I have tried a number of multiband wire antennas at GB2GP over the last year and have never been really happy with the results. The current antenna is a 1/3 2/3 split OCF dipole, which seems to work but still causes me a few problems. The main issue is that there is huge BCB breakthrough from Brookmans Park which is in LOS, so I am using a high pass filter at the transceiver to reduce this to a reasonable level. The filter is designed for 50 ohm impedance and the OCF is no where near that on all bands and even though the radio ATU can tune out any mismatch we toasted one of the filter torroids during JOTA due to the mismatch.
The answer seems to be to use a resonant antenna for each band of interest. One of my neighbors, G0RPM, has had good results with a parallel dipole made by Alpha Delta. I called the UK importer Martin Lynch to enquire about these and was told by an unhelpful person they were out of stock and didn’t know when they would get any more in. As a result I have decided to stop being lazy and build one!
The plan is to have an antenna for the 80-10m contest bands. This means four dipoles, 80m, 40m (which also works on 15m), 20m and 10m which I measured out in my hall from wire I had knocking about in my store.
The answer seems to be to use a resonant antenna for each band of interest. One of my neighbors, G0RPM, has had good results with a parallel dipole made by Alpha Delta. I called the UK importer Martin Lynch to enquire about these and was told by an unhelpful person they were out of stock and didn’t know when they would get any more in. As a result I have decided to stop being lazy and build one!
The plan is to have an antenna for the 80-10m contest bands. This means four dipoles, 80m, 40m (which also works on 15m), 20m and 10m which I measured out in my hall from wire I had knocking about in my store.
Measuring dipole wires
The next job was to build some spacers for the elements. A search on google suggests the spacing should be wide as possible to make tuning easier. I have a miniVNA which should simplify tuning so I decided to use only 75mm between wires. I picked up a length of PVC pipe from my local hardware shop cut it into pieces then 3mm drilled holes in my workshop (aka the kitchen).
Spacers cut and ready to drill
Feeding the wires through the holes was a simple job, but securing the spacers was more difficult. I tried hot melt glue, which was partially successful, but ended up using cable ties to produce my ladder effect. I had a spare commercial 1:1 balun which I put at the feed point and the antenna is ready to go in the air. Hopefully, installation will be an easy job, but I hope that I don‘t get too cold trying to tune the thing as the temperature here is not predicted to rise above freezing for a few days.
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