Hello Roelof,
Could you send me a copy of your mini-whip antenna ?
I work with the selective voltmeters Type SPM-12 for LF reception with
narrow bandwiths
as you do.
For antennas I use both loop and whipantennas.
I agree with you that sometimes the loop and sometimes the whip antenna
gives a better signal
to noice (or interference) situation.
Depending on the type of interference and the distance to the source of this
interference.
Is the smal book you refer to number 182 by Franzis ?
Regards, Theo (PA3AYK) located near Zutphen The Netherlands.
----- Original Message -----
From: "Roelof Bakker" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 18, 2006 4:51 PM
Subject: LF: Mini-Whip
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
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