Static discharge control from open wire line antennas?

[K1ZJH]

I must be missing something.. The WW resistors still have a pure resistive, and an inductive reactive value. Wouldn't the two be in series, effectively increasing the impedance above the R value?? I don't see why the inductance wouldn't beneficial?

Pete

What about interturn capacitance?  The LC network WILL, at some frequency, become resonant.

As to the R across the L, that's been a way of lowering Q of rf inductors for quite some time....  I've never done it with a WW, but...  Another thing to consider there is this:  HV Resistors are wound like an 'edge wound' inductor (being done with VERY little cross sectional area, using strap).  Wirewounds are wound, like a standard inductor.

The edge wound (like a piece of strap) will have WAY less C between turns than the standard one will...  Hence the properties of the inductor acting different (when looking at a HV rated carbon resistor vs. toaster wire).....


I just measured a 5w, 5ohm, and it had .3uH of inductance across it.

Just looked at it with the VNA, and the same resistor listed above gets squirrelly above 6 mhz.  Would make a great resistor for the use above, but gets all kinds of nice odd resonances that I wouldn't want in my feedline straight to ground above 6 mhz.

--Shane

Does the VNA ever show the impedance going much below the marked resistance?
Resonant or not, L reactance is still in series with R component.

Pete

[ke7trp]

Spent the afternoon working on the system.

Opened up the KW matchbox and found that some IDIOT bypassed the relay by jamming electrical tape into the relay. This was done many man years ago and the contact was now showing signs of wear..  I unbolted the RF feed strap from the Coil to the Relay and moved it over to the incomming stud.. This is the way to bypass the relay.. Now My RF has a solid in and out path NOT through the contacts.

We also found one of the LINE Studs was loose on the inside.. Also found about 4 or 5 loose screws holding the variable caps down.

My LARGE coil is grounded. I tested it with a meter. I can see the ground path. 

I also put in connectors on my open wire line and bolted them to the back of the tuner so I had a good connection.

All of this totaly through off the tuning chart. I had to sit down and make a new one. I cant tune 20 meters anymore. at best its 1.5 to 1. I guess usable.

I also noticed that the lower ground lug is the one you want to use as it is the one that runs to the coil.  The one up at the top is just grounded to the case. I am now using the lower one and it has a shorter path.

Right now I have 9 SU of static with Crashes up to 40DB. 

We tried 200K and 20K resistors from the open wire line to ground.  The 200,s and 20s where both 50 watts each. This had NO effect on Recieve or Transmit. The tuning was unchanged. So the BIG 50 watt HV resistors work fine on 80 meters. I did not try other bands. 

The resistors had no effect on the RX pops at this time. I looked on intelicast and the cont US is COVERED in Lightning strikes.  Cant fix that with resistors.

Clark

[KD6VXI]

Does the VNA ever show the impedance going much below the marked resistance?
Resonant or not, L reactance is still in series with R component.

Pete

Pete,

I'm not the one to interpret the readings here, but I swept the resistor from the lower end of the VNA to 50 mhz....  It got REALLY squirrely above 30 mhz.

MHZ     R     X
 1.7     5     0
 2.1     6     0
 2.9     7     0
 3.7     8     0
 4.39   8     1
 7.8     9     1
11.3    10    17
17.5    11    29
24.6    12    43
27.4    13    49
44.8    8     90
45.28  0     100
46.5   19    101


In all measurements above, ALL the x was inductive, so you are correct in that it would be additive...   Although I'm not sure I still like introducing any unnecessary reactance into my feeders, since we all use tuners on balanced lines, I'm thinking it's a moot point.

The problem is, a WW resistor is nothing more than a plate choke, on a smaller scale.  Look above, and see what happens from 44 to 46 mhz.  OUCH, a direct 'short' would work a tuner out.

Bottom line, if you where to do the wirewound resistor method, I'd sweep each resistor to ensure it's Fresonance wasn't in a band you want to work.  Otherwise, as Pete said, it would be an additive quality, the inductive reactance it would add, as long as you can tune it out.

Also, in the 'graph' above, The VNA I have 1.7 mhz IS the lowest measurable freq.  I'm not sure if it has any resonances below, but 'probably' not.  BUT, this resistor, would be safe everywhere in HF...  in VHF low (I didn't test mid or hi), it's a losing proposition.

--Shane

[K1ZJH]

Bottom line, if you where to do the wirewound resistor method, I'd sweep each resistor to ensure it's Fresonance wasn't in a band you want to work.  Otherwise, as Pete said, it would be an additive quality, the inductive reactance it would add, as long as you can tune it out.

Also, in the 'graph' above, The VNA I have 1.7 mhz IS the lowest measurable freq.  I'm not sure if it has any resonances below, but 'probably' not.  BUT, this resistor, would be safe everywhere in HF...  in VHF low (I didn't test mid or hi), it's a losing proposition.

--Shane

At VHF, that might make sense, since stray capacitive reactances might be present directly across the two poles of the resistor. My guess is that the R and L reactive components are pretty much intermingled, making a series-resonant  L - C low-impedance path around the resistance unlikely.  I hope my babbling  is halfway coherent 

Pete

[W1VD]

Don't recall anyone suggesting that a 5 ohm wirewound resistor was appropriate in this application...

[ke7trp]

I am going to install the RF chokes next week outside in a box. I think this is going to be the best bet for my situation. I already have a solid Ground rod right at the window.

I wanted to point out that I believe grounding the coil inside the KW matchbox wont do anything. The reason is that the lines run through the variable caps.  I studied the inside of mine and the schematic and it would seem that you would still have to arc over the plates of the cap if the coil was grounded. Here is a schematic of the KW so you can see what I mean.

For now, I am using TWO, 200K, 25 watt bleeder resistors from each leg of the open wire line to ground. These have no effect on 40 and 80 meters. Tuning is unchanged on the transmitter or tuner with them hooked up. Maybe this will save the Solid state rigs I run sometimes and limit the noise on the tube recievers.

Clark

[kc2ifr]

I wanted to point out that I believe grounding the coil inside the KW matchbox wont do anything. The reason is that the lines run through the variable caps.

Your correct........it wont do a thing.

Your best bet is the chokes.....just get the correct size.

Bill

[KD6VXI]

Bottom line, if you where to do the wirewound resistor method, I'd sweep each resistor to ensure it's Fresonance wasn't in a band you want to work.  Otherwise, as Pete said, it would be an additive quality, the inductive reactance it would add, as long as you can tune it out.

Also, in the 'graph' above, The VNA I have 1.7 mhz IS the lowest measurable freq.  I'm not sure if it has any resonances below, but 'probably' not.  BUT, this resistor, would be safe everywhere in HF...  in VHF low (I didn't test mid or hi), it's a losing proposition.

--Shane

At VHF, that might make sense, since stray capacitive reactances might be present directly across the two poles of the resistor. My guess is that the R and L reactive components are pretty much intermingled, making a series-resonant  L - C low-impedance path around the resistance unlikely.  I hope my babbling  is halfway coherent 

Pete

Makes total sense.

Might also be a double whammy, as it would make a dandy low pass filter, as well.

I'm going to try to find some more ww resistors around here to see if any of them get squirrely at HF...   If not, learned something new....  If so, we all learn.

--Shane

[kc2ifr]

This is not rocket science here folks.............u need a "device" that will pass dc and block ac...in this case rf frequency's.......and that "device" is a choke.

What is the problem?

Example........in every toob amplifier there is a choke at the output of the amp to ground. Guess what its for.......if the plate coupling cap shorts, this choke will short the HV to ground keeping the high voltage DC from the power supply from reaching the antenna and hopefully blowing the power supply fuse.


Bill

[K1ZJH]

I think the first assumption the problem was related to a slow build up of a static charge until the voltage reached a flashover point some where in the antenna system.

But, if this is blowing RF chokes apart I'm beginning to wonder if the OP isn't experiencing atmospheric discharges direct to the antenna instead. It doesn't seem to be wind induced static buildup. Something more onerous?

Pedro

[kc2ifr]

Pedro,
The chokes should not allow ANY dc voltage to buildup on the ant. Any DC voltages  will be passed to ground. Anyway that is the theory.....
Bill

[KD6VXI]

I think the first assumption the problem was related to a slow build up of a static charge until the voltage reached a flashover point some where in the antenna system.

But, if this is blowing RF chokes apart I'm beginning to wonder if the OP isn't experiencing atmospheric discharges direct to the antenna instead. It doesn't seem to be wind induced static buildup. Something more onerous?

Pedro

This is quite amazing when it happens.

Literally, lightening bolts shoot from his vertical (I haven't seen the wire antennas, been a couple years since at his QTH).  I always thought it was from the wind picking up sand and that inducing static across the fiberglass vertical, but Clark said his wire antennas are NOT covered, so I can't see that being the problem here, unless they are enameled or ...  And then I'd question it.

I was only worried about a LC combo finding it's way across the thing and him blowing something up because of a resonance.  I only had a 5 ohm 5 watt to test with, and since I am incapable of getting up and out of bed at the moment, any additional testing will have to wait.  The resistor I had here to look at, I could only find a resonance in the VHF range....  Learned something new.

But, there is a serious amount of power here.  It's blowing apart chokes rated for 1A or more current.  If he's using the ones I'm thinking, I've used them to pass > a couple amps, when using them as bypass on DC lines for bias in solid state stuff.  The things should NOT be blowing apart on RX, period.

The antennas at his QTH, with NO radios attached, can at times resemble a Van de Graff or a Tesla coil.  And they are blowing apart chokes grounding the feeders rated at LEAST at a half amp.  Regardless of how it's done, that's a bit of power to dissipate.

--Shane

[K1ZJH]

Pedro,
The chokes should not allow ANY dc voltage to buildup on the ant. Any DC voltages  will be passed to ground. Anyway that is the theory.....
Bill

Not what I meant... Would the choke stop a lightning discharge?
I know it would drain static buildup. But it sounds like he is experiencing
something quite different.

[kc2ifr]

Chokes are NOT lightning protection............they bleed off any dc voltages that slowly build up on the antenna. The only way to protect ANY antenna from lightning is to take it down OR disconnect it from your shack and hard ground it before it enters the house. Even if u do this and the ant takes a direct lightning strike.......all bets are off.


Bill

[ke7trp]

Let me explain further. 


Today while on 40 meters AM, my friends T368 was showing 40DB over solid.  Then, I hear Zeeeorch POP. The arc is inside the tuner on that one.  The SX100 S meter goes to 0 and slowy comes back up and I gain Recieve again. 

This happens on the 1000D, FT450, SX100, 101, 110,390 ect ect ect..

Its a Discharge inside or mainly outside the tuner to ground of high voltage. When a storm approaches this happens in 1 second intervals.. POP.........pop.......pop........pop.....pop.  This can go on for an hour.

I have noticed that if I am on certain bands with the tuner it will arc internal and other bands it arcs external. There is a simple explination for that. The plates are close on the caps on some bands where others they are open.

I have the chokes comming. They will be here next week. I will report back as to if this solves the issue.  As for the vertical.. I have tried many different things.  I just unplug it and stick the hardline in a glass Jar.  If you use a Coax style Lightning arrestor, It blows the Gas tube and you have to put in another, only to blow that one.

What I am worried about is that even with the chokes, I will still have the ARCs on the antenna and it will still blank out the RXer.

Clark

[KD6VXI]

Don't forget, their is literally, 12 to 24 inch long bolts of HV that shoot off the vertical antenna when this is happening...  Not just in the tuner.

The vertical is(was) hooked directly to hardline...  You could get a 'zap' across a PL connector, as well as watch lightening bolts shoot off the van de graf....  err...  Vertical antenna.


--Shane

[ke7trp]

Yes.. The old vertical which was a Sheakspeare unit, Died.. Something inside of it fried.  THe Imax 2000 that is up now gets arcs from the scew together sections and off the tip.. Normaly.. For some odd reason, the bolts go Northwest.  I use Half inch Andrews hardline that is Grounded to the tower as it goes up.  The insulation was stripped back and it is grouned to the round tower sections and sealed with coax seal. This is how Andrews suggests this line be installed.   

So far after 3 years+ the I max is not dead.  It covers all of 10 meters, 12, 15 and 17 just fine!

The wire antenna just arcs in the house at the tuner.


Clark

[KF1Z]

What bugs me the most, is what the heck is causing this in the first place?

I mean, yes, "snow-static", blowing dust, obviously a nearby lightning storm....

But happening on a daily basis? 

Do you live really close to any of those BIG high voltage lines?

I'm just amazed you could be experiencing this on such a regular basis.....


Wow, I'm glad I don't have to contend with any of that. !

[KF1Z]

Huh, you said the "bolts" go North-West.....

Directly towards Phoenix then ?

Curious...........       



Somewhat makes more sense to me, now I know where you are...
Guess the dry air would make a huge difference, from up here in th emoist north-east...

[ke7trp]

Guys. This does not happen every day...  It is a seasonal/weather thing.  I might go for months in the winter and not have the issue.  This last month was really bad.  Its arcing over today.  But let me make this clear that it is not daily. It just happens during dust storms or overcast weather.. If its real clear out.. Then I dont have the issue.

For some strange reason, we noticed that off the tip of the Vertical.. The bolts go North to northwest. Someone was commenting on that one night as we sat out in the night and watched the discharges.

Clark

[W1GFH]

“Corona Discharge”. The sharp pointed ends ("tips") of verticals are the worst case for this normal phenomenon. If it’s a metal vertical try installing a round metal ball at the top. The bigger the ball the better it will work.

[ke7trp]

Yeah..  I took everyones advice...

I have the two 200K 50 watt resistors across the open wire line and I ordered the Array solutions chokes.

As for the vertical.. Its up at 85 ft and need a bucket truck to get up there.  Its not worth the effort. I just leave it unplugged and in a glass jar unless its clear and I want to use that antenna.  10 meters is dead for me now so its realy not a big deal.

If I grab the open wire leads in storm will this happen?

 

[K1ZJH]

Chokes are NOT lightning protection............they bleed off any dc voltages that slowly build up on the antenna. The only way to protect ANY antenna from lightning is to take it down OR disconnect it from your shack and hard ground it before it enters the house. Even if u do this and the ant takes a direct lightning strike.......all bets are off.


Bill

I NEVER said they were lightning protection. But, from a previous post:

"I tried two small Chokes like you suggested.  Just in the listening mode.  This took the noise down.. Then, they both exploded into smoke. I guess this was the voltage hitting.. LOL.  They did work for a little while. I never transmitted through them.  I will need the large coils to drain that huge voltage and current.

Clark"

It seems there is something more potent than simple static build up going on, or the chokes wouldn't have smoked. 

Pete

[kc2ifr]

Ok OK....
I use 2 chokes on my feedline and I run A LOT of power and have never had a problem.....this uhf, vhf stuff is a lot of bunk in my opinion..........sorry.

[ke7trp]

Keep in mind that the chokes I ran where the small type you see inside a CB or 10 meter radio. THe ones that have three sections of wire (looks like string) wound on a bobbin.  They are made for low power. One hit off that wire and they smoked.  THe big coils I ordered are just heavy wire on a form. I dont think they will be bothered.. Time will tell.


Clark