I made an interesting discovery regarding this tuner at the weekend. As I am back on the bike, I am packing my MTR3b to keep the weight down. Last year, I swapped out my 20m wire for a 15m wire, so that the antenna would be a half-wave on 30m rather than 40m. I was not originally impressed with 30m, OE6RDD had always complained that the Fuchskreis did not work well on 30m with a 20m wire, where it would be around a 5/8 - 3/4 wave. He recommended rolling up a few metres in the reel to shorten it. For that reason, I kind of gave up on 30m and satisfied myself with 20 and 40m. However, after switching my antennas to make them resonant on 30 (ie. 15m long) rather than 40m, I have never looked back and 30 is now easily my favourite band. The only problem is that the MTR3b is tri-band and I would like to have good performance on all of the bands if possible.
I solved this last year by adding a link for 20m, so that I could shorten the antenna to an exact half-wave on 20m. This worked very well and I viewed 40m as a justifiable sacrifice in order to have these 2 bands. The antenna was made of very thin switching wire and eventually broke. I replaced it with slightly thicker wire but did not add the link.
This year, whilst playing about in the park, I noticed that I still have a perfect tune on 40m, even though it is a 3/8 wave rather than a half-wave. As my other antennas have radiated well as 3/8 waves, I decided to give it a try on the Heukuppe on Saturday. I wasn’t disappointed:
Reports were generally around the 559 mark and very satisfactory for 4 watts through a 3/8 wave. I got similar results in the afternoon on the Dreimarkenstein:
What I did notice, is that 14 MHz had less contacts, although that could just be down to conditions on the day. The antenna is 3/4 wave on 20m, but I have no idea if this could have any negative effect on radiation; certainly I don’t see why off the top of my head. That said, I may add another link at 10m to make the antenna a perfect half-wave on 20m and give me as good performance as I think you can expect from such a set up. I had always just assumed that the tuner must be used with an exact half wave of wire, or multiple thereof. I think it’s good to know that it will still tune and transmit well on other lengths. In particular, changing the length of the wire slightly (generally shortening it in my case) can help you get the SWR down if it is a bit high on certain bands.
More than anything, I prefer the shorter wire length when the antenna is a resonant 1/2 wave on 30m. It also means that the antenna is proportionately higher off the ground when on the resonant band and using a 5m mast, although again, I wouldn’t like to say how much effect this has on radiation.
73 de OE6FEG
Matt