SDR# Blocking AM radio station?

Randyk4661

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Jun 27, 2019
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619
Location
Garden Grove, CA
I have a AM radio station at 1480 about a mile from me that comes through all the way up to 30MHz.
I have used the notch filter in the IF processor (SDR#) to blank out the frequency but it still booms in anywhere in the short wave spectrum making it impossible to listen to anything.
I had this problem when using an older computer years ago and I fixed it, I just don't remember what I did.

Can someone give me any advice on what I can do?

Thanks, Randy
 

ka3jjz

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Jul 22, 2002
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Bowie, Md.
There are much better quality AM filters put out by PAR electronics and Mini Circuits. Do some google searches and you should find a potful. Here are just a few...


While this list concerns itself with FM filters, just look around the website and you should find AM filters too. Always check to see if the filter is effective at the problem frequency. Use the response charts to see. It would be helpful if we knew the offending station's frequency

Mike
 

ka3jjz

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Jul 22, 2002
Messages
25,785
Location
Bowie, Md.
OK now when you consider your filter look at the response curve and see whether 1480 falls within it's bandpass.
'
For example look here


Now click on the High pass filter and you will get a response curve. You can see that the filter ranges from 40 to 70db of attenuation.

This is the sort of information you need to make an informed decision

Mike
 

vagrant

ker-muhj-uhn
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Nov 19, 2005
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California
Over a decade ago I purchased a PAR AM broadcast band High Pass Filter. It has a switch to enable, or bypass. It helped attenuate an AM broadcast station tower about a mile away.

A few years ago I purchased a Flamingo+ AM broadcast filter via Amazon (Version 2). I swept each filter to review how wide the skirt was, as well as attenuation at the skirt edges and the AM broadcast range itself. The difference was negligible and may have been slightly better on the Flamingo IIRC. The bigger difference was the price of the PAR $80 versus the $20 Flamingo filter.

My PAR filter is in a box while the Flamingo filter is inline with my SDR. I have an additional Flamingo filter I use with a different SDR, 9:1 transformer and a bit of wire when I go camping. The smaller size and weight of the Flamingo, price, SMA connectors and performance make it the solution I use. * Please note there is an original Flamingo AM filter, but the one to get is the Flamingo+ V2. Below is a sweep of the version 2 a buyer posted on Amazon.

51RtKVr-FaL.jpg

Below is a sweep posted by PAR for the AM HPF. Pay attention to the skirt (edges) on both of these filters. One may serve you better than the other. Remember, it is not only the attenuation of the AM broadcast band, but whether the edges of a filter will attenuate signals you may want to monitor...or not.
BCSTHPFP.jpg

* * One more thing. You can run two filters inline to really clobber the unwanted AM broadcast. The Flamingo+ AM filter I use at home also has an AM HPF in front of it. That special filter is mainly for my Amateur HF radio as I transmit through it, but when switched to the SDR, it benefits from the additional filtering even if just for RX.
 
Last edited:

mayidunk

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Joined
Jun 10, 2006
Messages
173
Another thing to consider is if you might be getting swamped by any spurs that transmitter may be tossing out. Here's a link to an RF Harmonics calculator. Plug in the frequency of that AM transmitter, and if you see images at any of the harmonic freqs, then no AM blocking filter will help, as you're receiving those spurs at the actual SW freqs being tuned by your SDR.
 
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