[Elecraft] Loop antenna's

Tue Aug 13 07:54:48 EDT 2013

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, k3ndm at 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 at 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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