I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

On Mon, 14 Aug 2006 07:44:10 GMT, "Lee"
wrote:

I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

It will work perfectly, because the TV coax is good HF quality.

Why do you use a 4 turn choke?

w.

"Helmut Wabnig" *_.-_- wrote in
message ...
On Mon, 14 Aug 2006 07:44:10 GMT, "Lee"
wrote:


It will work perfectly, because the TV coax is good HF quality.

Why do you use a 4 turn choke?

w.

Sorry, typo!.........Balun!!

Thanks, thought so.

Lee.....de G6ZSG......

On Mon, 14 Aug 2006 07:44:10 GMT, "Lee" wrote:

I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

Hi Lee,

Consider this: If your QFH has a 50-ohm terminal impedance, the mismatch is only
1.44: 1. Therefore, the loss due to the mismatch is 0,14 dB, insignifiant--use
the 72-ohm line and forget the miniscule mismatch.

Even if the mismatch was 2:1, the reflection loss is only 0.51 dB.

Concerning the 4-turn choke, nothing happens to the matching operation, because
nothing inside the coax changes due to the coiling of the coax.

Walt, W2DU

Please leave me out of this. I'm mentally handicapped!

I don't know, never did know, how to use an old fashioned, mid-20th
century Smith Chart.
----
Reg.





"Walter Maxwell" wrote in message
...
On Mon, 14 Aug 2006 07:44:10 GMT, "Lee"
wrote:

I`m building a QFH NOAA weathersat antenna and wish to use low loss
t/v coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm
RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i
believe i can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

Hi Lee,

Consider this: If your QFH has a 50-ohm terminal impedance, the
mismatch is only
1.44: 1. Therefore, the loss due to the mismatch is 0,14 dB,
insignifiant--use
the 72-ohm line and forget the miniscule mismatch.

Even if the mismatch was 2:1, the reflection loss is only 0.51 dB.

Concerning the 4-turn choke, nothing happens to the matching
operation, because
nothing inside the coax changes due to the coiling of the coax.

Walt, W2DU

"Lee" wrote in message
k...
I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v
coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i
can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

Hi Lee

There are alot of affordable amplifiers designed for TV that you could use
at the base of your QFH. You might consider building your owm amplifier to
fit in the base of the QFH.
I wouldnt recomend the use of a pre-amp at the antenna for NOAA satelite
station. They often cause more problems than they solve.
All Electronics has alot of ferrite tubes that can be used to fit over the
coax so you wouldnt need the "4 turn choke".

Jerry

"Walter Maxwell" wrote in message
...
On Mon, 14 Aug 2006 07:44:10 GMT, "Lee"
wrote:

I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v
coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i
can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

Hi Lee,

Consider this: If your QFH has a 50-ohm terminal impedance, the mismatch
is only
1.44: 1. Therefore, the loss due to the mismatch is 0,14 dB,
insignifiant--use
the 72-ohm line and forget the miniscule mismatch.

Even if the mismatch was 2:1, the reflection loss is only 0.51 dB.

Concerning the 4-turn choke, nothing happens to the matching operation,
because
nothing inside the coax changes due to the coiling of the coax.

Walt, W2DU

"Walter Maxwell" wrote in message
...
On Mon, 14 Aug 2006 07:44:10 GMT, "Lee"
wrote:

I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v
coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i
can
but, will the impedence affect
the 4 turn choke ????...

Should read `Choke Balun`....sorry, my typo...

I`m following a design by Bill Sykes G2HCG & Bob Cobey G0HPO
which calls for RG58 with a four turn choke balun....


Thanks.

Lee......de G6ZSG.....

Hi Lee,

Consider this: If your QFH has a 50-ohm terminal impedance, the mismatch
is only
1.44: 1. Therefore, the loss due to the mismatch is 0,14 dB,
insignifiant--use
the 72-ohm line and forget the miniscule mismatch.

Even if the mismatch was 2:1, the reflection loss is only 0.51 dB.

Concerning the 4-turn choke, nothing happens to the matching operation,
because
nothing inside the coax changes due to the coiling of the coax.

I`ll try making the feed RG58 with the choke balun and then feed that with
72ohm...

Thanks....

Lee......de G6ZSG.....

"Jerry Martes" wrote in message
news:hU%Dg.12256$hH1.9718@trnddc08...

"Lee" wrote in message
k...
I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v
coax
which is
72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58
specified
over a 100ft run!.... ( RF pre-amps aint cheap! ).......

What are the pros and cons... can i use CT100 72/75ohm..... i believe i
can
but, will the impedence affect
the 4 turn choke ????...

Thanks.

Lee......de G6ZSG.....

Hi Lee

There are alot of affordable amplifiers designed for TV that you could
use
at the base of your QFH. You might consider building your owm amplifier
to
fit in the base of the QFH.
I wouldnt recomend the use of a pre-amp at the antenna for NOAA satelite
station. They often cause more problems than they solve.
All Electronics has alot of ferrite tubes that can be used to fit over
the
coax so you wouldnt need the "4 turn choke".

`4 turn Choke Balun`.....typo....


Jerry

Thanks Jerry, i`ll give it some thought as i`m right under some pmr towers
which breaks through a little from 150megs pagers and a preamp may worsen
things...

Lee....de G6ZSG....

Reg Edwards wrote:
I don't know, never did know, how to use an old fashioned, mid-20th
century Smith Chart.

Reg, I'm curious how you would solve this stub problem
without a Smith Chart.

| 45 deg | 45 deg |
Source====Z01=========Z02====open

Stub sections are lossless. Z01 = 600 ohms and is 45
degrees long. Z02 = 50 ohms and is 45 degrees long.
What is the impedance looking into the stub from the
source?
--
73, Cecil http://www.qsl.net/w5dxp