QRP Six Metre Portable Dipole
With a trip to Cornwall on the horizon I had to make some decisions as to what bands I would operate on and what aerials I would use. I decided on a twenty metre dipole so that I could try for some HF DX and some sort of portable dipole for six meters.
As we were going to stay in a first floor apartment with a balcony I decided to create something that could be used atop of my lightweight camera tripod. My plan was that both antennas, IC-703, LPF, 7AH SLA battery and charger plus a few tools would fit into my laptop bag – a complete station on my shoulder! So the six metre dipole had to collapse in something less than a foot or so long.
As it happens I had already used the 1.3 metre long whips from Maplin when I came across an article by G1EXG entitled
X-antenna in which he used four of them to create a portable six metre antenna.
The article spurred me on to construct my own aerial using two of the whips with extensions to bring the dipole to resonance around 50.150 MHz (see left, click on the images to see a larger version).
It would include a balun made from co-ax and connect via a UHF socket so that the connecting co-axial cable could be carried separately from the aerial.
Construction:The dipole consists of a central box (one from Maplin which I already had), M4 fixing bolts with solder tags for the two whips towards the top of the box. As these bolts would have to stand up to the the whips being screwed on and off I used large washers on both sides of the case and a second nut to lock the first nut tight. As can be seen from the picture above I have removed the caps from the top of the whips and added extensions, these are made from copper wire and are 150mm in length. Brass connectors from a connector block are used to attach the copper wire extensions.
The UHF socket is mounted on one of the end panels.
My plan is to attach the dipole to the camera tripod with a couple of re-usable cable ties but one could use a couple of Terry clips as G1EXG did or use pipe clamps to fix the dipole to a vertical pole.
The balun consists of six turns of 50 ohm coax wound on 50mm (2 inch) former - a bottle of lemon juice found in the fridge! I used cable ties to hold the coax together and a cable clamp to secure the balun in the box. The two ends were left just long enough to connect to the solder tags and to the UHF socket. It looked rather neat until I forced it in to the box!
Results:The dipole was constructed and mounted on the camera tripod in the living room just to check that it was functional, it was fed by some five metres of co-ax to the IC-703 via a low pass filter. The fully extended length of the dipole works out to be 2.9 metres long which is good for 50.100 MHz in the open. Band noise was up some 12 db on the fan dipole and although the band was more or less dead I was able to catch a CW station and a data signal which confirmed the increase in signal levels compared to the fan dipole. The Icom IC-703 was able to tune the dipole over the whole band and the SWR was checked every 100 KHz from 50 to 52 MHz. The 703 easily tunes the dipole to a SWR of 1:1 over the whole of the band regardless of the fact that one arm is a foot above the TV and a large central heating radiator! Hopefully, I'll get to use the dipole in Cornwall and will get to post some results here!
During our week in Falmouth, which was not primarily a radio holiday, there were a couple of openings into Europe that coincided with the radio being on. One day there was an opening to Germany and to Italy on another. The furthest station worked was IK0KNQ/P with a report of 57 at a distance of 1580 km, the furthest German station was DH3UAK at 1100 km.
Packed up and ready to go!