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Author Topic: RG 6 Coax  (Read 1899 times)
WT8E
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Posts: 55




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« on: December 15, 2012, 11:12:49 AM »

I want to install a Hustler 6BTV ground mounted and feed it with RG 6 Coax.  What kind of problems can I expect if I use RG 6 instead of RG 8.
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WB6BYU
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« Reply #1 on: December 15, 2012, 11:30:03 AM »

Losses are probably lower using RG-6, but the 75 ohm impedance means the SWR may
be a little higher in the shack (depending on the length of the coax.)  If that is a
problem on a particular band, try adding a few extra feet of coax and see if that
makes a difference.  You might not get all the bands to have low SWR with the same
coax length:  in that case, either provide a way to switch in some jumpers or use
a tuner in the shack.
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N6AJR
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« Reply #2 on: December 15, 2012, 12:45:12 PM »

It will work fine up to a couple of hundred watts. Most rg 6 is made as receiving coax, and comes with F connectors, so either add your own rg6 connectors, or get some F to pl259 adapters for it.  the antenna end calls for a couple of spade lugs if I remember right. use dome rain coat tape to seal the, ( also called rescue tape.)  you may be able to find these at High Sierra, they have lots of parts available.

just keep the power below 200 watts and  expect to see a 1.5 to 1 swr when tuned to lowest  point.
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WB6BYU
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« Reply #3 on: December 15, 2012, 01:19:11 PM »

Quote from: N6AJR

just keep the power below 200 watts and  expect to see a 1.5 to 1 swr when tuned to lowest  point.



Well, not necessarily.  If the antenna is 50 ohms then the SWR on the 75 ohm coax would
indeed be 1.5 : 1, but the SWR relative to 50 ohms at the transmitter end could be as high
as 2.25 : 1, or it might be 1 : 1, or anywhere in between, depending on the length of the
coax (in wavelengths.)

For example, if the RG-6 is 1/4 wave long, then 50 ohms at the far end would get transformed
to 112 ohms at the shack.  But if the coax is 1/2 wave it would be 50 ohms.  Of course this
would vary with frequency, since a quarter wave at 40m is a half wave on 20m.

It gets even more complicated because the antenna might not be exactly 50 ohms.  Let's say
that the SWR at the antenna relative to 50 ohms is 1.33 : 1.  If this is because the antenna is
37.5 ohms, then a quarter wave of 75 ohm coax would transform it to 150 ohms, and the
SWR in the shack would be 3 : 1.  But if the antenna were 66.7 ohms (which would have
the same SWR) then a quarter wave section would transform it to 85 ohms, for an SWR of
1.7 : 1, which is probably still usable without a tuner.

If the antenna happens to be 75 ohms, then we'll have a 1.5 : 1 SWR in the shack (measured
relative to 50 ohms, as will be the case with most equipment) regardless of the coax length.
But with 50 ohms, or other impedances that would give a usable SWR on 50 ohm coax, it will
vary more widely due to the transformation effect of the 75 ohm coax.

If you cut the feedline to a half wave on 40m (which would be about 55 feet) then it will
be close to a multiple of 1/2 wavelength on 40, 20, 15 and 10m, and should give a usable
SWR without too much trouble.  On some other bands you might need a tuner.
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W9GB
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« Reply #4 on: December 15, 2012, 04:03:22 PM »

Quote
I want to install a Hustler 6BTV ground mounted and feed it with RG 6 Coax.  What kind of problems can I expect if I use RG 6 instead of RG 8.
Proper installation of coaxial connectors on RG-6/U coaxial cable (CRIMP connectors/Snap-N-Seal -- Impossible to solder aluminum braid/foil used on RG-6/U) and
QUALITY Adapters ($$) to the UHF connectors used with HF amateur radio equipment.
« Last Edit: December 15, 2012, 04:06:52 PM by W9GB » Logged
W0BTU
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« Reply #5 on: December 15, 2012, 04:08:50 PM »

Below 20 meters, RG-6 will handle the legal limit continuously (AM, RTTY); and intermittently (SSB and CW) above that. See figure 2 on http://vk1od.net/transmissionline/RG6/ .

It has about the same loss as RG-213 (see figure 1 there).
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WT8E
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Posts: 55




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« Reply #6 on: December 16, 2012, 08:07:24 AM »

Tnx guys, that is the kind of information I was looking for. Just going to be running 100 watts max and I do have a couple of tuners as well as the internal turner in the rig.
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KB2HSH
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« Reply #7 on: December 26, 2012, 08:06:06 AM »

I have a portable 10m dipole that I have used for YEARS with RG-6/U as the feed, with BNC compression fittings.  That antenna has lasted many Field Days and many portable operations. 

John
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