Interesting stuff.
Here's a story. Back in the mid 70's I was an engineer for the FAA up in
the New England Region. At the time we were working on improving ground
systems on our radars. I was with a team doing ground measurements at the
Winthrop, MA long range radar site. It involved setting out ground probes
and measuring the ground resistance from the station ground to those points
with a megger. We were getting strange results. We put a scope in place of
the megger - and observed 3/4 volt modulated signal. After a bit of
investigating it turned out to be WBZ - local radio station with
transmitting antenna a couple miles away!
Needless to say we put some effort into improving that ground system.
73 and Happy holidays to all, Wayne N1WR
--------------------------------------------------
From: "Joe Giacobello, K2XX" <k2xx@swva.net>
Sent: Sunday, December 25, 2011 12:00 PM
To: <k3lr@k3lr.com>
Cc: <topband@contesting.com>; <richard@karlquist.com>; <lrpmbt@comcast.net>
Subject: Re: Topband: 1820 BCB + My Problem Partially Solved
> You said it, Tim! I started tuning around the AM band on Thursday and
> noticed that in addition to the spurious AM stations on 1840, there were
> several BC AM signals above 1610 KHz. They shouldn't be there. Then I
> noticed that my 4-square RX array had lost directionality. I use
> diversity reception on 160 and 80M with the array connected to my SDR-IQ
> and main RX and a vertical on the sub RX. Obviously, the SDR's output
> is what's shown in the spectrum display and what my observations of the
> 1840 AM signal and the signals on 1810 KHz, etc. were based on.
>
> I switched things around so the vertical was connected to the SDR. The
> 1840 AM signal and the 1810 and related signals disappeared. I went out
> and physically checked the array and found that one of the elements had
> shimmied down its mount so that its bottom was in contact with the
> ground. After making repairs, things returned to normal: directionality
> returned to the array, the 1840 AM signal was gone and the 1810, etc.
> signals were minor blips. It appears that the element's contact with
> the ground was acting like a detector and the resultant signal was mixed
> and amplified by the element's local amplifier. (I probably should
> install a BC trap to get rid of those blips.) I've contacted both AM
> stations and told them that the problem originated here.
>
> The original problem with the strong wobbly signal on 1836 with smaller
> peaks on 1808.5 and 1847 still persists. But since I have been
> exploring the AM bands in AM mode with 9 KHz selectivity, I've gotten
> some clues to its origin. It may be some kind of motor control or
> related. I have eliminated my own house as the source. The nearest
> houses are at least a half mile away. The hunt goes on.
>
> Thanks to all who offered suggestions. Happy Holidays to all.
>
> 73, Joe
> K2XX
> On 12/22/2011 11:53 AM, Tim Duffy K3LR wrote:
>> That is a VERY important point Joe.
>>
>> "getting mixed somehow"- often occurs without fault from either of the
>> two
>> mixed stations - but as a result of a nearby rectification area (the
>> right
>> metal hardware (rectifiers) coupled to a antenna of some sort with good
>> primary RF energy from the stations) - that maybe located many miles from
>> both stations - but "breeds" the mix. And that is what you hear on 160
>> and
>> 80.
> [snip]
>> 73,
>> Tim K3LR
>>
>>
>> Subject: Re: Topband: 1820 BCB
>>
>>
>> At this point, I'm convinced that the source of the problem
>> is the 24 hour station and that the WPIN and WGFC signals are getting
>> mixed somehow to produce the AM signal on 1840.
>>
>> 73, Joe
>> K2XX
>>
>> I started to search in earnest for the source of the noise.
>> Typically, I only tune 160M between 1815 and 1840 and use that range
>> on my SDR-IQ panadapter.
>> Today, I opened up the range and immediately saw an AM signal on
>> 1840. I was able to make out the audio and identified two local AM
>> stations: WGFC (1030 KHz) and WPIN (810 Khz). The first is a low
>> power Mom and Pop station about eight miles away and the second is a
>> Blue Grass and Gospel station about 15 miles away. Both are daytime
>> stations and QRT at around 5 PM at this time of year.
>>
>> I contacted both stations and both were extremely agreeable and
>> helpful. It turned out that the engineer at WPIN was a very
>> knowledgeable ham who also worked 160M. He was able to control the
>> 810 TX remotely, and while we were on the phone together, he turned it
>> off. The AM signal on 1840 disappeared, but there was still a strong,
>> narrow carrier. The carrier was also visible and equally strong on
>> 1830, 1820, etc.
>>
>> After installing an RX 4-square last year, I had observed very low
>> level signals every 10 Khz on 160M, but they were so weak that I
>> ignored them. However, this season they were somewhat stronger and
>> today, as the night progressed, they became extremely strong,
>> comparable to W1AW's S9 signal at this QTH. Because the signals
>> tonight were as strong as I'd ever heard them, I could detect some
>> audio, but it was unintelligible. I also observed that the broad
>> signal around 1836 was as strong as I'd ever seen it, and there was a
>> similar, though weaker, signal centered around 1808.5 that I'd never
>> seen before.
>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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