Max2000 cap in center section

[rumblefish]

I recently checked the continuity of the center section of this antenna and it read infinite resistance.
That leads me to believe it's a capacitor and not something to keep the wire inside from banging around.
I have the "Max" 2000. I pretty sure its no different than the "Imax" 2000. If that is the case, then the schematic floating around on the internet is false. I'm not to savvy with the antenna modeling, but I wonder if it is possible
to generate a plot with the capacitor in the radiator. Maybe somebody knows the precise location of the capacitor
in the center section.

 

[The DB]

I recently checked the continuity of the center section of this antenna and it read infinite resistance.
That leads me to believe it's a capacitor and not something to keep the wire inside from banging around.
I have the "Max" 2000. I pretty sure its no different than the "Imax" 2000. If that is the case, then the schematic floating around on the internet is false. I'm not to savvy with the antenna modeling, but I wonder if it is possible
to generate a plot with the capacitor in the radiator. Maybe somebody knows the precise location of the capacitor
in the center section.

Sure, can model a capacitor in a radiator. I've done it with a Gain master model and a few other models. In that location (as opposed to a capacity hat setup) a capacitor would have the opposite effect on overall antenna length as a loading coil, or you would need to make the antennas physicaly longer to compensate.

I would need the capacitance of the capacitor to model it however...


The DB

 

[rumblefish]

Sure, can model a capacitor in a radiator. I've done it with a Gain master model and a few other models. In that location (as opposed to a capacity hat setup) a capacitor would have the opposite effect on overall antenna length as a loading coil, or you would need to make the antennas physicaly longer to compensate.

I would need the capacitance of the capacitor to model it however...


The DB

I don't have the means to check the value, but there is a chance its a 4 pf. It's 23 ft. to the base of the antenna. I also have the ground plane kit on it with the 6 ft. radials at 30 degrees to the horizon. The soil conductivity here is poor. DB that would be great if you would generate a plot we could look at. I seem to remember an advertisement for the imax 2000 when it first came out. something about extending the current in the center section. thx.

 

[The DB]

When I get some time I'll make one for you, might be a bit though. How far from the tip of the antenna is the cap, and how high is the antenna mounted?


The DB

 

[Marconi]

I don't have the means to check the value, but there is a chance its a 4 pf. It's 23 ft. to the base of the antenna. I also have the ground plane kit on it with the 6 ft. radials at 30 degrees to the horizon. The soil conductivity here is poor. DB that would be great if you would generate a plot we could look at. I seem to remember an advertisement for the imax 2000 when it first came out. something about extending the current in the center section. thx.

RF, I think the ad claim you noted was for us mortals, and simply describes the 5/8 wave height advantage over a 1/4 wave and a 1/2 wave mounted at the same feed point height ...like noted in the attached image below.

I think the only capacitor in this antenna is the 2.5" x 3/4" brass tube connecting the matching network to the base of the wire radiator in the schematic you noted.

Just my opinion.

 

[rumblefish]

When I get some time I'll make one for you, might be a bit though. How far from the tip of the antenna is the cap, and how high is the antenna mounted?


The DB

Thanks DB,Very much appreciated. The cap would be 143 inches away from the top of the antenna. feed point is 24 ft. from the ground. top of antenna is at 47 ft.

 

[rumblefish]

RF, I think the ad claim you noted was for us mortals, and simply describes the 5/8 wave height advantage over a 1/4 wave and a 1/2 wave mounted at the same feed point height ...like noted in the attached image below.

I think the only capacitor in this antenna is the 2.5" x 3/4" brass tube connecting the matching network to the base of the wire radiator in the schematic you noted.

Just my opinion.

the center section did not show continuity from one end to the other. if it was just a straight piece of wire it would have shown continuity.

 

[Marconi]

the center section did not show continuity from one end to the other. if it was just a straight piece of wire it would have shown continuity.

If the antenna is as you suggest and good, then the object could be as you say.

I have a Solarcon version. I will check the middle section of my Imax.

 

[rumblefish]

If the antenna is as you suggest and good, then the object could be as you say.

I have a Solarcon version. I will check the middle section of my Imax.

If you have the same result that I did, we may have to take another look at this antenna.
I've noticed you have done your fair share of antenna modeling. I'm curious as to how this capacitor affects the radiation pattern. I always assumed the center section was just a straight piece of copper. I was very surprised when a continuity check showed there wasn't any. At first I thought maybe I broke it taking it down. I crossed my fingers and put it back up on the mast. It's performing very well. Thank you for your input on this marconi.

 

[Needle Bender]

If the antenna is as you suggest and good, then the object could be as you say.

I have a Solarcon version. I will check the middle section of my Imax.

I have a friend who had an Imax fall and break the center portion. He confirmed there was a capacitor in the center of the 8' of wire and I presume it's more for high voltage isolation than performance, - but I could be wrong about that.

I expect the value to be so large that it shouldn't have much effect at all on the correct length of a 5/8 wave wire.

OH! I just found this: IMAX
I've read it before but so long ago I forgot.

 

[rumblefish]

I have a friend who had an Imax fall and break the center portion. He confirmed there was a capacitor in the center of the 8' of wire and I presume it's more for high voltage isolation than performance, - but I could be wrong about that.

I expect the value to be so large that it shouldn't have much effect at all on the correct length of a 5/8 wave wire.

OH! I just found this: IMAX
I've read it before but so long ago I forgot.

I'm thinking they put the coupling capacitor in there to raise the current higher on the antenna. That should in theory put more of the radiated signal on the horizon. I've scoured the internet looking for this antenna properly modeled with the coupling capacitor. All I can find is it modeled as a simple 5/8 wave. The downloadable enzec software online won't allow me to do this. I was just hoping someone on this forum could help me model this particular antenna. 73

 

[The DB]

I'm thinking they put the coupling capacitor in there to raise the current higher on the antenna. That should in theory put more of the radiated signal on the horizon. I've scoured the internet looking for this antenna properly modeled with the coupling capacitor. All I can find is it modeled as a simple 5/8 wave. The downloadable enzec software online won't allow me to do this. I was just hoping someone on this forum could help me model this particular antenna. 73

The current distribution of a 4 pF capacitor put in the middle of a .64 wavelength vertical ground plane antenna. Someone above suggested the 4 pF size, I used that as no one had the data the I asked for above.

The DB

 

[rumblefish]

Thank you DB. I appreciate your time. I'm not sure what to make of it though. It doesn't look good. I can't imagine how bad the radiation pattern is. I must be miles off on the cap value.

 

[The DB]

When it comes to inductors and capacitors in an antenna (assuming series connection of said devices), the devices are opposite in more ways than many people realize. One of those ways is how they provide a low impedance (or effectively AC resistance) to an RF signal. With inductors, low impedances come with low inductance values. Capacitors are the opposite of this, high values present lower impedances, the higher the better.

To give you an example of how high of a value we are talking about to get a lower impedance, I did the same model above with 1000 pF (indead of the 4 pF used in the image above), while gain went up slightly, the pattern is about the same, and the current distribution is near as makes no difference to the the image above. To get significantly less signal attenuation at this frequency range through the capacitor, you need one that is so prohibitively large in the real world that it isn't worth the effort.

Another thing that few people take into consideration is how sensitive an antenna is to a given amount of inductance and capacitance changes with frequency. Higher frequencies are more sensitive to capacitance, while lower frequencies are more sensitive to inductance. The CB band is low enough in frequency that it is far more sensitive to changes in inductance in an antenna than it is capacitance.


The DB

 

[357]

show up @ solarcon and ask for a tour?
someone must know someone that works there.