AM Radio Crud - How to Eliminate?

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W6JHB
Posts: 8
Joined: Thu Dec 21, 2017 5:59 pm

AM Radio Crud - How to Eliminate?

Post by W6JHB » Tue Dec 26, 2017 10:08 pm

I've just hooked up an RSP2pro on Windows 10 running under VMware Fusion on an iMac, and I have SDRuno. Have two antennas in use for my initial testing. Antenna 1 is connected to a ham radio 2m/70cm ground plane. Antenna 2 is connected to an 88 foot long doublet about 45 feet in the air. Using the Ant2 connection I can listen to FM broadcast and ham radio 2 meter repeaters, no problem, sounds great.

However, when I switch to Ant2 and try listening to either general coverage SW broadcast or the HF ham bands (especially 80, 40, and 30 meters) I'm bombarded with what sounds like harmonics from AM broadcast stations all over the place. It appears that it is not the same one, but several. Is there any sort of filter available in this radio that can eliminate this junk, as it makes using these HF frequencies just about impossible.

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Jim Bennett / W6JHB
Folsom, CA

WA2ZKD
Posts: 6
Joined: Tue Dec 26, 2017 11:23 pm

Re: AM Radio Crud - How to Eliminate?

Post by WA2ZKD » Tue Dec 26, 2017 11:36 pm

I fixed it on another SDR with some notch filters on the strong AM stations
Last edited by WA2ZKD on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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pgoelz
Posts: 47
Joined: Fri Jun 02, 2017 11:05 am

Re: AM Radio Crud - How to Eliminate?

Post by pgoelz » Wed Dec 27, 2017 1:00 am

How strong are the AM stations when you actually tune to them?

Have you tried lowering the RF gain? Note that by default the "RF Gain" slider indicates RF gain reduction so UP is LOWER gain.

Have you tried using the HiZ input for your doublet (might require a broadband balun) and activating the BCB/FM filter (only available on the HiZ input)?

Where I live, the strongest AM station is weaker than some SW stations so AM stations don't bother me. But I have seen Radio Havana on 15MHz at about -45dBm (way stronger than the AM stations) and even with the RF gain all the way up and the A/D in indicated overload, it doesn't have much negative effect.

Paul

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W6JHB
Posts: 8
Joined: Thu Dec 21, 2017 5:59 pm

Re: AM Radio Crud - How to Eliminate?

Post by W6JHB » Wed Dec 27, 2017 6:02 am

Thanks for the input, folks. Since doing any DX / SWL’ing on the AM broadcast band is at the bottom of my list, the idea of a high pass filter came to mind. Did some Googling and found an inexpensive filter on Amazon that looks like a perfect fit. In fact, quite a few positive reviews of it by other SDRplay owners facing the same issues I have. Will arrive on Thursday, so I’ll report back with my findings.

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Jim Bennett / W6JHB
Folsom, CA

g1hbe
Posts: 494
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: AM Radio Crud - How to Eliminate?

Post by g1hbe » Wed Dec 27, 2017 9:41 am

Don't forget the RSP-2 has a MW(AM) rejector which you can enable. It puts about 30dB attenuation in from 500 KHz to 1.7 MHz and it may help you. Below is a shot of how LF looks here in NW England on the RSP2 using the Hi-z input with an external 500 KHz filter. Antenna is a Wellbrook 1530 active loop. I use the Hi-z input as the LF response of the other inputs is poor.
Attachments
lfsmall.jpg
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Andy

NoelC
Posts: 137
Joined: Sun Nov 27, 2016 11:50 pm

Re: AM Radio Crud - How to Eliminate?

Post by NoelC » Sat Dec 30, 2017 8:56 pm

g1hbe wrote:Don't forget the RSP-2 has a MW(AM) rejector which you can enable. It puts about 30dB attenuation in from 500 KHz to 1.7 MHz and it may help you.
RSP1A has the feature as well. I found it quite effective when I tested as compared to RSP1.

-Noel

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KE2KB
Posts: 30
Joined: Fri Dec 02, 2016 1:11 am

Re: AM Radio Crud - How to Eliminate?

Post by KE2KB » Thu Jan 04, 2018 5:12 pm

Hey guys;
I just upgraded my SDRUno from ver 1.13 to version 1.21. I have an RSP1.
Immediately on starting up the new version I was hearing AM broadcast stations on all bands, and no matter what frequency was tuned the AM stations did not change. Even if I changed bands, I heard the same stations. Reducing IF gain did help, but I needed to reduce IF so low to the point that I had trouble receiving ham stations on all bands.

I tried playing with the settings, changing everything back to what I had in version 1.13, but nothing changed.
My final solution was to un-install the new version (1.21) and re-install the old (1.13). Now the AM stations are gone, and all is working as it should.
I suppose that this problem has been reported to SDRPlay? If not, I will submit a bug report.

If you want the older version of SDRUno and cannot find it to download, please PM me and I will send it to you via e-mail.

Frank

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sdrplay
Posts: 978
Joined: Wed Jan 07, 2015 7:58 am

Re: AM Radio Crud - How to Eliminate?

Post by sdrplay » Thu Jan 04, 2018 6:49 pm

Frank,

I can't think of what could cause that - if you can show screenshots of both versions (including as many windows as possible) I'd like to understand why you are having that issue.

Best regards,

SDRplay Support

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NoelC
Posts: 137
Joined: Sun Nov 27, 2016 11:50 pm

Re: AM Radio Crud - How to Eliminate?

Post by NoelC » Fri Jan 05, 2018 1:12 pm

You can have both installed if you choose a different installation folder for each.

If you do that, do you see a difference when you run one version vs. the other?

Also, have you tried tuning the various ham frequencies using numerical entry (i.e., by NOT pressing one of the 160, 80, etc. buttons to the right of the RX CONTROL window)? They change more things than I like (e.g., they change from Low-IF mode, which I prefer, to Zero-IF mode, as well as changing the Decimation). I don't use those particular buttons at all for that reason.

-Noel

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KE2KB
Posts: 30
Joined: Fri Dec 02, 2016 1:11 am

Re: AM Radio Crud - How to Eliminate?

Post by KE2KB » Fri Jan 05, 2018 8:54 pm

OK. I will install the latest rev (1.21) alongside the older (1.13) version. Play around with it for a few hours, then report back.

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