On 08/03/2010 04:21 PM, Wimpie wrote:
On 3 ago, 04:08, Alejandro 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

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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.

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.

I also plan to use the 75 ohm cable to feed a vertical for 20 meters 32º
high, that is to say aprox. 22 feet.

With that high, the impedance is 100 + i145 ohms. The reactance is
inductive and I will tune it out with a 80 pf capacitor in series made
with the same cable.

The feed line will be 1 +1/4 lambda so at the input of the line the
impedance will be (75 x75)/108 = 52 ohms

The 8 radials will be 4 feet long with loses of aprox 5 ohms, so
efficiency will be near 94%.

Alejandro Lieber
Rosario Argentina
LU1FCR

http://1fcr.com.ar

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