Bleeding off static from a vertical

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K3RW, Jan 6, 2018.

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  1. K3RW

    K3RW Ham Member QRZ Page

    I read an article about the downside of the Hustler series verticals (5BTV, etc.) in that they don't have a way to bleed off static from wind loading. I'm new to the vertical world and didn't know this was one reason that some verticals are noisy. I also have a telescoping whip (17') on a Wolf River coil on a portable base--I suppose this may also be susceptible.

    I read a few different techniques about placing resistors in line, etc., but I didn't get a handle for any specific technique, and even the value of the resistors seemed to be widely in conflict between several articles (10k to 1M). I'd like an effective and simple way to do it, if possible.

    So, in layman's terms (please), how much of a problem is wind-induced static on a vertical, and are there suggested ways to bleed it off? Is it more of a problem for receiving, or transmitting as well?

    Also, I wondered if it is a problem for verticals, is it potentially a problem for dipoles and yagis as well?
     
  2. KW1K

    KW1K Ham Member QRZ Page

    If you are worried, just add an RF choke to ground.
     
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  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    True, but whether it's an RF choke or a resistor (either will work) it must be rated to handle the voltage across the feedpoint so it doesn't flash over.

    A typical carbon resistor is only rated 300Vdc, and in many cases that's not good enough. A "transmitting" type RF choke with a longish winding should be fine. A couple of resistors in series to stretch out the terminations should also be fine.

    I use a 1mH transmitting type choke with multiple windings to avoid resonance, about 2" long and it handles a kilowatt across a 50 Ohm antenna (even with a 3:1 VSWR at band edges) fine.
     
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  4. W9GB

    W9GB Ham Member QRZ Page

  5. K3RW

    K3RW Ham Member QRZ Page

    Are the chokes band-specific, impedance-specific? Where do these install on a vertical?

    [​IMG]

    Per this diagram it looks like it goes from the shield of the coax, and is elevated above the ground plane (however slightly), but looking at the top wire coming off the coil it looks like it goes to the center conductor? Or if I look at the shield connection a different way, it looks like it connects to the center AND shield.

    I'd love to see what this looks like in person, particularly with radials connected.

    FWIW, I run a 1:1 balun on my dipole and I wonder if static on a dipole is an issue. I notice it is quieter than my vertical but I have some horrible noise sources in the neighborhood (S9 100 over on 15m) that even it can't get through.
     
  6. K3RW

    K3RW Ham Member QRZ Page

    Here's a whole bunch of RF chokes on eBay, but I'm not sure what value to consider. Glad they aren't overly expensive but the sheer number of different offerings (look under the drop down for MODEL) '2.5 MHy 40ohm' and probably 20 different combinations of these various values, makes me think getting the right range is critical, just me thinking aloud.

    https://www.ebay.com/itm/CHOKE-RF-TRANSMITTING-RF-CHOKE-2-5-mHY-HAM-RADIO-/253339410796

    Right now I'm using a W2AU line isolator--not sure if that's making any difference or is 'good enough'.
     
  7. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

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  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The line isolator provides no static bleed to ground.
     
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  10. W2WDX

    W2WDX Subscriber QRZ Page

    A "line isolator" is a good idea on a vertical, but not really for static noise. It's more a matter of keeping common mode currents off the shield (meaning noise created on the coax from these currents is reduced somewhat) and for preventing the shield from becoming part of the radial system. The best approach (as mentioned above) is using an inductor to ground with a high enough inductance for it to be invisible to RF, but will pass DC (and very low frequencies) to ground. They need to be fairly big so they can handle the voltages present at the feed-point; depending on your power levels.

    In the past I have used a an NPO doorknob type DC-blocking cap in series on the feed center conductor, a big 320uH toroid inductor to ground on the antenna side of the cap, with a resistor to ground on the transmitter side. Worked like a charm on my Hustler 6BTV.

    Gaps do nothing more than make sparks. What is the result of a spark? ... RF pulses. Nope, sorry; not a solution to noise.

    Bear in mind, if you live in a suburban or urban area, most man-made noise exists vertically polarized and verticals are sensitive to this. The inductor may not help reduce noise of this type. However, true DC static build-up from wind, rain and snow are.
     
    Last edited: Jan 6, 2018
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