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 Post subject: SX-71 Alignment HELP
PostPosted: May Mon 06, 2019 12:06 am 
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Location: Latham NY
I am having trouble understanding these steps. No 3 says to set for max out but with an unmodulated signal. I am stuck on this step.


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 Post subject: Re: SX-71 Alignment HELP
PostPosted: May Mon 06, 2019 12:37 am 
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Location: Montvale NJ, 07645
You need to set the IF at the exact crystal frequency. So the idea here is to get the signal generator to that frequency, whatever it is, and then align the rest of the IF without moving off that frequency.

With modulation, you will have the carrier plus the 2 sidebands which will make it harder to find the crystal frequency because of the extra peaks.


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 Post subject: Re: SX-71 Alignment HELP
PostPosted: May Tue 07, 2019 11:18 pm 
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I am thinking of injecting my cw signal at the grid of the 2nd IF and monitor the avc voltage to find the crystal frequency. Does this sound like a good idea?


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 Post subject: Re: SX-71 Alignment HELP
PostPosted: May Wed 08, 2019 4:48 am 
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It isn't critical where you inject the 455 kHz as long as it is before the second mixer. If you are have trouble finding the exact crystal frequency, I would use a modulated signal at the sharpest crystal filter setting with the BFO off and peak the output by adjusting the signal generator frequency. Then turn on the BFO and turn off the modulation. Adjust the BFO frequency for a tone between 400 and 1000 Hz. Now slightly adjust the SG frequency to re-peak the output. That should be the crystal frequency. The AVC should be off during this procedure. I have and use an output meter for aligning my receivers. They aren't very popular these days, so some other way to measure the peak is always an option.

Norm

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