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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 4th Aug 2020, 7:27 pm   #1
Jon_G4MDC
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Location: Welwyn Garden City, Hertfordshire, UK.
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Default Kenwood TS130V and S - RX on 30m

I wonder if any forum member has had, or even still has, one of these? I have a TS130V which I like very much - since about 1995 or so. I liked to use it for 30m CW (10MHz).

When conditions were good I noticed the band contained very many AM broadcast sprogs. These would disappear if the 20dB Attenuator was switched in - but of course very often so did the wanted signal.

I mulled over why that might be and my conclusion was that the rig has an 8.8MHz IF so for tuning 10-10.5MHz the oscillator runs between 18.8 to 19.3MHz. I think strong signals in the 31m broadcast band, about 9.2 - 9.4MHz, produce 3rd Harmonic in the RF Amp/Mixer, becoming 27.7 to 28.2MHz. These mix down with the LO to produce the IF again and appear as spurs. (This is all fairly classic stuff)

The preselector filter in the TS130 is compact and so the selectivity is not that great (~zero?) between 10 and 9.2MHz. I think others must have noticed this effect.

I have been trying to work out a way to improve it but that is hampered by the fact my copy of the manual has missing detail about the preselector filters. Does anyone have something better perhaps? Has anyone done any reverse engineering of this preselector filter? My circuit diagram looks quite unfinished in this area!

The filter looks like one of those designs that is unterminated - a dual gate MOSFET sits on the output end. There is a wideband transformer to scale up the impedance at the input end. My guess is it works at a Zo of around 450 Ohms but I could be very wrong.
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