UA9TC "RS" Yagis

[ZL1RS]

Earlier this week a "new" batch of Yagis from Russian designer Boris UA9TC appeared in the latest 144MHz VE7BQH G/T chart ... http://www.vhfdx.info/VE7BQH.html ... look for the UA9TC 11RS, UA9TC 12RS, and UA9TC 14RS entries.

They exhibit good gain, Ta and G/T figures when compared to other offerings of the same boom length (especially the 12 element version) ... and do it with a 50 ohm feed point ... and with very wide SWR and gain bandwidths! This combination (and the RS suffix!) piqued my interest, but a Google search did not bring much joy (despite, as it turns out, that the idea for these Yagis was developed more than 2 years ago).

Coincidentally, yesterday Vladimir UR5EAZ sent me an e-mail pointing to the Russian "VHFDX - Forums" web site and a link to download the pertinent antenna analysis program files:
http://www.vhfdx.ru/faylyi/view-details ... /ant-ua9tc
(click on the USA/UK flag symbol to translate to English)

Opening the .nec antenna files with 4nec2 displayed an exceptionally clean radiation pattern which is clearly the reason for the good characteristics shown in the VE7BQH G/T Chart and should mean good receive performance in our increasingly RF polluted urban environments:

UA9TC 11RS plot

Further examination of the geometry in the files showed the "secret" of the performance was the effect of a U-shaped reflector element.

UA9TC RS geometry

ua9tcREF.GIF (3.39 KiB) Viewed 2186 times

This u-shaped reflector theme is carried into the antenna name ... e.g. UA9TC 11RS where RS = Reflector Staple (or Staple Reflector in English grammar). No, nothing to do with my callsign suffix!

The shortest of these Yagis (the UA9TC 11RS as shown above) has a boom length of 6.2 meters which is fairly easily handled. The 50 ohm driven element feed point impedance can be conveniently fed with a split dipole and "ferrite" balun or sleeve balun, or made as a folded dipole to step the feed impedance up to 200 ohms for use with a 4:1 halfwave coax balun to reduce static pick up (which is probably as good a reason as any to go with the folded dipole driven element on any Yagi?)

There is some discussion about Boris' designs at:
http://translate.google.co.nz/translate ... 6prmd%3Div
... including his latest release today of a 17 element monster on a 11.4 meter long boom.

Perhaps these Yagis are worthy of consideration for your next antenna project?

73, Bob ZL1RS

[YU7WL]

Here is one of UA9TC antenna: 14RS, near 9m boom length.

[VK2ZRH]

Intriguing results.

What is it with this notion about using a folded dipole to "reduce static" ? That will change the antenna pattern. You'd have to run the whole simulation again.

What would be wrong with a centre-tapped RF choke across the feedpoint, centre to ground ?

Posted in the interests of: "Ask a silly question".

73, Roger Harrison VK2ZRH

[YU7WL]

Hi,

first I made folded dipole but result was rather poor with a high SWR. Length of folded dipole was calculated 2X open dipole -10mm, but it doesn't work. So i decided to use open dipole.

Current choke missing and will be added latter.

Before this, I made UA9TC 10RS antenna with folded dipole and it works decent.

73 de Voja/YU7WL

[ZL1RS]

PART 1:

... What is it with this notion about using a folded dipole to "reduce static" ?

... probably me getting trapped in another of the multitude of ham radio's "old wife's tales" ???

Having time on my hands since "retiring" I've been doing some practical trials that have shown what a load of cr@p us hams feed each other as being the gospel truth

Some examples:
Loop fed Yagis reduce rain static ... no, the same 20-30/9 rain static on a loop fed Yagi as I had previously on a split dipole fed Yagi. (As well as the closed loop providing a DC short across the feed line, the loop's center point opposite the feed point was connected to the boom with a bolt so there was a DC path to "ground").

Note to self: must try a "centre-tapped RF choke across the feedpoint, centre to ground". I suspect the result will be the same, in that the "static" heard in the radio is at RF and so the RF choke will not eliminate it ... or maybe "rain static" and other "static" are two different animals? (My silly question for the day).

A certain "hybrid balun" works .... no, measurements of common mode current on a feedline here with or without a hybrid balun on a test Yagi here were more or less exactly the same. One clip-on ferrite over the coax feed line near the feed point did a better job ... and 4 did a very adequate job as a current balun (if the job of a balun is to balance a dipole's currents and reduce common mode current on the feed line?)

Stainless steel is lossy at RF and makes a poor HF antenna wire ... no, not according to simulations. Maybe 0.5 to 1dB down on copper, but not what I'd call "poor" (unless one uses poor "stainless steel", but that is not really stainless steel anymore). I'm about to do A/B comparisons between two HF antennas, one made of copper wire and one made of SS wire, but I am almost certain that normal HF QSB will make definitive results difficult to determine.

.... so, I'll take the "using a folded dipole to "reduce static"" comment back until someone (maybe even me) has physically proven it is correct (or not). If my observations with a loop fed antenna are anything to go by, the comment was in all probability a load of bovine excretion.

PART 2:

... That will change the antenna pattern. You'd have to run the whole simulation again.

Silly question number 2 for the day ... yes, but is that to do with my (ill conceived?) comment about "reducing static"? ... or something else ? (e.g. a folded dipole altering the clean pattern of the RS series Yagis).

(Not "picking holes" or "getting at you" Roger, it is a genuine question)

73

[VK2ZRH]

Hi Bob,

Thanks for outlining the folded-dipole & static palaver

Re: silly question number 2 . . . not connected to the reducing static claim (which you have effectively scuppered). I understand that, if you take a Yagi design that has a split dipole and then substitute a folded dipole, you'd need to run the antenna simulation again because the new "object" is quite different to that it replaced.

I'd like to see some shorter-boom RS Yagi designs for 2m (eg. 3m or 4m boom). And what of 6m designs ?

73, Roger Harrison VK2ZRH