Sunday, January 18, 2015

Driveby System - 44.485 Mhz

This morning I was hunting around for the source of some power line noise that plagues me while I was still at home (before taking the Driveby System back on the road today).

Above is a video of what I 'finally' found.  (not sure why I didn't really search for this years ago).  Anyway I use HDSDR at home as a "pan adapter" for my large radio which is connected to my 57 foot long 10 element 50 Mhz yagi.  I've been hunting for a way to be certain that the noise I'm hearing *IS* power line noise.  One way I've read about is to analyze the AM audio and look for FFT spikes that are relative to 60hz increments.  So this would mean that you would see (possibly) 60hz, 120hz (definitely), 180hz, 240hz and so on when you analyze the audio from the AM signal.

Well guess what?  I already had been using a tool that could do this "HDSDR".  So with the pan adapter setup I use for my large ham radio the 9 Mhz IF output to a Nooelec "Ham It Up" HF to 125 Mhz up-converter.  Then I configure HDSDR to look at -134 Mhz.  Which puts me zero beat on the frequency in HDSDR that I'm trying to SEE visually.

Anyway...long story short.  I found something very interesting this morning.

Between around 44.235 Mhz and 44.6 Mhz (the best centered freq seems to be 44.485 Mhz) there is an EXTREME signal LOADED with power line BUZZ/HUM.  Looking at the Audio analyzer in HDSDR (lower FFT display on my screen in the video) you can CLEARLY see the 120hz, 180hz, 240hz .... spikes.

Knowing the actual center frequency of the Arcing noise source REALLY helps!  With that information I can program the frequency into and RTL or my Walkie-Talkie like HT (VHF/UHF handheld radio) capable of AM, FM, WFM reception.

I'm planning today to use the 49 Mhz RTL graph and mapping to be re-coded to use 44.485 Mhz.  because of what I've found this morning.  After I've mapped that all out I'll present it here as an update to this blog entry.

This signal is approximately in the 300-335 degree azimuth from my tower.  Here is a map of that area.

Also see a followup remapping post HERE.

(click image to see larger)


After driving around with just my HT radio and a tiny whip antenna I'm pretty sure I've spotted the worst of my noise sources.  It's located just behind a local middle school.  And the source pole was actually within about 6 feet of where I suspected the noise has been coming from.  As noted earlier this morning (see red line above map).

This map shows the location of the pole which you can see via satellite image.

(click image to see larger)



Um 2x WTF !!!  Notice the school, Notice the Fence, Notice this dangling Loose Ground wire is within reach of any stupid Middle-School Child that reaches for it?

Now check this out! Driveby confirms!

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