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 16:1 Balun 
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Post 16:1 Balun
Can anyone point me in the right direction for building a 16:1 balun?

I've built plenty of 1:1, 4:1 and 9:1 but never a 16:1.

I found this but I'm not sure if it's a balun or a unun..

Image

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Matt
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Thu Dec 19, 2013 5:43 pm
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 16:1 Balun 
Silent Key

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Post Re: 16:1 Balun
That's an UnUn, not a BalUn.

I'm not sure what your application is, but the easiest solution could be a 4:1 voltage balun followed by a 4:1 current balun.

Steve G3TXQ


Thu Dec 19, 2013 7:02 pm
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 16:1 Balun 
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Post Re: 16:1 Balun
It's for a T2FD.

I'm experimenting with the design and currently using a 4:1 balun with a 300 Ohm terminating resistor. I want to try a 820 Ohm resistor so I will need a 16:1 balun to feed it with.

How would I arrange the 4:1 baluns?

Coax --> 4:1 current --> 4:1 voltage ->antenna?

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Thu Dec 19, 2013 7:47 pm
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 16:1 Balun 
Silent Key

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Post Re: 16:1 Balun
Yes - that way round!

Steve G3TXQ


Thu Dec 19, 2013 8:04 pm
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 16:1 Balun 
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Post Re: 16:1 Balun
So, what's your reasoning for using 820 Ohm ?

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Paul


Fri Dec 20, 2013 2:39 am
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 16:1 Balun 
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Post Re: 16:1 Balun
I'm experimenting with the design. First off, please no comments about how the T2FD is just a large dummy load (as many would have you believe) as I have a good logbook that says otherwise. Also, I am experimenting with local, short range, UK based communication only so it's not for busting DX pileups although I have worked the states using it.

** The long answer **

The commonly available T2FT from the likes of Icom and Yaesu use a termination resistor, a balun at the feed point and is around 80' long. In the case of the AH-710 from Icom, the termination resistor is made from 3 "rings" of 10 x 3.6K 3W resistors and an unknown (because I haven't measured it) Balun at the feed point. They (Icom) claim that it covers from 1.9MHz to 30MHz with an SWR of < 2:1 @ 1.9-18 MHz and < 2.5:1 @ 18-30 MHz. I have used an AH-710 and it does work as stated. Yes, some of the power is soaked up in the terminating resistor but that's the trade off for having a broad band match without an ATU.

I've always been fascinated with the design and built my own heavy duty version from 2mm SS marine rigging wire. I made a simple Excel spreadsheet where you enter the lowest frequency of operation in MHz and it calculates the required dimensions for several different versions of the T2FD; A "full size" 1/2 wave version, the original 1/3 wave version and a shortened 1/4 wave version. My version follows the original US Navy design (1/3 wave at lowest operating frequency) and has a 300 Ohm, 30W termination resistor and a 4:1 balun. It's designed to operate down to 3.5MHz which makes it 93'9" long with a top range of 5x the lowest frequency which makes it 17.5MHz. I get an SWR of < 1.7: @ 3.5 - 18MHz, < 2.2:1 everywhere else below 3.5MHz and up to 28MHz and I get an SWR of around 2.5:1 at 50MHZ.

** The short answer **

I've been low (300 Ohms) and had interesting results and now I want to go high and compare. I managed to source a 820 Ohm, 180W (continuous) non inductive resistor and thought it would be a good match to a 16:1 balun. I'll swap over the termination resister and balun on my existing T2FD (a 15 minute job) check to see how the SWR characteristics change and spend some time comparing field strength readings and on air performance.

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Fri Dec 20, 2013 6:41 am
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 16:1 Balun 
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Post Re: 16:1 Balun
M0LMK wrote:
First off, please no comments about how the T2FD is just a large dummy load (as many would have you believe) as I have a good logbook that says otherwise.


The initiated realise it's a travelling wave antenna :D


Fri Dec 20, 2013 8:45 am
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 16:1 Balun 
Silent Key

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Post Re: 16:1 Balun
"Travelling Wave" ... is that what the Queen does when riding in her limo ;)

Steve G3TXQ


Fri Dec 20, 2013 11:03 am
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 16:1 Balun 
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Post Re: 16:1 Balun
G3TXQ wrote:
"Travelling Wave" ... is that what the Queen does when riding in her limo ;)

Steve G3TXQ

:D :thumbsup:


Fri Dec 20, 2013 12:54 pm
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 16:1 Balun 
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Post Re: 16:1 Balun
Am I right in saying that a "Ruthroff" is a voltage balun and a "Guanella" is a current balun?

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Fri Dec 20, 2013 1:24 pm
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 16:1 Balun 
Silent Key

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Post Re: 16:1 Balun
Correct!

Steve G3TXQ


Fri Dec 20, 2013 1:35 pm
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 16:1 Balun 
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Post Re: 16:1 Balun
Thanks Steve. :good:

Just out of interest, would a 1:1 current balun followed by a 16:1 unun work too?

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Fri Dec 20, 2013 3:02 pm
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 16:1 Balun 
Silent Key

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Post Re: 16:1 Balun
Yes, it should do. But it gets increasingly difficult to maintain a wide bandwidth with the higher ratio ununs and baluns.

Steve G3TXQ


Fri Dec 20, 2013 3:32 pm
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 16:1 Balun 
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Post Re: 16:1 Balun
Great, I'll give the 2 4:1 baluns a go first. :good:

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Fri Dec 20, 2013 3:35 pm
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 16:1 Balun 
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Post Re: 16:1 Balun
Sorry to butt in, but having enjoyed all of this so far, I wonder if people have read the T2FD designer's original (late 1940s) QST article and his two further articles from the early 1950s?

I have no idea just how well researched it was at the time, but it's a good read. For example, the author states that when using values of terminating resistor other rather than the 600-ohm original design, choice can become quite critical: for example, using a 390-ohm rather than a 300-ohm terminating resistor resulted, for him, in a 'tremendous gain - approximately 30dB' (gulp).

I'm not sure how the antenna became patented by B&W. Some years ago I got hold of an early model (with the frequency range quoted in metres!) of theirs that was made for the USN for 'Arctic use' (no, I don't know why: that's what I was told when I rang B&W - jokes about keeping the terminating resistor in the tent are unwelcome :)
I played around with a 16:1 balun (because their's weighed in at nearly 2kg!) and in the end I found that with the bits I had to hand a simple 16:1 transformer (on a 35mm torroid) and a simple 'choke balun' worked better for me than a 2 X 4:1 un-balun pair or other designs. Their terminating resistor measured 840-ohms.

AFAICS, none of today's commercial T2FDs are to the original design, yet seem to enjoy a far greater performance.

OT. I also played with linear loading on T2FDs to try to get LF ones fit in small gardens, but it all got out of hand with all the bits of plastic pipe everywhere and after a while I left it alone.
However, once you get bitten by the T2FD bug and you read (original article) that it doesn't really matter if you've only got wire-wound resistors...


Fri Dec 20, 2013 7:18 pm
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