Need wire suggestion for inside ATU's / HF amps.

Discussion in 'Homebrew and Kit Projects' started by N2EYE, Dec 4, 2020.

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  1. N2EYE

    N2EYE Ham Member QRZ Page

    I need some lightweight shielded wire to carry RF (HF) inside the chassis. What should I use? I'm so tired of scrounging around for bits and pieces of old wire for project / repairs. May as well purchase several feet but I don't know what cable to select (say RF Parts). I seem to need short runs of several inches maybe a foot. Not QRP but certainly less than 2kw pep. 'General purpose' for bench?

    I also recall that when making such short coax connections for RF, only 1 end of shield should be connected to ground (prevent looping), is that accurate?

    Thanks for reading my question
    Ned, NYC
  2. KM3F

    KM3F Ham Member QRZ Page

    RG 174 is 50 ohm.
    You can't lo0k this up?
    N2EYE likes this.
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    I personally use Rg400 for everything like that, but I got a spool real cheap.

    N2EYE likes this.
  4. W9WQA

    W9WQA Ham Member QRZ Page

    you can try just a piece of wire. short run needs nothing in most cases.
    dont worry too much
    N2EYE likes this.
  5. K9YLI

    K9YLI Ham Member QRZ Page

    make your own.. slide shield off old coax. sllp over satisfactory hook up wire and stretch to snug it up.. ...... shielded wire on the cheeeep..
    N2EYE, AD5HR and KP4SX like this.
  6. KU3X

    KU3X Ham Member QRZ Page

    For low power which would be the input side of the amp, I use RG 316. For high power, RG 400 is great but RG 303 is easier to find and less expensive.
    You can get both from Allied Wire. Since you only need a few feet, paying a high price should not be an issue.
    RG303 usually sells for under $1.50 / ft. RG400 is usually under $2.00 / ft.
    Using RG 8X on the input side should not be too intrusive.
    Check ebay. There's usually someone selling short lengths of the above coax cables.
    I think RF Connections out of Maryland has a very selection of coax cables and I think they stock all of the above?

    Barry G. Kery, KU3X
  7. AJ4SN

    AJ4SN Ham Member QRZ Page

    Ditto Barry!
  8. KC3TEC

    KC3TEC Ham Member QRZ Page

    when using coax only solder one end if using as shield (soldering both ends creates a loop of current carrying conductor
    shielded wire comes in many sizes and specifications of use. for example ca5 trunking cable, is shielded, coax is , premium 3 phase power cable can be gotten shielded( handles one heck of a lot of power but is definitely not cheap)
    any rf and a lot of 4 to 6 ma control circuits should use shielded conductors as they are prone to induced voltages.
  9. N7EKU

    N7EKU Ham Member QRZ Page


    The why in all the commercial amateur radio rigs, tuners, and amps I've seen do all the coax interconnects use both conductors (grounding the shield) on both ends?

    Anyway, that's what I think the OP was concerned with.

  10. KC3TEC

    KC3TEC Ham Member QRZ Page

    connecting between 2 separate devices that are individually powered (ie. power supply or ac socket) are usually grounded
    more so when using a grounding strap and coax connections for the rf are usually both conductors for matching and tuning purposes
    inside the same enclosure however 2 boards are also bonded but if the power of the unit is high enough and air core inductors are used, a section of interconnect wire can pick up harmful induced or nuisance voltage.
    a shield grounded at the power supply side only does not conduct current but will act as a receiving antenna to stray induced rfi and drain it to ground.
    we had to learn this in networking industrial automation control systems, errant induced voltages were not enough to harm the equipment but enough to throw timing of on machinery putting people in danger of harm or death.
    and our instructor was absolutely anal about it!

    with radio equipment you are not often running things on very high power and rfi is usually nuisance interference either received or transmitted,
    but its still important enough to eliminate as much rfi as possible

    on my qcx (40 meter) it will pick up interference with just the short jumper cable to the tuner. not because of the cable but because i do not have it in an enclosure yet (interference from the led magnified work lamp on the bench) so im going to order the enclosure for the radio and make a faraday cage around the lamp socket with screen from a microwave door.
    Last edited: Dec 8, 2020

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