JUMA-TRX1
main board adjustments
AGC threshold adjustment (R28)
-
Turn first the AGC threshold trimmer
R28 to noise edge by listening the audio noise
-
Feed -73 dBm (50 uV) with a RF signal
generator into the antenna connector
-
Adjust the trimmer R28 so that the S-meter
shows S9 (midpoint in the LCD bar display)
-
If a RF signal generator is not available
you can use another HF receiver as a reference
LO duty cycle adjustment (R68)
-
The purpose of this adjustment is to
null the 2f spurious response
-
Feed -30...-10 dBm 7 MHz with a RF signal
generator into the antenna connector
-
Tune the RX frequency to 3.500.50 MHz
and identify the 2f signal response
-
Adjust the signal generator level so
that the 2f signal is audible and there is S-meter reading
-
Adjust the trimmer R68 so that the 2f
response minimized in S-meter
-
If a RF signal generator is not available
you can locate a very strong BC carrier in 7 MHz band and listen it at
half of the frequency
Carrier (CW) RF output level adjustment
(R50)
-
NOTE
the pa board must be adjusted before this adjustment and the relative power
switch must be in forward position
-
Connect a 50 ohm dummy load, use 13.8
V / 1.5 A power supply
-
Switch to CW mode and key down and adjust
the RF ouput to 5 watts by the trimmer R50
-
Two bars below the maximum display in
the relative output display corresponds 5 watt
-
The power output can be verified wit
an oscilloscope, 45 Vp-p corresponds 5 watts
DSB RF output level adjustment (R41)
-
NOTE
the pa board must be adjusted before this adjustment and the relative power
switch must be in forward position
-
Connect a 50 ohm dummy load, use 13.8
V / 1.5 A power supply
-
Transmit in DSB mode, whistle with lips
almost touching the microphone and adjust the RF PEP output to 5 watts
by the trimmer R41
-
Two bars below the maximum display in
the relative output display corresponds 5 watt
Side tone frequency adjustment (R53)
-
In CW mode during transmit the TX frequency
is shifted 700 Hz down. Thus the side tone pitch can be used to tune to
the same frequency
-
Switch to the DSB mode, the side tone
is heared from the speaker also in DSB mode but nothing is transmitted
-
Key down and tune the side tone frequency
to 700 Hz by trimmer R53
-
You can use counter connected in the
speaker line, this adjustment is not critical, ± 100 Hz accuracy
is adequate
-
Alternatively the side tone pitch can
be compared by ear with a piano or other musical instrument, note F is
698.4 Hz