Where are you measuring the SWR? If you are measuring it at the end of
an arbitrary length of coax you will get all sorts of bad results,
including the possibility of seeing an inductive reactance for an
antenna that is too short. Ideally you would measure the impedance
directly at the base of the antenna.
D. Scott MacKenzie wrote:
> I keep cutting and cutting - and it is still too short
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com]On Behalf Of Dale Martin
> Sent: Saturday, December 09, 2006 3:05 PM
> To: firstname.lastname@example.org
> Subject: Re: [TowerTalk] 160m inverted l
> If you've got an antenna analyzer like the MFJ-359, you can see where the
> SWR is minimum. Cut off a few inches of antenna. See where the new minimum
> SWR point is. Then you can figure how many kHz per inch the minimum SWR
> point will move with each subsequent cut.
> For instance, cut off 6 inches of antenna and find the minimum SWR moves
> from 1818 to 1824. So, the kHz per inch is 1 kHz per inch. If you take off
> six more inches, the minimum SWR moves to 1830, or 10 inches to move to
> 1834, etc.
> Of course, it pays to be conservative when your are cutting wires, so always
> cut for a lower frequency than the actual target until you get with a couple
> of inches.
> For my 1/4-wave half-sloper on 80, instead of cutting the wire to move it
> into the phone band, I simply bring the antenna end back on itself to
> shorten the overall antenna. I use the same method of calculating how much
> will move how far, but without cutting the wire. :-)
> Dale, kg5u
save the cheerleader ... save the world
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