Tuesday, 24 April 2012

Mobile HF

Right, so now we have an antenna mount on the roof of the car for HF work. The tailgate mount is still a work in progress. The new mount is an SO-239 type, pretty much an allrounder that will allow me to put on pretty much any antenna, or connect up the field masts and their antennas.

Tried the 20m antenna on it (after proving it with the MFJ-259 and Bird load) and got a nice match in a sensible portion of the band. But 20m was poor today generally, so no QSOs made as yet. The 40m antenna has rather a narrow usable bandwidth, so i will have to decide where to tune that for, im thinking about 7100kHz.

The 80m antenna, well, forget it! Usable bandwidth is tiny, and as for efficiency... Instead, im going to look at using that antenna, or rather its parts, to make a shorter antenna for one of the higher bands. I want antennas for 17m 15m and 10m. 10m theres enough cheapo commercial jobs, so probably go with 17m, which is a favourite band of mine. I'll use a shorting wire to find a point on the 80m antennas loading coil that matches 17m, then  remove the shorted coil section, and shorten the coil former physically. I might look for matches for the other bands as well, with a view to making it a multiband tapped antenna.

I also cut a 2m 1/4w whip for on the M8 mount. This is for use on those occasions when the 5/8ths would be socially unacceptable, or when i need something that will work on 70cm as well. For those occasions when i really need to be able to operate efficiently on the lower bands (down to 40m), im in the process of putting together a link/jumper dipole