2007-10-21
DX-pedition with Peter VK2TPM
Peter VK2TPM suggested this little adventure as a DX-pedition as far as possible from the suburban noise without really going bush. North Head is only about 3 km from my QTH as the crow flies, but the great majority of it is completely devoid of power lines, computers; technology in general and its associated RF noise. Peter has recently built the Ozi-pole antenna and brought it and his FT-817 along. He also packed an MFJ-269 antenna analyser, 12 Volt SLA power, and everything else you need to get out from remote locations.
I contributed only my VR-500 and the 80 metre direct conversion receiver rig wise. My 80 metre DSB radio has developed a VFO problem and I figured 80 and 10 metres would be dead anyway, so I wouldn't be doing much talking. Of course I packed a noise bridge, dippers, balun, tools, other test gear, etc. For antennas I took a compact 80 metre doublet, End-Fed 80 and 40 metre half-waves, and a 40 metre dipole.
We picked our site, off the track a bit to avoid disturbing holiday makers taking in the spectacular views from the lookouts along the track. The flies were out in force, I'll be packing the Aeroguard next time! Perhaps sunscreen or shade too, I got rather badly sunburnt!
The area is wonderfully radio quiet, but lacks any tall trees to raise antennas with. Peter put the Ozi-pole up on a tripod which worked quite well, but there wasn't much chance of really testing out full-sized antennas. Next time we need a taller mast of some description if we want to try out other types of antenna.
Peter tuned around 40 metres with FT-817 and heard quite a few stations, many JOTA and some Sunday broadcasts from WIA-related stations around Australia. 40 wasn't in the best shape, with heavy QSB at times. The ARNSW broadcast seemed weak, but we weren't the only to comment on this.
I had a tough time getting the compact 80 metre doublet to tune up. It is about the size of a 40 metre dipole and is designed to be mounted as an inverted V. With no skyhooks available, the apex was only at about 2 metres, the ends just tossed over the brush, the feedline is very long as it is part of the matching network and it couldn't really be placed properly. It did tune up on 40 fairly well, and 80 was nearly dead anyway (not surprisingly), so we quickly gave up on it. I may need to add a turn to the link coupling in the matching box, it was consistently tuning up at about 32 Ohms resistive.
I tried out my old 40 metre dipole, its balun had become waterlogged so I cut it off and used the wire to test a new balun Peter had made. The antenna was short for the configuration we had it in (it used to be in close proximity to my home unit walls, so it had to be cut to resonance), but the balun worked fine, as did a new one I brought. I ended up joining the two halves and end-feeding it with the EFHA matching box. This tuned up on 40 metres pretty well considering it was about 1 metre off the ground at this point!
Doning headphones Peter and I listened on independent rigs to the broadcast callbacks. Peter had arranged a sched with VK2EVB, creator of the Ozi-pole, and we heard him call in, himself portable on an Ozi-pole. He was perfectly readable, even on my end-fed halfwave practically on the ground using the VR-500 receiver. Not bad really, from the Far-North Coast portable to portable with poor conditions. VK2WI was having problems hearing him, and couldn't hear us call in. Peter called VK2EVB but he sank into the QSB before contact was established. A bit disappointing, but encouraging none the less.
The Ozi-pole is a great antenna. It is very quick and easy to setup. The antenna analyser and my noise bridge both confirmed a dip in roughly the right places using the "starting point" lengths for the telescopic whips. The feedpoint generally isn't purely resistive at the places of lowest VSWR in-band, but it offers a better than 2:1 match over reasonable bandwidths without tweaking. It does seem to be generally resonant out-of-band with a fairly low feedpoint resistance, which is consistent with my assumptions about how the antenna actually works.
Peter was kind enough to loan me the Ozi-pole antenna and tripod for experiments. I tried it out on 10 metres later that afternoon, but Peter could hardly hear me from his QTH. I don't know which end was at fault, perhaps both, Peter was using his random wire I believe, and I was having RF feedback problems so I was keeping it wound back. I'll add a balun to the Ozi-pole before I do more experiments. I also need to complete the antenna analyser I am working on, and perhaps make a few other bits of gear to evaluate the antenna properly. In particular I want to measure its pattern and see how symmetrical it is without a balun vrs with, etc. Feedline radiation seems to be a problem on the higher bands, but as you can see in the picture above I was unbalancing the antenna with its close proximity to my 2 metre flowerpot and 17 metre compact dipole.
Thanks Peter for a great day. Check out his blog entry here.
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