CJU 70cm Antenna Quick and Simple
CJU Antenna ‘The little antenna that thinks it can and does’, it punches way above its weight. If you think I’m impressed, you’re right.
A while ago, I wrote an article about my 70cm FM wood and wire yagi. Very much a thrown together antenna, which I have used for a long time now. Mounted on an old camera tripod, and used on the upstairs balcony. This antenna has allowed me to regularly check into the 70cm ‘Wanderers” net on 438.075Mhz on Monday nights.
The wood and wire yagi has been an outstanding success; however even on 70cm the length is a bit long. This may sound strange, but that's the way things are for me at this QTH. I deploy the antenna and tripod on the balcony via the sliding glass door when needed. As some of you know I’m legally blind, so antenna, tripod, door, coax and me sometimes don’t align. Which although may seem hilarious to any onlookers, can lead to muttering of words that are not generally acceptable.
This is not going to be a full building tutorial; there is plenty of information on the web. Just Goggle ‘CJU antenna’ and you will find all the needed info. I built mine in what I like to call the MacGyver style, you know what have I got and how can it all be put together. Just used the materials I had and methods I'm comfortable with but tried to stay around the ballpark with measurements (within a few mm). I hope you can see everything you need from the photos. Happily mine worked first time good SWR and straight on the air.
Performance is really good, so much so that I now use this for most of my 70 cm work. It’s so small; getting it in and out the sliding door is a breeze. The first night I tested it from ground level, and had no problem working the ‘Wanderers” net on 438.075Mhz. Although I can do this with the other antenna, I felt the CJU held the repeater much better. When used on the balcony at about 10 feet, I get the Sunshine Coast repeater at full strength.
Lets see some photos...
A few notes on the build.
The boom is 20mm PVC pipe, all elements are 2mm aluminum welding wire.
One problem was not having a drill press. The method I used to align the holes in both sides of the PVC tube was to draw a straight line on the PVC pipe by holding a pen flat on the table and passing the pipe along it to get one straight line. Then wrap a piece of paper around the pipe and mark the circumference, divide this will give you the distance from the start line to the other side.
The Coax connectors were made by taking the brass inside of a ‘Choc Block’ and cutting in half with my trusty Junior Hacksaw. The result is two connectors with lock screws that you can solder to.
‘Choc Block’ insides are used to secure the elements in place.
If your wondering how I get things done, I can say I wouldn’t if not for my best mate/wife Shelley who helps me with all sorts of ham radio things.
Some more info about ‘The Wanderers’ net.
Started a little over a year ago, by Glenn VK4FSCC of the Sunshine Coast Amateur Radio Club on 438.075Mhz on Monday nights at 7.30pm AEST. This net has brought some life to 70 cm. Most Monday nights see a good number of stations call in via the repeater or echo link (Some overseas echo link stations as well). A great bunch of people, and it's always nice to know when there will be someone around on the band. 70 cm is a great band and we should support anything that brings more activity to the band. So join in on Monday nights, all are welcome and I’m sure you’ll have some fun. Note: Glenn VK4FSCC really enjoys 70cm and monitors this repeater a lot so say Hi.
The 438.075Mhz repeater, is located at Wilkes Knob, Maleny. About 53KM (28Miles) from me. On the first test night I was working into it no problems, 3.5 watts from my HT with the antenna on a tripod at ground level.
Sooner or later I'll get on 70 cm SSB maybe find a station the north or west of here at a good distance to do some testing, also want to make one of these for 2m SSB. So much to do, so little time.
Easy to build, low cost, small antenna that works. You can have all three.
73 AL (VK4BL)