Ham Radio and the XO: an Unlikely Geek Pairing

   
   
   
   
   

Long before the advent of the personal computer, ham radio operators communicated keyboard to keyboard. As early as the 1950s, Ham's used modes such as Radio Teletype using 5 bit code. Perhaps slow under current conditions, 45.45 baud (about 60 words per minute) is certainly fast enough for chat!

old school wifi
Monitoring Morse Code with XO

Plowing deeper we discover that hams were some of the first adopters of digital communications. Ever heard of Morse code? Quantized coding of the alphabet certainly qualifies as digital!

During the first part of the last century, Hams were the ubergeeks. Through the work of a few devoted Hams and XO geeks, digital keyboard modes are available on the XO!

Fldigi is a multi-mode program that has been "sugarized" for the XO. It can be integrated with a radio for Ham radio applications or can be used with the built-in speaker and mic sending data across a room via audio. It is a great way to demonstrate theories of digital signals and audio properties in a classroom setting.

Some of the modes are simple like Morse code. Other modes are more advanced such as Multi Frequency Shift, Phase Shift and Frequency Shift. Fldigi has a great frequency scope that can be viewed as a waterfall or scope style. With a simple shortwave receiver (with sideband or BFO) signals coming from around the world can be decoded using the XO!

So what else may be in store for the Ham/XO geek in the near future? Software Defined Radio implementation, rig control, and perhaps Digital Radio Mondiale. Only time will tell in this dual (radio and XO) realm where geeks rule!

Give Fldigi a try with the OLPC News Forum HowTo. Using a transceiver, my first XO/Fldigi contact was from here in Oregon to the Kamchatka peninsula! No wi-fi needed.

XOpher is an active PDX XO User Group member who reminds us all that geeks are timeless, its only the technology that changes.

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14 Comments

Cool, we made the front page. My first contact using PSK31 on the XO was less impressive: only spanning from Texas to Georgia. Still a cool feat if you're not used to ham radio! haha.

Ideally, the whole joining of radio and XO would result in some whiz-bang setup wherein broadcasters are able to produce a nightly OLPC broadcast and kids are able to tune their radios and download some ebook. Can you imagine how fascinating the world would become! Perhaps there's no library within safe distance of a kid's home. Perhaps the mesh network can't quite make the reach back to the schoolhouse. No problem, at least he or she will have some reading material as they download Tom Sawyer or Treasure Island from the nightly OLPC broadcast.

To get that far however would require significant work in the data-mode department. Currently PSK31 only does text. PSK63 can do email, but as of yet, no file transfer mode is working on the XO. Whats more, the only modes ham radio does any file transfers (however slow) is only SSB, a mode most price-conscious world-band radios do not feature. If suitable transfer speeds can be obtained via "wide AM", then we might have something to work with.

For now, check out PSK31 and the wonderful things available to you through the world of amateur radio!

i completely agree with tommy with his comment made earlier....

While PSK31 is all geekish and suited for Ham users (I was one once) chatting to each other on the keyboard maybe the file transfer mode is more appropriate for XO Kids?

PSK63 certainly sounds more appropriate to a computer user if they have a transmitter and receiver. These of course typically cost several hundred dollars. Usually way more than the XO would cost.

You mentioned in the article about sending e-books that remotely located kids could receive/download on their XO. This sounds like a far better use for the 'digital mode' on the XO and could really be useful by education facilitators.

Short Wave radio has been used for years in the Australian Outback on the School Of The Air to provide access to teachers for children living on remote cattle stations. Perhaps the dissemination of educational literature could be transmitted regularly by education departments and received on nothing more than an old shortwave receiver.

While not as versatile as a Wifi network, point to multi-point transmission of school material on short wave is a cheap and simple system.

Why does every kid need a shortwave receiver?

Just place a shortwave receiver and receiving antenna at the school to receiver the data (books, sound bites, etc). Then, copy over the mesh network and voila!

Shortwave AM broadcasts have enough bandwidth to provide a fairly-steady stream of text. By its very nature though shortwave has a LOT of static. One international broadcast station would only be able to deliver so much data because it would have to spread thousands of miles. If each country had its own individual broadcast however they could offer more throughput as they would have a clearer signal than some far-off station. It would also help with localization issues, as students in Nigeria could get local texts, Uruguay could get their own,etc. This would be especially helpful for villages that can't get satellite internet or are out of cellphone range.

Data rates won't be fast no matter they be local or international broadcasts because you're dealing with sub-optimal situations: a short wire antenna near ground level at the bottom of a valley for example. I'm sure you could get by with 300 baud RTTY at minimum for local broadcasts. You can get 175Kbytes of data over a 10 minute period at 300baud.

Simple shortwave receivers are very cheap to produce, looking at maybe 10$ for a receiver. With enough power from the transmitting station you'd only need 3-4 feet of antenna wire to receive it. However if you've got a "centralized" receiving location like a school, you could have a permanent receiving antenna which would offer much better reception.

See my post about an SDR shortwave chip that could be built into a USB dongle. This would be the ideal "radio" for individual XOs.

http://olpcnews.com/forum/index.php?topic=1675.msg12601#msg12601

Also, check out other "Ham" modes such as MT63 for somewhat faster throughput on shortwave (2 kHz bandwidth) with Forward Error Correction (provides error free copy with only 75% of signal decoded) not available in the PSK31/63 flavors.

http://www.qsl.net/zl1bpu/MT63/Technical.htm

Now Digital Radio Mondiale would be ideal, but seems to be a processor hog. It has several text and image options along with the ability to send stereo audio in 10 kHz of bandwidth.

'Shortwave AM broadcasts have enough bandwidth to provide a fairly-steady stream of text.'

Well under ideal circumstances one would use sideband on a low frequency best suited for short to medium range transmission. In most cases the transmission would be from a government controlled source. Perhaps the government education departments could provide the receiver to each school.

Transmissions could deliver text based news items as well as education resources.

There would be an issue of data integrity and perhaps even security issues. Valid message packets would need encoding and some error detection/checksum format to prevent misuse/abuse. Otherwise it would be easy for others to transmit their own information and have it received by the school server.

There may already be a transmission protocol for one way data (non-acknowledge) format.

XOpher - thanks for the link on MT63, a 25% acceptable error rate is awesome. A simple USB-dongle receiver should be easy to manufacture. They already make AM/FM receivers on a single chip, why not Shortwave frequencies?

Some form of sophisticated data compression scheme, mixed with encryption would help with both data rate and security problems. If the education dept. provided each school with decryption software using some form of public-key encryption scheme, that would go to great lengths to protect against "nefarious" transmissions.

Here's an interesting article on Fldigi:

http://www.linux.com/feature/59958

Also, here's the main Fldigi site, which lists what digital modes it currently supports:

http://www.w1hkj.com/Fldigi-2.x.html

No support for MT63 at the moment, although maybe one of the other supported modes could provide something similar.

Several of the Olivia modes/settings would be robust enough, but much slower I think.

@XOXOXO:
"Some form of sophisticated data compression scheme, mixed with encryption would help with both data rate and security problems."

Encryption is overkill, cryptographic signing is enough.

For text (and other things), Bzip2 compresses close to the theoretical limit and is standard Linux infrastructure. The cryptographic infrastructure is already installed, as it is used for the software upgrades.

Radio downloads are often used for nighttime newspaper distribution. I know of an 1980s project to distribute newspapers to the blind during off-time at night. The blind would then use speech synthesis to read-aloud the papers.

I think we all will not be able to predict the uses for ham radio on the XO. Say, a parallel newsnet. Note that all the XO's have cryptographic message signing build in. You can always validate a user (or better, a XO).

Winter

It occurs to me that that MT63 is sound card generated, and therefore could be applied as modulation to an AM broadcast transmitter, with minimal difficulty. It won't be as bandwidth efficient as using SSB transmission and reception, but the cost of entry is much less, and the requirements for critical receiver tuning are eliminated.

I expect that the biggest challenges in demodulating MT63 off of an AM transmission successfully will be that the receiver automatic volume control primarily tracks carrier amplitude, which when selective fading knocks out the carrier, on an AM receiver, will probably result in a second or two of distorted audio. With the interleave and symbol spreading of MT63, this is probably not an issue. AM receivers with synchronous detectors, or SSB receivers, will also help. Applying NVIS techniques as a propagation tool could allow good regional distribution of materials, with reasonable amounts of transmitter power, out to 400-500 km from the transmitter.

If the content being distributed is not of a timely nature (e.g. news is hopefully timely content) it can be repeated during subsequent transmissions, and if a protocol like the amateur radio satellite file transfer protocol is used to schedule blocks, and act as a wrapper to provide information about blocks being sent, that software can manage interleaving blocks of data from different files, with a decreasing frequency for each block, the longer it's been since the distribution of that file was initiated. The protocol also periodically sends a list of files that are in the rotation to be transmitter.

The companion receiving software would allow the school's primary operator to select the desired files, and the software would start accumulating them - perhaps automatically accumulating any new files, which for a day or two, would be retained against the later desire to actually keep the files for local storage or distribution.

That, in concert with the other techniques already present could both provide a way to distribute books and lessons, but even as a means of providing software updates for circumstances where internet access or a traveling update distribution source isn't possible or timely.

Note: I'm not an XO owner/user - comments from this forum were posted to an email list I'm a subscriber to, by one of its members that had a bit more of an itch to contribute to developing for this platform. Hi Bill!

Bob Donnell, KD7NM

I have just finished evaluating HamFax for its conversion as an activity for the XO.
Full source is available should compile nicely.

Unfortunately I dont have an XO to run it on. I will try to convert it to a .xo file and run it on my emulator.

Given the ease of use and simplicity of Facsimile kids with shortwave receivers could access weather charts to study and learn about weather patterns. This also has big advantages for farming communities in remote areas that have little weather information.

One fun part of HamFax is using speaker/microphone and sending images across the room to another computer.

Hello Bob. Looks like you are an APRS guy. I did that stuff awhile back too. MT63 will do proper file transfer. We have tested it via VHF FM for that it works fine. I've also used it numerous times on HF (SSB) and it is a nice keyboard mode.

So many folks here have great ideas. I think the concept of sending books and curricula to some distant school house is just great. I appreciate you putting in your 2 bits even without having an XO. We need to talk you into locating one I think!

Some of the newer ham Digital Radio Mondiale itterations (WinDRM, HamDRM, etc.) would be nice too. They can transfer files and awfully fast too. FDMDV would even make voice via digital HF a possibility for the XO. Not sure if it has enough horsepower for that though.

gMFSK does MT63 in Linux and I think the original IZ8BLY MT63 Terminal was a Linux prog. We may have to pressure our code freeks to get this stuff sugarized for the XO so we can perform some tests...

Any ham radio operator that sees this thing should immediately think..."That would be great for portable digital modes". At least that is what I thought when I first ran across the OLPC Project. I've taken laptops to the field before but the readability in bright daylight can be an issue.

The uses mentioned here are also a good tie in to the educational stuff.

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