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
