Bleeding off static from a vertical

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

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  1. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    A static drain connects directly across the feedpoints of the antenna; in your case, from the center conductor feedpoint to ground.

    A balun "usually" doesn't do this.
    K3RW likes this.
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Why bother? Have you ever seen a radio that doesn't have a DC short between the center pin and shield of its SO239?

    The only time it matters is when the coax is disconnected from the radio, and is laying on the floor? Most coax switches short the non-selected antennas.
  3. N1OOQ

    N1OOQ Ham Member QRZ Page

    Well, when snow is falling on my doublet, I get the zzzzzzZZZZZZ POP type of noise every few seconds. Needless to say, I don't operate much when it's snowing.
  4. W2WDX

    W2WDX Subscriber QRZ Page

    What? Huh? Putting aside I do not understand what you are saying (reducing static is a "why bother" issue? Seriously?), your punctuation makes no sense. Your second paragraph is a statement with a question mark. Are you stating something or asking a question?

    Plus, I have never seen a radio with a short across the SO239. Seriously? I have seen blocking caps, but not often. Most time I have seen capacitive bypass, not shorts. But that's not going to suppress DC static noise from the antenna.

    Well ... you can use the same technique, (whether coax or balanced feeder) to reduce that static on the doublet. On my doublets (at my old QTH where I could have them), I always used two large inductors to ground and blocking caps in series with the feeders on 600 ohm open-wire feeders. Rain and snow static pretty much gone. I used two big inductors, 16"long, 4" dia, 10ga wire, 7 tpi, which gave about 320uH. Probably could handle a 10kW power level. The blocking cap was a few pufs doorknob 20kV NPO. On the transmitter side of the cap you could also add a gas-discharge tube to ground to get rid the remain impulses, and a resistor to collapse the magnetic field of the inductors when big impulses do happen, like a nearby lightning bolt.

    Here's a pictorial and schematic of the prototype and total antenna feedline system. I have updated some of the choices shown here, like the feeder type. I went with 600 ohm open-wire instead of 420 Ohm ladder-line:

    arresterlayout.jpg lightningarrest.jpg
    Last edited: Jan 6, 2018
    KR2C and NH7RO like this.
  5. W5DXP

    W5DXP Ham Member QRZ Page

    For a vertical, the problem can be solved by the mobile shunt coil matching technique.
    KC8VWM, NH7RO and KD6RF like this.
  6. W9GB

    W9GB Ham Member QRZ Page

    AM Broadcast (550 kHz to 1700 kHz / 545 to 176 meters) engineers have used a variety of methods — from static balls, spark gaps to spark plugs — on their vertical radiators.
    Decades ago, I was visiting an AM broadcast site, during their Sunday “weekend maintenance period”. In the west, you could see a line of thunderstorms (at sunset) approaching.
    Inside the transmitter shack (shed), a “Buzz-Pop” would be heard every 30 seconds, or so.
    At the base of the tower — the spark gap was making the popping sound — with a slight smell of Ozone (O3) in its vicinity.
    Last edited: Jan 6, 2018
  7. KU3X

    KU3X Ham Member QRZ Page

    What you need is a 1 mh choke. To built a heavy duty one, get an FT 240-43 and wrap it with 32 turns of #18 or heaver wire.
    Here's where you can get a core if you don't have one. also sells ferrite.

    I make mine with #16 enamel wire but you can use #14 if you like.
    The choke has no resonant frequencies in the HF bands and is transparent to HF.
    You can put this is a 4" x 4" x 2" NEMA enclosure that you can purchase from either Home Depot of Lowe's.

    If you want a smaller 1 mh choke, use an FT 140-43. Here you will have to use #18 enamel wire of since the core is smaller. You'll need 45 turns of wire to make 1 mh.

    For those interested, you can even shunt one of these across a simple dipole to put the dipole at DC ground.

    Barry, KU3X
    NH7RO likes this.
  8. K1ZJH

    K1ZJH Ham Member QRZ Page

    Personally, I'd opt for a high value resistor--if voltage is a concern, use several in series. RF chokes can
    have series resonances that might be in a band of interest.

    FT-240-43 toroid is good--7 turns and you are to 50 uH already, about 500 ohms reactive on 160 meters.

    Spark gaps will allow a high voltage to generate before discharge--doesn't abate the noise issues and allows a large voltage charge before arcing.


  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Sure I have. Actually, none of my receivers or transceivers have a DC short between the center pin and ground.
    K1ZJH likes this.
  10. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    This ^^^
    Super easy. Problems solved.
    NL7W and K3RW like this.

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