Blocking Capacitor for Ladder Line

[W2VW]

So exactly what do those 2 hockey puck caps in the posted picture do?

[wa3dsp]

That is a good question. I would say that in the scheme of things the Gas discharge and RF chokes are the most important items. The caps would block DC should there be a breakdown event at the transmitter but since the chokes are there if the caps were not it would just short it to ground like the protection RF choke on the output of many tank circuits in transmitters. This is probably what you would want since any exposed wiring on the TX side of the caps would be hot with the DC.

As for lightning any fast rise time spike would probably be coupled by the caps just like they were not there. There may be some benefit to having them there but on the other hand  if they are the right size and rating for the lowest operating frequency there is no real downside to putting them in.

Interestingly the author of the ER article states he always disconnects the antenna from the rig when not in use. If that were always true then I suspect the caps would be of no benefit in the case of a lightning event.   

[AB2EZ]

At the risk of drawing verbal lightning strikes from the more passionate posters here:

If the OWL connects... at the antenna end... to just a pair of wires.... and there is no DC path (like a pair of suitable RF chokes to ground) on the antenna side of the capacitors... then:

Neither of the capacitors would be charged up (i.e. have DC voltage across it) until a load (like someone's body) is placed between either of the OWL wires and ground. Therefore... while they would prevent the continuous flow of direct current... they would not prevent one from receiving a nasty shock in the event that somehow B+ had managed to develop a path from the transmitter to the link at the output of the balanced coupler/tuner. The bigger the value of each of the capacitors, the more charge (current x time) would flow when someone first placed themselves between one of the OWL wires and ground.

As has been pointed out, the RF chokes will need to be placed at a location along the OWL where the wire-to-wire RF voltage is not too high. Doing so will minimize the impedance required to sufficiently block RF, and will minimize saturation effects (if each of the chokes includes a ferrite core). Since the SWR might be fairly high, and the location of voltage maxima will depend upon the frequency/band being used (and the length of the OWL, in wavelengths), the best location of the chokes might be very wavelength dependent. Saying this same thing another way: If the chokes are placed at a fixed location along the OWL (e.g. near the coupler/tuner), the effectiveness of the chokes in blocking the flow of RF may vary greatly with the frequency of operation. 

[Steve - K4HX]

To be clear, three points.

1. Todd, KA1KAQ is also an "owner" of this site. But it's not our web site. It open for all to use and exchange information. Our part is to keep the thing functioning technically (web server, software, updates, etc) and to maximize the value to the users/members. Only you can be the judge of how well we are doing that job.

2. No one is forced to be here. And no one has a right to be here. If this site is so problematic, stay away. The numbers don't lie, however. We have over 1300 active members. We get new members daily. We average over 200 members logging in and hundreds more visitors (that don't log in) daily. There have been over 200,000 posts on this site. We average almost 80 posts per day. We have 100's who have been active members for over a decade. Yet it's only one or two that have a problem.^** Again, the numbers don't lie.

3. I don't care if someone disagrees with me, as long as they do it without name calling. I'm not here to shout down opinions. You will notice that I don't post in the vast majority of the threads here. If it were about me wishing to control the conversation, I would be much more involved. Vigorously discussing an issue doesn't mean that I am out to get someone or in anyway dislike the person with which I am discussing the issue. The reality is that nearly all the discussions here are inconsequential in the grand scheme of things. In other words, I don't really care that much about any given topic. If you think I do, you are sadly mistaken.



** These troubled few always have the same refrain - they are being singled out, there is a clique, the moderators are heavy-handed, there's a conspiracy. Most have had problems on and/or been kicked off other forums and email lists. They think the rules don't apply to them. When the rules are applied they complain and come up with these silly excuses for their bad behavior. Anyone who thinks the site admins and moderators have the time to single someone out need a reality check. Anyone who thinks there is a clique needs to look up the definition of clique (I'm sure a group of 1300 is not a clique). While they are at it, these troubled few should look up the definition of paranoid.

Steve, you are a serious piece of work and just love to put your own very distorted spin on everything I say. You remind me of the media, simply trash anyone that says something they dont like.

Im thru wasting my time with your replies, just ignoring you is the way to deal with it and many others on here will soon get the same idea and you can have your own little clique to amuse.

Carl

I should remind you in case you've forgotten; this is Steve's website.  You are essentially an invited guest in his home by being here.  It might be wise to behave yourself like a polite guest.  

[Todd, KA1KAQ]

Thats a typical response from you and your boy wonder sidekick Steve

WHAT??!? Steve gets a boy wonder sidekick?? WHEN did THIS happen??

I dont drink or do drugs either

There's your problem right there. Throw down a couple good, stiff drinks before logging on and you'll see just how 'important' all this online stuff is. Seriously, it's just a hobby Carl. You're one of the most knowledgeable guys I know in this field, but you really seem to place far too much importance or emphasis on it. If someone doesn't know or understand something as well as you it shouldn't get under your skin but be an opportunity to pass on some of that knowledge.

As to the clique Steve has going here, it's somewhere around 1362 members at the moment, and that's after the database was cleaned out of inactive/duplicate accounts last week. He did quite well with the original AM Window site, too. All indications are that this is a pretty active, helpful site despite the occasional dust up.

OWL is a future project for me once we get outta this transitional place and into a place where we can really stretch out. Each time something comes up on the topic, whether this thread or 'KYV/Don's masterpiece line that he constructed, I learn something new. Keep it coming, gang. Everybody benefits from a civil discussion and as Steve said, no one is forced to participate.

I do plan on getting to the bottom of this 'boy wonder sidekick' thing, though....

[WBear2GCR]

regarding the AB5WG design mentioned earlier - wondering if the design is counting on the ability to arc to the copper plate from the feeding lines? This in the event of a hit or near hit from lighting. I'd expect the RF chokes to *bamm!* open like fuse wire.

My immediate thought is "I want a spark gap" on both sides of OWL.

Whooo, whoooo?

                         _-_-

[wa3dsp]

If you read the ER article the purpose of the RF chokes are to eliminate static charges and keep the OWL and antenna at a DC ground. You are correct, any kind of direct or probably even a near hit would toast the RF chokes BUT that is the reason for the gas discharge tubes. They conduct and short the spike to ground. He also points out in the article why a spark gap, often used in the past, is not a good idea because of the difficulty in setting it and the variation due to the environment. A spark gap alone would allow very high static levels to build up before arcing if it were set for the maximum operating voltage. Remember you are probably using this antenna for receive also.

The idea here is to, as much as possible, stop the lightning event from going past this point and into the house and equipment. The RF chokes are rated at 4KV and the author pointed out that he has used it at legal limit power on all HF bands through 6 meters. I suspect there could be some combination of antenna design, line length, and frequency that might tax the RF chokes but none were reported.

I would say eliminate the capacitors and the RF chokes would shunt the danger of any DC coming out of the transmitter as well as eliminate static buildup.

[WBear2GCR]

I ought to have been clearer, I envisioned spark gaps or gas discharge units across each RFC to ground.

In the case of the spark gap, it would not matter much if the gap was off by a bit because they would only operate when the RFC either saturated, was about to arc over or blew out.

                            _-_-bear

Anyone else have a comment on Stu's point about choosing the placement of the RFCs & box? Seems to me it naturally wants to be at the base of the antenna where the feedline turns to go to the shack?

[wa3dsp]

There is a lot more theory to this than meets the eye. The extremely high rise times of a lightning strike which can be at many hundreds of megahertz or more would not be immediately dissipated by the choke but it would fire the gas discharge tube. The Alpha Delta series of coax switches and lightning protectors use replaceable gas discharge devices.

From a standpoint of RF the position it is placed in the line given the wide frequency range it would be used on would not matter BUT for lightning protection it should go close to the entry point of the house near the ground with as short a ground connection as possible.

[W7TFO]

Lightning.  The sky's bully.

I've worked in broadcast since '64, also known as the business where now you hook a big computer to a lightning rod, and hope it stays on the air so they make $$ and can pay you.

Old school was protection, nowadays it is avoidance.

Send the bully elsewhere to strike. This technology works, and I have seen it perform many times:

http://www.nottltd.com/lightning.html

Put some of these on your towers and poles, you'll be $$ ahead.

I have no interest in Ron's products, but have used them a lot to complete satisfaction.  There are other firms marketing similar devices.

73DG

[W2VW]

Lightning.  

Put some of these on your towers and poles, you'll be $$ ahead.

I have no interest in Ron's products, but have used them a lot to complete satisfaction.  There are other firms marketing similar devices.

73DG

People are listening. View from my office window:

[KM1H]

Put some of these on your towers and poles, you'll be $$ ahead.

But all that low level ionization must raise havoc with ham style reception I would think even when the storm is miles away. It may not bother Beverages or other on the ground antennas far enough away from a tower.

Looks easy enough to home brew however, maybe time to fire up the grinder and TIG welder. There is plenty of SS scrap at the local recycler.

The concept also gives some credence to those who claim their ungrounded towers have never been hit and have a "cone of protection". There are certainly lots of sharp points on the usual Rohn tower....Ive donated enough blood over the years to prove that point

Carl

[WBear2GCR]

In a previous thread the suggestion for hams: stainless steel chimney brush.

[aa5wg]

Tom, Phil, Steve, Carl, Al and all,

Sorry for not getting back sooner.  The flu hit me hard.

I am working with a link antenna tuner.  

My interest is getting rid of static build up on the balanced antenna and ladder line.

When I said DC blocking capacitors I should of said blocking capacitors inline with both sides of the ladder line on the output side of the "traditional" link antenna tuner.  

The author of the January 2013 Electric Radio article states, "The purpose of this capacitor is to block the static currents present on our antenna system from flowing back into your transmitter or receiver.  This will allow the choke and GDT to take care of the static currents and isolate your equipment from the antenna static currents."


Please jump in and correct me.  It seems if I add door knob capacitors inline with the ladder line I would be changing the antenna system electrical length, for a given frequency?


Chuck

[wa3dsp]

Chuck,

First of all if the value of the capacitors is large enough for the lowest frequency of operation they will have no effect on the RF operation of the circuit. They will essentially represent a short circuit at the operating frequency while  blocking DC. Think of this like any coupling capacitor, it is design to pass the desired frequencies while blocking DC.

The reactance of a .01uf cap at 1.8mhz is about 9 ohms, .001uf = 90 ohms. So it depends on the impedance the antenna represents to the load. If it is quite high you  might be able to get away with even 500pf and likewise if you are operating only at higher frequencies you would be able to use a lower value.

I think one could argue that with the RF chokes and Gas discharge tubes the capacitors would be unnecessary. It would be impossible for any DC buildup to exist with the RF chokes to ground. I really think the RF choke or direct DC ground on the antenna is a much better approach then trying to isolate it with only capacitors.

Also if the static buildup was sudden the capacitors would pass it anyhow depending on its rise-time but this would generally not be the case except in a storm situation. 

[KM1H]

Im glad we have the actual application answered 

While gas tubes do the job they have a finite life and the series caps add a bit of extra insurance at low cost. Here is antenna specific info that may be of interest and not usually discussed by the generic manufacturers.
http://www.nexteklightning.com/pdf/Gas%20Discharge%20Tube%20Maintenance%20v3.pdf

The choke handles the low level pulses without destructing, the gas tube can be purchased at a wide range of firing voltages and protects the choke in normal use and 20KV 1000pf caps just might save a variable cap or switch from arcing.

The big question now is how to spec the gas tube?

One other thing to consider is a BIG choke such as used in a BC station at the antenna feed point. It will be a very low DC resistance to ground but will have to be swept for the ham bands wanted but the right one will take a lot of near miss abuse.

Carl

[AB2EZ]

Carl

"and 20KV 1000pf caps just might save a variable cap or switch from arcing."

If these capacitors are connected to the two ends of an output link (coil)... how will they protect the variable cap or switch from arcing?

There is no path (except stray/parasitic capacitance) through which DC can flow to charge up these capacitors.

Stray/parasitic capacitance to ground will form a capacitive voltage divider in combination with these series capacitors. But, since the stray/parasitic capacitance will be much less than the capacitances of either of these two series capacitors, and since the leakage resistance to ground associated with the stray/parasitic capacitance is likely to be high compared to the leakage resistances of the added series capacitors, the majority of the static voltage, if any... (i.e. if there are no RF chokes present to provide a DC path to ground, or if for some reason the RF chokes open up)... on the antenna side of these capacitors will still appear between the tuner/coupler side of these capacitors, and ground.

If there is a grounded center tap on the output link of the tuner/coupler, then these capacitors will be able to charge up to drop the static voltage (if any) between the antenna aside and ground... but adding a grounded center tap brings with it a separate set of problems... and obviates the need for the capacitors to block DC.

Stu

[KM1H]

Stu, since when are the Johnson Matchboxes NOT considered "Traditional" link coupled tuners?   

Carl

[AB2EZ]

Carl

I give up. Since when?

In a Johnson Matchbox (275W or 1kW model), there is a variable capacitor between each of the balanced output terminals and ground. These variable capacitors, depending upon the settings, will have values that are much less than the 1000pF or 10,000pF capacitors that are contemplated as added series capacitors in this thread. The leakage resistance to ground of each of these variable capacitors can be assumed to be higher than the leakage resistance across each of the contemplated series capacitors. Therefore, in the event of static charge buildup on the antenna and/or the OWL wires... adding the contemplated series capacitors will not block the associated voltage. Most of the voltage will appear between the variable capacitors and ground. 

Stu

[KM1H]

Carl

I give up. Since when?

Since long before you even had your first license, however short, but you may have seen ads.

With a 20KV 1000pf fixed in series with a 100pf maximum at 3000V Peak DC in the small tuner the fixed cap will protect it until it breaks down and that is with a perfect cap in dry air. It doesnt take much to develop 3000V in a fairly close lightning strike.
The big tuner is 7000V Peak DC

Carl

[AB2EZ]

Carl

I disagree with your analysis. With a 1000pF capacitor in series with the tuner's 100pf... going to ground...charge injected into one of the antenna conductors will result in a voltage across the pair being split such that 10/11 of the voltage will appear across the 100pF capacitor and 1/11 of the voltage will appear across the 1000pF capacitor. The same current must flow through both capacitors. Therefore both capacitors will have the same amount of charge. V= Q/C. Therefore the smaller capacitor will have most of the voltage across it.

Stu

[W7TFO]

The whole deal of putting anything between your OWL and your tuner other than a grounding switch is 'much a'do about nothing', if I may quote the Bard.

73DG

[WB4AIO]

The whole deal of putting anything between your OWL and your tuner other than a grounding switch is 'much a'do about nothing', if I may quote the Bard.

73DG

I did two things. I put high value resistors (6.8 Megohms 10W noninductive) across the line and from each side of the line to ground. My idea is that precipitation/storm-front static can't build up to arcing and snapping levels with the resistive drain, however high it might be. So far it seems to work.

And, to protect against nearby strikes, I added quick-disconnect connectors right at the point where the balanced line enters the house. If I see lightning or hear thunder (or am leaving for a while), I disconnect the feeders and toss them 20 feet or so away from the house. I always do this, even if it's already started raining heavily.

73,

Kevin, WB4AIO.

[KA2DZT]

So far with this thread, Kevin has the correct (IMO) method for lightning and static build-up protection.

High value resistors to continuously drain off static charge build up and disconnect the feeders during rain and lightning storms.

Fred

[AB2EZ]

Kevin

I think the use of high value resistors is an interesting alternative to RF chokes for draining static buildup.

Do you have any experience comparing the behavior of the antenna system with respect to static buildup effects (or lack of those effects) with and without the resistors in place?

I'm wondering whether the values of resistance that you mentioned would be able to drain the charge quickly enough to prevent the buildup of high voltages?

I have no idea whether they would or they wouldn't be able to drain the charge quickly enough to be effective.

Best regards
Stu