[TowerTalk] cutting phasing lines

[Jack/W6NF]

I also double-checked the coax after doing the calculations suggested by Jim
Lux...they checked nicely.

I'd forgotten about that...thanks for reminding me...


On Sun, Apr 11, 2010 at 4:29 PM, jimlux <jimlux at earthlink.net> wrote:

> vk3pa at vk3pa.com wrote:
> > Gdy all, my Q is I need to cut phasing lines for 7.050 Mhz of 84
> > degrees es 71 degrees! ok So far,  now 360 degrees = 1 wave length, so
> > 0.5 wavelrngth (=180 degrees) would be 468/freq /vf es / by 180 would
> > be 1 degree so x by required degrees  eg 84 es 71  ok ! so now how do
> > I convert 84 es 71 degrees to a frequency so I can cut the lines WITH
> > my antenna bridge rx vector analyst autek VA1?? OR AM i  WAY OFF IN MY
> > THINKING!! 73 es tnx Al vk3pa
> >
>
>
> I tend to use metric for this, since 3E8 m/s is a nice round number.
>
> 7.050 MHz = 42.553 meters
> 84/360 * 42.553 = 9.93 m
> 71/360 * 42.553 = 8.39 m
>
> Multiply those lengths by the velocity factor of your coax (e.g. .80 or
> whatever)
>
> But, to cut it with your antenna analyzer...
>
> Say you want it to be 74 degrees at 7.050 but 90 degrees (e.g. it looks
> like a short) at the test frequency.  That means your test frequency
> needs to be higher (e.g. more degrees for the same physical length)..
>
> 7.050 * 90/74 = 8.574 MHz... That is, a piece of coax that is 90 degrees
> at 8.574 MHz will be 74 degrees at 7.050.
>
>
> So, if you've got 80% VF, cut that coax to around 6.7 meters (80% of
> 8.39m).. hook up the analyzer, and start trimming til it reads shorted
> at 8.574.
>
>
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-- 
Jack, W6NF
Silver Springs, NV
DM09ji