To whom who would like to use TS-870 as a contest rig, I would insistently recommend to make three proper mods, that I recently did.
The first is intermod mod available from Kenwood for S/N below 801XXXXX.
This modification shifts gain distribution from RF stages to IF stages. Involves changing of about 8 resistors.
The second is filters mod. Yuri recommends to put two 2.1 KHz INRAD filter instead of two 3 KHz filters for both 8.83 and 455 IFs. I don't have INRAD fliters, so I replaced both (8.83 and 455) 3 KHz filters for another Kenwood filters 2.4 KHz: YK-88S-1 (the same size) and YG-455S-1 (needs much more free space and two coupling capacitors to avoid DC short circuit). These filters are quite good compromise due to the mixing and shifting scheme for various bandwith. I ploted curve for original filter and new, the slopes were about the same due to DSP action. But there is a big difference in overload and intermod due to strong adjacent signals from edges of the filters. DSP is too late after the IF chain, strong signals outside of DSP bandpass but inside of filter bandpass will "pump" the stages ahead of DSP and "confuse" it. This is why good filters make huge difference.
The third is external receive antenna switching mod. After this mod : when "ANT2" is selected - Ant2 connector is for both TX and RX, when "ANT1" is selected - Ant2 connector is for TX only and Ant1 connector is for RX only, i.e. I can use another external antenna for RX.
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