TopBand: TS-870S IMD improvement Mod

Earl W Cunningham
Wed, 03 Dec 1997 00:57:45 EST

Bob Kile, KG7D wrote:
>I've scanned as 800/700 jpeg image the TS870S IMD modification. This is
>for EARLY units only.(below SN801XXXXXXX) No guarrantee expressed or
>implied. This requires high SMT skills and service manual. The same
>quite possibly could apply to TS570D as well and I am checking. So for
>those technically inclined you may find the file at:
The so-called "IMD" problem on CW in the early TS-870S's is due to the
wider IF selectivity stages before the IF DSP.   i.e., if the DSP is set
to say, 100 Hz, strong signals within +/- 1.5 kHz or so of the receive
frequency will cause AGC "pumping".  Apparently, from what Lars, SM3BDZ
wrote on 1 Dec, Kenwood has alleviated this problem by decreasing the IF
gain in the offending IF stage before the DSP.  To make up for the gain
loss, they've increased the gain in a later non-offending IF stage.

This problem should not apply to the TS-570S because it uses AF DSP.

I (like Carl, KM1H) am seriously considering upgrading to the 870.  It
would be appreciated if TS-870S users would report to Carl and me their
"IMD" problems, if any (or not), with the modified or late-model 870
during the upcoming ARRL 160 Contest, where the band will be crowded with
many big CW signals.

73 es tnx, de Earl, K6SE

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