I have a nonresonant-in-any-ham-band 44' doublet in my attic peak at 31'
above ground. Only 26' is actually "flat top" while the rest droops
down at the ends. I have 16' of 450 ohm ladder line coming through a
slit in the ceiling just above a linen closet. In that linen closet, on
a shelf right below the ceiling is an SG237 auto coupler. From that
point onward to my "shack", the coax feed line is nice and clean and
length no longer matters.
I've had this antenna up there for four years now and have yet to find a
more effective solution for my antenna restricted QTH. I've
experimented with other attic solutions, including various full, random
and partial wave loops. Outside, I've experimented with "temporary" end
fed wires in different configurations, random "stealth" wires, and
vertical antennas. They've all worked but so far nothing has
consistently outperformed my attic doublet, day in and day out, for
effortless frequency agility between 40 meters and 6 meters, inclusive
of all bands. It loads on 80 meters also, well enough to provide me
with some winter time entertainment. Without "bragging", this doublet
has earned me QRP WAC, WAS, and a QSL album with a host of impressive
QSO not only with KW stations and large antennas but with some very
modest stations using simple wire antennas in some remote locations
around the world.
"Attic success" requires, in my opinion and experience, two conditions:
1) an "RF Friendly" attic and 2) Enough height. An "RF Friendly" attic
includes no metal foil building insulation and shingles that do not
absorb RF, no HVAC, and "luck". "Enough height" suggests that a two
story (or higher) attic trumps a low ranch style home. The antenna is
looking for height above ground, not height above the attic floor!
There is much talk of distorted patterns, RF absorption, and other
consequences. At HF frequencies, there is very little RF absorption in
wood. And who cares about pattern distortion as long as the antenna
works well ;)
With 53 years of ham radio behind me, I've yet to find any simple
wire antenna --overall-- that beats a resonant dipole for single band
work or a parallel line fed doublet and a coupler for frequency agility.
P.S. - the autocoupler is in the closet below the attic to keep it out
of the intense summer heat and winter cold. Attics are not the greatest
environment for electronic equipment.
My two cents,
Stan WB2LQF
On Mon, Aug 12, 2013 at 10:54 PM, [email protected] wrote:
> Let me throw some stuff out. Electrically small loops can work out
very well if they are constructed correctly. I was impressed with the
Alexloop that one of our Field Day operators brought to the site. It was
used for an unrelated station on site that the operator was using to
demo his new KX3 using PSK-31 on 20 meters. He had the loop because he
wanted a portable antenna that might work. The Alex fit his needs
nicely. However, there are much more effective antennas that can be used
in a fixed location.
One of those antennas is a 1/2 wave dipole up in an attic, fed with
open wire to a point below the ceiling where there is a transition to
coax using a balun and a tuner. The 1/2 wave length is dependent on
room available in the attic, and it doesn't need to be in a totally
straight line. The antenna can have some bend at the end. The antenna
tuner will work out the impedance issues. I put one of these up for a
friend who has a two story house with a very high pitched roof and
enough room to install 66' of wire. He has been happy working 40-10
meters. My friend lives in an antenna restricted development just as
the initiator of this thread.
And lastly, A loop antenna made of wire the traces the outside roof
periphery using insulated wire colored to match the roofing will also
work well. It can be fed just like a loop sky wire ( shown in ARRL
pubs). Your neighbors won't see it and it can work out pretty well. I
would get too anal about total wire length as open wire is pretty low
loss stuff, even at very high SWR, and a balun and tuner will take
care of the issue with coax. Just make sure that the tuner is as close
to the open wire as possible.
Antennas are fun. Every ham has his own idea about what is best. I
make no claim as to how close to best these are, but they do work.
Best of luck.
73, Barry K3NDM
----- Original Message -----
From: "Bill Ross" To: [email protected] Sent: Monday, August
12, 2013 3:50:17 PM Subject: [Elecraft] Loop antenna's
I read the two posts about the MFJ loop antenna and thought I would
add my own personal comments on my experience’s with loops.
Years ago, I bought a MFJ 36” loop with the remote tuner and while it
worked from indoors from 30m to 10m, it wasn’t earth shaking. I was
always the weakest signal in a round table. That was when MFJ was
still recommending using the loop in a horizontal position rather than
vertical as they do now.
Now, I had been reading some reviews on the MFJ loop antenna tuners
and decided to get one and try it out. I got the MFJ-935B tuner that
comes complete with the tuning cap and matching cap plus a RF current
meter for tuning, so all you need to add is a loop to make it work.
3’ dia. loops are fine for the higher HF bands, and if you are going
portable with it, then it might be the right antenna for you, but if
you are living in a antenna restricted home as I am, and have to use
indoor antennas let me tell you that I have used many different
configurations of antennas and find that the loop is working the best
for me, so far. I have used a Super Antenna MP-1 coil loaded vertical
like a mobile whip, I have used homebrew Buddipole, and various indoor
doublets so I have some data to compare them to. I use the Reverse
Beacon Net for getting accurate reports back on my signal with the
various antennas.
As I said above, the 3’ dia. loop is fine for the higher bands, and OK
for 20m and 30m but if you want to really get out as good as you can,
then the homebrew loop that is bigger, is the way to go. MFJ says that
a 7 foot wire or copper tube will make a loop to go with their series
of loop tuners that will cover 20m, 17m and 15, and it does, but, if
you want to maximize your signal on 20m the way to go is to use a 13
ft. wire or tube which doesn’t make that big of a loop and gets out a
lot better on 20m.. My 7 ft. loop got a 12 dB SNR from K7EG RBN and
the 13 ft. loop got a 18 dB SNR from him just a few minutes later and
at the same power input from my K3.
On 40m MFJ says a 20 ft. wire will tune 40m and 30m and it does, but a
28 ft. wire will give you maximum output (for a mag loop) and it does.
I think I got about 8-10 dB more out of the 28 ft. loop than the 20
ft. one on 40m. MFJ says you can hang these larger loops form a
curtain rod or draped over a bookcase and that’s what I do, it’s not
critical but you do have to be very careful and not touch the loop
when transmitting as there is a lot of RF in that loop. I made two PVC
standards that sit on top of my bookcase/desk where I operate from and
have the 28 ft. wire forming a square shape hanging from the top of
the standards, coming down to a shelf just about eye level and I have
the tuner there so I can adjust it as needed. With this loop and the
K3 at 5 watts I contact my buddy Dale, K6PJV up in Sacramento just
about anytime I want to, just fine from Marina Del Rey, CA and
remember this loop is indoors on the second floor of my home. That’s
almost 400 miles.
On 20m with the 13 ft. wire in a diamond shape on a cross piece made
out of PVC that sits on the tuner, I work AL7V up in Juneau Alaska
with 50-100 watts on a pretty regular basis in the mornings. So if you
are restricted to indoor antennas you might find the loop antenna is
the way to for you.
Usual disclaimer, I don’t work for or have any financial attachment to
MFJ, just a happy customer.
73, Bill k6mgo
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