[30m] Re: 30M Stealth Antenna

[David Dorrance]

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