HBØ/SMØW – Liechtenstein holiday style DXpedition
On the other side of the move.. I have not been very busy on the blog lately. Me and my fiancee just moved to a new house 5 weeks ago and alot of time have been spent unpacking all boxes etc.. that needs to be done =) But still decided to do a very relaxed DXpedition to Liechtenstein just before the hamconvention in Freidrichshafen Germany. I wanted to try a new DXpedition holiday concept antenna. Criteria for the antenna would be,
2. Very lightweight (Whole antenna + 100m of transmission line + tuner + glassfibrepole <10 kg of weight)
3. Very low loss
So the week before our trip I made a vertical dipole out of 300 ohm twinlead for 28 MHz. At the ends of the antenna i mounted cableshoes that fits into cableshoe joints. For 28 MHz there is just a small short circuit plug and then I made extensions for the other bands. In this way I got optimal monoband vertical dipoles for all bands 10, 12, 15, 17, 20 and 30m. The vertical dipole is just taped to a 10m long glass fibre rod that fits neatly into the travelling bag.
The folded monoband vertical dipole at resonance is very close to 300 ohms, which means that I fed the antenna directly with 300 ohm twinlead! Twinlead as all balanced lines has very low loss. This means you can have several hundred meters of transmission line and barely loose anything.
This is the basic sketch of the antenna:
At the shack end the balanced 300 ohms needs to get down to 50 ohms unbalanced, so a simple "lumped element L-network tuner" was built. Basically just a small variable capacitor capable of taking the power you are running that sits in between the leads of the twinline. After that a short piece of twinlead (different for each band) is inserted as a lumped L. The two components in the L-network bring the impedance down to 50 ohms balanced at very low loss. Then I wound 10 turns of small lightweight teflon coax on a 43 material ferrite bead. This will make the balanced to unbalanced part of the tuner and also make sure nothing spurious escape from the shack to the antenna.
Here are some more pics, enjoy!