[Elecraft] K3 - Numeric SWR Display

[Tom Childers, N5GE]

On Thu, 18 Sep 2008 09:44:42 -0700, "Ron D'Eau Claire" <ron at cobi.biz> wrote:

>That's true. Indeed, if you have an "antenna tuner" (built-in automatic or
>external manual) you don't even need to do that. That's what made them so
>popular in recent years; they "fix" impedance problems at the rig end
>without fiddling around with the antenna at all. 
>
>The issue then becomes feed line loss. It can get quite high, especially at
>the higher frequencies and with longer lengths of coax. It's not unusual to
>throw away 50%, 75% or more of your RF as heat along a coaxial line that
>way. 
>
>But, if your antenna is designed to provide a decent match, or if you've
>done some adjustments 'on the ground' that suggest you're at least
>approximately correct, you're not likely to experience such drastic losses
>even though things will change when the antenna is raised to its final
>position.
>
>Doing measurements up on a tower is one of the major reasons for the
>popularity of the modern "antenna analyzers". They're self contained and
>small enough you can carry one up to the feed point. Most Hams only need to
>do that at rare intervals, which is why many Ham clubs have a "club
>analyzer" everyone's contributed to buying so members can borrow it on
>occasion. 
>
>A much cheaper approach is, as Bill says, to cut some coax to a multiple of
>1/2 wave, electrically. Then the impedance you see at the end on the ground
>will be the impedance at the antenna. The issue there is "how many times do
>you want to climb the tower"? Perhaps a buddy at the rig on the ground and
>you in the air with some HT's is the answer to that.
>
>Ron AC7AC
>
>-----Original Message-----
[snip]

I bought an AIM 4170 analyzer at the Ft Worth Hamfest this year and love it.
When measuring antennas with it I calibrate the coax before making the antenna
measurement with a piece of 100 ft RG213 on a ten foot mast.  After I have done
that I can measure the antenna as though the analyzer is attached to the
terminals at the antenna.   Then I put the antenna on the tower and measure it
again with the same calibrated coax to find out what changed at the additional
height.  If it checks ok I connect the LMR600 to the antenna and call it good.

 
Tom, N5GE - SWOT 3537 - Grid EM12jq

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