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Bleeding off static from a vertical

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

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  1. W2WDX

    W2WDX Ham Member QRZ Page

    I think @N8CMQ brought up a good point. What we were originally discussing was the problem of noise from P-Static. Corona effects are created by different means, and are not mitigated the same way. I was not referring to lightning or electrostatic charge. There is a theory that says you increase the likelihood of coronal effect by DC grounding an antenna; as I suggest for mitigating rain or snow static buildup. However, where a "creeper" first reaches up during a storm is dependent on the surrounding terrain of the antenna.
     
  2. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    Yes, it does matter, as WA7ARK mentioned, if the current of the discharge has to travel into your radio and out to ground, then the noise of the current will be brought onto the radio. If the current remains at the antenna, the noise will be attenuated through the coax. A simplistic view, but it does show how noise can be attenuated, or enhanced by the path of current flow.

    Another point, your antenna DC/static/lightning ground should go from the base of the antenna or tripod straight to ground as possible, this will also help reduce noise from P-static. But each install is different, and this is conjecture until the antenna is installed and used for a period of time.
     
    K3RW likes this.
  3. K3RW

    K3RW Ham Member QRZ Page

    I came across a static bleeder from Palomar Engineers, and it used a tee, but in a much different way. But I'm a bit lost on how it would be connected.

    [​IMG]

    Per their instructions, I'd get a tee and place this funny looking plug thing on it. Looks to me like a coax connector but cut off.

    The Palomar Engineer instructions:
    "To use procure a coax “T” and a male to male connector. Connect the SB-1 to the male to male connector and thence to the coax “T”. Static voltages are bled off from the center conductor to the outside conductor (braid of the coax). At the entrance to your radio station ensure that the outside conductor of the coax transmission line is grounded so as to provide a sink for the static electricity on the antenna center conductor. The SB-1 static bleeder is usually installed near the radio shack entrance on the antenna side of any 1:1 baluns/line isolator"

    [​IMG]

    So if I read it correctly, it is cut off so I can connect the SHIELD to ground... so I'd need to run the cutoff end of the plug to a grounding rod, etc.? So I'm imagining a short wire connection from the top of this thing, which looks like it is epoxied over. Hmm.

    But then as we discuss where to bleed it off, it seems some want to do it as close to the antenna as possible to have the coax attenuate remaining static, but the Palomar Engineers instruction appear to advocate doing this close to the shack.

    If I ran only a vertical, perhaps that's exactly what I'd do. But we get tons of rain and high winds at time. Its hard for me to know if this would also be of benefit to a dipole at all. Or an end-fed, etc. And if the PE instructions want me to put it close to the shack, then I would have this going just barely out the window pass-thru to a grounding rod below.

    Confusing stuff! But I'm risk-averse to leaving anything up in a rare once a year lightning event, so mitigating lightning for me is as simple as tipping the vertical over and disconnecting the feedline, and dropping the dipole down to the ground. So I'm only really interested in mitigating static, which I'm not sure is even a problem for me. But we get tons of residential noise anyway, so I'm not sure how much true static I'd even notice through it.
     
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I haven't opened one of those up, but it's almost certainly a high value resistor in the Megaohm range soldered onto a PL-259 that you screw into the T connector. All it does is provide a high impedance DC bleed path between the coax center conductor and the coax shield. It could be a gas discharge tube but again all it does is equalize DC potential between the coax center and shield when a high enough voltage builds up. That's step one in dissipating static charge, get the two conductors to the same DC potential.

    Step two is make sure the overall system is grounded somewhere along the cable run. From a DC static dissipation standpoint it doesn't really matter where that coax shield is grounded, it could be right at the antenna feed point, it could be where the T is inserted into the coax and it could be at the point the coax enters your house. That last option also satisfies NEC cable entry requirements that says your coax shield should be grounded at the point the cable enters your house and that ground must be bonded back to the AC service entry ground point.

    So from a purely DC static dissipation standpoint it doesn't really matter where along the cable run you ground the shield. But to keep the overall installation clean, compliant with NEC codes and better suited to handling lightning induced surge currents (typically not direct strikes but regional lightning that can induce surges in either your antenna system or more commonly in the local AC distribution system) you should ground the coax shield at the point the coax enters your house and have that ground bonded back to the AC service ground with a heavy gauge conductor.

    That last step, ground the coax shield at the point the coax enters your home, should be followed regardless of whether you use this Palomar DC dissipation device as that follows code and is good insurance for surge events.

    The device you've linked is convenient since you don't have to cut any cables or solder any connections but it's just as easy to tack a high value resistor across your antenna feed point or use a shunt inductor of sufficiently high value across the feed point, they all do the same thing which is allowing a DC bleed path from coax center conductor to shield without negatively impacting the RF match.
     
    Last edited: Jan 23, 2018
  5. K3RW

    K3RW Ham Member QRZ Page

    Ok--so if I understand it correctly, as long as the coax is grounded near my station, I don't need to solder anything to this device?

    Too bad I'm on a second floor and the AC main is probably 30' away. There is a ground rod down there somewhere that I've seen, but it is a huge concrete RV pad so that might just have to do. Nothing simple it seems. But running this portable at the beach where I might expect high winds or blowing sand, I'd definitely tap in a ground rod for the rigs. I'm never quite sure if the coax and the rigs need to be grounded separately (i.e. 2 ground rods).
     
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Correct
    Yeah, ideally you'd ground the coax down at ground level, enter the home and then run the coax indoors up to your operating position but do what you can...
     
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