Re: Ground noise on 23cm?
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I would agree with others that a filter in front of a preamp is an almost must now, I have built ones for 23cm and 13cm using the information on this site and the difference is night and day, If you prefer to buy you can also have a look at PE1RKI site he produces nice filters as well.
From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> On Behalf Of John Lemay
Sent: 17 September 2020 07:49
Subject: Re: [UKMicrowaves] Ground noise on 23cm?
I completely agree with Richard’s analysis of the likely cause of interference on 23cms. My QTH is line of sight with the Sudbury TV transmitter, and it gave me lots of grief until I introduced a bandpass filter. A notch filter at 650MHz provided an element of improvement and indicated I was on the right track.
You can read about my findings at http://www.g4ztr.co.uk/amateur-radio/23cms/ , just scroll down past the yagi info.
Maybe I can use this mail as a thinly disguised commercial for my own interdigital filter, which can be found at www.aerial-parts.co.uk. Quite a few of these are in use around the country and I’ve yet to hear of anyone who has not been able to improve reception.
I have a filter designed by G3XDY plumbed into my system after the amplifier. https://www.qsl.net/g3xdy/QRO%2023cm%20Harmonic%20Filter%20and%20Reflectometer.htm
On RX I have an (almost) mast head pre-amp (located in loft, with the amplifier, under the antenna outside, a Tonna 35ele that seems to be intermittent at times so something else is needed). The pre-amp has an onboard hairpin bandpass filter and this also feeds an interdigital filter which connects via 30ft of coax to the SG Labs transverter. Other than radar pulses I have never noticed any unusual noise from any direction – even with a well loaded water tower only 400 yards away. Mind you not saying this won’t change when I get a decent antenna up there.
Regards to all,
Colin de G8LBS.
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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.