[ADXA] ADXA Meeting and 3L40

Mon Sep 23 11:24:25 EDT 2024

Very pleased you could make the meeting, Stan.

Interesting design. The model looks good. Could you please send me additional info?

73 Joel W5ZN

From: adxa-bounces at mailman.qth.net <adxa-bounces at mailman.qth.net> On Behalf Of Stan Stockton
Sent: Sunday, September 22, 2024 11:31 PM
To: ADXA <adxa at mailman.qth.net>
Subject: [ADXA] ADXA Meeting and 3L40

Big thank you to Joel and Kim for hosting the meeting.  It was the first one I have attended and it was great  It was fun to see the faces behind all the emails. 

You can stop here if you don’t have interest in 40m antennas.

I sent this to someone and thought I would include a copy here.  Doing what I enjoy most, I was playing around with a 3L Yagi and wanted to get rid of that crazy long cross piece like used on a Moxon (You can make a 2L that is equal to or better than a W6NL Moxon with this arrangement).  Anyway, this is what I get on a 39 foot boom with short elements - about 50 feet that do not have to be as robust to survive as well as Moxon elements.  The loading from the short cross pieces (about half the length of the ones on a W6NL style Moxon) is #14 stranded wire. Compare this to a 4L OWA on a 46 foot boom and 350 pounds sold by JK for about $6,500.  It is 8.26 dBi (.59 dB more than 7.67 dBi which only varies .08 dB from 7.0 to 7.25), SWR curve is better of course, and peak F/R, which he shows at some frequency, is the same.  This has the F/B and F/R where you want it. If you were not a CW operator it could easily be optimized to have a good SWR curve from 7.075 to 7.275.  It would require a Balun Designs Model 1232 or equivalent (25-50 ohm unit) and a choke as it is designed for 25 ohm feed. The 2L version is 50 ohm feed. This 3L is on a short boom for a 3L Yagi and would require a boom many feet longer to design it for 50 ohms but would also have more gain. The elements in the model are way overkill as I started with the taper schedule Kevin had made for a W6NL type Moxon which started with 2 inches in the center.  I believe this type of element design will allow him to not have to truss the elements.  

It would be extremely easy to make a rotatable dipole without loading coils or other methods of loading and a flat rotatable dipole is a pretty good antenna on 40m with significant front to side. It’s about an S unit down from this antenna.  A dipole should be mounted in line with the boom of a multi-band Yagi but could go just above it by a couple feet with no interaction.  If you have a good scrap pile of aluminum tubing you could make a rotatable dipole for next to nothing.

7.000

21.39

-8.73

1.500

7.67

180

12.21

12.21

7.075

24.44

-2.04

1.089

7.60

180

18.50

18.50

7.150

24.76

4.05

1.177

7.55

180

28.92

26.52

7.225

22.80

11.08

1.598

7.59

180

23.33

23.33

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