Meridian Drift Scan

[Steve714]

My recent foray into meridian drift scanning has produced traces which are inverted compared with what I would intuitively expected ie a dip in magnitude of the received (noisy) signal rather than a peak. This drop is recorded at exactly the expected time of the radio source transit and the transit time is precisely what is predicted (Radio-Eyes). This is repeatable for varying starting times and has been recorded for both Cass A and Cyg A.  I am using a dish antenna at 3.4GHz. Would be grateful for any insight into this from more experienced practitioners.

[robin_astro]

Just a thought. Does your receiver  have an AGC? Could it be something to do with the AGC  reducing the gain when the signal is received, dropping the noise background ? What does it do on strong sources like the sun/moon ?

[robin_astro]

Steve,

Is there a description of your setup somewhere ?  (dish diameter, receiver and how you are measuring the signal strength)

Thanks

Robin

[Steve714]

Robin, Thanks for that. The receiver does have AGC  but the signal strength is relatively low so this shouldn't be a issue. Have seen 18dB increase in signal strength with no problem pointing at the sun. Having said that, I think that the SDR receiver is causing problems (eg image signals) and that I need to upgrade to a spectrum analyser (and a larger diameter dish). I would be grateful for any suggestions.

Thanks,

Steve