Hello all
What determines the Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a
Lindenblad Antenna for 2 Meters

its asked to use

RG-59 polyethylene foam coax with stranded center conductor

I think the VF is .66

I cant find any stranded center cond where I am,so I want to try it with
Solid,but it seems all the solid is VF .88

anyone have any input on this

thanx

howard

sorry I should mention the RG-59 is used for impedance matching not feed
line
thanks again
Howard

"Howard Kowall" wrote in message
...
Hello all
What determines the Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a
Lindenblad Antenna for 2 Meters

its asked to use

RG-59 polyethylene foam coax with stranded center conductor

I think the VF is .66

I cant find any stranded center cond where I am,so I want to try it with
Solid,but it seems all the solid is VF .88

anyone have any input on this

thanx

howard

"Howard Kowall" wrote in message
news
sorry I should mention the RG-59 is used for impedance matching not feed
line
thanks again
Howard

"Howard Kowall" wrote in message
...
Hello all
What determines the Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a
Lindenblad Antenna for 2 Meters

its asked to use

RG-59 polyethylene foam coax with stranded center conductor

I think the VF is .66

I cant find any stranded center cond where I am,so I want to try it with
Solid,but it seems all the solid is VF .88

anyone have any input on this

thanx

howard


It's principally the relative permittivity of the dielectric that determines
the velocity factor. Air alone would yield a value of unity but the
presence of a spacer of some sort means practical values are smaller. Foam
can get close to air.

I wonder why you need a Lindenblad for 2 metres - do you really need good
circular polarisation over a range of elevation angles (and omni HRP, of
course)?

Chris

On Mon, 9 Feb 2009 15:30:50 -0600, "Howard Kowall"
wrote:

sorry I should mention the RG-59 is used for impedance matching not feed
line
thanks again
Howard

"Howard Kowall" wrote in message
...
Hello all
What determines the Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a
Lindenblad Antenna for 2 Meters

its asked to use

RG-59 polyethylene foam coax with stranded center conductor

I think the VF is .66

I cant find any stranded center cond where I am,so I want to try it with
Solid,but it seems all the solid is VF .88

You might want to consider using RG-6/u instead of RG-59. These daze,
the quality of RG-59 coax is rather marginal. I've seen 80% coverage
shielding and cable unsuitable for outdoor use. Meanwhile, the CATV
people have switched to RG-6/u for everything. Much of it is quad
shielded and UV resistant. Velocity factor is usually 0.66 for solid
dielectric and anywhere between 0.7 and 0.9 for various foam
dielectric mixes. When you find a suitable piece of cable, grab the
manufacturer and full part number. Then, lookup the VF on the mfg
data sheet.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

You might want to consider using RG-6/u instead of RG-59. These daze,
the quality of RG-59 coax is rather marginal. I've seen 80% coverage


Beware of the Aluminum foil and shields though. Once it gets wet there is
no stopping the internal corrosion and will generate broadband noise under
power. This includes both RG6 and 9913 and LMR types. They have been
banned from all commercial sites around here.

Bring a knife with you and inspect before you buy. Tinned Copper braid is
better, Silver clad rigid is best.

On Tue, 10 Feb 2009 16:04:16 GMT, "JB" wrote:

You might want to consider using RG-6/u instead of RG-59. These daze,
the quality of RG-59 coax is rather marginal. I've seen 80% coverage

Beware of the Aluminum foil and shields though. Once it gets wet there is
no stopping the internal corrosion and will generate broadband noise under
power. This includes both RG6 and 9913 and LMR types. They have been
banned from all commercial sites around here.

Amazing. I can see it's possible to create a diode mixer junction
with electrolytic action between the aluminum foil and copper braid.
I've never seen broadband noise from coax cable. Usually the foil is
mylar or polyester coated and the copper is tinned or silver plated to
eliminate any points of contact. Most of the radio sites I've seen
are stuffed LMR-400 and LMR-600. Heliax is better, but also far more
expensive. Incidentally, if you want to generate RF noise and mixing,
there's nothing better than an abraided Heliax outer jacket, with the
copper shield touching the zinc galvanized tower.

If intermod were really a problem with foil shielded coax, then the
common residential CATV distribution system would have a big problem
with intermod and mixes. While the buried coax is semi-rigid with a
solid aluminum shield, the pole to house drops are usually quad
shielded RG-6/u (sometimes with a messenger wire) with foil and braid
shields.

Bring a knife with you and inspect before you buy. Tinned Copper braid is
better, Silver clad rigid is best.

Mylar or polyester coated aluminum foil is more important. Scrape the
insulation and see if it flakes loose from the foil. I've seen this
on very old 9913 and some new LMR-400 of dubious origin.

Slight change of topic.... do the commerical sties that ban foil
shielded coax also ban nickel plated connectors? Just curious.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

In article ,
Jeff Liebermann wrote:

Beware of the Aluminum foil and shields though. Once it gets wet there is
no stopping the internal corrosion and will generate broadband noise under
power. This includes both RG6 and 9913 and LMR types. They have been
banned from all commercial sites around here.

Amazing. I can see it's possible to create a diode mixer junction
with electrolytic action between the aluminum foil and copper braid.
I've never seen broadband noise from coax cable. Usually the foil is
mylar or polyester coated and the copper is tinned or silver plated to
eliminate any points of contact. Most of the radio sites I've seen
are stuffed LMR-400 and LMR-600. Heliax is better, but also far more
expensive. Incidentally, if you want to generate RF noise and mixing,
there's nothing better than an abraided Heliax outer jacket, with the
copper shield touching the zinc galvanized tower.

If intermod were really a problem with foil shielded coax, then the
common residential CATV distribution system would have a big problem
with intermod and mixes. While the buried coax is semi-rigid with a
solid aluminum shield, the pole to house drops are usually quad
shielded RG-6/u (sometimes with a messenger wire) with foil and braid
shields.

I don't think those cases (commercial/repeater and CATV) are
comparable.

As I understand it (anecdotal report and discussions with other
repeater owners/builders), the problem with LMR-400 and similar cables
occurs when the cable is used in a duplex application, with RF
transmit power and the incoming receive signal being carried on the
same cable simultaneously.

Under these conditions, it doesn't take very much broadband noise
generation at all (from the cable, connectors, or nearby
metal-on-metal contacts) to cause a problem. The transmitter might be
pumping 50 volts RMS of power into the cable, while the receiver is
trying to pick off a signal of less than a microvolt at a frequency
only 600 kHz away. That's a rather critical environment which really
can't tolerate more than a tiny percentage of noise generation in the
cables, connectors, or duplexer.

I don't think there's any problem with using these sorts of cables in
commercial or amateur service in *simplex* applications... they can
handle transmitting, or receiving, just fine. It's only when you try
to do both, simultaneously, through the same cable. that the noise
generation can become a problem.

The same can be true of some classes of antenna problems. The
repeater system I help maintain developed a serious desensitization
problem, due to internal corrosion/oxidation which occurred in the
antenna after several years up in the weather. I doubt that the
corrosion/oxidation effect would ever have been noticed if the antenna
were in service as a normal (simplex) base antenna - it didn't affect
the transmit SWR or the receive sensitivity at all,

I believe that CATV distribution is a rather easier situation for the
cable to handle, since the signals being carried are all of a fairly
similar and moderate power level. The downstream carrier levels
delivered to the home seem to be around 1 millivolt... that's more
than 60 dB higher than what a repeater's receiver has to be able to
pick out when it's receiving a just-usable signal from the outer edge
of its service area.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Feb 9, 3:26*pm, "Howard Kowall" wrote:
What determines the *Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a Lindenblad Antenna for 2 Meters.

The velocity of propagation (v.p.) in each branch of the feed harness
won't affect the relative field radiation pattern of such an antenna
array as long as the same electrical lengths of coax are used between
the power divider outputs and the feedpoint of each element of the
array.

The v.p. of the main transmission line from the tx to the input of of
the antenna power divider in this scenario is irrelevant.

RF

"Howard Kowall" wrote in message
...
Hello all
What determines the Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a
Lindenblad Antenna for 2 Meters

its asked to use

RG-59 polyethylene foam coax with stranded center conductor

I think the VF is .66

I cant find any stranded center cond where I am,so I want to try it with
Solid,but it seems all the solid is VF .88

anyone have any input on this

thanx

howard

Hi Howard

I am interested in reception of CP signals from all points within the
upper hemisphere. I am curious about your purpose for this Lindenblad.

Jerry KD6JDJ

"Jerry" wrote in message
...

"Howard Kowall" wrote in message
...
Hello all
What determines the Velocity Factor of a coax cable.
Is it the center conductor awg,dielectric,shield or all combined
I am building a
Lindenblad Antenna for 2 Meters

its asked to use

RG-59 polyethylene foam coax with stranded center conductor

I think the VF is .66

I cant find any stranded center cond where I am,so I want to try it with
Solid,but it seems all the solid is VF .88

anyone have any input on this

thanx

howard

Hi Howard

I am interested in reception of CP signals from all points within the
upper hemisphere. I am curious about your purpose for this Lindenblad.

Jerry KD6JDJ


Ever tried crossed 'wilted' dipoles?

Chris