Monday, February 23, 2015

When Hobbies Collide

Two years ago I rode in the Tour of Southern Rural Vistas (TOSRV), a two-day bike tour from somewhere just north of Tallahassee FL to Albany Ga.  Had a great time, you can read all about it here in a previous blog post.  One of the cool things about the whole production was that a local ham radio club, the Tallahassee Amateur Radio Society (TARS), provided support communications all along the route.  In these days of cell phones, perhaps this is not as completely crucial as it used to be, but there are still many backwoods spots with little-to-no cell coverage and besides, but it's not about doing things the easiest way, it's about doing things the fun way.  It's a good excuse for these hams to get out in the fresh air and use their portable VHF/UHF capabilities.  After all, if the sole objective was to simply get from Tallahassee to Albany with the least amount of trouble, why bother with a bicycle when I've got a perfectly good car?

OK, so I kept looking at these hams having a good time in the sun at every rest stop, and I couldn't help but thinking that, while I was having fun on the bike, I could be having fun on the radio at the same time.  With this in mind, I started gearing up to do both in at TOSRV-14 when *screech* the event was canceled.  Damn.  Well, I was busy with The Shop in the same time frame anyway.  So the project was sidelined until this winter.  Finally wrapped things up this weekend, as you can see:

Here's a close-up.  
Saddlebag, as well as any other gear can still be attached to the rack.  Perfect for touring.

The radio's just sitting on the rack, you don't actually ride with it like that.  Sooner or later I'll have to rig something where it can clip on the handlebars (there's more than enough coax to reach) but for last Saturday's test I just stuffed it in a jersey pocket for the ride to the Bay Bridge.
The view from the top is spectacular, either in the visible or VHF spectrum.

The 85' crest gives a 13 mile radio line-of-sight radio horizon, making it easy to hit both the Biloxi and Slidell repeaters, each 25 miles away, which have antennas at 300' and 1000' respectively.  On a mere 5 Watts, I easily made contacts through each repeater and received fine signal reports.

Construction Notes
This is pretty easy.  I started with WX2NJ's Jurassic Duck 2 meter VHF antenna design.  It's essentially a J-pole stuffed up a piece of CPVC pipe.  The big innovation was that all of the lengths were adjusted for the change in c due to the CPVC's properties.  To add a few notes: 
(1) Cut the radiator wire about 12" longer than specified in the plans, then trim to adjust the SWR.  I cut and hoped, but ended up soldering on an additional 8" of wire to get things right.  
(2) Get a rack with pannier side struts.  This makes it easy to zip-tie things on, far easier than that the weird shower fixture in the original plans.  Stronger too.
(3) Leave the PVC pipe a bit long, so that the matching stub inside it is positioned well above the rack.  Otherwise the stub can interact with the rack's metal, leading to unknown but probably bad performance.  Extra antenna height is always a good thing anyway.
(4) 300 Ohm twin-lead is a pain to work with, but about the only material that's right for the job.  Get the real twin-lead type, not the encased jacket type, which is nearly impossible to work with.  Take your time, be ready for several tries.  Trim out the solder points for the coax on the stub before you cut the whole thing to length off of the roll of twin-lead.  That way, you can whack off unsuccessful tries as they happen and only lose a few inches of twin-lead each time.
(5) Punch a little hole through the twin-lead near the top and hang it inside the pipe with a short length of string.  That'll keep it from sliding down and bunching up.
(6) You can leave the bottom end open, but a quick wrap of electrical tape will finish it nicely and discourage bugs from crawling up in the thing.

Well, as I mentioned earlier, it works and works well.  In fact, I've made a second on to go on a backpack as a hiking antenna.  Back to bikes, TOSRV may be gone but there'll be other ham-supported bike events in the future.  In the meantime, it's always good to have around for hurricane season, and good for occasional fun during less-serious times.  Finally, to allay the fears of fellow cyclists who are not so technically inclined:
it detaches and re-attaches as needed in less than a minute.

One more note: Thanks to Jeff KK4SNA for pointing out the original Jurassic Duck antenna plans on the web, and to Gary N5AHM for help analyzing and sorting out this antenna's fine tuning.

ps: adding "CX" to this post to make it show up better in searches.

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