Adventure in Antennas: A Learning Experience in the Field

My first HF adventure radio trip was in February last year, in the Brecon Beacons. The antenna used was a 40 meter dipole, inverted V, with a 3 meter fibreglass pole in the middle.

I had attempted to tune the antenna in my back garden, so that I would have a low SWR when in use in the Brecon Beacons. I soon realized that this did not work, maintaining a good match is simply impossible with an antenna close to the ground that will be used in a variety of environments.

The antenna was too close to the ground, and any slight variation in the setup of the dipole (ie. moving one of the elements 50 cm to the right), and the feed point impedance was varying greatly. Nonetheless, I took the antenna with me, and called CQ, no QSOs, one or two stations trying to call me, but then fading. (There was also another problem with the set as well, I had presumed that the case of the kit I had built was connected to 0V, the antenna wasn't even connected to 0V!).

Two days after arriving back from this trip, Foot and Mouth hit and operating portable had to be put on hold for many months. I realized that I needed to either get the antenna up higher, or make up a simple matching unit. I decided the best option was to get the antenna up higher. With one of these 10 meter fibreglass masts, some RG174 coax, I gave the antenna a test on Dartmoor. After putting up the mast, and getting the dipole sorted out (a long process) I managed to work a G4 in Leeds on 40 meters with 1watt. I was reasonably happy with this setup. I did some testing on holiday in Cornwall with a low dipole and an ATU. Although no real "testing" was done other than to see what I could work, the result was; no QSOs. The antenna was very low, so I was not too surprised, but you always hear about these people who work the world on a few watts and a low antenna. Still, didn't work for me.

The next big test for the antenna was a backpacking trip in the Lake District. It worked OK, but could have been easier to setup, it took some time to guy the mast, and put up the dipole, I also had no indication of any SWR, unsure of how all the different environments I was operating from were affecting the performance. Lugging round the 10 meter fibreglass mast was also not something I enjoyed.

Next trip, back to the Lake District, not backpacking this time. I play around with all sorts of methods to support the dipole, in the end it came down to taking the 10 meter fibreglass mast, or my 3 meter fibreglass pole. I'm not a huge fan of carrying a fibreglass mast on my back that sticks up 1/2 meter or so above your head, especially not when some scrambling is involved on the route. So I decided that the 3 meter fibreglass pole would serve as a walking stick, was lighter, so this was the support for the dipole. My plan was to get the mast on top of one of the summit shelters, getting it higher off the ground, and hoping that the match would be reasonable, as it was fairly high off the ground, getting close to the edge of the summit ridge using the steep drop of the side of the mountaining, giving rapid drop in electrical ground. In practice the summit conditions were awful, it was impossible to get the fibreglass mast to sit on top of the summit shelter, it was too windy. I am almost certain the 10m fibreglass mast would not have stayed up in these conditions.

Getting the dipole up was fiddly, the wet rocks and high wind made it hard to stay on your feet, so trying to put wires in allsorts of places was a difficult task! Fiddling around with wires requires taking gloves off, the longer the antenna takes to put up, the colder your hands get! The antenna was not very well set up at all, I doubt it was more than 2m above the ground at any point, it was too windy to get it any higher, and the rain made it difficult to move over the rocks to adjust the dipole. With no tuner, it was going to be doubtful of any sort of a decent match from the antenna to the rig. After 20 minutes of CQs and calling other stations, I gave up cold and wet.

I was certain that it was time to change the antenna, the 10m fibreglass mast was too big and heavy and would also be unsuitable for use on a windy summit, the 3m mast was good, but was too short, without any sort of matching between the rig and the antenna.

I made a list of all the possibilities of antennas:

+ A 40 meter dipole on the 3m pole, matching the dipole to the rig with a simple ATU. High SWR in coax creates losses, the SWR on the transmission line was likely to be high with the low dipole, so I decided this was probably not the best option.

+ A 44 foot doublet using 3m pole for centre support. I had seen a model of this antenna and it looked like a good performer on 40m as well as all bands from 40-10m, making multi band use possible. At the moment I do not have a multi band rig. After speaking to various people, it was not recommended laying open wire feeder on the ground, and it would have probably.

+ An end fed on a kite, an attractive option to get the antenna up high, but useless for backpacking, as the idea of choosing a site to camp is that it's sheltered from the wind!

+ After working John, G3WGV, on his recent trip up Catstyecam. I was surprised by this as we exchanged good reports each way, I was using 5W (I guess John was using the same?), I don't know the exact distance, but from Cumbria down to Dorset is a (for me) typical day time distance on 40 meters. John was using some wire layed on some rocks. Though John did point out to me that although the antenna was only about 2m above the ground, the key point was that it the ground fell away for several hundred metres in all directions, within 1 wavelength. Still I decided I had to try this out for myself.

I made up a simple matching unit and an LED SWR meter. Cut a 1/4 wave radial, cut about 19 meter of wire for the radiating element, and threw the radiating element in some trees in my back garden.

It tuned up OK. I wanted to give it a proper field test though. So with the ATU, 1 radial (I may try 2 next time, as I could detect some detuning), 19m of wire, rig, key, batteries, and gloves, and plenty of warm clothing, the antenna was ready to be testing properly. I did not have any idea where I was going to set up the antenna, but it soon became clear it wasn't going to be on Yes Tor, heading over from West Mill Tor then on to Yes Tor, the conditions were not very, wind, a wet mist and it was cold. Coming down off High Willhays, the conditions improved, though it was still cold.

Perched on a grassy ledge on Black Tor, I set up the wire, it was sloping at about a 35 degree angle, going from the Tor down to some boulders. I had planned to find a rock to place near the ATU end of the wire, to reduce the tension in the wire, but after searching around a little, I couldn't find any small rocks, so I reduced the tension in the wire, this meant parts of the antenna were now closer to the ground. Next time I will take a tent peg, to reduce the tension of the wire near the ATU. The time to put up this antenna was minimal; it was much much less fiddly than a dipole, and a lot quicker. I had some trouble tuning up the antenna, I could not see the LED to clearly, and could not get it to fully go out, but I had read that some times they did not fully go out even with a perfect match, so having tuned the antenna by ear on the noise, and checking with the LED, I was happy I was providing a reasonable match, so I started calling CQ, after my second call G3NYY replied, I was surprised at how strong the signal was, so loud that if I had an attenuator on the rig, I would have used it.

My hands had got cold just putting up the antenna, so I decided to leave my gloves on, it was hard going sending CW in gloves. Walt was in Tewksbury, he was running 50W, I gave him 599, I was running 600mW, he gave me 569. I would have liked to have seen what else could be worked seeing how far I could workto find out how much of an NVIS antenna it was, but time was limited and I was getting cold. Taking the antenna down was quick and easy. Although that was only my first trip with an end fed AND no mast, I was impressed. I will be interested to do further testing, investigating using more radials, checking the LED SWR meter with a "real" SWR meter. Testing the antenna on "flatter" terrain will be a key test to see how well the antenna performs.

In conclusion:

The main problem with the antenna in the Brecon Beacons was the poor matching, this was also the problem with the second trip in the Lake District. So why not use the dipole and make up a simple matching unit as I did with the end fed? Well the coax is much heavier, and as shown in previous trips, the dipole is, in my opinion a more fiddly and time consuming antenna to put up. The SWR on the transmission line would probably be reasonably high with a low dipole, introducing losses. From the antennas I have tried so far, in a mountain environment, out of the two, the end fed would appear to be a better system, more testing will be done over time.

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Matthew Balmer, M5EVT, is an avid QRPer and outdoorsman living in Sherborne, England. To see photographs of his outdoor excursions, visit his web site: www.qsl.net/m5evt