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Author Topic: Your best clear spots in the 22 m ISM Band?  (Read 1239 times)

Offline MojaveBeaconeer

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Re: Your best clear spots in the 22 m ISM Band?
« Reply #15 on: October 31, 2018, 1620 UTC »
ops correction: 13560, 13562 kHz rather than incorrect 13360/13362 (sri!) MB

Offline Ed H

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Re: Your best clear spots in the 22 m ISM Band?
« Reply #16 on: November 06, 2018, 2120 UTC »
That noise region certainly checks out here in Northern Calilfornia. I should bring a receiver to work - we have lots of tools with RF generators, I'll bet the ISM is a riot here in San Jose!

Offline Exo

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Re: Your best clear spots in the 22 m ISM Band?
« Reply #17 on: November 12, 2018, 0616 UTC »
If you examine the way-cool waterfall SDR screen-grabs Exo made above of the 22m ISM band, there seems to be at least two broad (hash/hiss) bands between 13560 and 13562 kHz, this is heard globally and is almost "always there" when there is even some prop. on 22m, even if it just riding the MUF. 

Does anyone know what creates this global hash/hiss band(s)?  It seems to be a complex "mash" of discrete A0 carriers all co-mingling.

Just guessing, these 1-to-3 kHz wide noise "hiss" signals seen around 13.56 MHz ISM are possibly due to the use of "Low EMI SSC" techniques in some of the ISM generator transmitter designs.

SSC is so-called Spread Spectrum Clock oscillators, which have an intentionally frequency-dithered output.
(Not really spread spectrum as in SS communications)

In other words, the SSC is a clock oscillator that is frequency modulated with either a triangle wave or low pass filtered pseudo white noise.

This provides the same working power output for the generator, but legally fools the EMI testing standards into measuring an apparently lower signal strength level.
The EMI testing uses audio bandwidth time-weighted level measurements.

It also gives the ISM signal the appearance and sound of noise hiss on communication receivers.

   
« Last Edit: November 12, 2018, 0620 UTC by Exo »
Exo
HF aficionado. On the coast of northern California.
Various receivers, transceivers, and broadband antennas.
kiwiSDR receiver on private LAN for multi-freq HF monitoring.

Offline Ed H

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Re: Your best clear spots in the 22 m ISM Band?
« Reply #18 on: November 12, 2018, 2154 UTC »
That is an interesting supposition Exo.

Since I work at a manufacturing facility that uses RF generators, I could ask. It is also a perfect excuse to bring the portable listening setup to work :)

Offline Ed H

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Re: Your best clear spots in the 22 m ISM Band?
« Reply #19 on: November 19, 2018, 1730 UTC »
Last week I brought the Lowe HF150 in to the office. It has a sensitive Hi Z active antenna input. Alongside a few carriers within ISM limits, was a massive broad-band hash from all the other equipment and lighting circuits. In fact this was plenty audible with the whip antenna switched to the straight 50 ohm input. I didn't get chance to monitor from outside the building.

One last thing - There was a nice clear dasher signal.. traced to the NFC/RFID transponder of my smart-phone!