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Here are a few pictures taken by my mom during the Nats…not too many because she was a helper most of the time. (http://www.wo-society.org/photo-gallery/2009/nats)
As some people may know, I lost a F1A model the last round of the F1A contest on a 2:15 DT! (the max was 2:30 but I early DT’ed using RDT) The model spiraled for 8 minutes in a thermal before landing. However, someone picked up the model and brought it to their home which led us on a wild goose chase for 2 days. I’d like to share my experience finding the model so check out the story here: http://www.wo-society.org/latest-news/2009-nats/87-72809-2-models-found
Finally, my mom took some random bits of video footage during the Nats (which I still need to go through). Here’s a video of me launching a TLG: http://www.youtube.com/watch?v=p58_JUeTDRU
Thermals,
OliverHi Dean,
We used a Radioshack antenna that was cut down. I don’t know the exact model but it looked something like this: http://www.radioshack.com/product/index.jsp?productId=2102469 except it was modified/cut down really short (the frequency is important). It’s neat cause it has a magnetic base that you can quickly stick to the roof of your car. The BNC coax cable goes in between the car frame and the door.
Tom Vaccaro told me that there was a Sympo article that he read discussing this antenna and that it should be cut down to specifically 14″ (I don’t know the science behind it cause I haven’t read the article yet).
Art Ellis uses it on long chases/flyaways and has found Tom V’s F1B model ~5 miles away from the field in the middle of Muncie. Once you get close, simply switch to the Yagi antenna.
Oliver
(Edit: the antenna is the same as the one in the posted link, Radioshack 20-032)
Thanks Oliver, that is what I have been looking for. You wouldn’t know which Sympo it was in possibly? Failing that, next time you have a chance, I would appreciate the length of your antenna and the frequency of your particular series of trackers.
Thanks again. 😀 😀
Hi Dean,
From the NFFS site’s list of Sympos, I’m guessing that article is Model Retrieval with Auto-Mounted Whip Antennae by William Prensky from the 1999 Sympo. I’ll have to check it out myself when I get the time. 🙂
The antenna we used was cut down really short, 6-7 inches. I don’t know if this effectively reduced the chances of finding a signal, but hey, we got it from ~3 miles away (with the model inside a house).
Re: antenna length, I think it has to do with frequency and wavelength (stuff I learned in physics are kicking in). I did a Google search of “antenna length” and the results came up with a frequency-wavelength calculator. If you go here (http://www.crompton.com/wa3dsp/hamradio/antcalc.html) and type in 217 MHz (the frequency of the 3 Walstons that I have, I’m using the Quad type), you get 13 inches for the quarter wavelength. Now, I don’t know which wavelength measurement is more important, quarter or half. I would think that a quarter wavelength would only give you half the amplitude. So, does that mean cutting the antenna at, let’s say, ~30 inches give you better reception? (receiving full amplitude?)
Another Google search brought me to this: http://www.flyesl.com/News-y-Articles/featured_article.asp?FORUM_ID=7&TOPIC_ID=95 If you scroll down to “Antennas”, you’ll see that they mention first harmonics. So, perhaps receiving few additional harmonics of the actual tracker frequency may lead to better reception?
There’s a lot of guessing here on my part. 😕 This info is probably in the Sympo article.
Oliver
Ok, so I did a little more searching. The reason why people choose quarter wavelength is because it is the minimum antenna length in order to still effectively receive a signal.
Using the calculator here (http://www.k1dwu.net/antennacalc.phtml), a full wavelength would be around 54 in, or 4.5 ft. This is a bit long for an antenna. I think that half wavelength would be most reasonable, getting you closest to the frequency without a really tall or short antenna.
There is something slecial about 1/4 wavelength.
Read about it here under “What’s so special about 1/4 wavelength:
http://www.microwaves101.com/encyclopedia/quarterwave.cfm#propertiesI wish I could understand the terms in that article. 😛
Most articles that come up are related to ham radios. This article explains a simple dipole antenna and how two quarter wave antennas act together as a half wave antenna (scroll pages at the top).
Another article confirms the previous one. If you use just a quarter wave antenna, it should be grounded as a ground reflection makes the antenna a half wave antenna. However, radials and grounding are not needed when mounting on a car.
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