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Author Topic: What coax to use between my radios, tuner ,amp etc. (inside shack not to antenna  (Read 11656 times)
KB2HUK
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« on: December 11, 2011, 05:39:12 PM »

Hi All , I am remodeling my shack and would like to use as flexable cable as I can to go from Radio , to tuner , amp etc. I am talking about HF freqs only and at 1500 watts.Length of cableling will be no longer than  6 feet .  Thanks for your help in advance John Molenda kb2huk
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N3WAK
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« Reply #1 on: December 12, 2011, 04:24:08 AM »

John--There's a lot of coax information on the web, and in books, like the ARRL antenna book.  You really should do some of your own research, because it's all out there and instantaneously available.  Here's one link to get you started:  http://www.radio-ware.com/
It has a handy "coax applications" chart. 

Good luck.  73, Tony
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WX7G
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« Reply #2 on: December 12, 2011, 05:34:10 AM »

RG-8X is fine and is what I use.
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N3WAK
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« Reply #3 on: December 12, 2011, 10:47:20 AM »

John--WX7G is right for the most part, but I'm sure your tuner is between your amp and your antenna.  While it's fine to use RG-8X between your transmitter and the amp, you can't use it on the antenna-side of your amp.  1500 watts is too much for RG-8X to handle. 
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W7ETA
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« Reply #4 on: December 12, 2011, 04:20:56 PM »

Old ARRL Hand Books, from the 40s, 50s and early 60s, have tons of useful information presented in easy to read format.  They are cheap on eBay and qualify for cheap mailing rates.

For what you are doing the loss in the jumpers for HF will be insignificant.  The SWR should be very low.  The "power" between your rig to amp is very low.

Since the SWR between your amp and the tuner will be very low, as others have mentioned, you can use RG8x.

I prefer to use coax with almost or 100% braid.

If you use RG8X, consider double checking that none of the center strands connect with the braid.  As i discovered, it is easy not to see one of the copper strands is touching the shield inside of a PL259.

73
Bob
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W8JI
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« Reply #5 on: December 13, 2011, 07:19:00 AM »

John--WX7G is right for the most part, but I'm sure your tuner is between your amp and your antenna.  While it's fine to use RG-8X between your transmitter and the amp, you can't use it on the antenna-side of your amp.  1500 watts is too much for RG-8X to handle. 

Every test bench at Ameritron, since the 1980's, has used RG8X. One amplifier after another, some running  well over 2000 watts, is tested on carrier through RG8X.

My shop test bench uses RG8X jumpers. I cook amplifiers at up to 3 kW carrier on that bench. The cable gets warm on 15 or ten meters at a few kilowatts for a few minutes, but I've never once had one fail.

I use it myself here for in-station jumpers at 1500 watts without a problem. I even have it on my siz meter amp that runs 1300 watts output on CW.

Better quality RG8X is perfectly fine at 1500 watts, provided the connectors are installed properly and the cable has some exposure to air.

73 Tom

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N3WAK
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« Reply #6 on: December 13, 2011, 07:33:58 AM »

Well, then, I will certainly defer to the experts--such as Tom, W8JI.  I based my view that RG8X wouldn't handle 1500 watts based on the Belden specification sheet that I found on the Davis RF website.  That showed that Belden's RG8X was good to 1000 watts at 10 mHz.  If amateur practice shows that to be too overly conservative, then I am wrong. 

Sorry I provided inaccurate information. 

73, Tony
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KB2HUK
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« Reply #7 on: December 13, 2011, 08:50:52 AM »

Doesn't the length of the run effect how much it can handle as well ?  I would be using jumpers under 6 foot in length at 1500 watts ?  John kb2huk
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VE3FMC
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« Reply #8 on: December 13, 2011, 04:41:23 PM »

Doesn't the length of the run effect how much it can handle as well ?  I would be using jumpers under 6 foot in length at 1500 watts ?  John kb2huk

I use RG8X for all of my station patch cables. I have run 1000 watts through them and never had one fail or have any SWR issues. I prefer RG8X as it is more flexible than RG-213 when it comes to running the cables behind the equipment.

In fact my 40 meter dipole is also fed with RG8X, 50 foot run. No problems there either and the loss in that length of RG8X is not an issue at that frequency.
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W7ETA
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« Reply #9 on: December 13, 2011, 09:27:43 PM »

I used to use it to feed an 75 meter inverted Vee.
73
Bob
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W5LZ
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« Reply #10 on: December 15, 2011, 03:58:32 PM »

If the impedance is the same as the rest of the system (50 ohms) it doesn't make a lot of difference what you use as long as it's of decent quality.  I'd stop at RG-58, nothing 'smaller'.  For use after an amplifier it wouldn't hurt to use something maybe larger than RG-58.  Except for that, use whatever you happen to have enough of.
 - Paul
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KA3NXN
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« Reply #11 on: December 22, 2011, 06:49:03 AM »

I too have used good quality RG8-X for patch cables and have run 2KW through them  for almost 30 years with no issues what so ever. For connectors don't use the cheap Chinese imports. Use quality Amphenol solder-on connectors. In fact Radioworks, the company that makes the Carolina Windom antenna sells and recommends RG8-X for use with all their wire antennas.

Jaime-KA3NXN
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K1CJS
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« Reply #12 on: December 30, 2011, 06:50:46 AM »

Well, then, I will certainly defer to the experts--such as Tom, W8JI.  I based my view that RG8X wouldn't handle 1500 watts based on the Belden specification sheet that I found on the Davis RF website.  That showed that Belden's RG8X was good to 1000 watts at 10 mHz.  If amateur practice shows that to be too overly conservative, then I am wrong. 

Sorry I provided inaccurate information. 

Don't be, Tony.  There are some cheaper RG8X knockoffs that shouldn't even be used at 500 watts.  Note that Tom said better quality RG8X.  73!
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WB6BYU
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« Reply #13 on: December 30, 2011, 01:52:14 PM »

And Tom did acknowledge that the cables get warm on the higher frequencies.  I suspect that
the Belden spec is for 100% duty cycle for cables packed into conduits where there is little
opportunity for heat dissipation.  At a lower duty cycle and in free air the heat build-up won't
be as much of an issue.

Quote from: KB2HUK
Doesn't the length of the run effect how much it can handle as well ?

Not really.  Length affects the total losses in the transmission line, but the power rating is
really based on three different factors:

(1) the maximum voltage that the line can handle without arcing over
(2) the maximum current that the line can handle without burning out
(3) the maximum heat per unit length that the line can dissipate due to losses

#1 is independent of frequency, but depends on the SWR.  What works between the amp and
the tuner might not be a good choice on the output of the tuner, where the SWR (and hence
the voltages) will be higher.  It is degraded by poorly-installed connectors and mechanical
damage such as driving over the coax, cinching a tie-wrap too tight around it when securing
it to a tower leg, or simply bending it too sharply in the hot sun.  The foam insulation is more
prone to compression than solid polyethylene types.

#2 is rarely a problem, as the other limits will be usually be reached before the center conductor
acts like a fuse.  It might be more of an issue with higher impedance lines that have a thinner
center conductor.

#3 is what most folks have been discussing on this thread:  each cable will have a loss in dB
per unit length that increases with frequency.  That causes heating along the whole cable
until it reaches thermal equilibrium where the heat radiated is equal to that being generated.
If it gets too hot the insulation is likely to melt.  The better the air flow around the cable, and
the lower the loss, the higher the power it can handle without overheating.
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KC8Y
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Posts: 240




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« Reply #14 on: January 10, 2012, 04:25:36 PM »

Ever since I've been in the hobby (+40 years), use ONLY RG-8x & RG-58 coax cables (inside) between xcvr, tuner & some meters /never run more than 100-watts
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