Any Astro Plane Fans ?

[The DB]

I didn't want to go back to this waste of time... But I failed.

In the Sirio Gain Master design, the coax IS the antenna

Yes.

and therefore, since the high voltage node is at the bottom of the radiating portion of the antenna (at the top of the choke)

Yes, that is where a voltage node appears on that antenna by design.

they are using a voltage choke to stop the voltage, not current, from continuing to charge the coax

No they are not...

OK, let me explain this. On an antenna voltage and current are 90 degrees out of phase. That is complicated sounding, but all it really means is where you have a current peak you have a voltage null and where you have a current null and you have a voltage peak. This is key to understanding why their is a voltage peak at the choke on the Gainmaster (and really all antennas that incorporate a choke). And Needle Bender, I know that you understand this to at least some extent as prior discussions that you took part in required it (either that or the bs was strong with you)..

What the choke is doing is forcing the current where the choke is to a null, and by extension, because voltage and current are 90 degrees out of phase, this forces voltage to peak. Their you have it, the explanation in a nutshell, and why you have a voltage peak where the choke is.

If their were something as you propose that resisted voltage, that would cause a voltage null (and by extension a current peak), not the voltage peak you are bringing up, long story short, you have the cause of the voltage peak you are referring to backwards.

All voltage is is potential, nothing more, and potential cannot be resisted. Its like the muscles in your arm, they can lift a certain amount of weight, it doesn't matter if you are actually lifting that weight or not, the muscles can lift that weight.

OK, now on to more interesting things, namely the antenna being discussed. Post forthcoming.


The DB

 

[Needle Bender]

I didn't want to go back to this waste of time... But I failed.



Yes.



Yes, that is where a voltage node appears on that antenna by design.



No they are not...

OK, let me explain this. On an antenna voltage and current are 90 degrees out of phase. That is complicated sounding, but all it really means is where you have a current peak you have a voltage null and where you have a current null and you have a voltage peak. This is key to understanding why their is a voltage peak at the choke on the Gainmaster (and really all antennas that incorporate a choke). And Needle Bender, I know that you understand this to at least some extent as prior discussions that you took part in required it (either that or the bs was strong with you)..

What the choke is doing is forcing the current where the choke is to a null, and by extension, because voltage and current are 90 degrees out of phase, this forces voltage to peak. Their you have it, the explanation in a nutshell, and why you have a voltage peak where the choke is.

If their were something as you propose that resisted voltage, that would cause a voltage null (and by extension a current peak), not the voltage peak you are bringing up, long story short, you have the cause of the voltage peak you are referring to backwards.

All voltage is is potential, nothing more, and potential cannot be resisted. Its like the muscles in your arm, they can lift a certain amount of weight, it doesn't matter if you are actually lifting that weight or not, the muscles can lift that weight.

OK, now on to more interesting things, namely the antenna being discussed. Post forthcoming.


The DB

You've got to be kidding, right?

You say voltage & current are 90° out of phase (correct) and so if the current node is at the feed point in the center of a center-fed antenna, like the GainMaster, the voltage will necessarily be high at 1/4 wave, or 90° away.

On a center-fed 1/2 wave dipole, the current is max at the feed point in the center and minimum at the ends where voltage is maximum naturally.

With the GainMaster you have high voltage 90° down because of having high current generated by the incoming RF at the center.

You're not "forcing voltage to peak" - the voltage node occurs naturally because the current is high in the center, at the feed point, therefore the voltage will naturally go high 90° or 1/4 wave above & below it.

 

[The DB]

Talking about where the choke should go on an astroplane, I can model that.

The model I am using is not my own. I am using ghz24's model, actually I have modified it slightly, two of the elements were in backwards, and while this doesn't affect things like gain, impedance, and SWR, those wires did not show phase properly...

Anyway, taking the mast, and the discussion on its length, I can graph the change in mast length in 4nec2 and post the results here...

Lets start with SWR... SWR from 1 to 5 is charted on the left, and in number below the chart is the length of the mast before an isolation point.

As we can see, just above the mark labeled 102,right about where it would be 1/4 wavelength from the feed point, the SWR spikes up. How high does it spike? Lets see...

That is pretty high, it almost makes it all the way to 1300...

Looking back to the first SWR graph, any amount that is a little over 1/4 wavelength for the mast would be ideal. Even at the point of 3/4 wavelengths, the SWR on the model does not spike up to even 1.5 to 1.

Shall we look at other data? How about impedance next...

Here we can see why the SWR data above stayed so low over such a long area, once you get a little past the first 1/4 wavelength both X and R seem to be somewhat stable, especially R which is a little above what is should be.

And finally gain...

Here we see a pretty large variation in gain at the 1/4 wavelength point as it spikes both high and low. We see this again to a lesser extent at the 3/4 wavelength point. The area in between, however, is very stable.

Based on all of this information, I would suggest going a certain amount longer than 1/4 wavelength of mast/coax, length. Half wavelength is fine as it is in the middle of the stable region. Although some people may think it strange, the 1/2 wavelength mast/feed line has a current distribution that resembles a 1/4 wavelength mast/feed line, and I will show this below.

This phase shift is caused by the presence of the "basket area" (lower two wires and the hoop around the mast/feed line) of the antenna, namely the capacitance between the basket area and the mast/feed line, it causes a phase shift, much like a loading coil, although in this case in the opposite direction, making the element electrically shorter, thus requiring more physical length to compensate.


The DB

 

[bob85]

"I must've overlooked this backhanded slap the first time through"

Its not a backhanded slap NB,
how can we talk about chokes when you are using different laws of physics to the rest of us ?


"On a center-fed 1/2 wave dipole, the current is max at the feed point in the center and minimum at the ends where voltage is maximum naturally"

correct, that's the v & i distribution of a 1/2wave

"With the GainMaster you have high voltage 90° down because of having high current generated by the incoming RF at the center"

This is where you are going awry, you think current max is alway at the center of a dipole and current distribution starts from that point outwards, that's not how it works,

voltage and current distribution starts at the ends with voltage maxima and works back towards the feedpoint,
whatever angle the wave is at when it runs out of conductor at the feedpoint determins the end impedance of the element,

current maxima is not at the center of the gainmaster, its about 1/16 wave from the feedpoint, voltage max is at the tip and choke 1/4wave away from current maximas,

theres no such a thing as a voltage choke, you can't show us examples from respected sources because its straight off page 47 of karaoki physics,

"You're not "forcing voltage to peak" - the voltage node occurs naturally because the current is high in the center, at the feed point, therefore the voltage will naturally go high 90° or 1/4 wave above & below it."

without the choke the distribution could be anything because we don't know how long or what the coax is connected to at the far end, ( its common mode electrical length )

when you insert the choke you create a high impedance & voltage maxima,
you don't place the choke at the voltage maxima because as you say its naturally there because its not there until you insert the choke,

in short you have it all ass backwards.

 

[The DB]

You say voltage & current are 90° out of phase (correct) and so if the current node is at the feed point in the center of a center-fed antenna, like the GainMaster, the voltage will necessarily be high at 1/4 wave, or 90° away.

Their are two current nodes on the GainMaster, both of them equidistant from the center point. They used to have a nice animation out that showed that however I am not seeing it at the moment so I will have to use this.

Take a close look at figure 2, their are two current peaks present. Any center fed antenna longer than 1/2 electrical wavelength but shorter than one electrical wavelength will be like this.

On a center-fed 1/2 wave dipole, the current is max at the feed point in the center and minimum at the ends where voltage is maximum naturally.

With the GainMaster you have high voltage 90° down because of having high current generated by the incoming RF at the center.

You're not "forcing voltage to peak" - the voltage node occurs naturally because the current is high in the center, at the feed point, therefore the voltage will naturally go high 90° or 1/4 wave above & below it.

Where you are going wrong is assuming that the feed point is the point that determines where the voltage and current nodes are. This is an assumption on your part that is being treated as inviolate, or in other words you refuse to question it. I have demonstrated to you that this is incorrect, not only by my words, but modeling, and directly quoting the text and images of electrical and broadcast engineers that are far beyond either of us. If what you are saying is true, why do they teach would be engineers the exact opposite of what you are saying? I would really like an answer to this question.

Another question, if it is the feed point of the antenna that determines where the voltage and current nodes and nulls are, then why do we need a loading coil on a shortened mobile antenna? The reason said coil on these antennas is needed is because the voltage node is at the tip of the antenna, and the next nearest resonant point (that luckily also presents a low impedance) is electrically 1/4 wavelength from that point. If it were the feed point that determined the voltage/current distribution, their would be no need for using loading coils on mobile antennas because the voltage and current at the feed point would not change due to antenna length!

Alas, as I have said above, this is a

waste of time...

The DB

Edit: Look what I found, the animation I mentioned above, it clearly shows two separate bubbles of RF, which is caused by two different current nodes... A center fed half wavelength antenna would have one large bubble with no weak point in the middle like this animation clearly shows.

 

[Needle Bender]

"I must've overlooked this backhanded slap the first time through"

Its not a backhanded slap NB,
how can we talk about chokes when you are using different laws of physics to the rest of us ?

If your latter point were true then I'd agree with your former.

You & The DB are quick to condemn but as of yet I haven't heard a reasonable explanation why your theory of choking the current at the voltage node on the GM doesn't see an efficient current choke, as in 3T - 5T instead of 16T.

 

[The DB]

Please define what you mean by reasonable explanation, please, what will it take to get you to see the truth that is right in front of you that you refuse to see.

All you have to back up your statement is a single web site, and as we all know if it is on the interwebs it must be true right? I am always willing to look at additional data, so if you have more, please do share.

In comparison, I have shown you models that clearly demonstrate this, I have quoted words and images out of books used to teach actual engineers, and this isn't even all of it. And this was in addition to this being explained multiple times in multiple ways by multiple people.

Seriously, what do we have to do, pray to some hethen god to grant you understanding? If these resources aren't enough for you, what the hell is?


The DB

 

[HomerBB]

I haven't got a dog in this race, but either I missed something, or, there hasn't been a very well explained, or clear, reason why, as NB asked above, the 5 turns on a 4.5" current choke is not employed for the GM. I know this isn't a GM thread so it can be answered elsewhere if someone knows why. A theory was forwarded by NB, and it was disputed in terms of whether the voltage node with its consequent current maxima began at the end of a center fed antenna or the feedpoint. Yet, I agree that no precise answer regarding why the extremely long number of wraps for the choke are used. I have suspected it is just window dressing. It isn't necessary to force or create a voltage node, and it isn't necessary to diminish CMC on the feedline as a shorter 5tx4.5"d will do that. So what is it and why. This I've wondered since I first saw it a few years ago. Just so many ideas and contradictions employed by different folks. . .
Respectfully,
Homer

 

[The DB]

I haven't got a dog in this race, but either I missed something, or, there hasn't been a very well explained, or clear, reason why, as The DB asked above, the 5 turns on a 4.5" current choke is not employed for the GM. I know this isn't a GM thread so it can be answered elsewhere if someone knows why. A theory was forwarded by DB, and it was disputed in terms of whether the voltage node with its consequent current maxima began at the end of a center fed antenna or the feedpoint.

I didn't ask that question, Needle Bender did. I put forth two possibilities for why they choke that choke design was used, one, smaller and longer air wound chokes tend to have a wider choking bandwidth, and two, it looks better (never underestimate marketing especially when it comes to CB antennas).

Answering a question for you in the amateur radio antennas section I stumbled across a third possibility. When modeling a few chokes for you I found multiple situations where there were cmc's after the choke, and the largest determiner of this was the length of the feed line between the choke and the far end (where it attaches to the radio). If this length presented a voltage node to the choke, it didn't matter where the choke was from the antenna's point of view, their were still cmc's on the feed line. It was at this time that I noticed a longer choke of the same impedance did a better job of choking CMC's than a smaller choke. I have looked at this further, however, this needs some more research on my part.

Yet, I agree that no precise answer regarding why the extremely long number of wraps for the choke are used. I have suspected it is just window dressing. It isn't necessary to force or create a voltage node, and it isn't necessary to diminish CMC on the feedline as a shorter 5tx4.5"d will do that. So what is it and why. This I've wondered since I first saw it a few years ago. Just so many ideas and contradictions employed by different folks. . .

To get a precise answer I fear you will have to talk to Sirio directly, more specifically the engineer(s) that designed that choke. They have put out no information that I have found on why they used those choke dimensions, and everything that has been discussed is only conjecture on out parts.

I am aware of several people who claim to have successfully made a Gainmaster clone using a 5 turn on 4.25 inch form choke. The "schematic" put out by Gainmaster simply calls for a "low loss coaxial RF choke", here is the "schematic" as it exists on their site. How many turns does it show for said choke? (answer 5.5 turns of an unknown diameter)

Respectfully,
Homer

If you like, when I get some time, I can create models showing a given antenna with chokes at different parts of the antenna, and wherever the choke is you will see a corresponding current minimum, which by definition is also a voltage maximum.

It is always a pleasure to talk to you Homer.


The DB

 

[HomerBB]

I didn't ask that question, Needle Bender did.

Corrected!
Thanks, DB.
Sorry for mixing the handles. The thread is longish and somewhat convoluted. It was very late after a very long day and I should have waited until this morning to post.
Yes, I recall the thread you ran for me. It was enlightening. I'd like to see more on the choke models.
Never got around to building a homebrew GM. However, becoming a Ham has me thinking beyond single band antennas, and a coax choke doesn't seem to do the job so well for multiband applications. Still reading and learning.
Now back to the AP?

 

[The DB]

Air wound chokes are really only good for a limited number of frequencies. Ferrite is the way to go for multiple bands imho, I like ferrite so much I recommend it for single band antennas as well. Maybe its just me but I think it is easier to put a few ferrite beads on the coax, and the cost isn't a big deal for me either as I have access to a local electronics store that carries said ferrite beads in stock (no shipping, which costs as much as the beads themselves sometimes). Also, if you need a larger choke with ferrite beads, you simple add more beads, they act like resistors in series.

Now that I am thinking of it, here is a thought. The ferrite chokes I make all have the beads in the same place. What if I spread the beads out over an area of the feed line. Lol, one more thing to play with...

When it comes to models with chokes, I have been meaning to play with that some more. I haven't really had the time, but I would like to look at multiple different choke configurations for multiple different antennas, and perhaps even use some graphs like I did above, which track the change in SWR, gain, and impedance over different lengths of mast/feed line. Now that I know someone else is interested, when I get to it I will create a new thread and post my results on this forum.


The DB

 

[bob85]

DB
can we see the patterns for the above models,
with the mast isolated up at the ring where NB suggests,
isolated 1/4wave below the hoop & 1/2wave below the hoop,

thanks

 

[Needle Bender]

...after wading thru all the muddy waters of overly long posts, condescension, ad hominem attacks & red herrings, it's plainly obvious, Homer, they have no answer to the real question they sidestepped of why 16 turns, other than the DB quoting the chapter in his one-off copy of The Bible Of Aesthetics on the ugliness of 5 Turns versus 16 Turns, and 4.25" vs 3" - lol

Oh, and don't forget how he brought in the irrelevancy of the center additional 1/8 wave of radiating surface which the 5/8 wave GainMaster has over the 1/2 wave GainMaster, as if that had anything at all to do with the subject matter at hand - that being the relevant similarities of both, each using a 16T choke at the voltage node.

I'll admit they almost had me questioning my Elmer whom, clear back in the '70s, said,
"Ya don't use a voltage choke at a current peak and ya don't use a current choke at a voltage peak", until I recalled why.

High impedance will choke current but not voltage, non-resonance blocks voltage from creating an efficient current radiator.

What do you find at the feed point of an end-fed 1/2 wave antenna? High impedance.

There's also going to be a matching network, but that's just to present a 50Ω input impedance for the transmitter & coax, but the antenna is still 1500Ω-2500Ω impedance at the fed end of the 1/2 wave antenna. It likes high impedance.

The 5T x 4.25' dia current choke provides around 5 KΩ impedance, according to the graph provided in post #223, whereas a 16T x 3" provides much less impedance, somewhere around only 500-750Ω, but happens to present a terrible resonance at the frequency in question, 1/3 wavelength.

16T x 3" is terrible for resonance, only poor to mediocre for providing high impedance.

Sirio aren't stupid, nor interested in minimizing. their profit margin, it's 16T (not an efficient 5T current choke) for a reason, and it's not to present high impedance to current at a voltage node, it's to present high non-resonance to the voltage at the voltage node in order to prevent the RF voltage from exciting radiating current below that point.

A voltage choke, NOT a current choke placed at a voltage node not at a current node.

That's how I was taught, it's what I see when I look out the window at the GM, but if I'm wrong...

Tom, where are you?
- Come on in and straighten this whole thing out please.

...and the 1/2 wave GM is only 11.2' tall? oops, typo!

 

[Needle Bender]

DB
can we see the patterns for the above models,
with the mast isolated up at the ring where NB suggests,
isolated 1/4wave below the hoop & 1/2wave below the hoop,

thanks

...up at the ring? If you're referring to the Astroplane, I suggested isolation at the feedpoint, and IF locating the coax down the isolated mast, again at 1/4 & again at 1/2 wave below the top feed-point 1st choke.
But I plan to pull the coax off at a right-angle horizontal with appropriate chokes, not .run it down through the AP along the isolated (probably fiberglass or wood) mast.

 

[The DB]

after wading thru all the muddy waters of overly long posts, condescension, ad hominem attacks & red herrings, it's plainly obvious, Homer, they have no answer to the real question they sidestepped of why 16 turns, other than the DB quoting the chapter in his one-off copy of The Bible Of Aesthetics on the ugliness of 5 Turns versus 16 Turns, and 4.25" vs 3" - lol

If that is all you got, I actually gave three possibilities. In the end I also stated that to know why for certain you would have to talk to Sirio, which you, the one who is making the out of this world claim has not done. The burden of proof is on you.

Oh, and don't forget how he brought in the irrelevancy of the center additional 1/8 wave of radiating surface which the 5/8 wave GainMaster has over the 1/2 wave GainMaster, as if that had anything at all to do with the subject matter at hand - that being the relevant similarities of both, each using a 16T choke at the voltage node.

I what? When did I say that the additional 1/8 wavelength of the Gainmaster was irrelevant? I honestly don't remember that, and if I said anything of the sort it wasn't in this thread. You mind providing a link to where I said that?

I'll admit they almost had me questioning my Elmer whom, clear back in the '70s, said,
"Ya don't use a voltage choke at a current peak and ya don't use a current choke at a voltage peak", until I recalled why.

Are you sure he didn't use the word "balun" instead of "choke"? If we were talking about baluns this discussion would never have happened like this. Unlike voltage chokes, their is such a thing as a voltage balun.

High impedance will choke current but not voltage, non-resonance blocks voltage from creating an efficient current radiator.

High impedance will not choke voltage, nothing will choke voltage. Also, and this is a bit out their for most people, resonance, in and of itself, isn't a determiner of how well an antenna performs. I have on multiple occasions used a field strength meter to tune an antenna to maximum field strength, and it isn't always on the resonant point. Sure, it is the next logical step after assuming SWR tunes for maximum gain, but it also isn't the end of the story. Their is more to learn for those who choose to learn.

What do you find at the feed point of an end-fed 1/2 wave antenna? High impedance.

There's also going to be a matching network, but that's just to present a 50Ω input impedance for the transmitter & coax, but the antenna is still 1500Ω-2500Ω impedance at the fed end of the 1/2 wave antenna. It likes high impedance.

No argument here.

The 5T x 4.25' dia current choke provides around 5 KΩ impedance, according to the graph provided in post #223, whereas a 16T x 3" provides much less impedance, somewhere around only 500-750Ω, but happens to present a terrible resonance at the frequency in question, 1/3 wavelength.

Posting numbers as a fact? G3TXQ's chart disagrees with you, at least on the 5T x 4.25" choke, it shows it peaks over 8KΩ of impedance, but if you have better information than someone who actually measured one of these chokes, I would love to see it. The 16T x 3" choke has the same, if not higher impedance than the 5T x 4.25" choke. When you use a smaller diameter form you need more windings to compensate, that is all. This is common knowledge, and looking at the G3TXQ chart is all you need to confirm that.

16T x 3" is terrible for resonance, only poor to mediocre for providing high impedance.

Chokes don't care about resonance, never have and never will. They all work the same irregardless of their design.

Sirio aren't stupid, nor interested in minimizing. their profit margin, it's 16T (not an efficient 5T current choke) for a reason, and it's not to present high impedance to current at a voltage node, it's to present high non-resonance to the voltage at the voltage node in order to prevent the RF voltage from exciting radiating current below that point.

Sirio isn't stupid. I like several of their antenna designs, including the one in queastion here. That being said, you have no information on why they used that choke, which you are heavily mistaken about, you have no source of any kind, and you have nothing but conjecture.

A voltage choke, NOT a current choke placed at a voltage node not at a current node.

Voltage chokes don't exist. Please find me one reputable source anywhere that says otherwise.

Tom, where are you?
- Come on in and straighten this whole thing out please.

I'm not sure who this Tom fellow is, but if you are saying he is a source I would love to talk to him.


The DB