By Alex Whittaker.

 

 

9:1 baluns are good for listening to HF as they can be lower noise than other baluns. They can also be transmitted through as well should you have the need to. However keep in mind that these baluns favour a longer longwire over a shorter longwire antenna.

 

 

So lets get to and make one then shall we!

 

What you will need:

 

- A plastic box

 

- A red and a green 'post' terminal

 

- 1x SO239 (UHF female) connector

 

- Wire, multi-coloured for less confusion. (telephone wire is good for this)

 

- 1x Ferrite Core (suggested one is a T130-2 Iron Powder core or similar)

 

I got most of my parts from Jaycar, $16.15 for the lot. (apart from the wire)

 

 

Here are the plans I used:

 

 

 

So according to these plans:

1. You will need to wind your wire around the ferrite ring 8 times.

2. Drill 3 holes in your box, one for the UHF connector, one for the red terminal (antenna input) and one for the green terminal (ground), then install the connectors.

3. Connect A red wire to the Antenna input terminal (red).

4.  Join C yellow wire to B red wire.

5. Connect E Green wire to the centre conductor on the UHF connector.

6. Connect D yellow wire to either the E green wire or the centre conducter on the UHF connector.

7. Connect F Green to the chassis of the UHF connector and to the green (earth) terminal..

8. Glue everything down, make sure everything is connected up and then seal the box from the weather.

 

Here is what I ended up with:

 

 

I will Test SWR later to find out how it performs on 27MHz, then I will test its receive performance on HF.

 

 

 

Update - 31/07/09:

 

I have done a little testing with the balun and the results so far:

A 6 metre longwire: SWR 2.5 on AM CB

A 10.5 metre longwire: SWR 1.4 on AM CB

 

The 1.4 is better than my base station vertical so I'll set it up properly soon and do some more in depth receive testing and share my results here.

 

 

 

Update - 01/08/09:

I just put up a new longwire antenna and did some more testing on the balun, the longwire is roughly about 25 metres long and i obtained the following results.

27MHz Marine Band SWR:

Ch: 68: 1.2
Ch: 72: 1.2
Ch: 82: 1.1
Ch: 86: 1
Ch: 88: 1
Ch: 90: 1
Ch: 91: 1
Ch: 94: 1
Ch: 96: 1
Ch: 98: 1

27MHz CB SWR:

Ch: 1: 1.6
Ch: 10: 1.5
Ch: 20: 1.3
Ch: 30: 1.2
Ch: 40: 1.2

I will try SW and AM BCB tonight and report back my findings..

 

 

 

Scanning Tasmania would like to thank Alex for sharing his project with us all, if you have something similar you would like to share then please contact us!