After 7.5hrs in the field today and a further 6 hours building mark 2 of the matching network I am pleased to report that we have successfully provided some modifications to the 80m antenna to transform it into a 160m inverted L. While only 12m high, with a tuned radial plus resonant loading wire we have achieved successful daylight QSOs to several stations. I acknowledge that it isnt very efficient, but it is better than no 160m antenna at all (and hopefully will be a little more effective than the dipole I took to Niue last year).
Steve VK5SFA helped immensely with the tuning and setup today, including loaning me the high voltage capacitors needed for the matching circuit. The 160m design is based partly on those published by DJ0IP showing how to build low band antennas on a 12m Spiderbeam pole.
The 80m design is a scaled up version of one of Steve VK5SFA’s 40m designs that I used on Niue last year. One of the big differences was that it needed the large shunt L coil you see the raise the impedence up to 50ohms to match the radio.
We then took the shunt L out of circuit and added some series C and a top hat wire to form the inverted L for 160m. To tune the 160m antenna, we started with a variable vacuum capacitor to find the correct C value, and then using Steve’s VK5JST Analyser, we then substituted the variable capacitor with some fixed ones that matched the required 350pf. We then tested the VSWR and were getting around 1.7:1 as our best result at the antenna terminals. Back at the radio, this was represented as better than 1.3:1 which was very good indeed.
Feeling like we had a working antenna, we then called Tony VK5TT and arranged for some on air tests. Tony is on the other side of the Main Mt Lofty range. He was reporting us at 5×9 over a daylight path. We then proceeded to do various trials with tuned radials as well as with adjusting the tuning of the top hat wire. We finally settled on a combination that certainly seemed to be working. Neil VK5KA also joined in the conversation on 160m and we had a very pleasant hour or so tuning and fiddling, while marveling at the fact it worked at all <smile>.
We then put it into 80m mode (bypassing the capacitors and reintroducing the coil) and had similarly successful contacts and then proceeded to tune it up the bands. On 40m it is a full height resonant 40m 1/2 vertical and we were getting 59 and 59+20 reports into VK3. We then verified that it would resonate at 30 and 20m as well before calling it a day, satisfied that apart from finalising some packaging we had a fully verified antenna package ready to take to Vanuatu!
Again – a huge thanks to Steve VK5SFA for all the effort and time he has put in to helping me get this antenna running. Also thanks to Tony VK5TT and Neil VK5KA for their on air testing this afternoon!
See you on 160m FT8 (mostly) from YJ0AG de Grant VK5GR – 2 weeks to go!