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<blockquote data-quote="s-band" data-source="post: 1025258" data-attributes="member: 407744">If you change the sweep speed, you should see the modulation more clearly and if you can set your analyser to zero span with a wide bandwidth, triggered on video, you'll see the 20Hz. It looks random as the sweep is not locked to the modulation. The amplitude mod is&nbsp; a reasonable 20Hz sine wave. This plot shows it triggered on AM demodulated video <a href="https://www.satellites.co.uk/forums/attachments/34-5w_11665_slope-demod_h-gif.109789/" target="_blank">https://www.satellites.co.uk/forums/attachments/34-5w_11665_slope-demod_h-gif.109789/</a>To me, it looks like the signal from the opposite polarisation is modulated by 20Hz AM. That applies to both pairs.This looks the same thing but a slower sweep speed. The waterfall shows that the AM is not locked to the sweep.I wonder if there is something going on that is allowing signals from one polarisation to get to the opposite but modulated? Perhaps a problem with the switching matrix? or some diagnostics, as you suggest, Llew?</blockquote>

[QUOTE="s-band, post: 1025258, member: 407744"] If you change the sweep speed, you should see the modulation more clearly and if you can set your analyser to zero span with a wide bandwidth, triggered on video, you'll see the 20Hz. It looks random as the sweep is not locked to the modulation. The amplitude mod is a reasonable 20Hz sine wave. This plot shows it triggered on AM demodulated video [URL]https://www.satellites.co.uk/forums/attachments/34-5w_11665_slope-demod_h-gif.109789/[/URL] To me, it looks like the signal from the opposite polarisation is modulated by 20Hz AM. That applies to both pairs. This looks the same thing but a slower sweep speed. The waterfall shows that the AM is not locked to the sweep. I wonder if there is something going on that is allowing signals from one polarisation to get to the opposite but modulated? Perhaps a problem with the switching matrix? or some diagnostics, as you suggest, Llew? [/QUOTE]

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