[DEMI] 2304 MHz Transverter (Old)

[Kevin Murphy]

Hi 
I have recently done some work on a older 2304 DEM transverter. One of
the problems I found was instability (Haha) on the LO,RX and TX strips. 
One of the problems was adjacent striplines to the hairpin filters
causing suckouts. The LO had about a < 6 dB suckout (notch) caused by
the adjacent stripline being about 1/2 wavelength. I added a SMD 100 pF
to ground at the centre of the stripline using a veropin/rivet/wire and
additional 100 pF's to ground at the Lo-Z ends of the stripline. The
100pF at the centre of the stripline caused the LO filter response to
flatten out and gave about 2 dB loss instead of about 6 dB.
I had similar instability in the RX converter which cured by a similar
treatment and I also modified the TX side for good measure.
The LO circuit was modified with a MAR8 acting as the multiplier with no
instability. After the multiplier filter a second MAR8 acted as the AMP
with no problems.
The TX side was a MAR3 driving a  NGA386(ERA3). I also had a 3 dB
attenuator between the TX mixer and the first filter.
Due to the use of MAR6 and MAR1 on the RX, the gain across 2-3 GHz falls
off very fast (12 dB drop in gain across that band
I modified the 2304 MHz transverter to work on 2424 MHz by shifting the
first tx BPF filter up  by about 200 MHz. With a little tuning of the
mixer,a small stub  between TX  and LO ports to improve LO rejection,
the result was a very clean transverter free of instabilities. 
Note that the early model 1296 DEM transverters have similar tracks
adjacent to the striplines. I have an early transverter PCB which I will
be investigating at a later date.

Kevin
ZL1UJG