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CLUB 4:1 BALUN

4:1 CLUB BALUN


After meeting with Richard vk3txd, Richard, presented a new lightweight 100 Watt 4:1 Balun for use with a Off Center Fed Antenna.



The club will be selling (Taking orders) for these trick light weight 4:1 Baluns.


Club Member Price

$65.00 (Payable to the club)


ORDERING

If you are keen on the new 4:1 Balun for the OCF. Please email the club vk3frcweb@gmail.com

Once an order is taken, your OCF will be built with you callsign on the orange faceplate.

Delivery time around 3 weeks. (Subject to parts supply)


PAYMENT

You can either pay at the club rooms or direct deposit via our bank details.

 NAB, Frankston 

BSB: 083-253 Acct No: 03-683-3688 


When making payment, please make note that is for the Famparc 4:1 Balun.



FACEPLATE

With your Callsign Printed on the Orange Label. (Below)



FROM RICHARD VK3TXD


This efficient 4:1 balun handles 100W SSB with ease. It is a 2 core Guanella (current) 4:1 balun ideal for OCF antennas.


Soon after I was licensed I settled on the OCF antenna. I built and tested my own 4:1 baluns and used them for years. The box I used was less than great though.


Recently at the electronics store I found a much more suitable box then decided to try to fit the balun into it. It has flanges that can be use to suspend it, and has a sealing gasket (I would silastic 3 sides of the box if mounting outside permanently though). I left it outside for 2 weeks, it certainly got some rain and on inspection it was dry inside.


After much effort designing and 3D printing a sled to mount to cores onto, I found it made a really nice balun.


VNA tests indicate it has around 0.1dB of loss from 160m to 10m into a matched (200 ohm) load.


SWR tests with a 200 ohm resistor show it is 1:1 for most of HF, rising slightly at 10m to around 1.2:1, which is pretty good.


There are also “balance” tests which shows if it is suitable for use on an OCF (not all baluns pass this test). See this website https://owenduffy.net/blog/?p=17389 – and it passed these with ease.


Building The OCF Antenna


I decided to cut an 80m antenna as I wanted to do the 80m Thursday night quiz at the high end of 80m.


Being an OCF, the 2 arms are of different length. There are many many options – I stuck with the old 1/3 and 2/3 lengths. If you want a 40/20 version then just divide the above lengths by 2.


So I used one arm 27m long, the other 13.5m long. This needs pruning, (I’ve not got around to doing that) it is too long being resonant around 3.5mHz rather than a little higher up where I wanted it. The SWR where it is resonant is excellent.


I mounted it on a 7m high squid pole (so not very high at all) and near my house which may well have been interacting with the antenna.

My MFJ-269 analyzer showed;

Freq

VSWR

R

|X|

3.5mHz

1.1:1

49

4

7.0mHz

1.0:1

48

2

14.1mHz

1.1:1

43

5

17.3mHz

1.0:1

49

1

24.9mHz

1.1:1

50

1

28.5mHz

1.2:1

45

1

I was concerned this was too good thinking there was a lot of loss making the SWR better. So I repeated the VNA loss tests, nope, the loss really is very low.


On air it worked very well. I put 100W into it, without a tuner, using my FT897D and it was happy. Like I said, it needs some pruning to bring it closer to mid-band. For another day!


BUILDING A OCF

Our clubs website has a page dedicated to the Off Centre Antenna (OCF) Click Here



Comments:

I have been using OCF antennas for many years, and also use a 80M OCF antenna at home for many years.. For those that are not sure about the OCF, one main advantage is it's ability to use it as a Multi Band Antenna.. for example a 80M OCF will work on 80M, 40, 20, 15, 10.


Very versatile.


Cheers.


Craig

vk3ncr



90 views8 comments

8 Comments


Unknown member
2 days ago

Could someone recommend a suitable ferrite* and source please? *(Having just read this https://palomar-engineers.com/wp-content/uploads/Choosing-a-Feedline-Choke-RFI-Tip-Sheet-RC-1-by-AK6R.pdf)

Am I correct in thinking that RG58 was used in the article illustration?

Thanks 🤓

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Unknown member
a day ago
Replying to

Many thanks Richard

73🤓

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Unknown member
Apr 17

After using these for years, the way the antenna is mounted, height, what is around it makes a substantial difference.

I was seriously concerned the SWR was too good on my first trial - hence I tested the balun again. I can only put it down to the house being fairly close etc.

Years ago. I remember my old 80m OCF had a large walnut tree underneath it. Over the years it got taller and taller - then I found it was strangely usable on 160m! I had a 10W SSB contact with Luke in country Vic (from Dandenong Ranges). There was probably a huge amount of loss on other bands tho.

Prior to the tree growing it was terrible…

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Unknown member
Apr 17

Would this be available to non club membrrs?

John VK5KJG

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Unknown member
Apr 17
Replying to

Hi John,

Yes mate.. I would say the freight would be say $20.00


Craig.


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Unknown member
Apr 17

What a great article by Owen Duffy. A4:1 balun built to his specs should give perfect Results


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Unknown member
Apr 17
Replying to

Yep.. agree Peter


Craig


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