HFU HF Underground
Technical Topics => Equipment => Topic started by: brotherstair on February 27, 2025, 0807 UTC
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Hello,
I'm hoping someone can provide guidance on a way to increase the bandwidth on this old transceiver. It is primarily meant for 6900khz transmission, so ideally I'd like to improve the audio quality, ideally 5khz or 10khz LPF instead of the usual 3khz, and HPF ~50hz instead of the usual 300hz.. I'm decent with a soldering iron, I just am in over my head with where to begin on this thing. I can usually find my way around a schematic more-or-less, though I can't say I fully understand them.
I struggle to even find a GX ii schematic, though the GX may have a close enough layout to where it can be useful to figure out where to start. Some guidance on what to look at and where to look would be great, I don't need my hand entirely held (though I wouldn't object), I just need some ideas.
At this point, if I don't hard cut high and low frequencies, it distorts horribly. I'm already attenuating the input by 24db from line-out to the external microphone input, and I've got the levels *reasonable*, but the high and low pass filters are absolutely killing me on SSB. I've reached my limit on what my audio processing chain can do, and I really need a little more headroom here.
Any ideas?
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Some light reading....
https://www.nu9n.com/Mods_TX_RX.html
Str.
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Some light reading....
https://www.nu9n.com/Mods_TX_RX.html
Str.
Well... *That* certainly started me down a bunch of rabbit holes, thank you!
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Might try using the PATCH/AFSK 600 ohm RCA input on the back instead of the mic imput (to see if that will bypass the filter) and refer to page 30 of the manual for adjustment. After that, see if messing with the COMP adjustment will do anything, though suspect it's for the mic. You might have to cable a switch to the PTT connector to transmit. Just throwing it out there.