Tuesday, March 13, 2018

The W3DZZ 40/80M Service

 Of all the antennas I have in my garden, the one I have always relied upon is the W3DZZ. It's a good design and an excellent antenna that over the years has brought me some good contacts on 40 and 80 meters.
Time has shot by and once again I find myself having to service the old W3DZZ! It was way back in Feb 2013 that I last took it down and did a proper service so I think it’s about time I did do it again.

The first thing to do is to actually get it off the 40ft mast, it’s in an inverted Vee shape so it’s pretty easy to remove off the mast especially now as the leaves are yet to grow back on the various trees in and around the antenna.

Once removed off the mast, I have to disconnect the two 40m traps these are attached by four simple old choc blocks and on un-screwing them, they show their age by literally falling apart in my hands, hmm, time to replace with some new ones!

Then it’s just a simple case of getting the old MFJ 259 out and seeing if the traps are still doing their job, the traps are showing a reading of 6.0881 & 6.0840 a little low as I want them both resonating at approx. 7.1 MHz, so I undo the waterproof tape and reset them by just gentle spacing the coax and taking readings from the MFJ. Eventually I get them both reading 7.1MHz and it just a matter of gently re taping checking as I go that both stay at the correct resonance.
The traps having been re-taped and cleaned are now ready to be put back with the antenna. The actual trap designs are from GM0ONX webpage and is very easy to construct, it's literally 11 turns of RG38 coax round a 40mm waste pipe 100mm in length. If you're starting out on trap building, his website is well worth a visit and he explains in very easy terms how to construct his take on the W3DZZ design. He uses these simple coax traps, so the winds are easy to do and it won't seem too fiddly! I think the original build took me a day or so to complete, so it wasn't long and it really is a great antenna.

Here's my MJF 259 with my homemade loop coupler for measuring the traps, loop couplers in the UK can be serious money!

Before I replace the choc blocks (I had to order some more), I’ll double check all the wire lengths again with the MFJ for SWR and I might lengthen the 80m portion a wee bit so that I’m not just tuned in on CW. Nowadays I’m finding I like to listen in on some local chat on LSB and I would like the ability to join a QSO.

Tuning the W3DZZ should always begin with the 40m working outwards, it's easier that way. Sure enough the maintenance work causes the SWR on 80m to be 1.0 at 3.600 so it has moved, I just needs to be trimmed a bit more, I'd like it around 3.7500. Typically as soon as you adjust 80m and get that right the 40m has moved and is reading a little high at 1.0 on 7.200, so I'll have to add a little more wire to drop the frequency down a bit.

The W3DZZ is mounted on the mast holding the cobweb in an inverted Vee format and one of the wires come towards about where the picture was taken, the other end would finish up hanging near the hustler antenna to the left. Interestingly after messing about with different positions around the garden I always end up mounting in this way

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