Friday, September 14, 2007

Moronic DIY Electricians

After the CHA250B antenna install I was doing some cleanup work on the roof. Went to ground the mast and noticed a bit of a tingle on my hands when I was holding the mast and touched the ground wire. I put my trusty Fluke multimeter on there and was amazed to find about 74 VAC on the mast! No current to speak of, which accounts for the fact that I didn't get zapped off the roof, but enough to feel it when barely touching the ground wire.

I headed back inside to do some testing. Poking around my shack, I discovered that some of the AC outlets had reversed hot/neutral wiring!! The only thing that saved me from destroying my gear (or myself) is that thankfully I'd never used a correct outlet and an incorrect outlet at the same time for anything that was connected. (e.g. computer on one and rig on the other.)

I'm annoyed beyond belief that the previous owner of my house did this. The real kicker is that he was also a ham. I suppose I shouldn't be surprised, because this isn't the first electrical oddity I've found in this house. Apparently Mr. Fixit fancied himself quite the handyman. I'm not going to name names here, but he's the moron that after 5 years still hasn't updated his license address in the FCC database.

Sunday, September 9, 2007

New Antenna!!

My wife spent the day visiting a friend, and took the girls with her, which left me about 12 blissful hours on a weekend to do whatever I wanted to do. I'd be intending to install a new HF antenna for some time, so this was the best and obvious time to do this.

I put out a call asking my amateur radio friends to come by and help. Bojan agreed, which was great. He's a bright guy, very creative when it comes to technology. If you're ever looking for someone who can turn ideas into reality, give him a call.

The antenna I chose was a Comet CHA250B. This particular antenna is unique in that despite being vertically-polarized it has no ground radials, and it will also tune all bands from 80m to 6m. The coax feeds into a large black cylinder which acts as a matching network. This particular antenna has been alternately praised and vilified on review sites like eHam. People are either giving it a 0/5 or a 5/5. There doesn't seem to be a lot of rhyme or reason to this; although it's interesting to note that people giving it a 0/5 tend to compare it to a dipole which might be unfair.

For me, I was willing to try it out. Considering that my comparison point was my aforementioned $2 "Speaker-wire Special" I suppose anything would seem better. The real challenge in the antenna install was not so much the outside work, it was deciding how to get the coax up to the roof from my shack. Doing so entailed slithering around in my attic, which is a complete mess after a roof replacement earlier this year. There were also a few setbacks, such as a broken lag bolt and a too-small bracket on another antenna (my HDTV antenna) which is now needs to be adapted to the new larger mast.

In the end we got the Comet installed, and two extra runs of coax. I fudged up a temporary VHF/UHF antenna (until I can get a replacement lag bolt and the new mast installed) by slapping a magnetic mount down onto a metal attic vent. I may also sell the VHF/UHF antenna I had on Craigslist and get something else because it's a 6m/2m/75cm tribander and the Comet now covers 6m.

As expected the Comet performs better than the homebrew. I'm getting signals where there were no signals before, I don't have RF-in-the-shack problems like I did before, and the antenna is clearly quieter (lower noise floor) than the homebrew. It tunes a lot of bands, so all in all I'm happy with it. I'm not quiet sure why some people have panned it so hard on eHam. I suspect that it may have to do with unfair comparisons to dipoles, but also it might be the install makes a difference. The Comet's instructions call for it to be installed 32 feet off the ground. Perhaps if it's not installed at that height the matching network doesn't work?

Wednesday, September 5, 2007

JT65A-HF, we hardly knew ye...

A while back I wrote about JT65A, the amateur radio weak signal digital mode being used on HF bands. My best contact was just before Field Day 2007 when I logged ZS6WN in South Africa; over 10,500 miles using 50 watts and an antenna made of speaker wire at the bottom of the sunspot cycle. It was a very interesting and powerful mode. And yet I haven't heard anyone on the bands in over a month. Which leaves me to ponder; why?

WSJT (the software for JT65A) was originally written for weak signal paths such as Earth-Moon-Earth. As with most weak signal modes, a trade-off is made where the amount of information transmitted is intentionally limited in order to pull weak signals up out of the noise floor. In JT65A, the total transmission cycle was one minute (actually, about 48 seconds plus 12 seconds for the recipient to react and respond) and in this minute only 13 ASCII characters could be sent. Not exactly a rag-chewing mode. So once I'd worked a station and logged them, I was basically done. I'd see someone calling CQ, note that I'd already logged them, and so wouldn't respond. And once I'd worked ZS6WN in South Africa, working non-DX contacts was (to be blunt) boring.

So my theory on the premature demise of JT65A on HF is this; everyone worked everyone and once they were done there was no point in continuing. Radio amateurs like to rag-chew, talk about stuff, brag about their rigs and such. Hard to do at 13 characters per minute. And without a conversation, it's hard to make friends. Sure, you could always get to know folks by hanging out in the Ping Jockey web chat, and there's certainly a core group of people who do just that, but if you're going to chat in a chat room then why bother with a radio? So I think JT65A on HF has turned into the one-hit-wonder of amateur radio.