RG-6 coaxil cable
 

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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RG-6 coaxil cable
 

"Alejandro Lieber" wrote in message
...
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


Yes you can.

Some RG-6 cable has an aluminum shield and can not be soldered to if that is
a problem for you.

RG-6 coaxil cable
 

Ralph Mowery wrote:
Some RG-6 cable has an aluminum shield and can not be soldered to if that is
a problem for you.

In June, we had a long discussion of RG-6 coax, the proper connectors to use
for it, and how well it works.

To recap, you need to buy COMPRESSION connectors and the correct tools for them.
"F" connectors are used all over the world in the cable tv and satellite
industry. F to UHF (aka PL-259) adaptors are available and work well.

In my case, I have a cheap source of BNC to to UHF adaptors, F to UHF adaptors
are hard to find and expensive. So I use compression BNC connectors for those
ends.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
To help restaurants, as part of the "stimulus package", everyone must order
dessert. As part of the socialized health plan, you are forbidden to eat it. :-)

RG-6 coaxil cable
 

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.

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.

RG-6 coaxil cable
 

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

--- 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.

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

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

RG-6 coaxil cable
 

"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.

RG-6 coaxil cable
 

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.

RG-6 coaxil cable
 

Alejandro Lieber wrote in
:

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.

That should be fine. See my notes at
http://vk1od.net/transmissionline/RG6/index.htm . See Fig 2, RG6 should
handle over 1kW continuous at 14MHz at unity VSWR, over 500W at 2:1
VSWR.

The article also shows a BNC connector option which IMHO is superior to
F connectors.

....
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

An alternative method of matching is to shorten the vertical a little
from a quarter wave, and use a shunt s/c stub. See
http://vk1od.net/transmissionline/QWVmatch/QWVmatch.htm for a
description of this and another method of matching.


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

This isn't entirely clear to me.

Owen

RG-6 coaxil cable
 

Owen Duffy wrote:

The article also shows a BNC connector option which IMHO is superior to
F connectors.

BNC compression connectors are available. They are much harder to install
properly than F connectors, but once you "get the hang of it", they work fine
and are sturdy. BNC to UHF adaptors are also available, and the ones I have
seen are better quality than the F to UHF ones.

I don't know if they are as water resistant as the F connectors designed for
outdoor use, but UHF (PL-259) connectors are in comparison sponges, so if
you are used to them, you should be able to deal with BNC connectors.

Note that there are different connectors for RG-59, RG-6 (not quad
shield) and RG-6 quad shield, and they can not be used on cables they
are not designed for. Either they don't fit on properly and don't make
connections, or fall off. :-(

You can buy a package of compression 50 BNC connectors and the appropriate
tool with international postage for about $50 on eBay.

There are three kinds of compression connectors I have seen so far.
One is a one piece solid connector, which when compressed, the back end
folds into itself (think of a metal accordian). The second is made from
two pieces fitted together, and when you compress it, the part in the back
is compressed into the front.

Both work well, and if you get the trimming right, will fit well. I found
on the two piece verisions I have, the center conductor has to be trimmed
to 3mm. 4 or more and they fall off. :-(

Note that when I say two piece, when you get them they are both one piece
and can not be separated. It's just obvious that not counting the ring,
they were made from one or two pieces.

There also is a third kind I have so far only seen in F connectors where
the front pushes into the back. I tried many in all sorts of ways and cables,
and either end up with it falling off, or making a solid fitting but no contact
to the shield (ground). :-(

Any advice on how to get them to work would be appriceated. I still have
around 30 of them.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
To help restaurants, as part of the "stimulus package", everyone must order
dessert. As part of the socialized health plan, you are forbidden to eat it. :-)

RG-6 coaxil cable
 

On 08/13/2010 06:20 PM, Owen Duffy wrote:
Alejandro wrote in
:

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.

That should be fine. See my notes at
http://vk1od.net/transmissionline/RG6/index.htm . See Fig 2, RG6 should
handle over 1kW continuous at 14MHz at unity VSWR, over 500W at 2:1
VSWR.

The article also shows a BNC connector option which IMHO is superior to
F connectors.

...
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

An alternative method of matching is to shorten the vertical a little
from a quarter wave, and use a shunt s/c stub. See
http://vk1od.net/transmissionline/QWVmatch/QWVmatch.htm for a
description of this and another method of matching.

The idea is to increase the radiation resistance, not to decrease it, so
has to increase efficiency.


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

This isn't entirely clear to me.

Owen

If I define radiation efficiency as:

Rr/(Rr+Rl)

where Rr; radiation resistance
and Rl: loss resistance

and take Rl=5 ohms for 8 radials of 8 feet each

For a 25º length radiator: 36/(36+5) = 88%
For a 32º length radiator: 100/(100+5) = 95%

Losses are reduced from 12% to 5% by only adding 5 feet to the 20 meter
vertical quarter wave antenna and with a 75 ohm coax of 1,25 wavelength
I can get a perfect match to a 50 ohm output impedance transmitter.

Alejandro Lieber
Rosario Argentina


Real-Time F2-Layer Critical Frequency Map foF2 at:

http://1fcr.com.ar

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