RF Wastelands

[Alfredo_T]

Although I am not on board with the 45-50 MHz re-purposing proposal linked in the thread The Future (or lack there of) for AM Radio, I did notice an observation in that proposal that in New York City, a scanner can go for several days before detecting a carrier. That makes me wonder, what are some little-used segments of the radio spectrum, which could be monitored for days or longer before any signals were detected?

So far, the ones that come to my mind are:

• 90 – 110 kHz — formerly LORAN C
• 1710 – 1800 kHz — formerly radionavigation
• 42 – 50 MHz — formerly public service and unlicensed consumer products
• 54 – 72 MHz — Formerly television channels 2-4

[Andy Brown]

54 – 72 MHz:

http://bit.ly/2LqucVU

1.71 – 1.8 MHz:

Cochrane Technologies Broussard LA

WNZG604 1.71084000 MHz. Active Exp. 2022
WNZG605 1.71084000 MHz. Active Exp. 2022
WPHW222 1.71584000 MHz. Active Exp. 2025

County Of Hudson Jersey City, NJ

WQFG689 1.71000000 MHz. Active Exp. 2026

90 – 110 kHz:

Boeing & Lockheed Martin still using 100 kHz

http://www.mediaeng.com/specialprojects/90-110kHzp1.png
http://www.mediaeng.com/specialprojects/90-110kHzp2.png

42 – 50 MHz:

10 pages of results with many still active

http://www.mediaeng.com/specialprojects/42-50MHz.png

Search results are not linkable in ULS like they are in the AM/FM/TV Query but you can rerun the searches by going to
https://wireless2.fcc.gov/UlsApp/UlsSearch/searchAdvanced.jsp

[SCOTUS9]

The Gray Spaces. 54 – 88 and 174 – 216 mHz.
DoD uses them.
NTIA wants them to extend rural wireless services.
Some broadcasting companies want them back.

[nosignalallnoise]

42-50 MHz is still used for unlicenced consumer products but they’re not as widespread these days as they were 15-20 years ago. Still you can program the following frequencies into any scanner and drive around any good-sized city, especially around complexes and tenement blocks, and you’re liable to hear at least a couple voluntary domestic surveillance transmitters baby monitors (ahem ahem), usually barfing out dumbass amounts of RF. Some are way, way overpowered for what they are.

49.300
49.830
49.845
49.860
49.875
49.890
49.895
49.970

You may need to deviate a few kHz from these frequencies to get a clear signal, depending how out of spec the transmitter you come across was when it left China. Scan around 45-46 and 49 and you might even hear some old grandmum who just won’t give up her 35-year old cordless phone for one of those fershluggin’ digital things all the young whippershnappers have.

[Alfredo_T]

I have a Zenith 7H820, which is a late 1940s vintage table radio that can receive both the original 42-50 MHz and 88-108 MHz FM bands. Years ago, I could occasionally hear a neighbor’s cordless phone, as well as some public service communications (possibly the Forestry Service). That radio needs to have capacitors replaced, as well as some other work, so I haven’t turned it on in a long time.

I also have some 49.860 MHz crystals that were salvaged from toy walkie-talkies that would be fun to re-purpose. I just haven’t figured out what to do with them. There is a 49 MHz experimenters’ group online, but I do not think that they are very active.

[Alfredo_T]

According to the ARRL, 50.40 MHz is the AM voice frequency on 6 meters. If were to build a converter using one of those walkie-talkie crystals and a NE602, I could hear 6 meter AM traffic using an AM radio tuned to 540 kHz.

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