QRP SPIRIT adjustment


From: Arjen Raateland, VYH/vet, puh. 90-4028 350 (Arjen.Raateland@vyh.fi)
Date: Fri Dec 30 1994 - 17:46:04 EST

I don't have all of the gear that the OHR instructions for the QRP
Spirit presuppose, so I used an alternative procedure to do some of
the adjustments of my 80 m QRP Spirit. My procedure doesn't address
the tuning of filters or VFO range.

1. Connect a hookup wire with a small clip to the cathode of zener
diode D7 which stabilizes the supply voltage of the TX carrier
oscillator (Q8) on the TX board. Connect the other end of the hookup
wire via a 330 Ohms resistor to a stable PS at about 12 volts. You may
adjust the voltage on the cathode of D7 to about 9 volts by raising
the output voltage from the PS. I couldn't hear the frequency of the
carrier oscillator (Q8) change as I listened to the beat on a GC
receiver when the voltage on D7 went up from an initial 6 volts to 8.7
volts, so the voltage on D7 doesn't seem to be critical.

2. Switch the rig on and listen to the beat note. The TX carrier
oscillator at 9 MHz is now working and its signal leaks into the
receiver beating with the local oscillator on 9 MHz. If the beat note
is weak or absent, adjust C109 on the RX board first until you have a
nice beat note. Switch the AGC off. Adjust the TX carrier frequency
with C56 for loudest beat note. Use an AC voltmeter on the audio
output if you like. This adjustment puts the TX carrier frequency
right in the peak of the IF filter passband.

3. Adjust the beat note to 700 - 800 Hz with C109 on the RX board
using e.g. a frequency counter. This puts the local oscillator (Q20)
700 - 800 Hz away from the IF filter centre/TX carrier frequency.

4. Remove the hookup wire from D7 so the TX carrier oscillator is off.

5. Make sure the local oscillator is on the lower side of the IF
filter passband by tuning over a signal on the band from high to low.
The beat note should go from high to low. If it goes from low to high
instead, reconnect the hookup wire to the cathode of D7, go back to
point 3 to find another position of C109 at which the beat note is 700
- 800 Hz.

6. Listen to the VFO output signal at somewhere between 12.5 - 12.6
MHz with a GC receiver. Set RIT to middle position. Tune for zero beat
adjusting the main tuning of either rig. With a dummy load on the TX
output, key the TX and observe the beat note in the GC receiver.
Adjust R27 on the RX board for zero beat at key down. Alternatively
you could also use a beat frequency other than zero and observe the
change when keying. Adjust for no change. This will put the VFO
injection for RX and TX operation at the same frequency.

When the RX is tuned to a signal at a frequency Fr for loudest
reception, the VFO frequency (Fv) is such that the signal is mixed to
the centre frequency (Fc) of the IF filter bandpass.

(1): Fr = Fv - Fc

The TX carrier is at the same centre frequency Fc (point 2). There is
also no difference in VFO output frequency between RX (w/o RIT) and TX
(point 6), so the TX output (Ft) will be exactly on the frequency of
the station we have tuned the RX to.

(2): Ft = Fv - Fc

>From (1) and (2): Ft = Fr

I suppose that when one follows the OHR instructions the TX output
will only be exactly on the same frequency as the RX if the 'nice
mellow tone in the other radio' used in adjusting the TX carrier
frequency (C56) is the same as the '700 or 800 Hz CW note' used for
the adjustment of the local oscillator (C109).

73 and best wishes for 1995 de OH2ZAZ, ex-PAoSCS
Arjen Raateland

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