[Moon] Fwd: Re: Velocity factor

[Johann Bruinier]

-------- Weitergeleitete Nachricht --------
Betreff: 	Re: [Moon] Velocity factor
Datum: 	Sun, 15 May 2016 10:17:59 +0200
Von: 	Johann Bruinier <520034211808-0001 at t-online.de>
An: 	Ingolf, SM6FHZ <ingolf.fhz at gmail.com>



Hi Ingolf,
my first 432 array in 1977 was built with open wire lines. I never used
any coax within an array.
After some experimentation I ended up with a VF 0,985 which means 1710
mm for 5/2 WL for vertical & horiz spacing of 4 LY in my case.
I use 3mm CuL spaced 13mm c/c. Spacers are 10mm round PTFE installed at
the (possible) voltage nodes.
Forget about plastics other than PTFE. I had acrylic glas melting at the
2 kW leavel. Which, of course, is not as important for TX as for a low Tsys
for RX.
Charlies suggestion is a good one for finding your individual VF.

73, Jan DL9KR.




Am 15.05.2016 um 08:18 schrieb Ingolf, SM6FHZ via Moon:
> Hi All.
>
> Once again I turn to the wealth of knowledge of the reflector.
>
> What velocity factor should on use for a open ladder feed line? In my case
> 283 ohm on 432 MHz for getting two 200 ohm antennas connected to each other
> and have 200 ohm at the feed point in the center between them.
>
> My ladder consist of enameled copper wire, 2.5 mm diameter with plastic
> tube supports at say every 80 to 100 mm.
>
> Should one use 0.95, 0.97 or 1 as the velocity factor when calculating the
> proper wl/4? I doubt is is 1, as there are some dielectric involved.
>
> Would it be the enamel or the plastic tube supports the contribute most to
> the velocity reduction?
>
> What is your experience? Any rule of thumb that is good to use? It might
> not be that critical as the band width of such a transformer will be quite
> large.
>
> 73 / Ingolf, SM6FHZ
>