Monday, December 1, 2008

Noise, The Hunt for RFI

I posted earlier that I have decided that I have power line radio frequency interference which is obstructing my amateur radio reception. The task now has turned to isolating the source.

Step 1. Isolate if source is in my house.

I set a battery powered SW radio to AM mode and tuned it to a frequency in the 80m band where the noise was particularly undeniable. Then I went to the breaker panel in the house and turning off the MAIN circuit breaker.

No luck, The noise level at 3630MHz was at Signal Strength 5 with or without power in the house.

Step 2. What Next?

Directional antenna? and What band?

These are not independent. A directional antenna can be used but only on VHF, and VHF also requires the noise source to be close by. For example a 440MHz Beam and a 440MHz hand held AM mode would do the trick. Examples are captured below I will have to decide if I need to go this route.

Cushcraft A4496S 6 Element 440MHz Amateur Radio Antenna

The Cushcraft A449 6S is an effective, economical choice for your 70 cm FM/Packet needs. Great for vertical or horizontal polarization configurations. Mast shown is not included.

  • * 3dB Beamwidth, Degrees E-Plane 60
  • * Boom Lenght ft.(m) 2.9(0.89)
  • * Forward Gain, dBi 10.5
  • * Frequency, MHz 440-450
  • * Front to Back Ratio, dB 18
Yaesu VX-7R Tri Band Handheld Amateur Radio Transceiver

Yaesu VX-7R Tri Band Handheld Amateur Radio Transceiver is a triple band (6M, 2M & 440 MHz) HT with extensive receive coverage, and leading-edge features. Power output on 6 meters, 2 meters and 440 MHz is 5/2.5/1/0.5 Watts. It receives the AM and FM broadcast bands, shortwave (AM), VHF and UHF TV audio, VHF Air and public service frequencies.

  • * Receiver coverage 500 KHz to 999 MHz (Cell Blocked)
Step 3. AM Radio from the Truck.

I decided to give the radio in the truck a try. I tuned the AM radio to 1700kHz, the very top of the AM broadcast band. Then proceeded to take a drive around the neighborhood.

My drive route took me past several locations where I thought I may find my noise source; street light standards, the well lighted neighborhood grocery parking lot, several hydro electricity transformers, (the neighborhood has under ground electrical distribution).

What I found was very odd.

There were a few highly localized hot spots quite far from my house.

One was on a housed street about 500m from home, the noise source had the typical 120Hz sounding signature but the source was very localized, as it only presented it self over a <20m class="blsp-spelling-corrected" id="SPELLING_ERROR_11">noise was remarkable strong was; (in descending order)
  • In my next door neighbor's driveway
  • In my own garage
  • In my other next door neighbor's driveway
more to come...

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