Sept 2004

Extending the Half Size G5RV for 80m

If you are restricted for space and can only run to a half size G5RV

and wish to operate on 80M you can extend the length of the half

G5RV with inductances and two small extensions of wire.  The loading

extensions can be either vertical or horizontal in respect of the main antenna

wire.

The general overview of the halfsize G5RV is shown below, with the

extensions in place.

Shown below are the inductances. The inductances are wound on

40mm white plastic tubing.  Be sure to use enamelled copper wire.

Do not use black plastic as this contains some carbon and will conduct.

After constructing the inductors, give them a good coat of varnish or cover them

with heat shrink material for waterproofing.  The extensions may be used in a horizontal

plane or if space is difficult, may drop down from the ends of the G5RV.

    Tuning the antenna with the inductors in situ is simple. With an SWR bridge in circuit,

select the area of interest on the 80M band and key the transmitter with a low power and

check the swr at your required frequency, if the SWR is high, tune the transmitter down to

the lower end of the band and check the SWR, it has dropped, the antenna is too long

retune the transmitter to the required frequency and check the SWR, then cut off about 1”

of wire and check swr again keep cutting off small amounts equally from both ends until

you get a low SWR on the required frequency.

     If the swr goes high at the lower end of the band then I suspect your extension is too

short, retune too the top of the 80 m Band and check the SWR, if the extensions are too

short, you will find that the SWR is low and you will need to extend the length of the extensions.

However, I doubt that you will find this is the case. It is more likely that you will find the extensions

too long for the SSB section of  80m and about right for the CW end.

It is simply a case of trial and error, just do not cut too much off at a time and do it equally at both ends.

   I personally do not use coaxial cable with the G5RV, I use 300ohm ribbon cable right back to the ATU.  I find that I get better results this way, however try it with coaxial cable and if you find

that it is still difficult to get a low SWR, try 300ohm ribbon to a balanced tuner, you might be surprised at the improvement.

With thanks to G-qrp club Sprat nr.93 and M0AJL for the idea.