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" <k6...@verizon.net> 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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
