Stan,
Right on. The idea of using a 40 meter length allows the operation
as described in the books as a "classical" multiband antenna. Few hams
have enough space for the 80 meter version.
Don't discount using an attic that has HVAC equipment in it. The
installation I described had HVAC and some power distribution in the
attic. The attic was a standup attic meaning we could run the antenna
wires a semi-reasonable distance from all of it. But you are correct
this is not the best. Unless you have a metal roof, I can't think of any
roofing material that will give you a problem, fiberglass and asphalt
shouldn't. It's only been in very recent years that home owners have
gotten the idea of using aluminum foil as a heat reflecting material in
the attic; most fiberglass batts use a paper backing.
I agree height does make a difference. It would be better to place
your attic antenna in a second floor attic vice a rancher's first floor
attic. But, loops around the roof periphery seem to work also. That was
used by another friend who decided to get his ticket a few years after
he moved into the community that wouldn't allow antennas. His attic just
was too difficult to get into and his rancher was ell shaped. The loop
was the only alternative. I would never have guess that it would work as
well as it did, but it did. Was it the best antenna around? No it
wasn't, but it got him on the air effectively enough so that he was
reasonably content.
I guess the best advice is find an old community with no antenna
restrictions. If that is not possible, pick your house carefully.
73,
Barry
K3NDM
On 8/13/2013 7:54 AM, stan levandowski wrote:
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, k3...@comcast.net 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: elecraft@mailman.qth.net 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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