"X" and Counterpoise

[ROC1]

Every commercially built antenna I've had on the suburban typically gives me "x" between 6 and 11, with "r" somewhere between 45 and 55 and SWR of 1.1 to 1.3.

In the process of winding up my first homebrew antenna this weekend for the mobile, and after a little too much adjustment (= cutting wire ), I stumbled across a very good fit on 28.5mhz. x=0, r=50, swr=1.0... I've never, ever seen that kind of match before and it got me thinking about the vehichle more and the antenna less.

If I'm able to achieve an x of 0 in the shorter wavelength but not on the target frequency, could it be an indication of inadequate counterpoise? At this point I've done no bonding whatsoever and have no reservation about experimenting with it. Just wanted to see if that train of though made sense...

 

[Dealer]

Every commercially built antenna I've had on the suburban typically gives me "x" between 6 and 11, with "r" somewhere between 45 and 55 and SWR of 1.1 to 1.3.

In the process of winding up my first homebrew antenna this weekend for the mobile, and after a little too much adjustment (= cutting wire ), I stumbled across a very good fit on 28.5mhz. x=0, r=50, swr=1.0... I've never, ever seen that kind of match before and it got me thinking about the vehichle more and the antenna less.

If I'm able to achieve an x of 0 in the shorter wavelength but not on the target frequency, could it be an indication of inadequate counterpoise? At this point I've done no bonding whatsoever and have no reservation about experimenting with it. Just wanted to see if that train of though made sense...

____________________________________________________________________________

First things first if I may

Are we talking about a vertical antenna ?

Cutting wire a little short ?? is that a stinger aka. whip or wire ? or what..

I have no bonding at all ??? How is it mounted to car,truck,ect ?

If it is mounted then it is bonded !! maybe not in the sense of ground straps to frame
but never the less it is a bond.

I Always expect to see R=50 X=0 SWR at 1.0 or real close !! the catch of course is
at what frequency.

Is those numbers where you want them and if not, can we assume they are at a higher
frequency than you want. If so then a longer stinger or wire or whatever will be needed.

You knew that of course. The counterpoise in a auto or truck is what it is !! No more or
No Less and to a very small degree based on where its mounted..

I run a Kw generally and have yet to ever bond to a frame,however with that said I
have my radios in a older model truck that has not the insulation properties newer
ones have..

The short of it is we need more information.......


Regards,
John

 

[555]

maybe it could use a little longer shaft on the bottom

 

[ROC1]

Dealer,

Yes we're talking about a vertical. I'm trying to get the antenna to resonate on 27mhz. Just for clarification the antenna itself is constructed like a wilson or Firestick. Copper coated wire wound on a fiberglass shaft, top loaded with an adjustable tip.

I wound up a new one today and as of right now I've got it at x=10, r=49 (probably do to the design loss), swr 1.2. x=0 is way off at 29.9mhz with r >100 and swr>25... Can't exactly find where this one is x=0, r=50 etc. I will say that @ 27.185, x is the lowest it gets anywhere near that frequency and it doesn't change a lot at the edges. Neither does "r".

Yeah, when I was speaking of "bonding" I was thinking more in the lines of doors, hood and tail gait to body and body to frame...

I'm still in the early stages of getting my learn on with this... Will be winding up another in a day or and will start with a little more wire and see where it ends up. I can alway "trim".

I guess the thing I'm struggling with is; every antenna I've tested on this, ends up with x over 5 and more often than not nearly ten... This makes me think there is something with the truck itself that I am missing.

You do bring up a point though I've forgotten about; I can't get a 102" whip or a single fighting stick to tune in this location (the rear puck) although they will tune in the front mount. The only thing that will tune at all in the rear location is something with a large coil (monkey made etc). If this antenna is behaving like a 1/4 wave whip, which most wire wound antennas do - it may be a location issue... I'll test it in the front mount tomorrow and see what it looks like. (thanks)

 

[ROC1]

maybe it could use a little longer shaft on the bottom

If I could tig weld I'd be goofing around with something like that! someday... maybe!

 

[Dealer]

Dealer,

Yes we're talking about a vertical. I'm trying to get the antenna to resonate on 27mhz. Just for clarification the antenna itself is constructed like a wilson or Firestick. Copper coated wire wound on a fiberglass shaft, top loaded with an adjustable tip.

I wound up a new one today and as of right now I've got it at x=10, r=49 (probably do to the design loss), swr 1.2. x=0 is way off at 29.9mhz with r >100 and swr>25... Can't exactly find where this one is x=0, r=50 etc. I will say that @ 27.185, x is the lowest it gets anywhere near that frequency and it doesn't change a lot at the edges. Neither does "r".

Yeah, when I was speaking of "bonding" I was thinking more in the lines of doors, hood and tail gait to body and body to frame...

I'm still in the early stages of getting my learn on with this... Will be winding up another in a day or and will start with a little more wire and see where it ends up. I can alway "trim".

I guess the thing I'm struggling with is; every antenna I've tested on this, ends up with x over 5 and more often than not nearly ten... This makes me think there is something with the truck itself that I am missing.

You do bring up a point though I've forgotten about; I can't get a 102" whip or a single fighting stick to tune in this location (the rear puck) although they will tune in the front mount. The only thing that will tune at all in the rear location is something with a large coil (monkey made etc). If this antenna is behaving like a 1/4 wave whip, which most wire wound antennas do - it may be a location issue... I'll test it in the front mount tomorrow and see what it looks like. (thanks)

___________________________________________________________________________

Just for conversation sake If i were to wind one which I would not BTW, then I would
want my load at the top of the antenna and close spaced, and here becomes the problem as i see it.
To get it very close spaced and not touching or by using a enamel coated wire which
is what limits the power handling of that type of antenna when they must touch.

I take it that you have layed hands on a 5ft firestick 11 with the adjustable tip and thats
the way i would try to wind one if i were to try such a thing.

Back in the day i ran one and swear by them to work when not anything else would work..

That said, a stake pocket mount would probley be the last place I would ever mount
any antenna and if I were to do so then its no doubt in my mind it would be at the front
pocket with the coil higher than the roof line, and bonded,bonded,bonded...

I have always used a big 4 disk mag mount on a steel gullwing toolbox mounted in center
of box and 8 inches back.. I subscribe to the KISS principal myself...

I believe the secret is in the coil were the bulk of wire will be. THINK about winding it
from the top down with lighter wire to make it narrow banded and dont worry about what
power it will handle at Least Not Now


Regards,
John

 

[ROC1]

___________________________________________________________________________

Just for conversation sake If i were to wind one which I would not BTW, then I would
want my load at the top of the antenna and close spaced, and here becomes the problem as i see it.
To get it very close spaced and not touching or by using a enamel coated wire which
is what limits the power handling of that type of antenna when they must touch.

I take it that you have layed hands on a 5ft firestick 11 with the adjustable tip and thats
the way i would try to wind one if i were to try such a thing.

Back in the day i ran one and swear by them to work when not anything else would work..

That said, a stake pocket mount would probley be the last place I would ever mount
any antenna and if I were to do so then its no doubt in my mind it would be at the front
pocket with the coil higher than the roof line, and bonded,bonded,bonded...

I have always used a big 4 disk mag mount on a steel gullwing toolbox mounted in center
of box and 8 inches back.. I subscribe to the KISS principal myself...

I believe the secret is in the coil were the bulk of wire will be. THINK about winding it
from the top down with lighter wire to make it narrow banded and dont worry about what
power it will handle at Least Not Now


Regards,
John

Actually I bought all the supplies at firestick... 100ft of wire, a few fiberglass shafts (7 and 9ft), adjustable tips etc. The shaft I'm using on this one is 9ft and I did wind it as a top loaded design. The rig is a suburban with hard mount pucks front and rear, so the stake pockets aren't an issue.

I'll be doing some additional reference testing today and will also try it in the front puck mount. This was the most cost effective way for me to try the mobile antenna build, but like you I'm not a big fan of this type of antenna. Pretty interesting stuff though.

From practicality point... well there really isn't any. If you can run 9ft of whip on a vehicle you're better off just doing that. I just thought it would be interesting to put together a 9ft top loaded antenna; or rather, see if it could be done and if it would work.

I'm still going to do a little bonding on the 'burban and see how it changes my numbers - it's pretty easily undone if something doesn't work.

thanks for the input!

 

[HiDef]

If you want R = 50 and X = 0 in a mobile installation where the counterpoise is sheet metal you will need to experiment a little.

Try a small amount of capacitance in parallel with the feedpoint. On 27 mega-hurts maybe 10 to 35 pf would be a starting guess. A small air variable can be used for testing. If it works the capacitance can be measured and later replaced with a doorknob type or something fashoned from a few plates and some teflon.

The stinger will require retuning or this trick will not work.

There are also ways to use an inductance across the feedpoint. That trick actually works better for hams due to the way it behaves across several bands.

 

[Dealer]

Actually I bought all the supplies at firestick... 100ft of wire, a few fiberglass shafts (7 and 9ft), adjustable tips etc. The shaft I'm using on this one is 9ft and I did wind it as a top loaded design. The rig is a suburban with hard mount pucks front and rear, so the stake pockets aren't an issue.

I'll be doing some additional reference testing today and will also try it in the front puck mount. This was the most cost effective way for me to try the mobile antenna build, but like you I'm not a big fan of this type of antenna. Pretty interesting stuff though.

From practicality point... well there really isn't any. If you can run 9ft of whip on a vehicle you're better off just doing that. I just thought it would be interesting to put together a 9ft top loaded antenna; or rather, see if it could be done and if it would work.

I'm still going to do a little bonding on the 'burban and see how it changes my numbers - it's pretty easily undone if something doesn't work.

thanks for the input!

___________________________________________________________________________

geezzzzz " no comprende" what a dummie sometimes I read and it dosnt soak in..

Its as if i read my own little story, so you will have to forgive me. Its a age thing you know
or at least thats what i blame it on.

Question if i may?? You bought a 9ft. shaft humm got me thinking but i promise I will
think quietly to myself.. O Heck i cant help it !! 20 meters wound top loaded, hehehe..

BTW, I said in a roundabout way that i like Firestick 11 antennas real well in the 5ft and
longer.

O yea what would you be winding a loaded 9ft shaft for ?? just curious


Regards,
John-KD5WJY

 

[ROC1]

___________________________________________________________________________

geezzzzz " no comprende" what a dummie sometimes I read and it dosnt soak in..

Its as if i read my own little story, so you will have to forgive me. Its a age thing you know
or at least thats what i blame it on.

Question if i may?? You bought a 9ft. shaft humm got me thinking but i promise I will
think quietly to myself.. O Heck i cant help it !! 20 meters wound top loaded, hehehe..

BTW, I said in a roundabout way that i like Firestick 11 antennas real well in the 5ft and
longer.

O yea what would you be winding a loaded 9ft shaft for ?? just curious


Regards,
John-KD5WJY

It was a... "I wonder if that would work" moment. LOL... It came after a lot of conversation with a friend about Firestick antennas and how their 7ft model doesn't have tunable tip and isn't quit up to handling power... not that we would ever do that on 11meter

So while I was thinking about it and talking to the owner of firestick I got to thinking about the benefits of a 9ft shaft (only because he had one against the wall... you know height is might).

Going back to our earlier conversation. I did test it today in the front puck mount and it tuned much better. Got x to three but could only get r to 43. this still falls short of my aluminum antenna. On that I can get x=0 with r=43. That said the home brew "tuned" better than the monkey made in either spot, but again you have to look at the design limitations. Continuous wound are very lossy so the "r" is likely a mirage...

At the end of the day if I'm going to throw something up that I can't drive around with, it will be the aluminum stick (or a pair of them). I just wanted to give it a go and try to put some practical experience into what I'm reading. Very interesting to watch the dance between x and r as the physical and electrical length changes along with the length and turn changes of the loading coil.

Before I dismantle it I'll put the analyzer on 20 meters and see what she'll do... if it's any good I'll send you some specs! LOL