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STRONG broadcast interference 3870 khz
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?
Comments
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!]
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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...
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.
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.
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 http://ka7u.no-ip.org:8075 and another single loop usually oriented NW/SE at http://ka7u.no-ip.org:8074 . 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 @ http://foxgulch.net:8073/ , and http://utahsdr.org/ 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.
73,
Ron
KA7U
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.
Ron
KA7U
Many thanks!