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Anecdotal Antenna Metric, was RoomCap Antenna
Ah, the "it works because I made contacts with the following DX"
antenna argument. This may be an extremely compelling way of measuring performance of an antenna system if done correctly. It's certainly the most compelling kind of marketing argument snagging prospective "magic antenna" buyers, especially those who don't have another antenna up for comparison. But is there a way to make such an anecdotal claim and have it mean something? I'm thinking something along the lines of probability of making contact with a station with identical equipment, averaged over a very very long time. If you know the statistical ionospheric loss for the path, the power levels involved, and antenna gain (or LOSS) you can calculate such a thing. I've heard an argument recently that a particular antenna system must not be too inefficient because it was able to produce contacts with stations in Australia and New Zealand. The data below are in the same category. How do you know that the RoomCap antenna contacts were not made because the stations on the OTHER END have much MUCH better antennas? The dynamic range of signals present on the amateur bands is enormous. You could have an antenna with a gain of -35dBi and still make regular contacts. That doesn't mean it's good. How about if we stick to dB gain relative to some simple reference antenna or the isotropic for antenna reporting? Don't get me wrong, you can have tons of fun with a bad antenna. I'm sure that all the great DX I can work with my 100 feet of magnet wire at 30 feet is largely due to the stations on the other end, and if you're doing the best you can given the limitations of the situation, then you're holding up your end of the DX bargain. I worked 9M2CNC the other day on 17m with my antenna system! Does that mean I get to sell it for $190 to suckers? Or does it just mean that the propagation was good, the station on the other end was good, and I'm managing to not turn all of my 100W into local heating? 73, Dan N3OX HERE A FEW RESULTS: QRV with RoomCap antenna on 80m On May 15th, 2006 I was QRV on 80 m during 1 1/2 hour. Tcvr: TS-50 (100 W PEP), QRG = 3.770 - 3.787 Mhz Antenna: RoomCap with 1.66m radiator length installed on my car. SWR = 1.0 QTH: Peripheral part of city of Basel. Conditions: The band was weak with a lot of QRN. Here follows the contacts and the received signal reports: 20:10 DJ6YF, 59+10, Hans, Bielefeld 20:10 DL3EAI, 59, Reino, Mittetal (nr border to PA) 20:14 DJ6LGB, 58, Peter, Lüneburg 20:17 G4KHM, 57, John, nr. Brighton 20:23 DL1JGG, 58, Renald,Plauen 20:30 DC4HW, 59 Walter, Lauenburg nr Lueneburg 20:33 DG6DAG, 59+10, Otto, Nord-Hessen nr Kassel 20:40 YO4RDW, 57, Romeo, Odfbesei, Rumaenien 20:50 F4AWH, 59, Jean-Luc, nr Besancon 20:55 2E0BOT, 59, John, Stratford UK 21:10 DF9YK, 59, Wolfgang, Mainz 21:11 SP8TDV, 57, Adam, Lublin, Poland 21:13 HB9AQA, 59+10 - +20, Ferdi, nr Lenzburg 21:22 9A4M, 59, Mate, Sisah, Croatia 21:28 G1RVP, 57, Pete, Dereham 21:30 DJ6MM, 59+10, Paul, Eifel 21:38 DK5WN, 59, Thomas nr Erfurt 21:39 SP1DTE 58, Luk Koloberg, Poland 21:40 HB9XJ, 59+10, Hans, Zuerich 21:43 QRT With best 73s Felix HB9ABX Small mobile antennas (in terms of wavelength) aren't generally very efficient. The above test only shows you can make contacts. It doesn't address efficiency or field strength in relation to a similar, but larger antenna. Have you put the plans online for this thing, or are you just using them to augment your net worth? 73, Tom Donaly, KA6RUH |
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