Re: Ground noise on 23cm?
Thanks for replies guys. The world's dtv transmitter mast is is plane sight about 15 miles away, from your input Richard I'm guessing that could be the problem. Filter time I guess.
From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Richard GD8EXI <perwick@...>
Sent: Wednesday, September 16, 2020 10:27:26 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] Ground noise on 23cm?
I doubt it can be ground noise if it is S5. On 23cms you are unlikely to see more than 3dB change in noise, between beaming into a hillside and beaming down hill. The antenna noise temp going from say 100 to 200K, so even with a RX noise temperature of 50K, only expect a 2.2dB difference.
As Andy stated more likely the presence of one or more very strong signals, mixing in your RX at the /P location.
Another common culprit is a DTV transmitter centred on about 650MHz. The intermodulation products look like white noise in a 3kHz bandwidth on 1296MHz. Also do not assume your beam will tell you where the source is, as the polar diagram will look very different on 650MHz.
Best test is a good 1296MHz bandpass filter in front of any amplification. The trouble is the path loss of about 1dB. I use a 650MHz notch filter in front of my masthead preamp and an interdigital one after it. The noise floor drops by 10dB on some beam headings, on adding this combination, even after correcting for insertion loss.
On 16/09/2020, 20:20, "Andy G4JNT" <andy.g4jnt@...> wrote:
The product is 2160MHz [which is on the edge of a 3G channel] - 2 x 1152 [LO] = 144MHz