RG-6 vs RG-58

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N4JWA, Jan 8, 2011.

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  1. N4JWA

    N4JWA Ham Member QRZ Page

    I use to be in the cable business. I worked for Time Warner. I have a roll of RG-6 Cable. Is there any reason RG-6 won't work just as good as the common and more expensive RG-58? Just wondering I am new to HAM and would like to know.
     
  2. K5PO

    K5PO Ham Member QRZ Page

    Depending on the application, it might work better. It is a lower loss cable than RG-58. This chart will give you some idea of the losses associated with many standard cables:

    http://www.timesmicrowave.com/cgi-bin/calculate.pl

    In terms of amateur radio use, RG-6 will usually not be the cable of choice as nearly all amateur radio cable needs require 50 ohm cable and RG-6 is a 75 ohm cable. That is not to say there is no use for it in ham, but a 50 ohm cable like RG-58 will be much more common.

    Perhaps more details on what you are trying to do with this cable will allow us to provide more specific guidance.
     
  3. K1DNR

    K1DNR Ham Member QRZ Page

    Lots of people here use RG6 in different applications. I have tons of it.

    The characteristic impedance is 75 ohms of course, and not 50 ohms.

    So you have a mismatch you may or may not need handle. It depends on the circumstances and what you are doing.

    It also depends on the length.

    The biggest challenge may be connectors. Its hard to solder aluminum.

    There are adapters, F to Pl-259 but the ones I've used tend to suck and don't properly fit some so-259's because they are too short. There's also no telling what the loss is. But it all depends on the application.

    Short answer is for most HF applications, you can use it.

    Check out VK1OD's calculator for information on losses.
     
  4. W0BTU

    W0BTU Subscriber QRZ Page

    Aluminum shielded CATV RG-6 is all I use here. I have over 1000' of the flooded variety running to different antennas, all using F connectors.
     
  5. 4L4AGU

    4L4AGU Ham Member QRZ Page

    Is there any wideband transformer design available, to match 75 ohm to 50 ohm transceiver output?
     
  6. W0SGM

    W0SGM XML Subscriber QRZ Page


    then using F to UHF adaptors ? I have quite a bit of rg6 laying around too I could use..not the flooded type though
     
  7. VA3CQC

    VA3CQC Ham Member QRZ Page

    Well for all my kvetching in the other thread I decided to try it. I found an old broken (as in: the memory is scrambled and resets every time you power on, the RF section is ok) 2m radio, and with a midland commercial antenna (162mhz, with some aluminum tape to make it sorta better on 2m) and some RG6 I went to work.

    I must say I pretty much broke off all the braid trying to clamp it down in the connector but eventually I got it, soldered it, and placed it outside. And it works quite well. Performance on transmit and receive is pretty good, though the location of the antenna could be better.

    Then I checked the SWR, and it was 3:1 in a best case and over 5:1 in a worst case. The best thing is, the radio still works and hasn't overheated. I wonder how long it will take? It's been a couple months now and I talk on it every other day or so.

    So I'd say it works. But working with the aluminum braid is NOT IDEAL, and it breaks constantly, I dunno what's up with that, maybe you need to use the tool instead of doing it manually.
     
  8. VK1OD

    VK1OD Ham Member QRZ Page

    Appropriate quality cable with appropriate quality connectors work just as 75 ohm line should.

    Hams started using coax to a larger extent following WWII, and lots of the coax being disposed of by the services was 75 ohm coax, so lots of it was used for ham applications. There is nothing new there!

    Sure, most radios these days are designed for a nominal 50 ohm load, but few HF antennas offer a very low VSWR 50 ohm load to the line, so HF antenna systems don't usually use near perfectly matched 50 ohm components.

    In many configurations, it doesn't matter a lot whether 75 or 50 ohm line is used, and RG6 may have better efficiency than RG8X.

    I wrote some notes at RG-6/U for transmitting applications . They discuss loss, power handling, cable types, connectors and impedance matching.

    Owen
     
  9. KM1H

    KM1H Subscriber QRZ Page

    Ive been using 75 Ohms for everything from 160M to 1296 MHz starting around 1979 when this town got wired for CATV. A couple of cases of beer each Friday got me lots of reel ends of everything from RG-59 to 1" hardline and several near full spools of hardline when the job was finished.

    Please note that 50 Ohms is not a world wide standard and the various import radios are built to work with anything from 50-75 Ohms. The difference into a 50 Ohm dummy load would be a 1.5:1 VSWR. Into an antenna there is often an adjustment option or a HF rig has a built in ATU if needed. Other times a compromise antenna requires an ATU anyway, even with 50 Ohm cable. Most times all that will happen is that the rigs VSWR sensor will simply see a shift in frequency of the lowest VSWR point. Note I didnt say resonant point.

    I run hardline to all antennas and CATV RG-11 for rotator jumpers and in the shack. RG-6 is used for all the rigs to amps, rigs to tranverters, transverters to amps, various FM xcvrs, and other interconnects. Ive even run a KW thru 100' of it to a 80M sloper.

    Ive never had a problem with F to PL-259 adaptors either. Always make up the F fittings with the center conductor extending about 1/8" beyond the edge of the barrel.

    There are several published 50-75 balun designs as well as commercial versions at one time, one was in the ARRL HB or Antenna Manual a decade or two ago; maybe still there. How well they work 160-10M I have no idea. Here is an overprriced one, Im sure a Google will find better ones. Its a simple enough formula to make one. http://www.arraysolutions.com/Products/baluns.htm#75:50balun

    For a monoband antenna an asynchronous transformer can be made. It is simply a mix of very short sections of both cables.
    http://www.seed-solutions.com/gregordy/Software/SMC.htm

    For VHF there was a company selling single band transformers made from copper water pipe to hardline. I used those with a couple of commercial UHF repeaters where the duplexers were very fussy about impedance matching. There it was all 50 Ohms from the repeater to the hardline which was a lot cheaper (free) than 200' of Andrew 7/8" Heliax and connectors.

    Bird used to sell a 75 Ohm Model 43, I have 2 of them and am always looking for another plus any elements.

    Carl
    KM1H
     
  10. VK1OD

    VK1OD Ham Member QRZ Page

    For those so interested, TLLC contains entries for a couple of hardline products, Commscope P3-550 CA and P3-750 JCA.

    Owen
     
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