[Elecraft] Carrier breakthru using SSB filter

[Sverre Holm]

Ian,

I was inspired by your attempts to figure out the BFO breakthrough, so I
tried some experiments. I worked from the assumption that the BFO must
be radiating. To start with, I have no S-meter bars lit for the
CW-filter settings (0.1, 0.4 and 1.0 kHz), and 3 bars for the OPT1
setting. The OPT1 setting was 4 bars like yours, before I implemented
the TF3MA AGC filter.

If the BFoscillator is stopped by decoupling pin 6 or 7 of the product
detector U11 with 0.01 uF to ground, the audio dissappears. But since
the AGC output is before U11, the AGC voltage should still be an
indication of what goes on. When the BFO is stopped, the OPT1 S-meter
setting went from 3 to 0. I wanted to check if there was any change for
the CW filter settings, so I turned down the RF gain slightly to get 4
bars for OPT1 and 3 bars for the 3 CW filter settings. When the BFO is
stopped, all four filters go down to two bars.

I then looked for possible radiators. It could be RP6 so I tried to add
extra decoupling capacitors (pin 8 direct to ground, and pin 1 to
ground), but no change. However, RP6 could be radiating from its top
into KSB2. This could be checked by replacing it with discrete resistors
under the PCB, but I didn't want to tear apart RP6 to try that.

I then tried to decouple the various control lines on J11 (SSB Control),
but I found no change.

Last, I grounded the two BFO crystals at the bottom, and I got the OPT1
S-meter indication from 3 to 2. The measurement in terms of S-meter bars
is quite unscientific, but this is an indication that the grounding
could play a role. I should probably redo CAL FIL now.

That's how far I got tonight, and I have for the moment ran out of ideas
for further experiments.

--
73, 
Sverre

------------------
Sverre Holm, LA3ZA
www.qsl.net/la3za



> -----Original Message-----
> 
> No, it's all bands Brett... by opening Cp and D4 (it's still 
> there) front end  and DSB generator are isolated
> 
> Ian