LinkBack Thread Tools Search this Thread Display Modes
Prev Previous Post   Next Post Next
  #5   Report Post  
Old August 14th 06, 03:34 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 167
Default QFH Antenna and 72ohm TV Coax

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





 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT +1. The time now is 08:10 AM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017