Excess coax-- what do you do with it...?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N4ATL, Jan 5, 2011.

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  1. N4ATL

    N4ATL Ham Member QRZ Page

    I am looking for advise on what to do with excessive coax. I am remodeling and will be moving my shack 40' from it's current location in a few weeks. I just put up my new antenna's and I don't want to cut my 150' coax. In the mean time, I have a 50' puddle of coax all over the floor. I have searched Excess coax, extra coax and coax in the forums and come up empty, I apologize if I missed a post.

    Coax is RG8X

    Antenna are G5RV and an Eagle One.

    Thanks!!!

    Michael K4NOG
     
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Obviously unused coax adds some loss that isn't doing you any good; however if you don't care about that, why not just neatly coil it up (a good diameter is 18" or so), and tie-wrap the coil so it remains neat? This can reside behind the equipment in the shack, or outside where you don't have to look at it.

    If you don't want it on the floor, coil it neatly and hang it on a hook behind the equipment.

    Coiling the coax does no harm in any way except to add the loss of the cable used.
     
  3. W8ZNX

    W8ZNX Subscriber QRZ Page

    Hello OM

    look up losses for 150 ft of RG8X
    look up losses for 110 ft of RG8X

    RG8X is not exactly low loss cable

    if you hang out on higher bands
    say 10 or 12 meters
    cut your losses

    cut it

    if you hang out on lower bands
    it does not matter that much

    not like RG8X is that expensive
    use the extra cable to make up jumper cables

    if it was my station
    would cut out the excess coax
    in a New York min

    yours truly
    mac
     
  4. G8DZC

    G8DZC Ham Member QRZ Page

    I would use part of the excess cable to make a choke balun.
    That is true. I hear that by having stacks of extra coax, you will find your SWR improving, which means that you get more signal out into the air. That might be wrong of course ;) I understand that SWR is God in many circles. :D

    As for any spare cable after the coax balun is made. I would cut it off. If in the future you should wish to extend your existing cable. You can always get connectors to do it.

    Trish
     
  5. VK1OD

    VK1OD Ham Member QRZ Page

    The G5RV operates the coax with standing waves, and there is benefit in using the shortest coax.

    Do you use the Eagle One with an ATU at the base, say an AH4, SGC237 etc, or do you use their 4:1 balun idea?

    Owen
     
  6. VK1OD

    VK1OD Ham Member QRZ Page

    Yes Trish, that is usually wrong.

    Increasing the length of the line increases line loss, and it does decrease the VSWR looking into the line, but in most cases it will result in less radiated power.

    In some unusual cases, the lower VSWR might just result in higher transmitter output power that more than offsets the increased line loss, but it is unlikely.

    Owen
     
  7. W5DQ

    W5DQ Ham Member QRZ Page

    WB2WIK is correct that it can be coiled up and stashed behind the desk but given the fact that it is RG8X and most RG8X coax is not premium quality anyway, if it were me, I'd cut the excess off and use it for jumpers, etc. Of course if it were me, I would not be using RG8X anyway, but then that's just me.

    A true G5RV design is optimized for 20M and has to be matched on other bands so there is already losses from that so by limiting the coax length, you'll help reduce losses in both RX and TX.

    Just my $0.02 worth.
     
  8. KA9UCN

    KA9UCN Ham Member QRZ Page

    A big coil of coax is not a good idea. It is not going to help any thing. The losses during TX do not make it to the antenna but can cause rf problems in the aria every thing from interference with other electronics to rf burns from metallic objects. On the receive end you just lose signal strength. Coax ends are cheap.
     
  9. W8JI

    W8JI Ham Member QRZ Page

    Coil it up outside just before it gets into the house, unless you never ever will need it that long ever again.

    If you are sure that is where stuff is going to stay, shorten it.

    As Owen says...with a G5RV you want the cable as short as possible while still having a nice routing.
     
  10. W6CD

    W6CD Ham Member QRZ Page

    If a pretty permanent antenna and coax run, I cut it to length. If something kinda temporary and subject to change, I try to leave the excess (unless the excess is excessive :)) coiled up outside by where my cables enter the house.
     
  11. K9FV

    K9FV Ham Member QRZ Page

    As the OP said,
    Maybe that is why he doesn't wish to cut the coax just yet.

    Ken
     
  12. VE3FMC

    VE3FMC XML Subscriber QRZ Page

    I have coiled up coax and never had an RF burn from it. How does that happen? :confused:

    It would have to be pretty bad coax to lose a lot of signal strength in 50 feet of coax.

    According to the charts I have he would lose 1.25 DB at 50 Mhz in 50 ft of RG-8X. Even less loss at 28.000 Mhz. Not worth worrying about from 3.5-14.000 Mhz.


    I'd coil it up like Steve said. Once you have your shack set up and think everything is going to stay the same for awhile then you can cut it down to the length you need.


     
    Last edited: Jan 6, 2011
  13. KC2UGV

    KC2UGV Ham Member QRZ Page

    I'd just coil it up. Tie it with a two zip ties (Not too tight), and be done with it. Cut it down when you get it to the permanent location.
     
  14. AE7F

    AE7F Ham Member QRZ Page

    Okay, this thread got my attention because I have a very similar scenario. I am also running a G5RV. The antenna mast for the inverted V happens to be 10 or 15 feet out the window. Since the antenna apex is around 30' and the G5RV spec for 300ohm twin lead is somewhere around 28', I only need a patch of like 10-15ft of coax to the present location of the radios. That leaves at least 85' of coax neatly coiled outside the window. I am not using a balun, either. I have heard/read that any db loss up to 3db isn't going to be noticeable to those receiving yoru signal. Is this incorrect or worth worrying about?

    2nd (related) question I have is that I have 50ft of 450ohm ladder line. Am I better off with my G5RV to ditch the 28ft 300ohm twin lead line and 100ft of coax and replace it with one section of 50ft of the ladder line? Why or why not?

    3rd, what is going to ladder line going to do to my existing SWR across 80, 40, and 20m if I switch? (I could probably slightly trim my antenna because it is only 2:1 on 20m without the tuner. With tuning, I have so far found at least 20 different band locations where SWR is flat.)
     
  15. K1DNR

    K1DNR XML Subscriber QRZ Page

    I would use the excess to spell out my callsign in cursive letters on the wall of my shack.
     
  16. K1DNR

    K1DNR XML Subscriber QRZ Page

    1 - 3db is equal to doubling or halving your power. In terms of an S meter, its around a half an S unit, or one S unit depending on the calibration. 3db is like turning the volume up one notch on your stereo. It can make or break a weak signal.

    2 - The twinlead section is used as an impedance transformer. You will change the match of the antenna. Yes, you can feed it with ladder line, but your will need a balun and tuner (or tuner with balun)

    3 - see #2. You will need a tuner.
     
  17. VK1OD

    VK1OD Ham Member QRZ Page

    The reason I ask is that the use of a 4:1 voltage balun as recommended by the manufacturer defies logical explanation. It will cause common mode current on the coax feed line, and possibly large losses if that feed line is buried or lying on the ground.

    The feed arrangment will create very high standing waves on some bands, and shorter low loss coax is the key to efficiency.

    In the article at An unloaded vertical as a multi-band HF antenna, under the heading "Zero Five configuration", I discuss the folly of the use of a 4:1 voltage balun in this configuration.

    If you are using a remote ATU, then feed line loss is low, and the shorter feedline will be better, but not hugely so.

    Owen
     
  18. WA4OTD

    WA4OTD XML Subscriber QRZ Page

    I would cut off the extra and put up another antenna :)
     
  19. W8ZNX

    W8ZNX Subscriber QRZ Page

    now
    thats the best answer
     
  20. AE7F

    AE7F Ham Member QRZ Page

    My tuner has a built in 4:1 balun.

    Question is, would it be worth it? So let's say I eliminated the loss of the 100ft of RG8X (I have that too). This requires bringing down the antenna, modifying it for the ladder line, putting it back up, then finding all the new tuner settings to get a flat SWR. So I get 1-3db back but I have no idea how much harder/less predictable it would become with a random chunk of ladder line.

    Spelling your name on the wall with coax.... now your talking!
     
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