"Wimpie" wrote in message
...
On 3 ago, 04:08, Alejandro Lieber wrote:
I would like to know if I can use RG-6 75 ohm coaxil TV cable to feed a
14 Mhz dipole with 100 watts PEP.

Thank you very much.

Alejandro Lieber
LU1FCR
Rosario Argentina

http://www.1fcr.com.ar

--- news://freenews.netfront.net/ - complaints: ---

Hello Alejandro:

If you can solve the mechanical issues, yes you can.

When it has an electrical length n*0.5lambda (n= 0, 1, 2, etc), VSWR
will be exactly the same as with a 50 Ohms cable. With other length
(especially 0.25, 0.75 lambda, etc) length, you may get change in VSWR
(can be both better or worse).

When your dipole is about 50 Ohms (antenna side), just match it at the
transceiver side if required, and don't worry about the cable loss due
to VSWR inside the cable. When the antenna itself shows VSWR=1 (based
on 50 Ohms), your VSWR at the transceiver side should not be worse
then 2.25.


Problem with all that is the dipole may be closer to 70 ohms than it is to
50 ohms. With 70 ohm cable, the swr will be close to 1:1. However most swr
and wattmeters that I have seen are for 50 ohm systems and will not show the
actual swr.
Cable losses with an swr of less than say 2:1 will be low enough not to make
any differance in the real world.

On Tue, 3 Aug 2010 12:21:37 -0700 (PDT), Wimpie
wrote:

On 3 ago, 04:08, Alejandro Lieber wrote:
I would like to know if I can use RG-6 75 ohm coaxil TV cable to feed a
14 Mhz dipole with 100 watts PEP.

Thank you very much.

Alejandro Lieber
LU1FCR
Rosario Argentina

http://www.1fcr.com.ar

--- news://freenews.netfront.net/ - complaints: ---

Hello Alejandro:

If you can solve the mechanical issues, yes you can.

When it has an electrical length n*0.5lambda (n= 0, 1, 2, etc), VSWR
will be exactly the same as with a 50 Ohms cable. With other length
(especially 0.25, 0.75 lambda, etc) length, you may get change in VSWR
(can be both better or worse).

Additionally the dipole may be a better match for 75 ohms than 50
depending on height and surrounding conditions.
I used 3/4" 75 ohm coax for low loss, long runs for years with no
problems and never paid attention to length.

OTOH at times using a commercial multi band vertical I had to play
with the 50 ohm coax length even when the antenna was a good match.

Stateside the F to UHF connectors are relatively inexpensive and
common. They may not be the best quality but work well indoors.

73

Roger (K8RI)


When your dipole is about 50 Ohms (antenna side), just match it at the
transceiver side if required, and don't worry about the cable loss due
to VSWR inside the cable. When the antenna itself shows VSWR=1 (based
on 50 Ohms), your VSWR at the transceiver side should not be worse
then 2.25.

You can use same common mode current suppression techniques (balun,
ferrite common mode chokes, trap, etc) as with a 50 Ohms cable.

Best regards,

Wim
PA3DJS
www.tetech.nl
without abc in the address, PM will reach me very likely.