On 12/07/15 09:58, Cottaging by the sea ... wrote:
going by adverts the k40 must be the best antenna on the market....can I cut
it for 15m ????


Never saw this antenna before ,but it seems to be a CB (27MHz) unit.
To modify it for 21 MHz (keeping the enclosed inductor as is) a length
should be added .
Perhaps the best is to temporarily replace the vertical wire element
with a piece of flexible wire a bit longer than 27/21 times the current
piece , suspend the complete unit vertically and check with an antenna
analyser ,showing an SWR 1:1 probably below 21 MHz.

Then start cutting short lengths of wire until SWR is 1:1 at say 21.2
MHz .Then replace the wire with stiff whip material with a length
slightly longer than the above resulting flexible wire , such that a
final adjustment can be made by snipping tiny bits off the top of the whip.

If the antenna is to be used on a car then the whole procedure should be
carried out on a car or a alternative similar area metal plate (or wire
mesh).

All in all probably a time consuming activity but a good learning
experience .

Good Luck

Frank , GM0CSZ / KN6WH in IO87AT