6M Half Wave Coax Stub Matched Mobile Whip

[VK6ZFG]

6M Half Wave Coax Stub Matched Mobile Whip

A simple 6M Half Wave can be made using a full size 27 MHz CB Stainless Steel Whip in conjunction with and thread adaptor to the 1/2" BSW spring fitted to a standard (Australian) HF whip mount. This combination gives a length close to that desired for a 6M half wave vertical.

Matching is simple. This can be achieved without any coils or tuned circuits. A simple shorted quarter wave coax stub, tapped a short distance up from the short end can be used.

The length of the stub will work out to be slightly shorter than a quarter wave as it has to compensate for the antenna base capacity.

On my vehicle installation a good match (1.2:1) was achieved with minimal effort. No attempt was made to improve on this as the temperature was rather hot at the time.

The match I use is as below but with other antenna bases the lengths required can be expected to be slightly different.

A length of RG58 coax feeder 535mm from the antenna base plug connector to the centre of a UHF Tee piece is used to connect to the antenna base. The Tee piece is away from the antenna base. Screwed onto the other side of the Tee piece is a shorted RG58 coax stub 177 mm long to the centre of the Tee piece. The normal antenna feeder is connected to the centre of the Tee piece. When one wishes to use a normal HF helical whip the shorted coax stub is simply disconnected from the Tee piece.

Half an hour after completing the antenna Rex VK6ARW in Exmouth, 1100km away, was worked from the car in the driveway.

This method of matching can of course be used to other bands. I use this method on my 10M half wave base vertical. Further possibilities are remotely connecting the shorting stub to achieve multi band operation.

Igor
VK6ZFG

[VK6OX]

Well done Igor! Courtesy of VK6RO I heard today via "another comms medium" the results.
I can remember in a parallel universe many moons backs (and north of the 26th parallel ) I built a similar antenna, and used it to great effect travelling from the NW of WA across to VK2 and wking quite a number of stations on 52.050 coz that's where we hung out bk then!!

73 and gud DX!! (on the whip of course!)