[30m] Re: 30M Stealth Antenna

[Steve Kallal]

Hi,

Have an MFJ loop model 1786. It tunes from 10 to 30 MHz. Don't confuse it
with the newer models that have a tuner with knobs right at the antenna.
This one is remotely tuned. Right now it is sitting in the garage collecting
dust. I bought a house 3 years ago, but tried it from an apartment balcony.
It did not work very well as I could not get it out in the clear. There was
stucco siding (wire mesh) with 4 feet of the antenna. So I don't know how it
would work in the clear.

I have an itch to put it up at my current location. My HF arsenal is a GAP
Titan DX vertical which is 25 feet long and mounted above my garage. I also
have a delta loop 3/4 wave on 80 meters feed with ladder line. So now I
could do some real comparisons.

In my apartment, I did make one QSO on 30 meters PSK31 with someone camping
out in Arizona. I am guessing he was 400 to 500 miles away and I got a 599
report from him. But that was the only real contact I made. I had more
success with a screwdriver type mobile antenna from the balcony, but was
always plauged my grounding issues.

Now I am tempted to try it out again. I don't expected to rival my other
antennas. But it is a very good receiving antenna which managed to filter
out a lot of computer hash. Even my delta loop is quieter than the vertical
when it comes to computer hash. Often I prefer to transmit on the vertical
and receive on the loop. Open wire feeders really do work when properly
installed and with a TRUE balanced tuner (no baluns on the output side).

The small loops are the only small HF antennas that really appear to work.
But care must be taken to properly keep the losses down. I am considering
one more 160, 80, and 40 because I have the space to try it now.

I might be willing to part with the MFJ-1786, but first want to do a real
evaluation from a normal location.

Jon, do you have your SDR-1000 yet. You emailed me awhile back. I am still
getting the hang of it. It is a real gem. It makes digital operating a
pleasure.

I will check out the times for the net and try to join in.

73,

Steve N6VL

-----Original Message-----
From: 30m-bounces at mailman.qth.net [mailto:30m-bounces at mailman.qth.net] On
Behalf Of David Dorrance
Sent: Wednesday, May 31, 2006 7:24 AM
To: 30m at mailman.qth.net
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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