NOTE: Text in italics is contributed by the analyst (Pine); regular font is contributed by the observer (Bennett).
Due to family illness, I was not able to journey to my favorite quiet natural radio monitoring site. I had to stay close to home and be ready to return on short notice.
I spent a day searching maps and using MAPQUEST® to locate potential electrically quiet areas within about a 30 minute drive of my home. I found only two possibilities.
Site One is at the center of a large expanse of undeveloped desert within the city limits of Las Cruces. The area is roughly rectangular, about 3-miles in the East-West direction and about 5-miles in the North-South direction. There are no buildings in the area. Unfortunately I did not realize until too late that several power lines cross the area, including a 375KV and two 200KV transmission lines.
Site Two is north of my home in at a remote desert location along the historic trail “El Camino Real de Tierra Adentro” (royal road of the interior). This site is about 5-miles away from the nearest power line along a seldom-used dirt road.
5 October Monitoring
As it had been over a year since I last monitored natural radio signals and used my monitoring equipment, I decided it would be wise to conduct a “dry run” monitoring session. So on Thursday evening, 4 Oct 2007, I loaded all my equipment in the truck and traveled to a location near the center of Site One. Just about everything that could go wrong did! The following are some of the highlights.
a. While setting up my equipment, I realized that I did not bring an adapter needed to connect the WWV receiver to the antenna. I tried to improvise an antenna and feed line from insulated wire but never got it to work. The end result was that I could not insert timing markers into the recording.
b. When I started to record, I discovered that I left my box of blank cassette tapes at home. I had to recycle a used tape. I finally started recording at 2040 local ( MDT ) time (0240Z 5 October 2007).
c. The worst problem was the extremely high levels of power line hum. The 60 Hz interference was so bad that it seemed to overload the VLF-3 receiver. I quickly concluded that Site One was not suitable for natural radio monitoring. Next morning I drove around the selected area and discovered the transmission lines.
I recorded for about 30-minutes then tore down my monitoring post and returned home. I reviewed the recording and confirmed that there was nothing on the tape of interest.
6 October Monitoring
I decided to try monitoring from Site One again. I hoped that the power grid noise levels would be less in the early morning hours as we had a brief rainstorm earlier in the evening. I have actually observed this effect in the past. I arrived at my selected site at 0400 local time and setup my equipment. I monitored at 0500, 0600, and 0700 MDT . During all three sessions, I observed very strong 60 cycle related interference, strong LORAN interference, intense and frequent tweeks and sferics. I switched the VLF-3 LORAN filter on and this eliminated the interference from LORAN. The only interesting signal I detected was a single weak Whistler that occurred at 06:01:47 MDT (12:01:47 UTC)
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10/06/2007 0500 MDT 1100 UT (2 minutes)
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| Dense sferics and tweeks appear as closely spaced vertical lines and sound like crackling and short ringing noises. Power line 60 Hz interference appears as dark horizontal bars near the bottom of the spectrogram and sounds like a steady low humming tone. LORAN shows up as horizontal bars, evenly spaced to the top of the spectrogram and sound like a steady clicking noise. The short tones (circled dashes) are the WWV tones at 1100 UT and 1102 UT. |
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The first 30 seconds of the above session. |
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The first 10 seconds of the session. The WWV tone is circled. In the box is the voiceprint of the WWV announcer. The red box encloses the LORAN bands. |
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| 10/06/2007 0516 MDT 1116 UT (1 minute) |
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This was a test of the L600S B-field receiver. The file starts with WWV tone and voiceprint followed by a brief gap while the receiver was being connected. The signal shows the strong 60 Hz signal at the bottom. Notice the complete absence of LORAN signals. |
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| 10/06/2007 0526 MDT 1126 UT (1 minute) |
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The next test of the L600S receiver was with the high pass switch on. Note the complete lack of 60 Hz signal. Comparing this file with the VLF-3 performance shows that the filter brings with it a drop in sensitivity. The strongest sferics and tweeks are audible, but the density is way down. |
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| 10/06/2007 0600 MDT 1200 UT (2 minutes) |
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This file was created with the INSPIRE VLF-3 receiver with the LORAN filter in. |
Field notes: General Observations:
1. Temp at 0615 has dropped to 60 o F.
2. 60 Hz interference seems stronger than at 0500.
3. Sferic/tweek seem less frequent and weaker than at 0500.
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| 10/06/2007 0700 MDT 1300 UT (2 minutes) |
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When I returned home, I reviewed the tapes and analyzed a short segment with an FFT program. I noticed that the Russian Alpha navigation signals were much stronger that I normally observe. I was surprised to note the absence of the communication signals that I normally detect between 10 and 20 KHZ.
The recording is a good example of what happens when one tries to monitor too close to power lines!
7 October Monitoring
For this monitoring session, I used Site Two. I arrived at the site a little late, at about 0445 MDT and had to rush to set up the monitoring equipment. I was able to monitor at 0500, 0600 and 0700 MDT . I observed 60 HZ related interference but it was much weaker than at SiteOne. LORAN was present and I had to monitor with the LORAN filter turned on. I detected three whistlers:
a. Pair of weak whistlers at 05:01:56 MDT (11:01:56 UTC)
b. Pair of weak diffuse whistlers at 06:00:57 MDT (12:00:57 UTC)
c. Strong whistler at 06:11:16 MDT (12:11:16 MDT ).
043006 1100UT 5 AM MST
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| 10/07/2007 0500 MDT 1100 UT (2 minutes) |
Sound file not available |
Again, on Sunday, dense sferics and tweeks predominate. In this file, the LORAN filter was switched off for a short time near the beginning and then switched on (box). The dense tweeks show up on the spectrogram as a dark region near the tweek “hooks” location at around 2 kHz (in red box). The blue box contains the first harmonic of the hooks, indicating that the tweeks are strong. |
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| 10/07/2007 0600 MDT 1200 UT (2 minutes) |
Sound file not available |
In the middle of this session (06:00:57 MDT (12:00:57 UTC) a whistler is logged. |
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| 10/07/2007 0601 MDT 1201 UT (10 seconds)
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Sound file not available |
The whistler logged above is difficult to find in the dense sferics, but it is plainly audible in the sound file. |
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| 10/07/2007 0700 MDT 1300 UT (2 minutes) |
Sound file not available |
Strong dense sferics, no tweeks. |
The monitoring session on 7 Oct was more successful than the previous ones. |