Hi
The board "S45035-D5142-.."(Ausgangsteil) has a simple BJT product detector and
BFO. The BFO frequency is tuned with 2250pF and it is shifted by S4, possibly
shifting it 1.85 below and above 100kHz as the switch is set to left or right. When
the 250pF is grounded it is LOW and when it has the two external
capacitors (above the switch on the front) in series it is HIGH.
The unmarked capacitors above the switch behind the front are 25pF styroflex and 25pf
air trimmer, I measured 41pF, but don't always rely on the instrument, and to the
calculation you may add some 50pF for the PTFE-cable.
Remove all plates and screws and when you still can't find a way to start modifications,
you should read the instructions, Chapter 4, MAINTENANCE -
only to discover that you can just as well put back some of the screws again and
remove the upper unbrako type screws instead - to slide the upper unit backwards.
It was a fight to remove the front plate, but it went after all. Careful with
all those
terribly small 2.5mm screws, nuts and washers!
First I thought of a capacitor, but it must be small enough and isolated
from ground behind the front plate. A better idea is a varicap diode
(BB112 or BB130), but diode must be shorted for USB,
it demanded a potmeter with an NC-switch and they are rare, so I decided
use a switch with 4 positions instead. An alternative is to forward bias the varicap
as a switching type.
Mounted 3 trimmers and fixed value capacitors in sort of dead-bug style
(45° angle backwards)on a bracket with pcb laminate where the old capacitors had been.
The 4 positions are now:
1. Shorted coax cable as earlier CCW (LEFT) with 1850Hz pitch for 80Hz filter.
2. 470pf+270pf + 100pf trimmer - to tune one sideband with 500-800Hz pitch
3. 56pf + 100pF trimmer, to tune the opposite sideband with 500-800Hz pitch
4. 22pF + 20pf trimmer (or 10pf fixed and 40pf trimmer) for CW (RIGHT) as before
used a six position switch, but couldn't think of the need to use more than 4 positions,
Didn't find any small shiches with long shaft, so the nut must protrude through the front plate,
so the hole must be widened a little for the nut.
Believe the audio level is terribly high, +1dBm/600 ohm is quite a lot, and
little margin for overload
hope you understood it, otherwise I'll have to write it in in German or
Norwegian and let Dick
PAØSE translate it.
73,
Jan_Martin
[email protected] (in JO38XC) http://www.laud.no/la6nca/la8ak/
NOTE: Because of heavy spamming now applying eremove.exe, please avoid odd titles!
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