STRONG broadcast interference 3870 khz

edited April 2019 in Signals Received
There is consistent, but varying strength broadcast intermod/harmonics rendering the Weiser SDR pretty much useless for AM or other modes monitoring - plus, at the same time, another seemingly related image out plus and minus 10khz of the 3870 kjz primary. This interference is also noted by me and other SDR users in direct reception here in the John Day area, and is visible on the North Utah and Half Moon Bay California SDR's, which would seem to eliminate faulty local radio installation as the cause. At times, this interference is extremely strong, other times less strong, but still annoying to the point of making the Weiser SDR essentially worthless for the dozen or more of us attempting to use it regularly on 3870 khz. Is there any hope in sight for resolution of this problem - or at least an explanation for it?


  • jksjks
    edited April 2019
    I'm sure Ron will have an explanation/opinion on this. When I looked just now I observed that KWEI-1260 is present in all those harmonics/IMD-products up and down 80 meters (I waited for some particularly egregious music from KWEI to come on so I could pick it out amongst the mixing). Ron even has a label marking the KWEI 3rd harmonic at 3780. Look at the images below. The 1260 fundamental is about S9+25 and other AM BCB signals are in this range. Not too terrible. Now look at the 3rd harmonic. S9! Seems very unlikely this is what's actually being transmitted.

    So my guess (purely a guess) is that this is local, non-linear rectification someplace causing all these mixing products that are then being re-radiated (the classic "rusty gutter forming a diode" analogy). But I am no expert at any of this. [Later: this guess is WRONG given the observations of others. It has to be a fault with the transmitter!]
  • Does Ron have band reject filter for MW BC?
  • edited April 2019
    Well, thing is, there are *2* copyable audio signals that can be detected on the 3870 signal here at my QTH, one is usually music, the other, superimposed simultaneously, is normally just voice, like a radio talk show. The 3870 interference IS copyable over a pretty wide radius from the general Weiser SDR location, so at least SEEMS to be a real, strongly radiated 3870 harmonic/spurious mixing, likely from 2 strong stations physically located close to each other (and Weiser?) - perhaps close enough that one or both THEMSELVES are actually re-radiating the HF spurs.

    NEXT, from here at MY QTH in the john Day area, we can't even HEAR the 1260 broadcast band signal, but DO hear the 3870 spurious quite plainly. If that's the case, not much the the Weiser SDR can do to eliminate what's actually there on 3870 khz legitimately, from what's also there spuriously.

    Strange thing is, like right now and since I started this thread a few hours ago, occasionally the spurs go away as though a switch (perhaps a wave trap?) is engaged that shuts down the radiated spurs. Sure would be nice to see it go away permanently - and I can't help but think that if it IS a mistuning at one or more broadcast transmitters, the FCC and the stations involved would be highly motivated to correct the condition!

    OH, and by the way the Weiser broadcast station KWEI is no longer in existence - the currently licensed Weiser Broadcast station is listed as KBXN 1260 AM...
  • jksjks
    edited April 2019
    Okay, I didn't quite understand that.

    Find an email address for the station, or media company that owns it, and send one to the attention of the "engineer in charge". Include the waterfall plots, maybe only on a followup email if you get a reply. I've done that here a few times when a group of AM stations (same tower) suddenly dropped 40 dB and the problem wasn't fixed within 24 hours (i.e. no one noticed). They told me it was a broken connection to the radial system, lol.
  • edited April 2019
    Just an added shot - I'm a licensed, extra class amateur radio operator, K7GLD - good on, and been licensed since 1959 - currently using a pair of Icom 7300 SDR transceivers, and a bunch of fairly modern Icom and Kenwood HF-VHF rigs - just a FWIW... :)
  • edited April 2019
    @Gary ,
    I placed a MW filter inline and it dropped 1260kHz from -28dBm to a -56dBm but the signal at 3780kHz remained at a -90dBm with and without the filter. So it is apparently a legitimate 3rd harmonic. I do have a notch filter constantly inline on 1260 and 1380, although 1380kHz is now off the air, so I should take that one out of line. As I have been typing the signal at 3780kHz has disappeared! You must have called and complained. :) So I have taken the MW filter out of the line, as I don't believe it is needed.

    As the days get longer the MW broadcasters have longer at full power. They cut way back at sunset. I do have a dual active loop that is more or less omni-directional at and another single loop usually oriented NW/SE at . These antennas don't have the gain, but they do lose some of the interference, of which there has been a lot lately. Electrical storms, grainery elevator motors, shop welders, etc. located about 1 mile away in Weiser. Most of this noise goes away after dark, except for the electrical storms of course.

    Other alternatives to my KiwiSDR's include W0AY @ , and a WebSDR belonging to KA7OEI.

    I'll do what I can, but some of this is just the way it is here. And my goodness the 3780kHz harmonic is back... -90dBm and after I went out and checked connections to the SGC SG-230 and retightened them, I now have an outstanding signal on 3780kHz of -62dBm. I don't have it on the other antennas. You can see I have the MW band attenuated into the dirt and this 3rd harmonic is all over the 75 meter phone band. I'll work on it.

  • Ron, I'm sure it is NOT a problem on your installation, I can hear various levels of it on several other west coast SDR's - but for sure, there's some broadcast station within your general area that apparently has some sort of intermittent issue - thanks for your attention, 73.
  • @Gary ,
    I think you are right. This morning there is no interference on 3780kHz or elsewhere on the 75/80 meter phone bands. I wonder if it will come back.

  • I asked the question.
  • Listening on 3870 again this afternoon, 4/28 - VERY obvious that someone, somewhere, is tuning something related to the broadcast interference. It was switching in and out over several minutes in time, and slowly changing in intensity as though a filter of some sort was being tuned - at one point, it was completely gone, only to return and gradually increase to an obnoxious level once more. Someone out there is aware they have a problem, but apparently unable so far to make a permanent fix. As I write this, and monitoring the 3780 interference, it is obviously being switched in and out and adjustments being made - hope they get it fixed permanently...
  • Please toss me a schematic for a single frequency notch at 1070 Khz --
    Many thanks!
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