Hi Jim,
Thanks, I agree with everything you have said, including that the bottom
line is the various factors noted have an effect on the resonant length of
the antenna.
73, Steve Davis, K1PEK
Davis RF Co.
www.DavisRF.com
978-369-1738
~ Davis RF Co., Div. of Orion Wire Co.,Inc.
Distribution to numerous industries, Andrew
Heliax; Times Microwave LMR; RFS Celwave and others.
Cable design engineering. RF Peripherals.
www.davisRF.com
Tel: 1-800-328-4773 (1-800-DAVIS RF) Tech'l: 1-978-369-
1738, Fax: 1-978-369-3484
~ DAVIS/ORION Marine Wire and Cable Co., Distribution and Design: UL/USCG
Marine Stds. Tel: 877-242-2253 Fax: 603-787-2221 (Direct tel to Steve
Davis: 978-369-1738 or Fax: 978-369-3484)
~Orion Wire Co., Inc., Design Engineers of Specialty/Custom Cable
Tel: 1-800-328-4773, 1-603-787-2200 Fax 1-603-787-2221,
email: j_stimson@davis-orionwiregroup.com
www.davisRF.com
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Steve Davis -Davis RF Co." <sdavis@davisrf.com>;
<towertalk@contesting.com>; <k7ddmjb@qwest.net>
Sent: Saturday, January 05, 2008 7:52 PM
Subject: Re: [TowerTalk] Veloc Factors - wire + Lad line - from DAVIS RF Co.
>
>
> -----Original Message-----
>>From: "Steve Davis -Davis RF Co." <sdavis@davisrf.com>
>>Sent: Jan 5, 2008 4:10 PM
>>To: towertalk@contesting.com, k7ddmjb@qwest.net
>>Subject: [TowerTalk] Veloc Factors - wire + Lad line - from DAVIS RF Co.
>>
>>I was asked by Michael Baker, K7DD, to provide the VF's for various
>>Flex-Weave Tm items. For the following reasons, there is no single answer
>>for this question without multiple factors being considered, however, the
>>"nominal" answer will certainly obtain optimal performance, short only
>>perhaps to "rocket science":
>>
>>
>>
>>Propagation on bare, solid, or stranded copper or CCS (cop clad steel)
>>wire
>>in a vacuum yields a VF of 100% or 1.00, the speed of light.
>>
>>
>>In air at sea level the nominal figure is 95%, used in dipole length
>>calculations.
>>In insulated wire, the figure varies around .90 - .95 - a good figure to
>>use
>>in calculations such as EZNEC, etc, since any solution will be affected by
>>altitude, temperature, humidity, insulation thickness variance ,density,
>>and
>>age, plus ultraviolet radiation and plain old dirt film.
>
>
>
> But this is not really a velocity factor. It's more of an empirically
> derived number that makes a dipole have no reactive component (whether you
> want to call it "end effect", "dielectric loading", etc.). Surrounding
> the wire with a dielectric (be it polyethylene or just dirt and grunge)
> will change the resonant length, but it's not something that is really a
> "velocity of propagation" kind of thing (other than epsilon affects both
> the capacitance and the propagation speed).
>
> Even an infinitely thin dipole of perfectly conducting wire is resonant
> (meaning no reactive term in feedpoint impedance) at slightly less than a
> half wavelength.
>
> And, the 0.95 thing is convenient (as Steve says, it's easier to cut or
> fold back the extra than to add some on the end).
>
>
>
>>
>>
>>If you are using the PE insulated versions of ladder line, either stranded
>>or solid, 450 ohm having a few awg sizes, or the 300 ohm, over time we
>>have
>>found that .91 VF is the number.
>
> Now those ARE transmission lines, and would have a velocity factor
> associated with them.
>
> Jim, W6RMK
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|