Super light coax?

Discussion in 'QRP Corner' started by N4QFY, Jun 17, 2020.

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  1. N4QFY

    N4QFY Ham Member QRZ Page

    I'm going to build a QCX+ 40m cw radio for backpacking and I'm going to make a dipole with the florescent 26 AWG copper clad antenna wire from DX Engineering. I'm trying to keep weight and bulk down because I'm hoping for a multiple day and later multiple week hike with it. The dipole will probably be made with a BNC to banana post adapter as the center.

    What's the lightest, thinnest, and most flexible coax I can mount BNC connectors to without creating significant loss? I'm also wondering what to use, if anything, for end insulators. Any line used will be 550 cord because I have a bunch and use it for so much in my hiking gear anyway.

    I'm building this low power kit as a fun learning experience and if it doesn't work well, I won't be out a lot of money and I already have a full size base radio at home. I've only ever made coax with pl259 connectors and usually with RG8x but that seems a bit heavy and bulky for hiking.

    I just answered my own question. Crimp on BNC work fine with RG58 and that's as thin and light as I know you can get. Any ideas about light small end insulators or should I just tie cord directly to the ends for a portable antenna?
     
    Last edited: Jun 17, 2020
  2. ON6KE

    ON6KE Ham Member QRZ Page

  3. N8TGQ

    N8TGQ Ham Member QRZ Page

    antenna01.jpg Consider using an end-fed half-wave antenna. The coax I use on mine is about 2 inches of rg174.
    Solder one end of the coax to the end-fed matcher, eliminating one connector.
    Then switch to an RCA plug and jack on the radio end. That takes up much less space and weight, much easier to solder to coax and will come loose when you trip over the wire at your campsite!
    I use cotton kite string and no insulators on my hand-carried antennas. Its plenty strong enough for temporary light weight antennas and will "self destruct" after a season or two if I lose a length up in a tree.
     
    Last edited: Jun 17, 2020
    N0BUP and KA0USE like this.
  4. K6CLS

    K6CLS Ham Member QRZ Page

    yeah, RG174, or RG316

    Also, consider using #24 wire instead of #26, it'll work better. Try it at home first.
     
  5. N4QFY

    N4QFY Ham Member QRZ Page

    Excuse the stupid question but I just woke up a min ago and am only firing at about half still. What makes the #24 work better than the #26? DX Engineering says that it has a break strength of 26lbs and 62ft only weighs 1oz. Better SWR over a larger portion of the band?
     
  6. N4QFY

    N4QFY Ham Member QRZ Page

  7. N4QFY

    N4QFY Ham Member QRZ Page

    I have looked at end fed. My biggest worry is that the PCB won't hold up for me. I tend towards a tightly packed pack with a higher weight. I'm afraid that an unenclosed matcher would get destroyed.

    I never thought about changing the antenna connecter on the radio to something else. RCA plugs are plenty light and it gives it a nice trip break. I've never soldered them before, you say it's easier?
     
  8. N8TGQ

    N8TGQ Ham Member QRZ Page

    RCA plugs are easier to solder than BNCs for sure! Plus you dont need a crimp tool. Plus if your wire breaks, you can strip it back an inch or so and just stick it into the plug. Plus I can buy them at the local surplus store for 10 cents a piece.
    Dont worry about wire size. If there is a difference, its so small you couldn't measure it.
    QRPKits.com sells a half-wave matcher that has a nice metal box. I've never had a problem with the pc board one from QRPGuys tho. Another plus for both is the built in SWR indicator.
    If I were building up a QCX kit, I would just build the matcher inside tha case. All you would need is a simple banana jack to plug the wire in!
    Heres the kit I use for weekend hikes. If I'm going out longer, I take battery pack made up of 8 nimh AA cells. If needed, you can pick up AA cells anywhere. pocketrig01.jpg
     

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  9. KI4POT

    KI4POT Ham Member QRZ Page

    This is interesting. I never considered using RCA plugs in lieu of proper coax connectors. I especially like the safety aspect of it.
    For you guys doing it this way, have you noticed any issues with your connections from a performance standpoint?

    Chris
     
  10. K7JEM

    K7JEM Ham Member QRZ Page

    Phono plugs (or the Motorola equivalent) have been used for decades on high power (100 watt) VHF and UHF commercial radio equivalent, with no detrimental effects. Should be no degradation at all on HF.
     

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