Having bad AM broadcast interfernce

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nsixvl
Posts: 8
Joined: Wed Jul 12, 2017 8:17 pm

Having bad AM broadcast interfernce

Postby nsixvl » Fri Jul 14, 2017 3:38 pm

While trying to sort out my port A issue (see my other post), I discovered I'm really receiving on port A after all. I did manage to hear WWV on 10 MHz on port A, which is loud and clear on port B. I was able to hear the callsign of the offending station. It's KFI AM 640 kHz in LA. No surprise, as it's about 3 miles away at 50 kW. And I've noticed the interference on port B on some frequencies. The MW/FM NOTCH button does nothing.

So I need a BCI filter solution ASAP. Most of the filters I've found online are designed from transceiver use, with a power rating. A receive only solution would be just fine.

de Steve N6VL
Last edited by nsixvl on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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g1hbe
Posts: 206
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Having bad AM broadcast interfernce

Postby g1hbe » Fri Jul 14, 2017 5:46 pm

Hi Steve.
Just a silly question, you are selecting port B are you? Sorry, I had to ask. Onto the MW/FM filters - On ports A & B the MW/FM notches work very well, but the lower frequency limit of the MW notch is 680 KHz so maybe it's not so effective at 640. The MW/FM notch does not work on the Hi-z port.
There are several HPF units available which suppress everything below 1700 KHz. I'm sure an enquiry over on the Facebook Group will get you sorted.

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Andy

dlritter
Posts: 27
Joined: Fri Dec 04, 2015 7:12 pm

Re: Having bad AM broadcast interfernce

Postby dlritter » Fri Jul 14, 2017 5:51 pm

RTL-SDR.com, RTL-SDR Blog Broadcast AM High Pass Filter and this can't hurt RTL-SDR Blog Broadcast FM Band-Stop Filter
both are $14.95 on Amazon.

73 Dave n6dl

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nsixvl
Posts: 8
Joined: Wed Jul 12, 2017 8:17 pm

Re: Having bad AM broadcast interfernce

Postby nsixvl » Fri Jul 14, 2017 5:56 pm

g1hbe wrote:Hi Steve.
Just a silly question, you are selecting port B are you? Sorry, I had to ask.

Yes I am selecting either port A or B when switching the coax between the ports. It's the first thing tech support asked me.

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nsixvl
Posts: 8
Joined: Wed Jul 12, 2017 8:17 pm

Re: Having bad AM broadcast interfernce

Postby nsixvl » Fri Jul 14, 2017 6:12 pm

dlritter wrote:RTL-SDR.com, RTL-SDR Blog Broadcast AM High Pass Filter and this can't hurt RTL-SDR Blog Broadcast FM Band-Stop Filter
both are $14.95 on Amazon.

73 Dave n6dl


I might just get one for the price. The only issue is that I'd like to listen to 160 meters as well. The filter cut off is 2.6 MHz.

And we almost have the same callsign!

N6DL de N6VL

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F1BJB
Posts: 103
Joined: Wed Jul 15, 2015 4:24 pm
Location: Beauvais France

Re: Having bad AM broadcast interfernce

Postby F1BJB » Sun Jul 16, 2017 9:08 am

HI
In case of local interference by a single transmitter a sharp notch filter tuned on the frequency
is the best solution.
It can be left permanently and it helps receiving stations very close to the strong one

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nsixvl
Posts: 8
Joined: Wed Jul 12, 2017 8:17 pm

Re: Having bad AM broadcast interfernce

Postby nsixvl » Mon Jul 24, 2017 4:05 am

I just received the RTL-SDR Blog Broadcast AM High Pass Filter and it absolutely works! Now Port A receives like Port B.

Yesterday I took the RSP2 back to HRO with my notebook and could find NO difference between Port A and B using their vertical antenna. Yet when returning home, Port A was unusable. KFI AM on 640 kHz is about 3 miles north of me, while HRO is about 6 miles east. And I figure HRO is about 7 miles from KFI. I'm surprised I'm so much more affected by KFI. But now the mystery is solved.

I agree with F1BJB that I need some sort of notch filter, one that notches out 640 kHz only. I thought of the 1/4 wave stub trick. But at 640 kHz the length would be prohibitive. I've read where shunting a series or parallel resonant LC network will work. But I'd need a old AM broadcast receiver variable cap, which is long obsolete.

Does anyone know of a cheap and easy way to notch out only one offending frequency?

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g1hbe
Posts: 206
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Having bad AM broadcast interfernce

Postby g1hbe » Mon Jul 24, 2017 7:58 am

As you've discovered, a coaxial stub would be the length of your street! The alternatives are either a parallel tuned circuit in series with the antenna feed or a series tuned circuit across the feed. Either way you will need an inductor and a variable capacitor. The values will be roughly in the region of 120uH and 500pf.
Note that the depth and width of the notch can be varied by altering the relative values of the L & C.

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Andy

dlritter
Posts: 27
Joined: Fri Dec 04, 2015 7:12 pm

Re: Having bad AM broadcast interfernce

Postby dlritter » Mon Jul 24, 2017 7:36 pm

the stub would only be 80850 mm or 265 ft or so.. according to: http://www.changpuak.ch/electronics/Coa ... gner.php...
it could be RG174..
:D

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