Help pls: 20m delta loop

[G7IVJ]

Gents, thanks for any help in advance

I am just about to make a 20mtr delta loop using 72foot wire, 4.1 balun, fed by coax.

I am going to use this antenna for DX and install as a three sided triangle (pyramid) with the apex at the top as that avoids having to use fibreglass poles to support the side legs if set up as inverted triangle. I am going to use a 40foot telescopic mast to support the top apex and tie the two bottom corners 12 foot off the ground, so the bottom horizontal section will be about 12 feet from the ground and obviously each section will be 24 foot long.

A couple of questions:

1) is it better to install as an inverted triangle for DX ?

2) where is the best point in the triangle to locate the balun as I am aware this quite drastically changes the antenna ?

Thanks for your help

73s Simon

[WB2WIK]

This article is pretty good:

http://w5sdc.net/delta_loop_for_hf.htm

I wouldn't use a 4:1 balun, as that's the same compromise electrically as using "no" balun at all.

The Z of a full-wave loop like this is about 100 Ohms. I match them just using a 1/4-wave section of 75 Ohm coax spliced between the feedpoint and the 50 Ohm transmission line to the station: Much less of a compromise, results in nearly a perfect match.

[VE3FMC]

Feed it in the corner for vertical polarization. Which makes it better for DX'ing.

Visit this website to see what I am describing above.

You can get away without the 4:1 balun if you make a 1/4 wave 75 ohm matching stub to put at the feed point. Then join that to your 52 ohm coax. When corner feeding or feeding it part way up the one leg this makes it easier dealing with the feed line as there is no balun hanging there.

Again, visit this website for the matching stub info.

Good luck, delta loops are quiet antennas and work great. I have had them up at low heights for 40, 30, 20, 17 meters in the vertical position. I also had a full wave 75 M horizontal loop up when I first got on the air. The highest point of that loop was at 28 feet. The lowest was around 10 feet. Not the best for working DX of course. I did manage to get WAS with 100 watts and also worked some DX, including VK land with that loop. It was not perfectly square as that was impossible to do on my city lot. But it worked, and if anyone was within 300-400 miles from me I was usually 30 over 9 with 100 watts

[KE7IHG]

I have an 242' rectangular loop feed with 450ohm ladder line and a 4:1 balun I made.http://rogertango.com/articleread.as...umber=34232411
it's not real high up but it works and it tunes all the bands. I've tried to run this without a balun and was unhappy with the results. I'm no expert but its quiet and it works!

[W5DXP]

A couple of questions:

Just to be clear, is this a single-band loop for 20m only?

1) is it better to install as an inverted triangle for DX ?

A delta loop with an apex at the highest point - fed in the middle of the low horizontal wire is a compromise, i.e. not the best configuration, but it works.

2) where is the best point in the triangle to locate the balun as I am aware this quite drastically changes the antenna ?

It will have a resonant feedpoint impedance of ~100 ohms with an SWR of ~2:1. A 4:1 balun will result in a feedpoint impedance of ~25 ohms and an SWR of ~2:1, i.e. no improvement. As previously suggested, use 1/4WL of 75 ohm coax for a better match to 50 ohms. SQRT(50*100) = 71 ohms.

Here's another matching idea that I have used on a single-band 1WL resonant loop. Feed the loop with 50 ohm coax. Install a parallel -j100 capacitor (112 pf at 14.2 MHz) at the feedpoint to change the feedpoint impedance from 100 ohms to 50-j50 ohms. This makes the loop a little too short electrically. Increase the length of the loop for minimum 50 ohm SWR (very close to 1:1) at the target frequency - enjoy. (This idea locates an almost lossless matching network at the antenna feedpoint.)

I've tried to run this without a balun and was unhappy with the results. I'm no expert but its quiet and it works!

The ladder-line transforms the feedpoint impedance to a different value because the SWR on the ladder-line is about 4:1. If the new transformed impedance is compatible with a 4:1 balun, it will work well.

[K8JD]

Just to be clear, is this a single-band loop for 20m only?
A delta loop with an apex at the highest point - fed in the middle of the low horizontal wire is a compromise, i.e. not the best configuration, but it works.
As previously suggested, use 1/4WL of 75 ohm coax for a better match to 50 ohms. SQRT(50*100) = 71 ohms.
will work well.

I have flat loops for both 40 and 30M and using them for short skip work at 1/4 wavelength above the ground.
In this configuration they can be fed at any point in the circumference. Using the 1/4 wave matching line of 75 ohm TV Cable drop coax works very well and has less than 1.5:1 SWR across the band.
My summer project will be a single Delta loop for 17M.
A convenient way to mount it in a tree has the point of the triangle at the bottom and this will be my feedpoint. Again using the quarter wave matching 75 ohm coax method and it should be a fair antenna for DX, bidirectional, aimed at Europe and the S. Pacific.
What You are doing on 20 m should have similar results.