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From: "Roelof Bakker" <roelof@ndb.demon.nl>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 18 Jan 2006 17:51:24 +0100
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Subject: LF: Mini-Whip
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Hello Mike and everybody else,

Thank you for your interest. The file is 65 kB and seems to be a little 
large for the list. I will send a copy to all who have asked for it. I have 
written an extensive article on this antenna and have send it to Electron, a 
Dutch Amateur Radio Magazine, almost a year ago. Unfortunately, it still has 
not appeared in print. This is the reason that the information is not 
available on a website yet.

Just a few words on the development of the antenna. Four years ago I have 
been building all kind of loops, as I was convinced that loops are best at 
LF. I spend a whole winter season and they worked excellent in receiving 
local noise. I almost gave up, believing that weak signal reception was not 
possible in a city environment. As a last attempt, I connected the 12 m long 
open feeders of my 80 m dipole together and used it as T-antenna. Though 6 m 
of the feedline runs close to the wall, local noise was much lower. 
Reception was much improved and using a RF-isolating transformer it worked 
even better.
Then I started experimenting with whip antennas. I have done a lot of 
research, which includes field reception tests in a RF-quiet environment, 
where I could not find a difference between a loop and an active whip. At 
home it is different.
I found that at LF local noise in the electric field is contained inside a 
building, whilst local noise in the magnetic field is not. The screening for 
the electric field can be as large as 30 - 40 dB for a concrete building. So 
far I have found one written source that confirms this phenomenon: a small 
German book on active antennas.

As you can read in the attachment, it was possible to reduce the size of an 
active whip considerable. The "standard" mini-whip is 8 cm long. At present, 
I am using one that has been squeezed inside half a film canister: 30 mm 
high! Passive electric field antennas have also been tested, using a 100 : 1 
RF transformer. In this case the "antenna" was a large 5 kg coffee tin. It 
worked fine.

Reception results have been very nice. At present my main interest is 
chasing NDB's. However, I have had solid qrss60 copy of VO1NA, WD2XKO and 
WD2XDW around 137.777 kHz. Regarding NDB's; in a little over three years, 
1250 different stations made it into my log. To be honest, I must confess 
that I am using narrow bandwidth aural reception with a basic bandwidth of 
20 Hz, provided by a SPM-30 SLM and a pair of modified PA0LQ active filters 
which reduce the bandwidth to 12 or 6 Hz. For NDB reception this compensates 
for a large extend the lack of directivity of the mini-whip.

I am not saying that loops are bad antennas. To the contrary, I still have 
an active loop and use it from time to time in a phasing system with my 
mini-whip. That is, when local noise is low. Last week I have been lucky in 
receiving a NDB from Alaska: station PVQ on 376 kHz, Put River, Deadhorse, 
6288 km. Reception was over a Polar path and the signal was very stable, 
without fading. Finbar O'Connor, EI0CF heard it a few days later, using a 
screened loop. This shows that both antennas can be great performers.

This all might sound a bit odd, but this antenna is for real. I have put a 
lot of work in it and it has been great fun. You do not have to believe me 
(probably I should not have done that myself, four years ago). But whoever 
wants a small antenna, just give it a try.  As you might have gathered: it 
does not work inside.

Thank you for the bandwidth.

Roelof Bakker, pa0rdt

P.S. the summery will be send a little later