going by adverts the k40 must be the best antenna on the market....can I cut
it for 15m ????

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.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 7/12/2015 6:25 AM, 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.

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.

--

Rick

On Sun, 12 Jul 2015 13:17:53 -0400, rickman wrote:

On 7/12/2015 6:25 AM, 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.

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.

The more you cut, the higher the antenna operating frequency.

The K40 is just a base loaded vertical antenna. The inductance of the
base loading coil is fixed, so the only way to adjust it is by either
cutting or stretching the whip. If you cut it, it DECREASES the
operating frequency. That's the common way to move it from the
original CB (27 MHz) to 10 meters (28 MHz). If you want to go the
other direction, you'll need to somehow lengthen the antenna.

Plug the original dimentia into this calculator to obtain the value of
the inductor (or just measure it with an RLC meter).
http://www.daycounter.com/Calculator...lculator.phtml.
Once you've established the value of the inductor, do some trial and
error guesses for the whip length at 21 MHz.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"rickman" wrote in message
...
On 7/12/2015 6:25 AM, 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.

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.


Rick

would a burner help ? ...

On 7/12/2015 3:03 PM, Jeff Liebermann wrote:
On Sun, 12 Jul 2015 13:17:53 -0400, rickman wrote:

On 7/12/2015 6:25 AM, 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.

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.

The more you cut, the higher the antenna operating frequency.

I guess I should have put a smiley at the end of that. When I worked
construction the guys would kid saying, "I've cut this board off three
times and it's still too short!"

--

Rick

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

"rickman" wrote in message
...
..

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.

The more you cut, the higher the antenna operating frequency.

I guess I should have put a smiley at the end of that. When I worked
construction the guys would kid saying, "I've cut this board off three
times and it's still too short!"


Reminds me of the time I had carpet put in and needed to cut down a door so
it would close. I cut it twice and it was still too long and rubbed the
carpet. Looked at the top and there was almost an inch gap. Good thing it
was just a closet door.

On Sun, 12 Jul 2015 16:15:13 -0400, rickman wrote:

On 7/12/2015 3:03 PM, Jeff Liebermann wrote:

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.

The more you cut, the higher the antenna operating frequency.

I guess I should have put a smiley at the end of that. When I worked
construction the guys would kid saying, "I've cut this board off three
times and it's still too short!"

"Insanity: Doing the same thing over and over again and expecting
different results." (Big Al Einstein).

Ok, you got me. I thought you were serious. I would have thought
that after cutting three times, you would have gotten the clue that
you were going in the wrong direction.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

On Sun, 12 Jul 2015 16:15:13 -0400, rickman wrote:

On 7/12/2015 3:03 PM, Jeff Liebermann wrote:

I don't get it. I've cut this antenna three times and the frequency is
*still* too high.

The more you cut, the higher the antenna operating frequency.

I guess I should have put a smiley at the end of that. When I worked
construction the guys would kid saying, "I've cut this board off three
times and it's still too short!"

"Insanity: Doing the same thing over and over again and expecting
different results." (Big Al Einstein).

Ok, you got me. I thought you were serious. I would have thought
that after cutting three times, you would have gotten the clue that
you were going in the wrong direction.

Indeed, I think that fact is what makes the joke funny, at least to some
of us.

--
Roger Hayter