20m spurs and directional antenna request

[David Hunt]

I am working on setting up an automated band scanner that creates a new web page each day for the 80m, 40m, and 20m bands. A small snippet from the band scanner of a 3 hour period in the 20m band is shown below. In the process of getting this working, I have been identifying some interesting noise sources. Most noise sources have some kind of pattern to them, or I can see them ‘turn-on’ or ‘warm-up’ during some parts of the day. Those patterns have been really useful in finding the noise source.

I have one noise source that is outside the house, and it has me stumped. It is has some unusual properties. It is always on, has an extremely stable frequency, and is part of a string of 6 harmonic images in the 20m band separated by about 61.050 KHz. Although they look like simple spurs at a distance, zooming in shows that each image is actually made up of several spurs with some kind of digital content.

The band scanner is running 3 RTL-SDR dongles, each paired with a SpyVerter. I also included images from an RSPduo running on SDRuno. All 4 SDR’s are connected to the same Comet CHA-250B vertical antenna.

First, I’m curious to know whether anyone else can see these spurs, or if someone has an idea of what they might be from.

Second, I am wondering if anyone has suggestions for building a (hopefully small) receive-only directional antenna for the 20m band that I can use to find out where it is coming from. I have done some googling on the subject, and just about everything I find is a combination Tx/Rx antenna, and big. I realize that is an option. I was just curious if anyone had some smaller ideas. I don’t think the antenna needs to be very efficient. I can throw up any piece of random wire 2-3 ft. long and hear it on a PL-880. What I think I need is just about any antenna with a good null.

Thanks,

Dave (AC1GN)

[caption id="attachment_71891" align="alignnone" width="270"] 20m band scanner[/caption]

[caption id="attachment_71892" align="alignnone" width="300"] 20m band SDRuno with marked spurs[/caption]

[caption id="attachment_71893" align="alignnone" width="300"] digital content of a single spur in the 20m band[/caption]

[Bill Barber]

Take a look at 6860 to 6910 KHz also. There has been a huge unidentified signal there the last several nights. It gets stronger later. Not there during daytime or early evening.

73,
Bill, NE1B

Attachments:

You must be logged in to view attached files.

[Author]

Posts