Sunday, July 29, 2007

Cayman Update #2

I wrote the following post while offline in the Grand Cayman airport, and had forgotten that I've covered a fair amount of the same material. I'm now sitting in the Charlotte airport, with the storms in Newark having delayed our return flight home, and I decided that rather than edit what I wrote, I'll just post it as written. Please forgive the duplication.

Sorry for the lack of updates from during the trip. This update is being written as I sit in the airport waiting for the first leg of my return flights home. Although my original intent was to provide a few updates during the trip, other matters, such as sitting by the pool, jet-skiing, eating, eating, eating, and the occasional (!) "adult beverage" seemed to take up a lot more time than I'd expected.

The Antenna Issues

As I mentioned in my first posting, I did have some trouble getting the Buddistick tuned. Over the course of the week, I discovered a few things that almost certainly causes the issues. First, as you'll see from some pictures (I'm not sure if they'll be in this blog or elsewhere, as I'm currently writing this offline) the antenna was mounted on a railing on the second floor of the house. We were quite close to water, but unfortunately the roof of the house was metal, which did cause problems. (I considered mounting the antenna on the grass in the backyard or on a patio table, but decided not to do that as I would have had to either operate outside or run the feedline over the backyard. Neither of those options seemed desirable.)

However, I think the bigger issue was that I was probably using a counterpoise that was too short. One of the nice things about the Buddistick is that you can experiment, and you can find that the antenna will tune with different combinations of coil and whip settings and counterpoise lengths, though not all of those settings are optimal. For a while I was using a counterpoise length of a bit over 10 feet, which at some point during my testing from home I'd found worked reasonably well. However, what I finally realized was that the bandwidth for acceptable SWR was pretty small, and I wasn't getting what I'd expected to see in terms of actual SWR. (I was getting a minimum of around 1.8:1, and I'd previously seen much lower, approaching 1.0:1). It finally dawned on my that my "assumed good" counterpoise length might be wrong, and I went back to square one and re-calculated what the length should be, based on a dipole with a center frequency of 14.250 mHz. (I was operating exclusively phone.) That came out to be something like 16' 3" (roughly; I don't recall exactly what I used), and when I used that and checked with the analyzer, I found that I had excellent SWR (1.2:1 or less), though too low on the band. I moved up a coil setting or two, adjusted the whip, and in about 5 minutes I had excellent SWR through the entire 20m phone sub-band. (Using the built-in SWR meter on my '706, it showed entirely flat.) Unfortunately, I didn't have this stroke of genius until Friday, which meant that I probabably missed out on a lot of contacts that I should have had. (Too much sun frying my brain?)

The Noise Issues

One other problem that I had was noise on the bands. It seems that there were a couple of reasons for this. The first reason was probably due to various electronics within the house where we were staying (or from the other houses in the area.) This type of noise did seem to come and go, so it could have been things like hair dryers or appliances being switched on and off.

The second cause of noise was something that I should have found before I left. Although I did hook up my laptop to make sure that the CI-V interface to my radio worked, and even hooked up the antenna, I never actually made any contacts with the complete setup, despite my "Practice makes closer to perfect" philosophy. That was a mistake. I discovered a couple of different sources of noise coming from the laptop. The laptop that I was using is a Dell D620, which has both a "mini-stick" mouse as well as a touchpad. Whenever I touched the touchpad (which is common during logging), there was a very loud buzzing noise generated. The fix for that was to use the "mini-stick" mouse, though it was a little annoying since it's difficult to not have the palm of your hand occasionally touch the touchpad while typing.

The second problem was related to the power supply. When I'd tested the setup, I didn't have the laptop plugged in to the power supply since I'd only intended to test for a few minutes. Apparently the power supply for the laptop is a noisy switcher type, and not only generated noise when plugged into the laptop, but also generated noise when plugged in at all. The fix for that, of course, was to leave the power supply unplugged. For the most part, this wasn't a problem, since most of my operating was limited to a one to two hour stretch, but I did forget to plug in once and found the battery dead. One thing that I'll check when I get home is whether some ferrites would have helped the situation.

More to follow soon ...

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