TopBand: TS-870S improvements

[K3BU@aol.com]

I started working on modifications of TS870, but as usual, ran out of time.
I installed the intermod mod, as mentioned earlier here and by Lars. It did
reduce the intermod problem on 160. I have not calibrated the IF stage gain,
rig seemed a bit down on sensitivity, but I had preamps anyway, so did not
pursue the detailed alignment etc.

I also got IR filters (they don't have specific mod/set for TS870) and I
replaced the Kenwood SSB 8 Mhz IF filter with 2.1 kHz bw IR filter. I am
going to look at the 455 kHz IF filters too (Kenwood uses little ceramic
jobs), time permitting. Will have to study the interaction between filters
and DSP and different modes, see what combinations work best. 
Due to lack of time, snow storm, and last minute fixes I had very little
chance to do serious observations, but definitely there was less "choking" on
ts 870 due to strong signals. This radio was used as a receiver on the right
ear "beaming" west. 
Hopefully with some more surgery, this radio can be upgraded to a decent
contest rig. Other features and size of it, makes it great expedition radio
too. 

I also managed to replace Icom filters in IC 781 with IR filters (+125Hz),
which made it really sharp (used as left ear RXs). 125 Hz filter helped to
take apart the blurr from occasional Eu pileup. IR filters seem to have more
attenuation, but again I did not have a chance to play with tweaking the
circuits. I am planning to replace the RF switching diodes too. (love that
panadapter) Used Timewave DSP599ZX.
I was ready to use the TS870 as a IF receiver/DSP from IC781 455 kHz IF, but
I didn't get chance/need to use it. This could be the ultimate combination
for selectivity and noise fighting gear. 

I will report on the progress with further mods.

73 and thanks for precious points in WW CW!

Yuri K3BU, VE3BMV

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