The VF (velocity factor) or CATV Hardline is *roughly* 0.8,
but the best approach is to measure it or verify that a 50 ohm
load is seen again at the end of the line.
For intermediate lengths, multiples of 1/2 WL work fairly well
over a few % bandwidth, i.e. 1/2 WL on 40M (~56 ft) is also a
multiple of 1/2 WL on 20, 15, and 10M. Another useful length
is 1/2 WL on 80M CW (3.6 MHz which is ~112 ft) and is also
a multiple of 1/2 WL on 40, (close on)30, 20, 17, 15, 12, and 10M.
Long runs get a little tricky on 10M because the band is so wide
and there are LOTS of 1/2 WL's in a long run. For example,
a frequency change from 28.0 to 28.56 (2%) times 12 half wavelengths
(17 ft) creates a 1/4 WL shift in a 204 ft long line SO a 50 ohm load
will look like 50 ohms if the line is tuned for CW but will look like
100 ohms at 28.56 MHz. For 10M one can live with the
minor SWR variations, tune the 10M antennas for 75 ohms,
or install matching networks at each end.
Tom N4KG
On Fri, 9 Aug 2002 "Markhasin, Vitaly" <Vitaly.Markhasin@UE-1.com>
writes:
> Hi Tom,
> 1/2 WL electrical? What is velocity factor of CATV?
> What if there is a remote switch for multiband antennas?
> What length would you use than?
> Thank you.
> 73! Vitaly (VE6JO)
>
>
> -----Original Message-----
> From: n4kg@juno.com [mailto:n4kg@juno.com]
> Sent: Friday, August 09, 2002 4:22 AM
> To: TOWERTALK@contesting.com
> Subject: Re: [Towertalk] cable TV hardline
>
>
> I've been using 3/4 inch CATV for my 300 to 600 ft runs
> in multiples of 1/2 WL (without baluns) for10 to 20 years.
> My BEST connections (long term - NO failures) have been
> to simple solder the center conductor from the flexible coax
> to the center conductor of the hardline and the use a cable
> clamp to hold a ground lug soldered to the braid of the flexible
> cable. Point the cables UP and cover with a plastic bottle.
> My first such connection is still going strong after 20 years.
>
> Tom N4KG
>
> On Thu, 08 Aug 2002 epetek1@att.net writes:
> > Have had very good luck using long runs, 400 feet of
> > 3/4" (maybe slightly less) hardline with 75/50 baluns at
> > each end. been in the ground three years w/o problem.
> > Wonder whether other towertalkians have had same
> > experience. Much cheaper than 50 ohm equivalent. In my
> > case free from the local provider. Connectors are quite
> > easy to modify. Pete W2YG
> > _______________________________________________
> > Self Supporting Towers, Wireless Weather Stations, see web site:
> > http://www.mscomputer.com
> > Call 888-333-9041 to place your order, mention you saw this ad and
>
> > take an additional 5 percent off
> > any weather station price.
> > _______________________________________________
> > Towertalk mailing list
> > Towertalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> ________________________________________________________________
> GET INTERNET ACCESS FROM JUNO!
> Juno offers FREE or PREMIUM Internet access for less!
> Join Juno today! For your FREE software, visit:
> http://dl.www.juno.com/get/web/.
> _______________________________________________
> Self Supporting Towers, Wireless Weather Stations, see web site:
> http://www.mscomputer.com
> Call 888-333-9041 to place your order, mention you saw this ad and
> take an
> additional 5 percent off
> any weather station price.
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today! For your FREE software, visit:
http://dl.www.juno.com/get/web/.
|