Ten-Element Yagi

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k6sti
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Ten-Element Yagi

Post by k6sti » 06 Feb 2016 19:48

This design uses ten elements on a 2.5 m boom. I optimized quite a few designs with various number of elements and reflectors before I arrived at this particular configuration. It has considerably more gain than either of the five-element designs and it has 30 dB F/R over the entire band. See the curves.

http://ham-radio.com/k6sti/ten.htm
http://ham-radio.com/k6sti/curves.htm

Read this before beginning construction:

http://ham-radio.com/k6sti/notes.htm

Brian

daveB
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Re: Ten-Element Yagi

Post by daveB » 14 Feb 2016 17:34

That is a very interesting development - I'm very tempted. In the UK whilst it is cheaper than 10 mm tube 5 mm rod is 50% more than 3/8inch 16 swg tube over here.

Can you use Perspex /Acrylic as an insulator? as you can get lengths of 12 x 12 mm which could be sawn down to 30 mm lengths and drilled to take the rods and fixing bolts. These could then be bolted to 20 mm x 20 mm ali tube. I can't find any actual 5 mm insulated clamps and I don't fancy how accurately I'd position the element holes in a round tube.

Next question - how in practical terms would you fabricate what is essentially the folded dipole? - I suppose it would be easier to bend 5 mm rod to a tight bend than a 10 mm tube - but it affects the overall length needed.
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

k6sti
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Re: Ten-Element Yagi

Post by k6sti » 07 Jul 2016 03:43

I've just discovered that a horizontal T-matched dipole can mimic the pattern-enhancing qualities of a horizontal folded dipole. I've updated the ten-element Yagi writeup with the new design, which offers slightly higher forward gain:

http://ham-radio.com/k6sti/ten.htm

The T-match permits 75-ohm feed with requiring a 75:300-ohm balun. You do need a series capacitor at the feedpoint.

Brian

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Julian Hardstone
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Re: Ten-Element Yagi

Post by Julian Hardstone » 07 Jul 2016 21:19

Brian - You provided a description of your T-match and feedpoint, and I note that you have the matching sections in the plane of the Yagi.

The T-match is of course a symmetrical feed arrangement, derived from two gamma-match sections.
The Gamma match is inherently unbalanced and provides both matching and balun to feed a dipole, and both types give the additional benefit that the dipole is a single element, unbroken at the centre and therefore mechanically stronger than two ¼-wave rods mounted at their ends on an insulator. The T-match requires a ½-wave phasing line to give unbalanced transformation, but this probably gives a more accurate balance than a Gamma match

It is just by coincidence that I have been looking at the two matching systems as I intend to make simple dipoles for the 6m and 4m amateur bands, the latter serving more importantly for OIRT reception. This dovetails nicely with a project at our local amateur radio society for members to make a simple dipole for 6m. They were debating where to get the tube (Wickes is the answer in the UK) and how to make the insulator. I suggested they would not achieve a satisfactory match with a simple dipole, and also would benefit from a balun and I proposed a Gamma match on a single-tube dipole, so I had prepared a few photos of commercial antennas with the two feed arrangements

Cushcraft use a Tee-match on their VHF antennas: here is the feed arrangement on an elderly 2m Yagi. Note that there is no capacitive tuning
Cushcraft feed.jpg
Cushcraft detail.jpg
Sirio made a dipole and various Yagis for 10/11m using a Gamma match. I intend to copy this for my two dipoles as it is simple and robust. The capacitor to tune out the inductance of the short-circuit transmission line which is the matching section, is here provided by concentric tubes separated by polythene sleeves. This provides a variable and waterproof capacitor which will handle some tx power
Sirio dipole.jpg
Sirio feedpoint.jpg
I have been working on this sporadically for the past week and more, but I hope soon to be making measurements

k6sti
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Re: Ten-Element Yagi

Post by k6sti » 07 Jul 2016 22:11

I called it a T-match because that's what it looks like. But it's primarily a convenient way to place a short radiating conductor where it enhances the pattern. The T-match must be located between the driven element and first director. Other orientations don't work as intended.

Brian

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Julian Hardstone
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Re: Ten-Element Yagi

Post by Julian Hardstone » 07 Jul 2016 23:04

Thanks for the details of the design. So, it's a radiating section more than a matching section.
To feed a simple dipole, split it in the center, attach coax, and add a current balun at the feedpoint.
... and a matching section if you intend to tx with it ;)

I'm glad we are greed on the mechanical benefits of these coupling methods

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pe1etr
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Re: Ten-Element Yagi

Post by pe1etr » 08 Jul 2016 05:43

Is Julian a Civil Seevant? Everything in triplicate.

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