Discussion in 'QRP Corner' started by KA9UCN, Dec 20, 2015.
The Anti-DX Loop Antenna
I have been using fullwave loops for 40M for decades.
Back in the days when Radio Moscow, the BBC, RFE, VOA, DW and others were blasting cold war propaganda back and forth across the Atlantic, right on 40M , My Idea was a high angle antenna to reject long skip from Europe and enhance closer in signals from Novices in North America. .
A fullwave, flat, loop up about a quarterwave above ground was the perfect answer.
I found a Square shape easiest to get up on my city lot and I used a quarter wave matching line segment made of 75 ohm coax and RG8 the rest of the way to the radio room. The SWR was less than 1.5:1 across the 40M band.
If you make the loop for 20m and the other DX bands nested in it, place it perpendicular to the ground and add a slightly smaller Square director element in front you have the CLASSIC cubical quad antenna. A GREAT DX antenna !
Works great right up to the time a jogger trips over one end of your stakes...
cool website... I do a lot of UL backpacking and similar things.
As for the loop antennas, I've tried them but I'm 100% PORTABLE and I found that the amount of wire wasn't worth the weight for me. I tend to use EF wire antennas with my qrp and field rigs with good results. I'll often use a homebrew matchbox/ band pass filter hooked directly to the rig with my wire as vertical as possible and usually with a somewhat horizontal ( inverted L type) leg at the top. I like loops, theyre a good bit more quiet, but they're a pain for my type of ops. I work a good bit of dx on 30m with an EFHW in an inverted L configuration. My bandpass matchbox helps quiet the noise significantly. I use band specific matchboxes or an elecraft t1 tuner with my wire. I have a weekly sked with a friend of mine in Italy and another in south america while running 12 watts maximum, but often less. We rarely have issues.
This is a neat topic. If I had enough land, I'd put up a permanent loop for sure.
I just got installed a loop, ~280' around, ~70' square. It is about 35' in the air, and is matched by a Icom AH-4 mounted at the feed point.
It has been up since the first of the year, and I am delighted to find I am getting good matches 160-6M. I've made quite a few contacts, but haven't spent much time on the air, repairing rigs, rearranging etc., weather issues, other cares. I'll say this, it seems to hear a lot better than the rotating dipole it replaced.
I tried an 80M loop at my previous city QTH. I could only get it up about 25 ft and it failed miserably. the QW height for a flat loop on 80 would be 65 ft and I just could not do that.
The lower loop proved to be about as good for short haul QSOs as a normal halfwave dipole, while using twice as much wire. !
I had a done horizontal back in the 90's for 40m. I was feeding with a 4:1 balun and had good success overall. But i then moved it into a slanting or sloper delta loop.