Original article - Revisiting RadioMirror
The nice mention of Revisiting RadioMirror by KE9V spurred this update. I'd been gathering notes since the Revisiting RadioMirror waiting for a good excuse for an update. Thanks Jeff!
The Use Case for RadioMirror
One of the Seven Habits of Highly Effective People that has become ingrained in my thought experiments such as this is Begin With The End In Mind. How do you want the idea you're trying to present to turn out in the end? Thus, with any new system, It's totally appropriate to ask "What problem does RadioMirror attempt to solve? What itch does RadioMirror scratch?" These are my answers.
- In my area, one of the primary Amateur Radio websites (no, I won't name it) that should be a primary reference for Amateur Radio activity in my area is horribly out of date. Websites for "amateur" organizations (those that don't have skilled / paid / motivated staff to maintain them) just... drift out of date, and out of relevance. Such sites are worse than useless - they detract from what they intend to help because the information they provide is inaccurate. Putting up one's own site is possible, but that's also not easy to maintain (and secure).
- The great hope of Automatic Packet Reporting System (APRS) was that it can (theoretically) be a universal guide to resources in an area. But that depends on resources to be constantly advertised via APRS. My (admittedly limited) experience is that APRS never quite lived up to this potential. But, maybe it could with the addition of RadioMirror being advertised. Imagine a RadioMirror Server advertised on APRS - "Tune 224.76 every evening from 12:00 - 3:00 for N8GNJ RadioMirror Update".
- We're Amateur Radio Operators - shouldn't we figure out a way to use Amateur Radio for distributing information?
- Disasters do happen, including widespread disasters can take down communications infrastructure. Despite my pessimism about the relevance of traditional Amateur Radio emergency communications, I think there can be a role for Amateur Radio to solve unique problems.
- A meeting I attended recently discussed two things that were conceptually inter-related. One emergency communications group is planning to update their master list of communications facilities - repeaters, simplex frequencies, net schedules, DMR talk groups, etc. A later discussion was "what to do about the group's communications van"? How often does the information in a comm van get updated? Wouldn't it be useful if a communications van had a RadioMirror receiver, constantly receiving updates, and if the comm van has to be activated in a hurry, wouldn't it useful that all the necessary information onboard was updated the previous evening?
- Ditto personal Go Kits. How many times have you grabbed the Go Kit, transported it, set it up to use it, and discovered that the last time you updated the info in the computer was way too long ago, impacting your ability to communicate? Add a RadioMirror receiver to the Go Kit and power just that unit while the Go Kit is in standby.
- RadioMirror allows each Amateur Radio Operator to contribute information into the community, to the limits of their ability and willingness to aggregate and present data.
- RadioMirror would be a great way to improve the utilization of our Amateur Radio bands, and especially make voice repeaters relevant again. Individuals (see line above) who don't have stations that can be heard simplex can use repeaters to make their information more widespread.
- There's ample room for innovation. One of my personal experiments with RadioMirror will be to experiment with transmitting simple HTML files so that the information I want to transmit will be easily accessible.
RadioMirror's Time Has Come?
As I discussed in my first article about RadioMirror, I think it's a concept whose time has come. In 2021, we have all the elements necessary to implement RadioMirror:
- Ample available channel time on our bands above 50 MHz, including unused time on repeaters.
- Inexpensive computers that we can dedicate to the task (Raspberry Pi). I'll discuss why dedicated computers are important for RadioMirror to work.
- Inexpensive "all band" receivers such as the well-designed, but inexpensive ($27!) RTL2832U software defined receiver. With such a receiver we can use any band above 50 MHz, including our underutilized 222-225 MHz, 420-430 MHz, and 430-440 MHz bands for RadioMirror.
- We have powerful software for both packet radio and the receive function. In particular, we have the Dire Wolf packet radio engine and it has three primary capabilities right now that lends itself to RadioMirror:
- 4800 bps speed (which reportedly works well even with radios that don't have "flat audio" input / output such as the FT-2980R mentioned below.
- Keep It Simple Stupid (KISS) interface that is a software bridge to the legacy RadioMirror implementation (necessary for prototyping "RadioMirror 2K")
- Implementation of FX.25 which is a Forward Error Correction (FEC) extension of the usual packet radio AX.25. Using FX.25 with RadioMirror would add additional robustness with little overhead, especially if higher speeds like 4800 bps were used.
- We have powerful radios (especially on 144-148 MHz). For example the Yaesu FT-2980R has a maximum transmit power of 80 watts (and uses a large heatsink rather than a fan). Ham Radio Outlet sells this radio for $149 at the moment. Yes, duty cycle would be an issue - I'll address that.
More than one RadioMirror is a good thing.
There's no reason to have only one RadioMirror system in an area. It would actually be a good thing to have more than one to avoid the "BBS SysGod Effect" that we endured in the Packet Radio Bulletin Board System (BBS) era where some BBS Sysops tended to censor (delete) any content that they didn't personally like from passing through their BBS (even "private" messages).
Federation
I can envision several RadioMirror systems in a given area, each with a focus. For example, my RadioMirror system would focus on data communications. Another might focus on Emergency Communications information. Another might be the files for a particular Amateur Radio club. There's no downside (that I can imagine) in receiving files from each one. Each night my RadioMirror receiver can tune to a different one to update my file system for each one.
RadioMirror and Bulletin Board Systems
I haven't yet discussed Bulletin Board Systems in the 2020s (a future article, likely to be a long one). RadioMirror is a perfect complement to BBS systems as it's an efficient method to distribute files widely into BBS systems. The nature of RadioMirror is that it's not a fast way way to retrieve a particular file (you have to wait for it to be transmitted in turn), whereas if you needed to quickly view a file, a BBS would be a better method of doing so.
RadioMirror as a First Project for new Amateur Radio Operators
Conceptually, a RadioMirror receive station can be as simple (and inexpensive) as a Raspberry Pi, an RTL-SDR software defined receiver, and a simple wire antenna such as a twin-lead J-pole. A (better) addition to the station would be a USB flash drive to store the received files. Everything else is a "simple matter of software". Because such a station is receive-only, you wouldn't even need to be a licensed Amateur Radio Operator to use such a system.
Duty Cycle
Despite the seeming robustness of the Yaesu FT-2980R mentioned above (large heat sink), in my experience, and what I've been told by much more experienced Amateur Radio Operators, is that any radio specifically made for Amateur Radio use is just not built for continuous duty cycle (no matter what the manufacturer says). It's simple - Amateur Radio Operators are price-sensitive. Thus radios manufactured for the Amateur Radio market are primarily optimized for cost. Thus, if you're going to use an Amateur Radio unit for transmitting RadioMirror, it would be best to not use it at 100% duty cycle (transmitting 100% of the time). If you do, the radio will inevitably fail. There are two solutions for this issue:
- Don't operate at 100% duty cycle. Perhaps transmit for one minute, wait one minute, then transmit for another one minute. Even on a radio like the FT-2980R, use a fan on the heat sink (use a bigger, slower one so that the noise isn't objectionable)
- Instead of a radio built specifically for Amateur Radio, use a radio designed for commercial use that can withstand a 100% duty cycle. Repeater Builder is an excellent reference for using (converting, adapting) such radios for such use.
My spring and early summer 2021 has been pretty full with personal travel, so I haven't had much time to do the many experiments and projects I have planned. RadioMirror is one project that I will be working on soon. Stay tuned!
But wait... there's more! Perhaps "RadioMirror 2021" isn't quite so conceptual after all! See my next article - RadioMirror, Meet flamp.
Thanks for reading!
Steve Stroh N8GNJ
Bellingham, Washington, USA
Portions Copyright © 2021 by Steven K. Stroh