[Scan-DC] Signal from 40.75 kHz Navy submarine communications station in PR
Andrew Clegg
andrew_w_clegg at hotmail.com
Wed Apr 14 09:50:51 EDT 2021
Updated signal strength plot after two days of monitoring:
http://www.w4je.com/nauv2.png
[http://www.w4je.com/nauv2.png]
Based on a bit of research on LF/VLF signal characteristics, the curves I'm seeing appear to be the nominal type of signal strength curves received at these low frequencies. The variations are caused by the daily cycle of ionization and recombination of the D, E, and F layers of the ionosphere.
73,
W4JE
________________________________
From: scan-dc-bounces at mailman.qth.net <scan-dc-bounces at mailman.qth.net> on behalf of Andrew Clegg <andrew_w_clegg at hotmail.com>
Sent: Tuesday, April 13, 2021 9:58 AM
To: Scan-DC at mailman.qth.net <scan-dc at mailman.qth.net>
Subject: [Scan-DC] Signal from 40.75 kHz Navy submarine communications station in PR
Not exactly "scanning" per se, but...
I recently ordered an LF Engineering L-400B active antenna for 10 - 500 kHz, and it arrived on Friday so I've had a few days to check it out. I first checked it out in the field, over at Dangerfield Island, which I've found to be a relatively interference-free site for VLF-HF (it's just south of National Airport off the parkway). Then I installed the antenna on the roof of my apartment, expecting to be overwhelmed by hash from all the computers, TVs, etc., in the area. Surprisingly, it is actually reasonably usable. The noise level is manageable, and I do not see any obvious evidence of overload from AM broadcast stations.
It does quite well at pulling out the various VLF (<30 kHz) and LF (30-300 kHz) military communications systems. I'm hearing Navy signals from PR, Washington state, Maine, and Hawaii, as well as some stuff from France. I'm also hearing WWVB on 60 kHz quite clearly. It seems to do about as well here at the apartment as W3HFU's Kiwi SDR using a 500 ft antenna in Westminister MD. However, I'm not able to hear as many aviation and marine beacons in the 200-300 kHz range that I could at Dangerfield, and I actually hear more on my VHF/UHF discone than on the active antenna, but I think I need to play around with various combinations of exact location of the antenna and attenuation settings on my receiver. Converesely, I cannot hear an 18.3 kHz military comms signal from France (HWU) at all on the discone, but I hear it clearly on the L-400B.
Yesterday morning I started automatically logging the signal strength from the Navy's NAU station in PR on 40.75 kHz. The plot of signal strength vs time is here:
https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fw4je.com%2Fnau.png&data=04%7C01%7C%7C5b050c8d47564ccd2d6808d8fe843d66%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637539191201810049%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ikWGJ%2FmR9aQFKo1c0Aay8bxYE%2B9C1SXjqAvGTFLYljU%3D&reserved=0
[https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fw4je.com%2Fnau.png&data=04%7C01%7C%7C5b050c8d47564ccd2d6808d8fe843d66%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637539191201810049%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ikWGJ%2FmR9aQFKo1c0Aay8bxYE%2B9C1SXjqAvGTFLYljU%3D&reserved=0]
I'm using the L-400B with an ICOM receiver connected to HDSDR. After 24 hours, the signal strength curve shows some interesting structure. It goes haywire around sunset and sunrise times. It gradually rises and falls during the day. I haven't experimented enough to know whether some of these effects (or all) could be due to local issues, such as the antenna (which includes the active electronics) heating during the day and cooling at night, but the dramatic signal strength changes right around sunset and sunrise seem real.
Anyway, this is just day four with the new antenna, so I'm looking forward to more experimentation with the exotic VLF/LF bands. I wonder if I can hear any whistlers around 10 kHz.
73,
Andy
W4JE
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