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Tech Corner
by Dave Oman VE3HCR from the YRARC Splatter February 1999

A Full Wave Loop for
80 - 10 Metres

Browsing through the local Canadian Tire store a few months ago, I happened across a 250 ft. roll of 14 gauge wire with a price I couldn't resist. when I got home with it, my wife asked the inevitable question, 'what's that for?'. She never really cares what it's for, just wants to know. I quickly replied, 'It was really cheap' and quickly got it out of sight.

Checking out the ARRL Antenna Handbook, I found that this much wire could finally solve a problem I have had for 30 or so years, namely, an antenna that might allow me to work all of the bands my rig, a Yaesu FT101ZD, would actually work on.

The easiest antenna to make and put up seemed to be a full wave loop for 80 metres. In the handbook the specifications for this antenna indicated it would' work on all of the bands above 80 metres also, that is 40 - 30 - 20 –17 - 15 - 12 and 10 metres. This seemed a pretty broad claim for an antenna that was a full wave loop on 80, and reading a lot more about this antenna on the Internet and in articles in QST and CQ, there was a lot of hype on both the pro and con of building something that supposedly work on all the low bands. Deciding to try it anyway, because after all, I did have this great piece of wire, I tied it to a tree at one side of the lot and split it in two. this produced a bonus because the supposed two strand 14 ga. was actually three, as it also had a ground strand, which was not mentioned in the label attached to the spool. Taking the construction instructions right out of the handbook, I stretched the first piece out and carefully measured it to see how much of the 250 ft. that I really had, suspecting that the price meant that some was missing. It turned out that I did have 250 ft. but of course I need 272 ft. Looking at the location that I was going to hang it in, it seemed that it would be a good idea to have the wire that could be seen from the streets ( I'm on a corner) be inconspicuous, so I decided to cut it to 136 ft. and use 1/2 in black and 1/2 in white.

The joint was made by overlapping the ends about 6 inches and spiraling 1/2 of each wire around the other and soldering the mess together. A piece of shrink tubing over the joint made it look nice. Scrounging through the junk piles in the cellar, (that's the big empty space under the first floor used to store stuff found at flea markets and other fine shopping places) I found some old ceramic antenna egg insulators that would just fit the bill.

I knew when I bought them at Atlas Radio in 1946 that they would come in handy. The property is 75 ft. by 100 ft. and has a line of Chinese elms along one side and a couple of good sized maple trees on the other side.

The Chinese elms are about 30 ft. fall and the maples are bigger than that, so I figured I would eventually have enough height to make the antenna work OK. I say eventually because: 1. The antenna should be 40 or more feet off the ground, though some had said that 30 ft. was acceptable. 2. My ladder is only 12 ft. long. Ignoring no.1, and using no.2, the antenna is about 15 ft. up at the corners and 10 -12 ft. in the middle.

I fed the antenna at the corner closest to the shack with some heliax that was laying around doing nothing anyway, and anchored it to the wire with a small square of Plexiglas. The heliax was extended with a short piece of RG58U to make it easy to fit through the Plexiglas and the inner conductor was soldered to one end of the loop and the shield soldered to the other end, both were anchored to the Plexiglas through 1/4 inch holes drilled in the corners of the Plexiglas. This method was declared to be acceptable by several of the sources found, and is easy, I like the easy part.

I have one other antenna here which is an inverted 'V' that I built a year or so ago from a design suggested by Doug VE3CWO. This antenna is constructed from odd bits of coaxial cable, PVC pipe and assorted hardware from your local CT store, and works very well on 80 metres. It is almost flat across the band with an SWR of less than 2:1 so I figured it would make a great comparison standard to compare the performance of the loop on 80 metres at least.

Using the 'V' and logging into ONTARS and requesting signal reports, I have consistently received good replies from all over Southern Ontario, so this antenna and the loop were hooked up to an MFJ antenna tuner which has a switch for several antennae on it. I set up the tuner and marked the position of each of the controls for each antenna so that I could between them in a few seconds and be able to compare the two under the same band conditions metres during the day.

Arranging to be ill on a day that looked to be pretty good for conditions, I logged into ONTARS on the 'V' and requested a signal report, and explained what I was doing. The noise level on the 'S' meter was S7 and the controller,VE3PSV Shawn in Cambridge, was 59.

He and several others, from Ottawa to Windsor, gave me a 5x9 report though the farthest ones I had a bit of trouble reading and I would give them a 3x4. I switched over to the loop and set up the matching unit and called in again. Switching to the loop I was getting an S2 on the noise and Shawn was coming in at an S6 on the meter but on transmit, the loop was down quite a bit from the "V". I was able to hear a mobile that was on the 401 just outside of Windsor that I could not hear on the 'V’ but the loop was barely audible to him and he could not read me.

My next test was to load up on the other bands and see what kind of results I could expect there. 40 loaded OK and worked a couple of stations with good reports. 30 loaded but it took all the matchbox would do and I couldn't find anyone to work, my CW being in the one to two WPM class. 20 metres loaded well and I worked YL2DX and RA3ATX, both countries for the first time. 17 loaded but no contacts. 15 loaded but no contacts. 12 loaded with all it could do but no contacts 10 loaded fine and worked a bunch of Latinos.

I will have to work on my CW a bit, I guess. The large difference in atmospheric noise made more of a change than the received signal strength so signals were easier to read on the loop on 80 metres than on the V though the V' produced higher S meter levels.

I will get the loop up to at least 30 feet in the next while and we will see what it will do then.

 

73 de Dave VE3HCR

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