HF in Low-VHF

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Joined: Sat Feb 27, 2016 7:53 pm

HF in Low-VHF

Postby AlanClark » Sat Feb 27, 2016 8:02 pm

Hi everyone.

I've had my SDRPlay for nearly six months now and I'm constantly learning and looking at new parts of the spectrum to explore.

I've recently upgraded my antenna and I now have a long wire for SW as well as a whip for VHF/UHF.

I'm now getting strong HF AM ghost signals in the lower part of the VHF band. I've attached a screenshot.

What the best strategy to deal with this.

hf-in-vhf ghost.jpg
hf-in-vhf ghost.jpg (123.4 KiB) Viewed 1398 times

Alan Clark
Near London, UK.
Last edited by AlanClark on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Posts: 125
Joined: Sun Feb 14, 2016 8:40 am

Re: HF in Low-VHF

Postby 13dka » Mon Feb 29, 2016 1:03 am

Not much feedback from the staff here lately. :| However, maybe I can give you some pointers....

- Your settings might be really prone to trigger images:

1. The LNA is on (often not really helpful at such a relatively low frequency). Also see below (about your SDR# version).

2. Your gain reduction is pretty low at 33dB, IOW gain is rather high, and your wire has certainly potential for a lot of output at some frequencies - that all asks for all kinds of non-linear mayhem. A good starting point for anything below the FM band may be 50dB GR with the LNA off.

3. You're in zero IF mode - switching to low IF mode and vice versa can remove or shift images showing up in the other mode, however I found low IF mode more robust in many cases.

4. Your IF bandwidth setting is at the maximum. The images are actually far away from your receiving frequency (so they may not do much harm actually, apart from looking appalling), but even if you've tuned into the middle of the images, changing the baseband width can make them disappear.

So changing each of these points can break the chain of events causing the images, a combination of some or all of them will hopefully do it. In some cases you may run out of luck though.

- Contributing to this might be that you're using SDR# build 14xx with the SDRplay 2.2 plug-in. For example, AFAIK the plug-in is based on an older version of the ExtIO.dll, where the LNA is switched automatically depending on the GR setting (so it can be activated when you don't want or need it) and so on. I don't know if the plug-in is doing the same as the ExtIO.dll in terms of gain staging and further processing in general. Try SDR# v1361 or HDSDR with the latest ExtIO.dll for the RSP instead, or SDR Console.
Last edited by 13dka on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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