signal in the
receiver. With proper adjustment you should just barely hear the
transmitter output. This should be "good enough" for use.
Now with the transmitter loaded into a dummy load, and listen to the
transmitter signal on the receiver using headphones. Listen on both USB
and LSB, switching the transmitter and receiver appropriately while
speaking into the microphone. If your voice sounds correct on both
sidebands, you're done. If one sideband sounds "bassy" and the other
sounds "hissy" you can adjust C6 _SLIGHTLY_ (+/- 100 Hz maximum) one
way or the other and retry. A DSB signal, which is what comes out of
the Balanced Modulator, has the carrier (suppressed) in the center, and
the audio sidebands on either side arranged with the low frequencies
closest to the center. Think of the process as the letter "M". The two
top peaks of the "M" are the two filter passbands, and you want the
Carrier Oscillator frequency to be in the "valley" between the peaks.
If the Carrier Oscillator is off to one side, the high frequencies will
be down the outside of the "M", making the audio sound "bassy". At the
same time, the lower frequencies on the other sideband will be down the
inside of the "M" making the audio sound "hissy".
If the transmitter doesn't sound "pretty good" with the Carrier
Oscillator set to 5645 kHz exactly, it's possible that you have a bad
filter. This is pretty rare in units that haven't been banged around or
otherwise mistreated, but does happen.
73, Garey - K4OAH
Atlanta
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Robert Ladden wrote:
Robert Ladden <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Hello again,
After more testing, I must be way off. Even though I have the carrier
completely suppressed now, I discovered that when I tune I have much
more plate current (150ma) and output power on LSB than USB. The voice
is intelligible on both LSB and USB, but LSB sounds "glassy", USB
sounding more rich with more low voice tones.
So I must not be balanced, but anything else results in a carrier
(about 40 output watts on LSB on the watt meter).
Do I have a major problem? A bad filter? Or do I just try some more
before shipping it out for someone smarter than me to fix?
Thanks and 73,
Bob Ladden WA3WQB
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