[30m] Re: 30M Stealth Antenna

[ik2ihy at libero.it]

From: <ik2ihy at libero.it>
To: "David Dorrance" <dldorrance at hotmail.com>
Subject: Re: [30m] Re: 30M Stealth Antenna
Date: Wed, 31 May 2006 23:41:19 +0200

Maybe someone feel some interest in a strange kind of a short antenna,
namely a µVERT form DL7PE?
Will some minutes of surfing
http://download.antennex.com/preview/archive4/Apr601/microvert.pdf be a
well spent time?

Best 73 ... Piero IK2IHY
*******************
----- Original Message ----- From: "David Dorrance"
<dldorrance at hotmail.com>
To: <30m at mailman.qth.net>
Sent: Wednesday, May 31, 2006 4:24 PM
Subject: [30m] Re: 30M Stealth Antenna


I have never operated on 30M, but the more I read about, and look at
propagation information, the more I realize that this is an amazing band!!
I
live in a deed restricted community, and I'm wondering if anyone has ideas
for a stealth antenna for 30M. I was thinking about a random wire, from an
MFJ-969, using insulated wire, run under the aluminum window and screen,
and
then run around the house on the facia. From what I've seen, it doesn't
appear that you need a lot of power. I also will be using digital modes
exclusively. Any ideas will be greatly appreciated.

73... Jon W1MNK

Hi Jon,

I also use digital modes exclusively and although I do not live in a deed
restricted community, I do not have sufficient space to string up a 1/2
wavelength antenna.  Maximum power here is 40W into an SWR of under 1.2:1.

My solution is a small transmitting loop antenna.  For 30 meters the
footprint could be a 3 to 4 foot diameter  pipe or a 3 to 4 foot square
copper pipe arrangement.  Currently I am using a commercial version made
by MFJ which is a bit expensive.  But I have built these loops out of
copper water pipe and high voltage variable capacitors.  For qrp one might
be able to use standard variable capacitors.  The MFJ unit is mounted at
18 feet on my roof; it would also work mounted on a 6 foot stand in my
backyard.

The advantages:  They are bidirectional, may be mounted close to the
ground, have a very narrow bandwidth which nulls out qrm and qrn and,
propagation wise,  work about as well as a dipole at 1/2 wavelength in the
air.

The disadvantages:  Remote tuning requires a geared motor due to the
narrow bandwidth.  You must re-tune when you move frequency.

The retuning is less of a problem with PSK-31 where the entire band is
within the bandwidth of the antenna; remote tuning is still needed to keep
the loop on center frequency as it changes with ambient temperature.

Here is a link to several versions of a homebrew unit for 20 meters, which
would work on 30 meters; make it twice as large and it would go down to 40
meters as well:
http://www.elecraft.com/TechNotes/loop_ant/wd8puoloop.pdf

There are literally hundreds of sites for small loop antenna, magnetic
loop antenna or small transmitting loop antenna, on Google.  Write me off
list if you have any interest.

Dave WA6YSO


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