[Ralph Mowery]

In article ,
says...

On Sun, 23 Apr 2017 20:34:31 +0100, highlandham
wrote:

It is useful to initially make the vertical radiator and radials ,say 10
mm longer than a quarter wave for the mid band frequency (somewhere
between 157 and 162 MHz).

Nope. You want to tune the antenna for lowest VSWR in the transmit
range (156.0 to 157.5MHz) and take whatever you can get in the 162MHz
receive only region. If you try to tune the antenna for the middle of
the 6 MHz split, you'll end up with lousy VSWR at both extremes where
you want to operate, and good VSWR where you're not operating.

Frank , GM0CSZ / KN6WH in IO87AT

Thats correct, tune for lowest SWR at the transmit frequency and take
whatever you get at the receive frequency. If you don't , most
transmitters cut the power back, or else you burn up the transmitter.