Reg Edwards wrote:
And the same applies to impedance Zo and attenuation.

How much could the Z0 vary for "50 ohm" coax?
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73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote in message
. com...
Reg Edwards wrote:
And the same applies to impedance Zo and attenuation.

How much could the Z0 vary for "50 ohm" coax?
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For coax, Zo = 60 * VF * Ln( D / d )

So Zo varies as VF varies.

You'll just have to measure VF or Zo.

Similar for attenuation.
----
Reg.

Cec,

Alternatively, place orders for one or two reels of coax with all USA,
Japanese, Chinese, Korean, German, French, Russian, British cable
manufacturers.

When your back yard is stacked high with full cable reels, cut off a
measured length of cable from each real, lay them in straight lines on
the ground and measure the velocity factors using a hand-held antenna
analyser at around 10 MHz. You will also need a good steel measuring
tape and a sharp cable cutter. Don't use an axe!

Discard outliers of the distribution - they are probably faulty. Use
your pocket calculator to find the average, max and min, and the
standard deviation and you will have the answer to your question.

Then set up a shop.

But I'll save you the trouble and make an uninformed guess. The
Standard Deviation will be around 4 percent of the VF with the 3-Sigma
limits at plus and minus 12 percent.
----
Reg.

All the info is very interesting. Thanks folks.

Just want to make two 50-ohm 1/4-wave section lengths to transform the
impedance of two linear-loaded 40 meter verticals (spaced 1/4 wave) from
around 32 ohms to about 75 ohms, and then extend the cable from the
"director" vertical element with another 1/4-wave with 75 ohm coax for the
90/90 phasing. Then I just "tee" the two feedpoints together to get one
common feed point that's close to 50 ohms. Have done this previously with
good results, and had a much better than expected match to the 50-ohm
transmitter feedline. The last time I did this, I used fence wire that was
staked into some flat farmland turf for the ground system. This time I will
have to create an artificial ground plane or counterpoise, as the present
mountain terrain does not lend itself well for creating a good low-loss
real-ground system. Still have my old RG-11 matching section for the one
75-ohm coax 1/4-wave extension cable, but the two RG-8 sections are no
longer around. So, thought I would use the smaller and cheaper RG8X this
time. Maybe I won't. HI
AK

Reg Edwards wrote:
But I'll save you the trouble and make an uninformed guess. The
Standard Deviation will be around 4 percent of the VF with the 3-Sigma
limits at plus and minus 12 percent.

Thanks Reg, I can live with 56 ohm coax.
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73, Cecil http://www.qsl.net/w5dxp