Any Astro Plane Fans ?

[The DB]

All chokes add impedance to the system, impedance is essentially AC resistance, and is in fact so similar to resistance that it has the exact same electric symbol. From here you can simply apply ohm's law to figure out what the impedance of a choke effects, and impedance always and only effects current.

While I haven't seen it on a home made Gainmaster, I have seen five turns on a 4 inch or so form chokes on several T2LT antennas in person (one of which was up in a tree in my back yard for a while), as well as many others made by people on the various forums I frequent, and on these antennas they work exactly like the chokes on the Gainmaster, they become the end point of the antenna and force a voltage node.

When it comes to the Gainmaster choke, perhaps their is a property with that choke design that Sirio finds desirable. For example, more winds on a narrower form tends to widen the useable bandwidth of an air choke. With everything else that I know of in the Gainmaster antenna, and how they achieved that bandwidth, would they not want to do everything they can to ensure the choke they use works as well as it can over the entire bandwidth all of the time? Also, that design is more aesthetically pleasing than the wider smaller version, as least IMHO...


The DB

 

[bob85]

No NB im not saying sirio are dummies for doing it the way they did,
i think its a very clever idea very poorly implemented, the only issue i have with the choke is its red and has shitty uv protection,

been longer and narrower does not make it a voltage choke but it does give it different properties such as Q,

it also has increased electrical length of coax so transformer action will be different when measured at the coax connector with an analyser.

 

[Needle Bender]

All chokes add impedance to the system, impedance is essentially AC resistance, and is in fact so similar to resistance that it has the exact same electric symbol. From here you can simply apply ohm's law to figure out what the impedance of a choke effects, and impedance always and only effects current.

While I haven't seen it on a home made Gainmaster, I have seen five turns on a 4 inch or so form chokes on several T2LT antennas in person (one of which was up in a tree in my back yard for a while), as well as many others made by people on the various forums I frequent, and on these antennas they work exactly like the chokes on the Gainmaster, they become the end point of the antenna and force a voltage node.

When it comes to the Gainmaster choke, perhaps their is a property with that choke design that Sirio finds desirable. For example, more winds on a narrower form tends to widen the useable bandwidth of an air choke. With everything else that I know of in the Gainmaster antenna, and how they achieved that bandwidth, would they not want to do everything they can to ensure the choke they use works as well as it can over the entire bandwidth all of the time? Also, that design is more aesthetically pleasing than the wider smaller version, as least IMHO...


The DB

I don't see the 5T x 4.25" RG-58 having a problem choking nicely everything from 25mHz to almost 30mHz, or the full spectrum the GM covers, so no need for 16T to increase bandwidth.
According to the choke impedance chart I posted, that frequency range between 25mHz & 29.5mHz is still green with 4K+Ω impedance at 5T so I can't entertain that as a viable explanation.
- But I agree it's aesthetically pleasing to the eye, though I'd have to see a 5T x 4.25" GM before I could say which I preferred.

No NB im not saying sirio are dummies for doing it the way they did,
i think its a very clever idea very poorly implemented, the only issue i have with the choke is its red and has shitty uv protection,

been longer and narrower does not make it a voltage choke but it does give it different properties such as Q,

it also has increased electrical length of coax so transformer action will be different when measured at the coax connector with an analyser.

I LMAO, Bob, at your "shitty uv protection" remark, I completely agree. It's such a rich, beautiful red and so pretty right out of the box Floyd, but then after only a month it's gone all PINK!

...and I'd like to hear more about this different ."transformer action", different than what?

 

[bob85]

NB
I mean the electrical length of the coax from its termination @ the matching stub down to the so239 is longer when using the 16 turn choke so impedance transformation on frequencies where the termination is not 50ohms will not be the same as when using a 5 turn choke,

what is the electrical length of coax between the point where the coax meets the matching stub and the so239.

 

[Needle Bender]

NB
I mean the electrical length of the coax from its termination @ the matching stub down to the so239 is longer when using the 16 turn choke so impedance transformation on frequencies where the termination is not 50ohms will not be the same as when using a 5 turn choke,

what is the electrical length of coax between the point where the coax meets the matching stub and the so239.

Why would it matter? It's designed to present a ~50Ω load on frequencies where it's meant to perform and that is where the choke is needed.
...or am I not understanding your point?

 

[bob85]

Not saying it would matter much only that it is a different electrical length,
we don't know what impedance the antenna presents at the matching point on different frequencies,
we know its not 50ohms across the useable bandwidth measured at the connector.

a local donated a snapped gainmaster for me to experiment with.

 

[Needle Bender]

The Gain Master will be an interesting test bed. What do you plan to do with it?

Getting back to my original post/point, you can't have an effective choke if you use a current choke at a voltage node.
What I might do is place a current choke just beneath the current-feed point on the Astroplane at the coax connector, AND another a 1/4 wave down, then a thIrd to prevent any 1/4 wave of current growing from one choke to the next, until it's well beneath the antenna, though now I'm considering suspending it between trees with Dacron line, and pulling the coax off to the side at a 90° angle.

My contention is that if it acts like a self-contained 3/4 wave antenna it won't need any additional metal mast added for a resonant condition/ low swr, regardless of any patent info interpretation - especially considering how mast lengths are bound to vary from installation to installation.

...and BTW, mine is the older style with expanded upper basket tubes instead of swaged lower tubes.

 

[HomerBB]

It might be what you're looking for, NB. I have suspected it is a fat 1/2^ center fed dipole with a cap hat on one end stood vertically. Don't get me wrong, I favor this antenna whatever it is.
Let's see what you come up with . . .

 

[bob85]

We have two issues with gainmasters NB,
They won't take 300w fm for long overs, people using kl500/b550 often report vswr climbing if they get long winded,
once you let it cool down vswr returns to normal,

past experience tells me rg58 size coax will take 600w+fm and get warm for years so long as vswr is low, 300w should be no problem,
i have a couple of ideas to try,

The other issue is they snap in high wind,
i think that can be improved without too much effort,

if you string the astroplane up and bring the coax out @90 degrees you will discover the astroplane does need the mast or other conductor such as the coax braid with adjustment to spacing in order to have a good match and pattern..

 

[Needle Bender]

We have two issues with gainmasters NB,
They won't take 300w fm for long overs, people using kl500/b550 often report vswr climbing if they get long winded,
once you let it cool down vswr returns to normal,

past experience tells me rg58 size coax will take 600w+fm and get warm for years so long as vswr is low, 300w should be no problem,
i have a couple of ideas to try,

The other issue is they snap in high wind,
i think that can be improved without too much effort,

if you string the astroplane up and bring the coax out @90 degrees you will discover the astroplane does need the mast or other conductor such as the coax braid with adjustment to spacing in order to have a good match and pattern..

Bob, what's supposedly the optimum length for a mast piece installed on an Astroplane?

 

[bob85]

imho it should be 1/2wave / isolated 1/4wave below the hoop

 

[Needle Bender]

imho it should be 1/2wave / isolated 1/4wave below the hoop

Why, - what do you believe a 1/2 wave pole is supposed to accomplish with regard to impedance matching, as well as current & voltage nodes?

 

[bob85]

We went through this in the past when somebody maybe you claimed the astroplane should be isolated up near the hoop,

I choose a 1/2wave mast because that gives the least mast current below the hoop screwing the pattern up,

mast & leg relative diameters and spacing directly effects impedance because its a transmission-line,

Before you start talking about voltage nodes you must learn what they are and how current chokes work,
forget the fairytale voltage chokes,

The patent tells us what happens when the mast is shorter than 9ft below the hoop,

they don't tell us what happens when its longer but there are enough models of antennas on different length poles both connected and disconnected from ground to have half a clue about what would happen with some length masts/coax,

what is the end impedance of a 1/4wave vs 1/2wave not connected to anything at the far end ?

What length mast produces the maximum unbalance condition at the end of the transmissionline formed by the legs and mast ?.

What length should the mast be if you want maximum current in the mast below the hoop?,

what length should the mast be if you want maximum current in the upper 1/4wave?

I want my current to flow where its supposed to flow,
one of us has already tested your no mast/coax idea and knows the answer..

 

[Needle Bender]

We went through this in the past when somebody maybe you claimed the astroplane should be isolated up near the hoop,

I choose a 1/2wave mast because that gives the least mast current below the hoop screwing the pattern up,

mast & leg relative diameters and spacing directly effects impedance because its a transmission-line,

Before you start talking about voltage nodes you must learn what they are and how current chokes work,
forget the fairytale voltage chokes,

The patent tells us what happens when the mast is shorter than 9ft below the hoop,

they don't tell us what happens when its longer but there are enough models of antennas on different length poles both connected and disconnected from ground to have half a clue about what would happen with some length masts/coax,

what is the end impedance of a 1/4wave vs 1/2wave not connected to anything at the far end ?

What length mast produces the maximum unbalance condition at the end of the transmissionline formed by the legs and mast ?.

What length should the mast be if you want maximum current in the mast below the hoop?,

what length should the mast be if you want maximum current in the upper 1/4wave?

I want my current to flow where its supposed to flow,
one of us has already tested your no mast/coax idea and knows the answer..

As there would be maximum current at the center of the 1/2 wave mast, it would be 90° out of phase from the center-fed dipole the Astroplane is.

In an antenna where there is maximum radiating current at it's center, why would you want to introduce a 2nd current radiator 90° out of phase?

 

[Needle Bender]

...
Before you start talking about voltage nodes you must learn what they are and how current chokes work,
forget the fairytale voltage chokes...

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

Let me go over this one more time, and if you still have no luck grasping the concept, I'll just leave you to your current .understanding.

In the Sirio Gain Master design, the coax IS the antenna and therefore, since the high voltage node is at the bottom of the radiating portion of the antenna (at the top of the choke) they are using a voltage choke to stop the voltage, not current, from continuing to charge the coax (below the SIXTEEN-TURN choke) with RF, which would cause unwanted radiation extending below that point otherwise.

That is why we do not see an efficient current choke of 5T on a 4.25" former or similar, because they are not choking current, they are choking voltage - it is a voltage choke.

Below the coax connector of any antenna I can think of offhand, a 5T x 4.25" current choke would work fine since most matching networks, 1/4 wave, 1/2 wave, 5/8 wave, 3/4 wave, 7/8 wave, approximate a high-current node at the coax connector in order to attain 50Ω.

If you wanted to further choke the coax below the coax connector on the GainMaster 1/2 wave or 5/8 wave antennas, I'd use your 5T x 4.25" but that's below the antenna.

Certainly a knowledgeable company like Sirio wouldn't waste money unnecessarily on adding an extra 8-10 Turns of coax where it would not be needed, at the voltage node, if a current choke were sufficient.