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#1
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Jeff Liebermann wrote:
On Sun, 12 Jul 2015 09:58:00 +0100, "Cottaging by the sea ..." wrote: going by adverts the k40 must be the best antenna on the market....can I cut it for 15m ???? The K40 is a CB antenna made for 27 MHz. 15 meters is 21 MHz and is therefore lower in frequency than what the K40 is tuned. You would need to lengthen, not "cut" the antenna in order to lower the frequency. It is a troll. |
#2
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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 |