Strange AM BCB Interference

[WA2SQQ]

Within this past 2-3 months I’ve been experiencing a strong signal with distorted audio at 1.900 mHz, and a secondary one at 1.820. They are strongest during daylight hours, typically about S9+20 and S9 respectively. After sundown both signals decrease substantially. I should mention that I live about 2 air miles from WABC (770 khz), a 50KW power house.

When I had my Flex 5000 I used an external filter that attenuated the broadcast band by -60db. With that combination I had no AM BCB interference what so ever. I recently upgraded to the Flex 6500 and found that its receiver was incredibly tight and no longer requires any external filtering. Yesterday I decided to identify this phantom signal at 1.900. It turns out that it’s WBBR @ 1130 khz, another 50KW station located about 7 miles from my location. So how is 1130 making its way to 1.900? 1900-1130(WBBR)=770(WABC) So for this mixing to occur I think there needs to be a third frequency which I suspect is another local station that drops its power at sundown. Here’s where it gets interesting

1. I can hear the 1.900 image on three different receivers and I can see it on an HP8920 spectrum analyzer.
2. On my Flex 6500 switching the external BCB filter in and out makes absolutely no difference. To me, this suggests that what ever is taking place is not occurring in my receiver.
3. I connected a step attentuator in series with the receiver. As the noise floor decreases, so too does the 1.900 signal.
4. Using a loop antenna, I get a sharp null in exactly the same bearing for both 770 and 1900.

I’m thinking this is actually mixing within WABC’s transmitter.  Before I reach out to WABC I’d really appreciate some feedback from some of you who may have some experience with such matters.

[KA2DZT]

The two BC signals may be mixing in or around your QTH.  Look for loose metal fittings, down drain pipes, metal fencing, BX electrical connections, etc.  Your antenna connectors should be checked.  I would look for it with a field strength meter tuned to 1900KC, but you could use a portable radio if you have one.

To answer your question, you don't need a third signal.  770KC + 1130KC = 1900KC

Fred

[Pete, WA2CWA]

I agree with Fred. Several years ago I was plagued with signals of various strengths at various points across the 160 band from a 50KW station out of New Brunswick. I went around and unscrewed every coaxial connector I could find and then screwed them back in. The signals disappeared.  Sometimes dis-similar metals, metal corrosion, maybe even some oxidation on the metals contacting each other, tend to act a diode receivers.

[KA2DZT]

I agree with Fred. Several years ago I was plagued with signals of various strengths at various points across the 160 band from a 50KW station out of New Brunswick. I went around and unscrewed every coaxial connector I could find and then screwed them back in. The signals disappeared.  Sometimes dis-similar metals, metal corrosion, maybe even some oxidation on the metals contacting each other, tend to act a diode receivers.

Exactly, I didn't mention the diode effect which is where the mixing occurs.

Fred

[WA2SQQ]

Time to start hunting - thanks for the suggestions

[DMOD]

I had a similar imaging problem locally a few years ago.

It turned out to be a malfunctioning Ibquity (IBUZ) AM exciter at a local 5kW transmitter.

They have since removed it. Problem gone.

As others have stated, don't discount a loose screw or connection somewhere acting as a diode.

Phil - AC0OB

 

[WA2SQQ]

I'm still leaning towards a problem at the transmitter. I'm, able to hear this from two different locations about 3 miles apart. Going to go out tonight and sweep my local area with a portable receiver I have. Just got the CE's name and e-mail for WABC so I may reach out to them. Former CE was a ham and good friend of mine, so mentioning that might help. There is also the mystery why it greatly diminishes around sundown. If this was a locally generated signal I would think the signal strength would be fairly consistent.

[AB2EZ]

Don't AM stations reduce their power and/or modify their radiation pattern, after sundown, to reduce interference with distant stations using the same frequency?

I.e. their signals propagate further at night.

Stu

[Pete, WA2CWA]

WABC AM Predicted Daytime antenna radiation coverage



WABC AM Predicted Night time antenna radiation coverage




To look at other radio stations, go here: http://radio-locator.com/cgi-bin/page?p=maps

[KA2DZT]

I'm still leaning towards a problem at the transmitter. I'm, able to hear this from two different locations about 3 miles apart. Going to go out tonight and sweep my local area with a portable receiver I have. Just got the CE's name and e-mail for WABC so I may reach out to them. Former CE was a ham and good friend of mine, so mentioning that might help. There is also the mystery why it greatly diminishes around sundown. If this was a locally generated signal I would think the signal strength would be fairly consistent.

The fact it changes at night probably doesn't mean much.  The stations steer their signal in different directions at night and propagation also is different at night.  So the signal strength of one or both is dropping enough to reduce the mixing.

Fred

[WA2SQQ]

Last night I did some measurements. @770 khz they give me -11.7dbm of signal. When I switch in the BCB filter it decrease to -86.7 dbm

Listening at 1900 khz that filter does absolutely nothing, so in my mind that confirms that it's not some IMD that is occurring in my receiver.

The weaker "image" at 1820 was confirmed to be that of WINS @ 1050 khz. Again, 770+1050 = 1820
Rode around for about a 1 mile radius and it is solid throughout.

Yesterday I reached out to WABC's CE and I'm awaiting his response.

[Pete, WA2CWA]

Last night I did some measurements. @770 khz they give me -11.7dbm of signal. When I switch in the BCB filter it decrease to -86.7 dbm

Listening at 1900 khz that filter does absolutely nothing, so in my mind that confirms that it's not some IMD that is occurring in my receiver.

The weaker "image" at 1820 was confirmed to be that of WINS @ 1050 khz. Again, 770+1050 = 1820
Rode around for about a 1 mile radius and it is solid throughout.

Yesterday I reached out to WABC's CE and I'm awaiting his response.

WINS is 1010 KHz

[WA2SQQ]

My error WHN 10150

[Pete, WA2CWA]

My error WHN 10150

Actually WHN doesn't exist anymore according to radio-locator.

WEPN (1050 AM) is a 24-hour Hispanic sports talk formatted radio station in New York City. Its transmitter site is located on the border of Secaucus and North Bergen, New Jersey.

[KD6VXI]

On the  subject of getting everything a hundred percent,  I'm going to assume you meant Syracuse,  Pete?


I on guess in cheek,  of course.

--Shane
KD6VXI

[Pete, WA2CWA]

On the  subject of getting everything a hundred percent,  I'm going to assume you meant Syracuse,  Pete?


I on guess in cheek,  of course.

--Shane
KD6VXI

I get in that mode at times; just finished proof-reading a manual for a well-known amateur manufacturer.

[flintstone mop]

I am not up to date on the latest changes in the AM band.  But WABC was/is a clear channel frequency 50kw non-directional 24/7.

[KD6VXI]

Wow.   Autospell sure did a number to tongue in cheek,  above lol.

I did proofreading work for a training company.   Tedious work.

--Shane
KD6VXI

[flintstone mop]

On the  subject of getting everything a hundred percent,  I'm going to assume you meant Syracuse,  Pete?


I on guess in cheek,  of course.

--Shane
KD6VXI

NOPE it was really Sorry-Excuse


I get in that mode at times; just finished proof-reading a manual for a well-known amateur manufacturer.

[VE3AJM]

As a BC band DX'er, (are there any on this site), the WHN callsign goes back a long way for me. I QSLed them back in the mid 80s, and they were a Country!! music station in NYC believe it or not, until they changed formats and became the original WFAN all sports radio on 1050. WFAN then moved to 660kc, WNBCs old frequency. I could only hear WHN in the clear when the local 50kw station CHUM was down for maintenance on a Sunday over night.

Al VE3AJM

[WA2SQQ]

UPDATE:
VE3AJM : Started DX'ing the AMBCB in the late 1960's - still quite active

Regarding 1050, (what was WHN), they are in Secaucus, NJ. In fact just about every metro NYC AM station is in the marshlands of Secaucus / East Rutherford / Kearny NJ.

Regarding my problem, so I've pretty much concluded that it's something locally that is causing this fierce mixing. If I listen to the signal, in addition to the distortion, I can hear a distinct 60 hz buzz. Yesterday I sat there watching it and all of a sudden it was gone for a second. Kept coming and going with a scratchy sound that sounded like a loose connection. Suppose to rain this evening so it will be interesting to see what happens. Time to get out and start looking.