Friday, February 8, 2013

W3DZZ Trap Service and 5MHZ Dipole

Since I’ve serviced the G3TPW Cobweb and completed the G3TXQ, I decided I might as well check the traps on the W3DZZ antenna and re-tune if necessary. Also I’ve successfully applied for the 5Mhz so I need to make up an antenna for that band. 

The W3DZZ has been up for a number of years and is a really good antenna for 40 and 80 meters. The 40m was originally set for the CW portion of the band and 80m set to 3.700MHz for some listening and the odd rag chew. 

The antenna was made from instructions I found off the web, a piece written by GM0ONX. I was that impressed I actually contacted him to say what a great antenna it was and how easy to build. He very kindly replied and informed me that it was literally built in a day and by chance he managed to get it published in Practical Wireless!

My particular W3DZZ uses the coax traps which were very easy to build and seem to work really well. GM0ONX's design is very easy to follow and simple to construct and if you're starting out this is an excellent way to get in to trap antennas.

You will require an antenna analyzer to tune up the traps

Recently I've noticed that the SWR has been reading quite high and I've been repeatedly having to tune up. So it was definitely time for a service; I removed both traps and did a quick check with the MFJ 259, the SWR was showing 1:1 at around 6.800MHz and it also looked like the coax on the tubing had slipped slightly and just needed some re-adjusting. 

It was just a matter of removing the electrical tape and adjusting the coax, then gently trimming the 40 meter portion until I got a good reading of 1:1 at 7.0030MHz, I also lengthened the 80 meter portion by 6" each end to drop the peak to around the CW part of the band. Once both bands were set with the correct trim it was just a case of re-taping the coax traps up and making sure everything was waterproof.

 Multi coloured trap (adds a bit of colour to the garden)!

Now SWR readings are good at 1:0 for 7.030 and 1:1 for 3.0550, it's funny how once all connected back up you'd swear the receive signals sound much better!

The 60 meters antenna will be an inverted Vee and I’m using the 1:1 ugly balun I made some weeks ago, (see previous posts), I’ve roughly trimmed it up and once I have it raised up in the silver birch at the end of the garden will do the final trim with the MFJ 259b.

The 5MHZ dipole complete with 1:1 ugly balun ready to be mounted in the silver birch tree, the red tag reminds me which is the positive end!

Having the MFJ 259b for measuring my home brew antennas does make building a lot easier. Another accessory you can buy (for some stupid sum of money) is the loop coupler for measuring traps and coils, my Brother in law has one which I borrowed when I first built the W3DZZ. 

 However, as he was away this week I realised I’d be stuck for doing the trap measuring. There was no way I was going to buy one , so I decided to have ago at making it, after all it couldn't be too difficult.

 Thankfully I had a 100 watt soldering gun and all it took was some reasonably thick copper wire and a male to male 259 connector and a simple case of soldering one end of the wire to the centre pin and the other to the outside ring. I've probably made the ring a bit too big, but hey the traps fitted fine for testing so it works and cost me nothing!

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