Comments on: Use a loop if you can

By: N4RP

N4RP — Sun, 22 Aug 2010 00:51:31 +0000

My feed line consists of about 20′ RG-8X to get me up into the attic, into a 4:1 current balun, then about 75′ 450 window line to the loop. It’ll load up fine w/o a tuner on most of 160, about 200kHz of 80, all of 60, most of 40, 20 & 15… Autotuners in the shack have never had a problem tuning it up on any band. I’m going to put an autotuner in the attic this fall, right at the 4:1 balun, so there’s never a high SWR on the 8X, we’ll see how that works out.

73, N4RP

By: kx4o

kx4o — Thu, 19 Aug 2010 04:25:59 +0000

If the feed line is actually “feed line” rather than two VERY widely spaced wires, you can’t really count it as part of the loop.

The parallel wires are not radiating parts of the loop to be sure, but are certainly part of the tuned feeder resonance length complete with standing waves.

To Elwood, my 543′ loop is less than 5ohms DCR, wire loss is pretty much a non-issue

Skin effect makes this more of an issue quick as frequency rises.

I operate my loop QRP 5W, phone and digital. My loop is only about 35′ high, and I’ve managed to exceed 1000mi/watt on 7 bands, during a solar minimum.

That’s awesome and speaks well of antennas with large effective apertures like this loop. It speaks well of your operating skills too.

I’d agree with go for the 525′ one, but don’t count the feed line as part of the length…

The thing to avoid is the presentation of a high impedance to the tuner at the end of the parallel line… no matter how good it is. We select a loop size plus feed-line length that presents the transmatch with something other than a spot on voltage maximum for each band we desire. In the case above, the parallel feed-line length is pretty much set leaving only the loop length to adjust.

I agree the 525′ loop is the target circumference, but the feed-line presents this feed-point impedance to the shack at a different impedance.

Of course, if we place an automatic transmatch at the loop’s feed-point our worries are less.

How long is your feed-line?

By: N4RP

N4RP — Thu, 19 Aug 2010 01:51:03 +0000

If the feed line is actually “feed line” rather than two VERY widely spaced wires, you can’t really count it as part of the loop…

To Elwood, my 543′ loop is less than 5ohms DCR, wire loss is pretty much a non-issue….

I operate my loop QRP 5W, phone and digital. My loop is only about 35′ high, and I’ve managed to exceed 1000mi/watt on 7 bands, during a solar minimum…

I’d agree with go for the 525′ one, but don’t count the feed line as part of the length. Also, if you’re planning to operate the loop on the harmonics, make it a little longer, remember 14.200/8 is only 1.775…

By: ecdowney

ecdowney — Sun, 21 Feb 2010 00:03:41 +0000

I would say just go with the 525 ft version. Longer will have more wire loss and the pattern will get even more complex as you go up in frequency.

If local noise is a problem you have the room to consider a Beverage antenna for receive. If you’re not familiar with them start here: http://en.wikipedia.org/wiki/Beverage_antenna .

Or, if you have access to QEX, there was a very interesting article about electronically steering an array of 160m verticals with a set of SDRs in the Nov/Dec 2009 issue.

73, Elwood, WB0OEW