Tom I think everything is real quiet while a bunch of folks are busy
looking at manuals and crunching numbers with their analyzers.
Wes,
The problem Jim suggests is real, but the numbers are so small at HF for
normal good cables they are meaningless. Until we get a really small cable,
w0ri...@sbcglobal.net
To: Bob Kupps n...@yahoo.com; topband topband@contesting.com
Sent: Monday, September 10, 2012 11:04 AM
Subject: Re: Topband: electrical wavelength
Hello Bob,
I have used the published velocity factors for years.
I made a 4:1 balan for my Telrex 20M546 a few years ago
Some flooded foam-core F-6 starts to show what could be problematic velocity
factor changes, for critical phased arrays, below 1 MHz.
Above 1 MHz any change is lost in either measurement errors or cable
dielectric density changes.
___
UR RST IS ...
On 9/11/2012 1:28 AM, Tom W8JI wrote:
but the numbers are so small at HF for normal good cables they are
meaningless.
Not quite. Some measured Vf numbers for Commscope 3227 (#10 solid
copper center, dimensions and shield like LMR400) are:0.8 at 194.5 kHz,
0.816 at about 900 kHz, 0.829 at
Hello Bob,
I have used the published velocity factors for years.
I made a 4:1 balan for my Telrex 20M546 a few years ago with RG14 coax. After I
cut it, I checked it
with my GDO and all was fine.
73 Price W0RI
Hi it's still flooded here but I wanted to fire up one of my verticals by
Let's do some quick math 234/1.82=128.57 gives us the length in feet of a
quarter wave at 1.820 mHz. Multiply that by a velocity factor ( say 85% for
LMR-400) and you get a length of 109.29 feet. The math will tell you that for
every percentage point of velocity factor, it equates to 1.28
On 9/10/2012 9:23 AM, Jim Hoge wrote:
Let's do some quick math 234/1.82=128.57 gives us the length in feet of a
quarter wave at 1.820 mHz. Multiply that by a velocity factor ( say 85% for
LMR-400) and you get a length of 109.29 feet.
That math is a bit too simple, because Vf VARIES as
Let's do some quick math 234/1.82=128.57 gives us the length in feet
of a quarter wave at 1.820 mHz.
That's not correct. The number is 245.8926/F, which is rounded to 246/F.
A quarter wave in freespace is 245.8926/1.82 = ~135.1 feet, not 128.57
234/F is a long way off.
My apologies to the group. I stand corrected. My incorrect constant and overly
simplified math clouded the point I was trying to make. The point was intended
to be that at top band frequencies, each degree of electrical phase winds up
being a little over a foot in length. With relatively
On 9/10/2012 10:44 AM, Tom W8JI wrote:
I firmly do not believe that is true.
Velocity factor in cable is the square root of the inverse of
dielectric constant.
Tom,
Respectfully, I suggest that you go back to your college textbook on the
fundamentals of Transmission Lines. The equations
I thought we were talking about RF.
73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
Likewise, Zo is only sqrt (L/C) at VHF. The more complete equation is
sqrt [ (R+J omega L) /( G + J omega C) ] At VHF, the equation SIMPLIFIES
to sqrt (L/C) At low audio frequencies, and up to VHF, G is insignificant
(leakage) so the complete practical equation is sqrt [(R+ j omega L) / j
Run the numbers and for RG-6 we see that sq root of L/C is good above a
couple hundred kHz.
Dave WX7G
On Sep 10, 2012 2:37 PM, Jim Brown j...@audiosystemsgroup.com wrote:
On 9/10/2012 10:44 AM, Tom W8JI wrote:
I firmly do not believe that is true.
Velocity factor in cable is the square
On 09/10/2012 07:42 PM, DAVID CUTHBERT wrote:
Run the numbers and for RG-6 we see that sq root of L/C is good above a
couple hundred kHz.
Does that have any consequences when planning phasing lines
for a receive 4-square that is to be used on eg. 137 kHz?
Are there types of coax that are more
Run the numbers and for RG-6 we see that sq root of L/C is good above a
couple hundred kHz.
Dave WX7G
I just ran it in MathCAD and it showed a Zo and Vf slope starting down
around 150 kHz, but I assumed the conductors were solid copper. Conductors
have to be in the thousands of a inch range
PM
To: topband@contesting.com
Subject: Re: Topband: electrical wavelength
Run the numbers and for RG-6 we see that sq root of L/C is good above a
couple hundred kHz.
Dave WX7G
I just ran it in MathCAD and it showed a Zo and Vf slope starting down
around 150 kHz, but I assumed the conductors
Hi it's still flooded here but I wanted to fire up one of my verticals by
itself on 160 and feed it with a half wave of Comscope RG6 since I don't have
enough 50 ohm line to reach it. I have a AIM 4170 to cut the line with but my
question to the group is - how much variation from published
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