G5RV JUNIOR DIPOLES - DO I NEED A BALUN?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K1KTF, Feb 20, 2019.

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  1. K1KTF

    K1KTF Ham Member QRZ Page

    Hi Amateur Radio Friends -

    I have always used a balun w/ my G5RV Junior (40-10m) dipole, but unfortunately I need to replace it due to wear and tear being in New England.

    Q: If I have an antenna tuner, do I need a balun for my G5RV replacement? I was always told (not exactly sure who told me) that you should use a balun w/ a G5RV Junior. Again, I do have an MFJ tuner so I'm not sure if I need a balun.

    Finally, any suggestions on a good weather proof G5RV Junior to purchase?

    Again, thanks for all your insight particularly for a "non-technical" ham. Much Appreciated.

    Steve (K1KTF)
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    I recommend using a common-mode-coax-choke (aka 1:1 UnBal, line-isolator) at the junction from coax to twin-lead. It helps balance the antenna, and reduces the possibility that RFI generated by devices in your house that couple onto the coax travel up the outside of the coax, enter the coax at the twin-lead to coax junction, and then travel back inside the coax to degrade the SNR of your received signal.

    Can you salvage the choke that is part of the existing antenna?

    How much space (end-to-end) do you have? Could you accommodate TheWireman #882 kit as a replacement?
     
    Last edited: Feb 20, 2019
    WB5YUZ likes this.
  3. KJ4VTH

    KJ4VTH Ham Member QRZ Page

    I've had good luck with RadioWavz

    Or build one for a lot less $$
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    If the antenna is constructed of the right robust materials, it will never wear out due to "wear and tear."

    For rough weather or swaying trees, you need a very strong and weatherproof center insulator (I prefer the Alpha-Delta ones, they're bulletproof and incredibly strong), strong insulated wire (insulated #12 copperweld is strong enough to tow a car), very strong end insulators (glazed ceramic/porcelain is pretty good), and strong end support ropes (I use 3/16" or 5/16" double braided Dacron); and if installed in trees, a method to keep the antenna reasonably taut while the trees sway, which means springs or a weight at on end that can bob up and down as the trees sway with the wind, snow/ice loading, etc.

    I've never had a dipole break, even when I lived in snowy/icy/windy northern NJ or in Boston. The ones at my last home in NJ were installed in 1986 and I know they're still there since I sold the house to a ham who still uses them.:)

    Definitely use a balun where the coax joins the window line or twin lead. A 1:1 current balun is all that's needed.

    A balun in the tuner won't do anything for this.
     
  5. KV4JW

    KV4JW Ham Member QRZ Page

    1:1 current balun is all you need. You can buy one, or you can make one simply by wrapping 8 or 10 turns of your coax around an old two liter pop bottle and securing it with electrical tape.

    Having a tuner only means you're going to "fool" the radio into thinking it's seeing a relative 50 ohm impedance, so it will transmit full power. A tuner does NOTHING as far as making the antenna resonant. A tuner also does nothing in terms of removing common mode current from the feedline, which G5RV's are notorious for.

    The 1:1 current balun is simply an RF choke of sorts, which keeps common mode RF current OUT of the shack.
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    Not so much... The air-core coax balun only works at one or two nearby bands because it has self resonance due to stray capacitance from turn to turn. The resonance can actually make the common-mode current higher on the higher bands.

    Ferrite based common-mode chokes have a much wider bandwidth and can cover from 3.5MHz to 30MHz in one device.

    Not so much if it placed at the antenna feed-point. If the coax feedline routing is asymmetric with respect to the dipole legs, a common-mode standing wave can develop on the coax even if a choke is at the feedpoint. In that case, you need two chokes, one at the feed-point, and the other just as the coax comes into the house, between the antenna and a ground rod, if a grounding system is present.

    I posted the "best" reason for placing a common-mode choke at the antenna end of the coax in post #2.
     
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