The filter on the NB board is only on the hi power models. Forget the computer stuff. You need a tone generator and a signal generator. I use a IFR 1200S and a Motorola two tone generator to adjust the SSB osc's. That is an EXCELANT mic!! Very valuable today. I used to sell them in my store for about sixty bucks. I have a few. With a stock mic I get people asking what mic I’m running? I run 301’s on all bands using transverters and Swiss displays and VFO stabilizers. Whens the last time you worked AM on 220 mhzs? Hi hi
Do you want a copy of the 9mhz alignment? There never was a service manual and the latest owners manual was obsolete when it was printed and can’t be trusted. The key is to listen to the receive signal on USB and LSB. They won’t be the same. That’s the problem. Your on it but it takes a bit of doing to tune it up right.
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On Feb 19, 2025, at 10:16 AM, atlasstuff via <
g4fph@...> wrote:
Digging into this a little more today.
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Using my SDR transceiver as a narrow-band, RF spectrum analyser, I checked the DSB TX IF signal going into the Filter Unit. Audio fidelity from the mic. I selected as best match to the '301 (an old Astatic MOD. 575-M6) was very good, with modulation sidebands extending to at least 4 kHz either side of the (suppressed) carrier, and with some signs of roll-off from around 3.3 kHz. So, I think the issue is likely to be the response of the second crystal filter on the NB (/ RF Processor) Unit.
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Even with the processor turned off, the (now SSB) TX IF signal still passes through this second filter, which seems like an odd decision by the Yaesu design engineer(s). I see references in the service manual that the filter is optional, but I think it is present in all three of the transceivers (one -301 and two -301D) that I own. It's not listed as an option in the English brochure that I have a PDF of.
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Later this week, I will pull a complete NB Unit from another '301 and try it instead of the one I have been using. Depending on results, I may even try removing the filter on the NB Unit to see what difference it makes. I assume it is present principally to clean up artifacts arising from the RF clipping process, so it would be nice to retain it for that. Perhaps a modification is possible...?
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I note that 'ELcon' () published a modification for the Filter Unit that better terminates the filters in order to improve the response on USB. My testing has all been on LSB so far.
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Regards,
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Mark, G4FPH.
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