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