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Old 19th Jul 2019, 3:36 pm   #1
Wendymott
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Smile Tuning up a SSB TX

Hi peeps. The saga continues..My homebrew 3 band SSB transceiver.
Should I include a sinewave AF oscillator to modulate the TX at low power to tune the ATU Match, and if I want to join a "QSO" how far away from the QSO should I frequency shift so I dont cause interference to the QSO.
Thanks
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Old 19th Jul 2019, 4:05 pm   #2
G6Tanuki
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Default Re: Tuning up a SSB TX

Rather than adding a separate oscillator the usual way to produce a whiff of RF is by unbalancing the balanced-modulator. If it's a diode type, putting a bit of DC through one half achieves this - all you need is a pot and a RF choke.

As to tuning-up techniques - there are ways to do this which involve radiating spectacularly-little power (using a resistive bridge, a detector and a microammeter) so you don't really need to worry about 'ofsetting' your frequency.

See http://www.zerobeat.net/g3ycc/res_swr.htm for example. I've got something similar here and it works fine on 5MHz when driven by a BC109 crystal-oscillator running from 12V.
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Old 19th Jul 2019, 5:08 pm   #3
Wendymott
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Default Re: Tuning up a SSB TX

Hi Tanuki.. The modulator is a MC1496, with a balance pot, so I can offset the trim pot.

Thanks for the tuning up info. As it happens the PA has just "died" again.. Grrrrrrrrrrrrrrr
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