Monday, May 28, 2007

Amateur Radio: 5,200 miles on 50 watts and a $2 antenna


Lately I have been getting prepared for the annual ARRL Field Day, which is an annual operating exercise and public showcase event for the amateur radio world. Amateurs all over North America will set up in campgrounds, parking lots, and fields and attempt to make as many contacts as possible using various "modes"; everything from Morse Code and "phone" (what normal people would call voice, talking into a microphone) to exotic digital setups which use computers connected to radios. My club (the Northern California Cactus Radio Association) will operate as K6SRA from a campground in Henry Coe State Park, near Morgan Hill CA.

I'll be running the digital station this year, and plan to use (in addition to the usual PSK31 and RTTY setup) a very new mode called JT65A-HF. JT65A isn't new to amateur radio as it's been used for a while for "moon bounce"; and yes, I mean literally for bouncing signals off the moon. Earlier in 2006, a few people decided to transmit JT65A signals over the HF bands; primarily 20 meters (14.076 MHz) and 40 meters (7.076 MHz). In only a few months this new mode has exploded in popularity, primarily due to the very high sensitivity afforded by a Reed-Solomon forward error-correction algorithm implemented this mode. It's mathematically provable that JT65A signals can be detected with 100% certainty even if the received signal is -22 dB under the noise floor.

In preparing for working JT65A-HF on Field Day I've been learning to use an application called WSJT which is used mostly by the moon bounce and meteor-scatter folks but now also HF enthusiasts. I've made some amazing contacts this way; just tonight I logged a contact with a guy in Australia using only 50 watts of power and a homemade antenna I built with $2 worth of parts I had lying around my garage. This is the equivalent of someone being able to see a 50 watt light bulb from space at a distance four times that of the International Space Station, or of someone talking from San Jose CA to San Diego CA on a CB radio. I expect we'll be seeing a lot more of JT65A in the HF bands, especially as radio amateurs suffer through the poor radio propogation conditions created by the current solar minima.

Update (15 June 2007) : I just beat my Australia record with a solid contact to ZS6WN in South Africa. 10,526 miles, same power, same antenna!

Update (24 Sept 2007) : WA3LTB has created a video demo of WSJT and posted it to YouTube.

4 comments:

John said...

While having a QSO with VK-land is great under any circumstances, I would hardly say that 210 miles per watt is anything out of the ordinary. I have made the same hop with my FT-817 at 3 watts.

John said...

...and you claim of 4 times the height of the ISS is dubious.

The ISS is parked at roughly 200 miles up.

http://en.wikipedia.org/wiki/Low_Earth_orbit

Sparqi said...

@John: Reading your comment my gut reaction was to that you'd turn out to be one of those "CW uber ales" guys. Reading your blog shows that, in fact, you're a kindred spirit in digimode experimentation.

When I completed my VK and ZS QSOs and wrote this post I had been licensed for less than a year and just upgraded to General. So at the time, being new to HF and digimodes, these contacts were a big deal for me. Had you posted the same comments back in 2007 I might have been properly awed and humbled by your QRPenis-waving.

You're right about one thing; 4x the distance to the ISS was incorrect. 5,200 / 200 = 26. So 26x, not 4x. Thanks for the correction.

John said...

CW is only relevant if you're:
A) Building a rudimentary QRP rig
B) Enjoy using it
C) In need of an advantage in a contest or entering a CW-only contest.

The CW forever crowd is shockingly similar to the old Spark Forever guys from the early 1920's. JT65 or Olivia 250/8 will beat ANY CW ops skill. Anyday.

QRPenis waving? Can't help you there...not my style. Besides, I don't fit the fanboy criteria. I have been a QRPer for one reason: Money. My 817 is the only the second new rig I've ever had...in 22 years no less. I'd like the power and features of an '897...but with kids and mortgage...out of the question right now.

Like the rest of your blog, however. (I deleted most of mine...it was created in 2007).

hsh