gamma on a mobile ?

[mackmobile43]

On the KOGB website, he talks about using an enamled wire, is this important? Or say a piece of copper tubing like you suggested Shock, would it need to be coated someway? Or is there no need for worrying about arcing?

It's to insulate one coil from the next in case of contact, the tuning of the entire coil will change or act as if it's shorter than it really is in this case.

A good stiff wire or tubing coiled should do well also without the enamel coating but the coating will also help prevent corrosion of the metal.

 

[6.0 Liter]

I will have to try that Mack, I suppose a guy could drill and tap the puck mount for a screw to fasten the other end of the coil.........hmmmm

 

[mackmobile43]

I will have to try that Mack, I suppose a guy could drill and tap the puck mount for a screw to fasten the other end of the coil.........hmmmm

Yup now that's thinking with your dipstick.

 

[ROC1]

Yup now that's thinking with your dipstick.

Not really... the height of the puck won't allow for a proper high power coil's overall size if it's going to be fed at the bottom of the vertical.

The coil ends up being fed into the shaft several inches above the feed point. I would also think the coils proximity to the body metal would impact especially at high power levels.

I don't think it was an accident that Dave ran a capacitor in the ROG along with the grounded coil.

 

[W5LZ]

I don't see a problem with putting a matching coil between a 'puck' mount and the bottom shaft of an antenna. Why do you think there would be a problem?
- 'Doc

 

[ROC1]

I don't see a problem with putting a matching coil between a 'puck' mount and the bottom shaft of an antenna. Why do you think there would be a problem?
- 'Doc

I think the puck is too short for the coil.

 

[mackmobile43]

Not really... the height of the puck won't allow for a proper high power coil's overall size if it's going to be fed at the bottom of the vertical.

The coil ends up being fed into the shaft several inches above the feed point. I would also think the coils proximity to the body metal would impact especially at high power levels.

I don't think it was an accident that Dave ran a capacitor in the ROG along with the grounded coil.

Kinda like when you have a coil style antenna too close to the cab of a vehicle huh?

But I don't think there is that much rf energy being released before the antenna shaft, if that where the case you'd need some sort of shielding and where ever you read about this topic they warn of encasing the shunt for reasons of changing the tuning.

 

[W5LZ]

The mount, whether it's a 'puck' or some other kind, is to merely furnish a way to hold an antenna in a particular place in a particular way. If it does that as it should, then it's the proper mount for that antenna. There are quite a few that can do the same thing, just different 'styles'.
That impedance matching coil is only there to change one impedance to another impedance by adding inductive reactance between the 'hot' antenna and ground. It can also be of several different shapes/sizes and mounting positions, as long as it adds the right amount of reactance in the right place.
Can that impedance matching coil be enclosed? Sure, it is very common for that coil to be placed in some type of enclosure, it just depends on the size of that coil and how it's made. An adjustable coil is a bit more difficult to enclose because you have to be able to get to it to do any adjusting. (That holds true for loading coils too, BTW. More a convenience thing instead of "impossible" to do.) If that coil is not adjustable, then it's much easier to put it inside of some enclosure since you don't have to 'get to it'.
Will enclosing a coil change it's inductance? It can, but if the 'size' of the inductance is picked right, then things work just fine. (Transformers are coils, enclosing those coils it about as common as it gets, right?)
There's no minimum height requirement for an impedance matching coil, or any maximum height requirement, other than the thing has to be of a particular size to produce the required inductance. The thing is connected from ground to the 'hot' of the antenna. There has to be enough space to allow there to be some insulation to keep the 'hot' from grounding out to start with, but that matching coil will bridge that insulator, that's why it works. There's no particular 'size' requirement for the mount. It's a 'mechanical' thingy, it's got to get from one side of an insulator tot he other and not flop around a lot.
So why would a 'puck' mount be too small/short?
- 'Doc

 

[ROC1]

The mount, whether it's a 'puck' or some other kind, is to merely furnish a way to hold an antenna in a particular place in a particular way. If it does that as it should, then it's the proper mount for that antenna. There are quite a few that can do the same thing, just different 'styles'.
That impedance matching coil is only there to change one impedance to another impedance by adding inductive reactance between the 'hot' antenna and ground. It can also be of several different shapes/sizes and mounting positions, as long as it adds the right amount of reactance in the right place.
Can that impedance matching coil be enclosed? Sure, it is very common for that coil to be placed in some type of enclosure, it just depends on the size of that coil and how it's made. An adjustable coil is a bit more difficult to enclose because you have to be able to get to it to do any adjusting. (That holds true for loading coils too, BTW. More a convenience thing instead of "impossible" to do.) If that coil is not adjustable, then it's much easier to put it inside of some enclosure since you don't have to 'get to it'.
Will enclosing a coil change it's inductance? It can, but if the 'size' of the inductance is picked right, then things work just fine. (Transformers are coils, enclosing those coils it about as common as it gets, right?)
There's no minimum height requirement for an impedance matching coil, or any maximum height requirement, other than the thing has to be of a particular size to produce the required inductance. The thing is connected from ground to the 'hot' of the antenna. There has to be enough space to allow there to be some insulation to keep the 'hot' from grounding out to start with, but that matching coil will bridge that insulator, that's why it works. There's no particular 'size' requirement for the mount. It's a 'mechanical' thingy, it's got to get from one side of an insulator tot he other and not flop around a lot.
So why would a 'puck' mount be too small/short?
- 'Doc

because the coil thingy is too big/tall when designed to accomodate high power. the coil will terminate several inches higher than the feed point.

This is where the theoretical hits the practical road. For everyone who's following along - myself included, it might be easier if you included an actual design of your concept as opposed to just the theoretical "it can work" stuff. I'd like to see how a copper tube coil taps into a 1.5" tall puck and feeds into the bottom of the antenna and still accomodates the power handling requirements of the application. I'm a visual kind of guy - I'm sure I'll understand it better when I can see it.

 

[ROC1]

The mount, whether it's a 'puck' or some other kind, is to merely furnish a way to hold an antenna in a particular place in a particular way. If it does that as it should, then it's the proper mount for that antenna. There are quite a few that can do the same thing, just different 'styles'.
That impedance matching coil is only there to change one impedance to another impedance by adding inductive reactance between the 'hot' antenna and ground. It can also be of several different shapes/sizes and mounting positions, as long as it adds the right amount of reactance in the right place.
Can that impedance matching coil be enclosed? Sure, it is very common for that coil to be placed in some type of enclosure, it just depends on the size of that coil and how it's made. An adjustable coil is a bit more difficult to enclose because you have to be able to get to it to do any adjusting. (That holds true for loading coils too, BTW. More a convenience thing instead of "impossible" to do.) If that coil is not adjustable, then it's much easier to put it inside of some enclosure since you don't have to 'get to it'.
Will enclosing a coil change it's inductance? It can, but if the 'size' of the inductance is picked right, then things work just fine. (Transformers are coils, enclosing those coils it about as common as it gets, right?)
There's no minimum height requirement for an impedance matching coil, or any maximum height requirement, other than the thing has to be of a particular size to produce the required inductance. The thing is connected from ground to the 'hot' of the antenna. There has to be enough space to allow there to be some insulation to keep the 'hot' from grounding out to start with, but that matching coil will bridge that insulator, that's why it works. There's no particular 'size' requirement for the mount. It's a 'mechanical' thingy, it's got to get from one side of an insulator tot he other and not flop around a lot.
So why would a 'puck' mount be too small/short?
- 'Doc

I think we're debating theoretical vs practical on a bunch of different levels... That's a no win. I'll say this in closing and then you can have the last theoretical word.

If the OP taps an existing puck like fatboys (I may be wrongly assuming he doesn't want to go to the trouble of machining a custom puck), then adds a matching coil made from copper tubing to it that will accomodate the power levels he is looking to use - as suggested above - I believe he will find it very difficult if not impossible to terminate that coil at the base of the antenna and achieve the desired impedance.

This is based on my actual experience of trying to do exactly what is being suggested and to this point I've been unable to do it... practically speaking of course.

I run a multi-element vertical array on my suburban and would love to run higher gain spacing with 20 something ohm resistance at the feedpoint that I could match externally (outside the truck). No luck so far, maybe you can show us an actual design that will work as opposed to explaining why it "should".

Not trying to bust your balls Doc, absolutely respect you, but there are always physical constraints and issues when we migrate from concept to paper to metal. In this situation I think you're still on the paper for this kind of appliation.

 

[6.0 Liter]

I can see where you are coming from ROC1, if a guy was running a full length antenna tho, what would be the harm of attaching the matching coil a couple of inches up? Other then being a pain in the butt. Mabe it would change the resonate length.....idk......guess I havn't tried it

 

[W5LZ]

The drawing is not to scale, but should give a general idea of one type of impedance matching device commonly used on mobile antennas.
The bottom shaft of the antenna goes down through that coil and connects to the mount 'clamping' that 'shaped plate' between it and the mount. The shaped plate just has to be of a size not to short to ground at that connecting point. The matching coil I used on a bugcatcher antenna used a copper plate soldered to the bottom winding of that coil. It worked just fine for a lot of years. Took a while to find the right tap point on the coil for that ground wire, but it's certainly 'doable'.
Power handling? The coil was made with #12 wire spaced about 1/8 inch between windings. It handled 500 watts just fine but that means that the antenna definitely had to be resonant! Depending on the amount of power you plan to use, it would be a fairly safe bet to use large sized wire and spacing. If the spacing ever get's to something like 1/2 inch, it's way over done. If the power was in the 1000 - 1500 watt range, I'd say #10 wire and 3/16 inch spacing ought'a do just fine. (That's a guess at the spacing, and probably a bit 'large'.)
- 'Doc

 

[AudioShockwav]

I am getting confused here.
Roc & Doc Are you guy`s talking about the same thing?
I have it in my mind that Roc was thinking about this ( again ignore the measurements, just look at how it works) Like L/one posted in the DaveMade Rod Of God Thread

73
Jeff

 

[AudioShockwav]

remember this was a 1/2 wave and the coil/caps are the matching network.
Maybe I am off in left field here.....


73
Jeff

 

[RickC.]

I am getting confused here.
Roc & Doc Are you guy`s talking about the same thing?
I have it in my mind that Roc was thinking about this ( again ignore the measurements, just look at how it works) Like L/one posted in the DaveMade Rod Of God Thread

73
Jeff

Yep, that's a different situation- an end fed half wave has a feedpoint impedance in the range of 3-4K ohms typically (I've built a few). I suppose those were Rick Made Wires of Fire or something?

Rick