HFU HF Underground
General Category => Amateur Radio => Topic started by: karlos on February 06, 2026, 0018 UTC
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Hey y'all. I just learned about the 13mhz ISM band the other day and it has my mind running wild, and believe I've got a pretty interesting idea!
I've spent the last few months making a Meshtastic<->JS8Call bridge for remote operation of my amateur station and realized 22m could use elements from both to create something unique. I understand the low power and propagation restrictions, but think a continent wide messaging system could be built on top of it. All for about $100/node.
My idea, a monobander QRP labs QDX with slight modifications to the low pass filter (maybe not even necessary) and omission of the BS170 amplifier stage. This would be right around 5-10mW and could easily be within legal limits for unlicensed operation (We all have family who absolutely will not get their amateur license)
The magic would be running JS8Call on slow mode, with a program hooked into JS8's API that controls a beacon system and messaging system (with ACK). Every node would have a callsign, and a mesh that could store and forward (even over the course of many days) messages reliably. There is endless potential for a flood or intelligent routing system which is automated. Flood in name only, I would anticipate hard coding many minutes/hours delay in each hop of these messages/beacons (in addition to messaging limits).
Been thinking about this for a couple days, and envision 20 word messages hopping 1000+ miles/day if there was a cooperative system in place.
Let me know what y'all think, and if you would be interested in setting up stations to facilitate a network like this. I would be happy to code up most of the logic (I've already done a sizeable portion for another project), and also would love input from other people!
An idea like this is useless without other people and a quasi-permanent infrastructure. Also, this would easily satisfy the beacon enjoyers
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Very interesting idea. I can also see this useful in mountainous terrain vs 900 MHz Meshtastic (line of sight) for more local comms. I'm interested in keeping abreast of your progress and would be happy to beta test when you get to that point.
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Thanks. I checked over on the QRP labs forum and the preliminary word is a 20m QDX would work without modifying the filters for 22m.
I think it has a bunch of potential as a fallback network, and the JS8-Meshtastic bridge I made is a bit of a legal minefield, if I allow non hams to TX on HF. This would be a great solution to that.
I'm going to grab a couple monoband QDXs ($69 with a diy 3d printed case), and will definitely need someone around 500 miles away for testing in, mostly likely a few months. I'm in central Texas btw
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So I just ran a preliminary test on 40m (dipole antenna at 15ft, so NVIS) JS8call using a 4.2W QMX (~37dbm or 36.23dbm). Connected up a 30db attenuator (measured 29.56db at this band) and changed to slow mode. I worked this out to be approximately 4.6 milliwatts
The follow message was delivered successfully "@GROUPNAME MSG 30DB ATTENUATOR, SHOULD BE ABOUT 7MW POWER!! :) TESTING IF MY 22M ISM BAND IDEA IS POSSIBLE " to two stations that could hear me with and without attenuator. That message took 4 minutes to TX and both stations were around 200 miles away.
My SNR Rx'd with attenuator:
Station 1: -19db
Station 2: -20db
My SNR Rx'D without attenuator:
Station 1: +11db
Station 2: -09db (This one took a few minutes after to get again, band changed?)
I think this is a pretty good proof this idea is feasible, especially since 40m band has higher d layer absorption, during the day, than the 22m band