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Author Topic: 43 Ft Vertical Blatant Lie  (Read 35879 times)
W5WSS
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« Reply #75 on: September 26, 2012, 07:43:53 AM »

Cecil and oh by the way I understand and have understood for many years how a single wire can be an RF transmission line. A perfect example of such use is found in the Half square where the horizontal wire is intended to be an RF transmission line and intended to purposely not radiate horizontal radiation.

You know the difference and I know the difference.

I agree with you that to emphasise the difference is an important distinction for the ideas that you are trying to share.

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W5DXP
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« Reply #76 on: September 26, 2012, 11:43:15 AM »

I understand and have understood for many years how a single wire can be an RF transmission line.

Thanks Robert (Bob?), hopefully you are not the only person who understands that I was trying to enlighten and not "mislead" of which I was falsely accused.

Quote
A perfect example of such use is found in the Half square where the horizontal wire is intended to be an RF transmission line and intended to purposely not radiate horizontal radiation.

Right you are and thanks for that example. Those horizontal sections are perfect examples of single-wire transmission lines. If they are made of #14 wires 30 feet in the air, their characteristic impedance is Z0=600 ohms.

Quote
I agree with you that to emphasize the difference is an important distinction for the ideas that you are trying to share.

Maybe this example will help. The RF currents in each wire of a 1/2WL folded dipole (made from 300 ohm twinlead) are in phase with each other so we can call them radiating antenna currents even though they are flowing through a piece of twinlead transmission line. Those in-phase currents cause constructive interference in the EM fields and radiate like crazy. Radiation efficiency is high.

The 300 ohm transmission line feeding the 1/2WL folded dipole ideally carries differential transmission line RF currents that are 180 degrees out of phase with each other. Those out-of-phase RF currents cause destructive interference in the EM fields that tend to cancel radiation so transfer efficiency is high..

Now consider a piece of twinlead that carries RF currents that are 90 degrees out of phase with each other, i.e. in quadrature. There is no interference between RF signals in quadrature. How much energy is radiated and how much is transferred?

Would you (or anyone else) like to continue this discussion re: why the distributed network/transmission-line/wave-reflection model is superior to the lumped-circuit model for those humongous 75m air-core mobile loading coils and why a 100 uH coil cannot exhibit a 3 ns propagation delay? It appears that w8ji is going to avoid any technical discussion of those subjects.
« Last Edit: September 26, 2012, 11:59:07 AM by W5DXP » Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5WSS
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« Reply #77 on: September 26, 2012, 12:55:01 PM »

We know that to maximize the RF transmission through the coil to the radiating element we must enlarge the diameter of the conductor to minimize both the inductance and the resistance or opposition of current and voltage flow. There exists a concept that I do not see anyone mentioning, and that is circulating differential current. The wider diameter air coil works to admit or facilitate RF transmission from source to load faster. I have not measured the difference in opposition time to RF transmission flow along the path thru the coil but 3ns seems rather extreme to me.

The wider conductor can be 1/2 wide 3/16" thick strips of Aluminium for example.
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N2EY
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« Reply #78 on: September 26, 2012, 02:10:34 PM »

I think I see the issue.

The equations for a transmission line are only meaningful if the dimensions of the line are small in terms of a wavelength. 30 feet is small in terms of a wavelength at 7 kHz but not 7 MHz.

Same for loading coils when they get really big.

Good to see you, Cecil

73 de Jim, N2EY

I am finding it difficult to agree because the coil is a single conductor and part of the antenna in series with the rest of the single conductor ...

Seems you are not familiar with the single-wire above ground transmission line equations in my Electronic Equations Handbook and on page 24-16 in my 20th edition of The ARRL Antenna Book. Just as for two wire transmission lines, the associated equations are given. Here is the one for Z0.

Z0 = 138 log(4D/d) where D is the height above ground and d is the wire diameter.

A #14 horizontal wire 30 feet in the air has a Z0 of 600 ohms. Does that remind you of any ham antennas? Installing a loading coil in a single wire transmission line is not unusual at all. Half of a dipole is just a 1/4WL open-circuit stub that radiates because the differential currents are far away on the other dipole element.

Balanis talks about considering antennas to be lossy single-wire transmission lines. Single wire transmission lines were fairly popular during the early days of the telegraph. Lightning strikes were a problem.Smiley


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W5DXP
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« Reply #79 on: September 26, 2012, 08:20:12 PM »

The wider diameter air coil works to admit or facilitate RF transmission from source to load faster. I have not measured the difference in opposition time to RF transmission flow along the path thru the coil but 3ns seems rather extreme to me.

Yes, that speeding up effect is called the "sheath helix waveguide mode" described by Ramo and Whinnery under "Slow-Wave Structures" in "Fields and Waves ..." Adjacent turns on the coil are coupling together so that the propagation time through the coil is about half the time that it would take if the current were following the wire in the coil. That's why a loading coil needs to be made of about double the amount of wire that it replaces in an antenna. The "axial propagation factor" is the speed of propagation through the coil. From that value, the velocity factor of the coil can be calculated.

http://hamwaves.com/antennas/inductance.html

3 ns propagation time through a 10" long 100 uH coil is impossible. That 3 ns measured by w8ji is not the propagation delay but is instead the phase delay while the SWR in the circuit is about 80:1 which makes the measurement meaningless. According to the above inductance calculator, w8ji's test coil has a VF of about 0.02 along the length of the coil which means that a 3ns propagation delay would violate the speed of light limit.

A lumped-circuit inductor allows for instantaneous propagation because it has zero length. That concept is the source of the large (75m) air-core loading coil disagreements over the past decade.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5DXP
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« Reply #80 on: September 26, 2012, 08:47:51 PM »

The equations for a transmission line are only meaningful if the dimensions of the line are small in terms of a wavelength. 30 feet is small in terms of a wavelength at 7 kHz but not 7 MHz. Same for loading coils when they get really big.

Yes Jim, that's it in a nutshell. When the phase shift in a wire becomes a certain number of degrees, it starts acting like a transmission line instead of a dead short, and the lumped-circuit model has to be abandoned in favor of the distributed-network model.

Likewise, when the phase shift through a large air-core loading coil becomes a certain number of degrees, it starts acting like a transmission line instead of a lumped inductor and likewise, the lumped-circuit model should be discarded in favor of the distributed-network model.

In particular, the lumped-circuit model does not work for calculating the propagation delay through a large air-core loading coil. Those coils are invariably installed in a standing wave antenna so the measured phase delay from end to end in the coil is meaningless when trying to measure the propagation delay. For pure standing waves, phase delay is zero over 90 degrees of wire or inductor. The phase delay in 90 degrees of wire in a real-world dipole is about 3 degrees according to Kraus. But that doesn't mean that a 4 MHz RF signal can travel down 60 feet of antenna wire in 2 ns.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
KA7NIQ
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« Reply #81 on: September 28, 2012, 06:28:51 PM »

OK, quick question, assuming someone has no plans to install a good ground system for a vertical for 20 and 40 meters, IS it true the 43 ft vertical will outplay a resonant trap vertical, because it has a higher feed point impedance, and is less effected by ground losses ?
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N3OX
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« Reply #82 on: September 28, 2012, 07:38:20 PM »

OK, quick question, assuming someone has no plans to install a good ground system for a vertical for 20 and 40 meters, IS it true the 43 ft vertical will outplay a resonant trap vertical, because it has a higher feed point impedance, and is less effected by ground losses ?

Devil's in the details but it's plausible, especially on 40m and especially with an absolutely awful ground system.  But to be honest I think you'd have to use a stupidly bad system.

My 10 foot 40m hatted vertical with a six ohm feed impedance does only a little worse (1dB) than a quarter wave with a 25 ohm feed impedance, my soil is terrible according to the maps, and I have 27 radials out to the edges of a rough 40x40 or 50x50 square.      Total wire on the ground is something like 1000-1500 feet of  18 gauge bare stranded wire that I picked up from a surplus place about six years ago for a good price.  It took me exactly one Saturday afternoon of hot hard work to put the system in and I've used a bunch of different verticals on it and had good results from 160 through 80m.


Setting aside trying to figure out anything specific from the two feed impedances, it's  a pretty good ground system in terms of relative field strength from a heavily shortened and ground-loss sensitive vertical vs. a tall one.  Even taller would be less of an incremental improvement, but would be an interesting check.

Of course people have real restrictions where they really can't put down radials. But sometimes people just don't seem to want to or they think they need a much bigger system than what will actually work just great.  
« Last Edit: September 28, 2012, 07:42:19 PM by N3OX » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W8JI
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« Reply #83 on: September 30, 2012, 05:15:44 PM »

OK, quick question, assuming someone has no plans to install a good ground system for a vertical for 20 and 40 meters, IS it true the 43 ft vertical will outplay a resonant trap vertical, because it has a higher feed point impedance, and is less effected by ground losses ?

Not if you have a good ground system. If the ground system is reasonable, then overall the trap vertical is probably better. It is certainly no worse.

As Dan says, with a poor enough ground and enough over-simplified feed analysis we can justify all sorts of things. :-)
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K9TEN
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« Reply #84 on: March 26, 2013, 08:19:33 AM »

I don't have any say in what is claimed greatness of the 43'Ft vertical but I have used it in one form or another for several years. Back home it was a 43 foot tapered aluminum pole 25 foot off the ground mounted in a tree with 1ea 170 foot  baseball shaped loop as a counterpoise/ ground radial, or what ever you want to call it. At the base was a a section of home brew 600 ohm ladder line (50 feet long) fed to a Balun Designs 4:1 Current Balun (NOT an UNUN). From the Balun to the LGD Tuner in the shack was about 12 feet of LRM-400 coax. I have worked all over the world, a few on 75 meters, but mostly 40 meters  through 10 meters. I only ran 100 watts. I am nor in Kuwait and have a 31 foot fiberglass pole with a slightly spiral wound wire (Length 43 foot). It the base is an 4:1 Balun Designs Unun. The antenna is mounted on a 3" PVC pipe  at 127 feet above the ground on my apartment roof. I have about 25 ground radials of various lengths attached to the "Ground terminal" of the Unun and of course the 43 foot wire hook the the other terminal. It is feed with 89 feet of soldered together pieces of RG-8X coax.  I have made contacts all over the world with this including the USA, which is now DX for me. This vertical is about the only multi-band antenna (Cheap anyway) that I can put up here because all the crap up on the roof. I am using the internal tuner of an Icom IC-738, it works great. All the data in the world will not change the fact that it does work and for a small footprint, cheap made, it gets results. If anyone wants to make me confused on the facts of not efficient, high losses, bad swr and etc; go ahead but the antenna does work.
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AF4RK
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« Reply #85 on: March 26, 2013, 08:40:36 AM »

This fellow has a good idea for 160-80. 43' does not work without base loading on the low bands. However, I do quite well with the DX Engineering UN 43 on 40-10, as ad5x states in this article. I have had no problems with an Alpha 86 running 1.5 kw on 40-15 with S9V 43' and UN 43, with a Palstar AT2K. Not a fan of 10

http://www.ad5x.com/images/Presentations/Vertical43RevA.pdf

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CHRISDX
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« Reply #86 on: March 26, 2013, 02:21:09 PM »

which MFJ model number is that?

[/quote]
I have that cool little MFJ RF Sensing tool, so I can "see" the current on my radials, fence, etc.
[/quote]
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GM3SEK
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« Reply #87 on: March 27, 2013, 02:34:08 AM »

which MFJ model number is that?

Quote
I have that cool little MFJ RF Sensing tool, so I can "see" the current on my radials, fence, etc.

A clamp-on RF current probe really does let you "see" where the current is flowing. It should be everybody's next piece of test equipment for antenna and RFI investigations.

I reviewed the MFJ-854 and the MFJ-805 a few years ago for Radcom magazine and found the 854 a very competent piece of test equipment. But the MFJ-805 was a definite Don't Buy - at some levels of RF current, the meter needle moved in the wrong direction! For only $20 more, the MFJ-854 is vastly better value.

www.ifwtech.co.uk/g3sek/clamp-on/mfj-reviews.pdf

On the other hand, you can very easily make your own clamp-on meter for under $20. A basic  version is a beginner-level project - just a clamp-on ferrite bead, a diode detector and a sensitive meter. This page gives examples:

http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm


73 from Ian GM3SEK
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