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

Build an OCF

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