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Author Topic: RG-11 Coax  (Read 4468 times)
KC0GCM
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Posts: 3




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« on: December 14, 2001, 04:53:44 PM »

just wanted to get some input on using RG-11 Coax instead of RG-8 I was just given a 500 foot spool and would like to use it if it will work right


   any info or comments welcom

       thanks


              kevin (KC0GCM)Kingman KS.
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AB0SY
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Posts: 1




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« Reply #1 on: December 14, 2001, 05:36:44 PM »

RG-11 is good coax but it's not 50 ohm.  It's cable TV coax and is used where drops (cable runs) from the pole to the house is too long for the smaller RG-6.

If you have an application for 75 ohm coax then this is the cable to use.
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KL7IPV
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Posts: 984




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« Reply #2 on: December 14, 2001, 07:54:03 PM »

Use it! It will give you an SWR of 1.5:1 and will work okay for most applications. It is double shielded (if I remember it correctly) and it is a dog to install connectors to, but after that, it will work okay.
73
Frank
KL7IPV
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WB2WIK
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Posts: 20595




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« Reply #3 on: December 17, 2001, 02:27:32 PM »

I guess it depends on what you need to "work right."

Good-quality (mil-spec) RG11/U is fine cable and performs about the same as good-quality (mil-spec) RG213/U, which is its 50 Ohm counterpart.  The fact that RG11/U is 75 Ohm cable isn't terribly important in many applications.

In fact, using 75 Ohm cable to feed a half-wave dipole up 1/2-wave above ground, you'll likely have a better match than you would using 50 Ohm cable.  Problem: Most amateur test instrumentation (like SWR bridges and Wattmeters) are designed for use in 50 Ohm lines.  When used in line with 75 Ohm cable, you'll get errors in readings.  Whether this is important to you or not, is up to you.

73 de Steve, WB2WIK/6
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AC5UP
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Posts: 3864




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« Reply #4 on: December 19, 2001, 07:18:23 PM »

Use It!

For HF work, and the low bands in particular, there won't be any significant difference once you have your antennas pruned. You can't beat the cost-performance ratio with a deal like that...
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AK4DD
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Posts: 5




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« Reply #5 on: March 15, 2002, 11:17:02 PM »

use it-hf uses as noted above-
very low loss on uhf.-1.6db loss on 440 makes a huge difference.
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DMB
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Posts: 1




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« Reply #6 on: March 25, 2002, 08:10:01 PM »

While some feel it is unimportant, and to a degree it is, here are some things to keep in mind. Depending on the type of antenna you are using, this will determine if 75 Ohm coax is the right choice. Loading is the thing that is the issue. Co-phased antennas need 75 Ohm leads cut at odd 1/4 wave intervals (1/4, 3/4, 5/4...) to the point where they merge, and at the point where they meet they act as a matcher back to 50 Ohm. You then continue your downlead at half wave intervals of 50 Ohm to the transmitter, unless they both merge at the amp itself. If you are critical about your equipment (reference work) you will want to properly "load" the amplifier. You can use these equations to determine the proper lengths of the coax in feet. For 1/4 wave you use 246 / desired frequency * velocity factor of the coax. For 1/2 wave double the first value to 492. You need to make sure your SWR readings are taken at the any 1/2 wave point of the centered frequency, (the frequency of antenna resonance) to ensure you will get the proper "reflective" reading back. So before you go and hook that SWR close to the amp and start taking readings make sure you have at least one half wave of any given coax used (remember that every type and make of cable can have different a velocity factor, thus it's length to be at 1/2 wave will differ) between the amp itself and the SWR meter. (no 3 foot jumpers in other words) If you have cut your lengths right, the SWR will fall at a 1/2 wave interval from the amp, and also a 1/2 wave interval from the antenna. (2 odd 1/4 lengths of 75 Ohm when merged will end at one multiple of a 1/2 wave) Can you use 75 Ohm for your rig? Sure. Is it prudent? This you have to answer for yourself. (my personal opinon is no)
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AA4PB
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Posts: 12836




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« Reply #7 on: March 25, 2002, 11:09:15 PM »

RG-11 is 75 ohms. If your antenna were 50 ohms then using it would result in a 1.5:1 SWR which is not too bad. If you have a dipole mounted high above ground your antenna impedance is likely to be closer to 75 ohms than to 50 ohms anyway so it might even provide a lower SWR than RG8. For HF dipoles and such it should be just fine.
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KC2YU
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Posts: 58




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« Reply #8 on: April 10, 2002, 04:01:30 PM »


I have a similar question:

I live in an apartment in NYC and the best (and only, according the Mrs.) route from radio room, as it were, to the terrace, where I'd like to put a 2 meter vertical as well as an HF dipole or loop, is using the already-in-the-wall RG6 (75ohm, quad shield CATV coax cable).

I understand (I think) that the match between the antenna(s) and the cable is something to look for.  Will I be able to match a 2 meter vertical and/or HF dipole/loop to the 75 ohm cable?  What about on the rig side -- for HF I've got a tuner, but not for VHF?

Is there a device that is pre-set to tranform 50 ohm to 75 (without loss)?

Thanks very much,

Joseph R. Skoler, kc2yu
joseph@compuhelp.com
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KQ6Q
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Posts: 976




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« Reply #9 on: July 27, 2002, 09:30:23 PM »

Using RG-6 already in the wall, you are skating on thin ice for RFI to your neighbors. You could get by using it for VHF/UHF keeping your power low (just your HT!). I would not run HF through it, unless you stick with QRP - again, not because of the power limitations of the cable, but because of the possibility of RFI to your neighbors. Proceed with care!
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KQ6Q
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Posts: 976




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« Reply #10 on: July 27, 2002, 09:32:00 PM »

The RG-11 is just fine for HF - and if you can run an antenna longer than 1/4 wave, it's perfect. I used RG-11 (surplus, free, just like yours) to feed a dipole with 45 foot legs on 20 meters - a 3/2 wave dipole, and it worked great. Give it a shot, you've got nothing to lose!
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