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Author Topic: Your favorite antenna wire.  (Read 41909 times)
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K1JJ
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« Reply #25 on: July 20, 2011, 01:45:55 PM »

I would like to see some scientific data on "pre-stretching" softdrawn stranded wire.

I also tried it years ago, and like Terry, found it stretched until it broke. (as expected) There must be a guideline, like stretch #10 wire  2% longer and then stop. 

Don't see a lot on the web about it from a short search.

So, what's actually happening - how is the wire changing its characteristics from a molecular point of view?  Does it actually get weaker as a result of the stretch, but have less tendency to stretch further from that point?

T

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« Reply #26 on: July 20, 2011, 02:57:06 PM »

I think the key is the term  Hard drawn which might be misleading.

Just found this on the web
Quote
hard drawn copper wire is wire that is not annealed after the drawing process. Annealing makes the copper more flexible. Hard drawn has at least 150% more tensile strength than annealed

And this
Quote
Thomas B. Doolittle (1839-1921): Doolittle invented hard copper wire. Copper wire is a good conductor of electricity but is mechanically weak. Iron wire is strong but not a very good conductor. He created the first hard-drawn copper wire made tough-skinned by a fairly simple process. This hard wire was used for line wire and vastly extended the range of telephone transmission.

When, however, the copper wire is intended to have a high tensile strength it is not annealed so frequently between the different drawings as in the case of iron.

Experiments have shown that the ductility of copper wire decreases as it tensile strength increases, but the experiments were not continued to an extent sufficient to show the exact ratio. A specimen of copper wire, thoroughly annealed, .128 inch in diameter, was found to have tensile strength of 330 lbs., and elongated 36 per cent. A sample of the same wire, on being drawn twice, to reduce its diameter to .104 inch, had a tensile strength of 330 lbs., and elongated 23 per cent. Another specimen, from the same piece, on being drawn thrice to bring it to the same diameter, namely .104 inch, was found to have a tensile strength of 415 lbs. and elongated but 3 per cent. Still another specimen from the same wire, drawn four times to reduce it to .104 inch, had a tensile strength of over 550 lbs. and elongated but 1 per cent. The average of a number of like experiments indicated that, in obtaining an elongation of 2.5 per cent. to 3 per cent., a reduction of 130 to 140 lbs. in the tensile strength would follow.

The term "hard drawn" is applied to distinguish the unannealed from the annealed copper wire; the only difference between soft copper wire and hard drawn copper wire being that one is annealed after drawing while the other is not. The process of drawing the wire through the die forms a thin, hard, polished crust, or shell, not exceeding the one thousandth of an inch in thickness, over the wire. Inside of this crust the metal is, seemingly, comparatively soft. The tensile strength of hard drawn copper wire appears to rest in this outside shell, for the lightest indentation made around the circumference of the shell with a sharp instrument will at once lower its breaking strain; and while, with an undented surface, the copper wire may withstand 5 or 6 bends on itself, with such a dent it will break in one bend. [/quote]

and they talk about broken wires in the process so the way we do it appears just fine.

Quote
As is is not an uncommon occurrence for wire to break in the act of drawing, the matter of jointing such broken wires in such a manner as to avoid the objections referred to, was one which received much attention from the manufacturers, and various attempts were made to weld the joint, mechanically, without materially increasing its bulk, or decreasing its tensile strength; but only with indifferent success. Of late, however, electric welding has been resorted to, for this purpose, with marked satisfactory results. In making joints, or welds, by this process, the ends of the broken wires are brought together, and are fastened to separate clamps. Wires connected with a dynamo machine are brought to these clamps, and a very strong current is then caused to pass through the tips of the broken wire, which speedily produces a heat sufficient to form a perfect union between them. For ordinary telegraph wire the time of application of the current is but a fraction of a second, but the time of application of the current, the extent of the wire exposed between the clamps, and the pressure with which the ends are brought together, varies with different wires. Welds made in this way have scarcely a perceptible burr, and tests have shown that the tensile strength of the weld is practically similar to that of the wire proper.
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« Reply #27 on: July 20, 2011, 04:30:23 PM »

I don't know anything about pre-stretching stranded wire. It does work with solid wire. I have done it a few times by trial-and-error: sometimes by hand, tying one end to a tree and the other end to a pipe or rake handle, and pulling with all my might. I was able to stretch a 100' length of #14 wire several feet that way. At first it stretches easily, but it quickly reaches a point where the stretch is no longer easy; I take that to be the limit of stretching, when most of the stretch is taken out of it. You can also tie it to a car bumper or trailer hitch or a tractor and the other end to a tree or utility pole, and use the vehicle to stretch, but it is easy to stretch it too much and break it if you are not careful.  A ratchet puller would probably work as well. Maybe there is a formula for the right amount of stretching. But for a serious antenna job I would still use copperweld, ready-made hard drawn wire, or phosphor bronze if I could find it.

I remember when I built my present radial system, which is made of #12 bare soft-drawn copper. I used a Mapp Gas torch and silver brazing rods to bond the radial wires to the common point. Right after the end of the wire was heated red hot and brazed to the copper strap at the tower base, as soon as it cooled down the wire would be extremely limp, almost as limp as a fabric rope or a strand of plastic cord.  But flexing it just a couple of times would restore it back to near its original stiffness.
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« Reply #28 on: July 20, 2011, 04:47:52 PM »

As a practical matter, I lost about 15Kc in about two years from end-supported, #12 insulated stranded electrical wire originally cut for 3850Kc.  

I knew the wire had stretched, but didn't really measure the impact at RF until the "AM Bandwarming Party" when I wanted to see how bad my VSWR would be during the event.

Turns out the shift downward in frequency (from the longer physical wavelength of the doublet) was a happy thing.

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« Reply #29 on: July 20, 2011, 04:48:18 PM »

I like copperweld for its long life and strength.   I have used flexweave and found that it frayed along edges of insulators.   It is good for a quick temporary antenna setup but avoid for any permanent antennas.   As with any exposed copper it is hard to resolder.

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« Reply #30 on: July 20, 2011, 05:18:42 PM »

Yes, that was my main problem with Flexweave - how do you resolder it after it has been browned by the wx?  I tried sandpaper and even dipped it into Radio Shack circuit board etching solution. Both did not work well.

Don, I think your idea of stretching until most of the give is gone is a good idea. I remember feeling that point too. I'll bet a come-along is the best method.  

From Terry's info, maybe a target of 1-2% stretch is about right. That wud mean about  2.5' for a 125' wire for 2%.  The data shows it's quite an increase in strength when the wire is stretched. (330 lbs to 550 lbs!) That's the opposite of what I intuitively figgered.  Maybe the stretch tendency is arrested by the increased/improved tensile strength more than anything else.  I wonder what they mean by "drawn twice" or "drawn thrice?"  Do they draw it and wait for a minute then draw it again? What is the significance of doing it three times vs: once if the diameter is still the same .104" in this case?

Paul, from your data, looks like your dipole stretched about 5.75" to go from 3850 to 3835. Not bad, really.

T
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« Reply #31 on: July 20, 2011, 05:48:41 PM »

The Navy used phosphor bronze for the long wires and lead-ins to the feedthru insulators into the radio rooms on upper levels or to 6" square conduits that ran thru the ship to the radio rooms and used solid #6 or larger copper wire for the inner conductor. Id guess the antennas were 5/16 cable and stretched tight 90' on the ship I was on; 2 on each side of center.

To connect the feeds to the antenna a pair of grooved phosphor bronze plates and 3/8" brass hardware were used. The plates had to be taken apart and wire brushed at least twice a year and the insides and wire were wire brushed.

While I was aboard for 2 1/2 years 1961-63 except a walkway between the pairs of midship towers was added before I arrived. Later a 35' whip was attached to the stack for the URC-32: http://www.bluejacket.com/usn/images/sp/a/ao109_waccamaw_a.jpg

After she got stretched:
http://en.wikipedia.org/wiki/File:USNS_Waccamaw_(T-AO-109)_1984.jpeg

Quote
Yes, that was my main problem with Flexweave - how do you resolder it after it has been browned by the wx?  I tried sandpaper and even dipped it into Radio Shack circuit board etching solution. Both did not work well.


Tom, dip it in a diluted hydrochloric acid, thoroughly wash, solder and then deflux. some splices done that way are holding up 30-40 years. I dont throw away useable wire Shocked
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« Reply #32 on: July 20, 2011, 10:17:56 PM »

leftover network cable! often free, decently strong and flexible, can be sealed up decently, ties in knots well.. and it is free!

The sun will eat at the outer coating after a few years but a 150FT stretch of it is still up at an old farmhouse in Gainesville TX, works great for SWL but has seen the occasional transmitter.
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« Reply #33 on: July 21, 2011, 01:37:34 AM »

I agree with Don about Copperweld which is a trade name, the junk is simply copper flashed as with welding wire or single pass plated at about .010".

Rural telephone wire is still available in #10 and 12 with .030" plating and a black nearly impervious jacket.

I measured the thickness of the copper jacket on my #8.  I was a little disappointed that it measures only .012". But I used that wire for my beverage, which has been up for almost a decade now, and shows no sign of rusting through. I have pulled that wire tight several times with a fence wire tensioner, which has steel teeth to grip the wire, and although it gouged visible marks on the surface of the wire, it did not break through the copper jacket and no visible rust has appeared at the tooth marks, so the copper seems durable enough and resistant to deterioration in the weather. I'll look for a sample of the #10 telegraph line and see how thick the jacket on it is.

I suspect the stuff that rusted through was cheap electric fence wire, plated only a few molecules thick. Microscopic pores or cracks in the copper jacket allow moisture to enter and attack the steel core, and as the rust build-up it expands and pushes its way through to the outer surface.

My method for measuring the thickness of the jacket is as follows:

1.  Measure the diameter of a sample of the wire.

2. Using a small fine-toothed square or triangular file, file a flat spot on the wire, being careful to file only until the jacket is just barely filed through at one point and the steel core just begins to become visible. The visible steel should appear as a thin straight band parallel to the axis of the wire sample. If you see any more core than that, you have already filed too far.  Find another spot on the sample and repeat the above procdure.

3. Measure the diameter of the wire at the flat spot.

4. Subtract the above figure at (3) from that the original measurement (1).

Something else to consider with the Copperweld is whether or not the copper jacket is thick enough to allow the skin effect at the lowest frequency to prevent the rf from penetrating through to the steel and thus increase resistive losses.
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« Reply #34 on: July 21, 2011, 08:29:49 AM »

We source our Copper coated wires from CommScope:
 http://www.commscope.com/company/eng/support_document/spec_sheets/bimetals/__icsFiles/afieldfile/2010/05/07/CCS40_0510_E.pdf

The coatings are applied is various thicknesses. They also supply Copper on Aluminum.
 A quick check on copper plated wire that they use in the lab here involves , I believe, Ferric Chloride. They quickly etch away the copper and measure the differences. This gives practical, usable readings on even the thinnest coatings.

  For larger areas , we use a Lamina Checker. It is a magnetic device that gives accurate measure of non ferrous coatings on a ferrous substrate.

   Adding a layer of Zinc plating between the steel core and copper jacket improves corrosion resistance by a large factor.
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« Reply #35 on: July 21, 2011, 02:53:02 PM »

Don, I was wrong about the copper thickness, got that and conductivity mixed up.

Anyway this is from ATSM B452

.
Quote
2 Four classes of copper-clad steel wire are covered as follows:

1.2.1 Class 30HS—Nominal 30 % conductivity hard-drawn,

1.2.2 Class 30A—Nominal 30 % conductivity annealed,

1.2.3 Class 40HS—Nominal 40 % conductivity hard-drawn, and

1.2.4 Class 40A—Nominal 40 % conductivity annealed.

The jacketed #12 Ive used in the past for Beverages and inverted vees for 160 was 30%. For 40% #8 it would be a minimum of .0116 and thats apparently what you have....good stuff.

My 160 wire verticals are stranded and jacketed #8 submerged well motor wire....tough stuff even outdoors for 20 years.

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« Reply #36 on: July 21, 2011, 05:35:33 PM »

Does that 30% and 40% conductivity figure mean 30 and 40 percent the conductivity of solid copper?

Of course, the situation is totally different for RF, since the skin effect keeps most of the current close to the surface. In that respect, solid copper is a waste, and steel would do just as well (actually better, strength wise) in the core where there is little or no RF current flowing.

Another advantage of copperweld is that it is practically worthless to scrap  metal dealers. I have been told it brings even less than solid steel.  But the dumb-ass copper thieves probably wouldn't have a clue until they had already destroyed a radio installation, only to be told that their booty would bring them a tiny fraction of what they had anticipated.
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« Reply #37 on: July 21, 2011, 07:21:15 PM »



Another advantage of copperweld is that it is practically worthless to scrap  metal dealers. I have been told it brings even less than solid steel.  But the dumb-ass copper thieves probably wouldn't have a clue until they had already destroyed a radio installation, only to be told that their booty would bring them a tiny fraction of what they had anticipated.

That's what worries me about my heliax.  it is mostly plastic, foam and aluminum.  I guess the Al is worth something but the shield under the jacket makes it look like a big fat piece of copper (but lightweight so I hope that is a clue).
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« Reply #38 on: July 22, 2011, 06:34:17 AM »

Does that 30% and 40% conductivity figure mean 30 and 40 percent the conductivity of solid copper?

Of course, the situation is totally different for RF, since the skin effect keeps most of the current close to the surface. In that respect, solid copper is a waste, and steel would do just as well (actually better, strength wise) in the core where there is little or no RF current flowing.

Another advantage of copperweld is that it is practically worthless to scrap  metal dealers. I have been told it brings even less than solid steel.  But the dumb-ass copper thieves probably wouldn't have a clue until they had already destroyed a radio installation, only to be told that their booty would bring them a tiny fraction of what they had anticipated.

Commscope data reads. AC conductivity equal to copper >5 MC
 DC conductivity better than 39% for their 40% copper clad by weight product.


It is on the chart that comes with the link I referenced earlier. If you care to read it.
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« Reply #39 on: July 22, 2011, 04:20:51 PM »

Don, the copper has to be real thin to affect 160 such as is on RG-6 copper clad steel and the skin depth isnt a concern on 80 and up. Solid copper RG-6 is available. With the commercial rural line cable its more than sufficient for 160, one of my 900' 2 wire Beverages is using it. Heck the others are using a copper/cadmium alloy and none require a preamp even way down at LF.

Since CATV only goes down to 5 MHz what happens lower isnt their concern but Ive measured a 500' hunk of 3/4" at 160 over 20 years ago and I needed a digital meter to measure...its that good.... but is copper over aluminum anyway.
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« Reply #40 on: July 23, 2011, 06:36:08 AM »

Dirty Copper!

I use #12 THHN.

Mike WU2D


* DirtyCopper.jpg (11.79 KB, 275x183 - viewed 926 times.)
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« Reply #41 on: July 23, 2011, 09:29:28 AM »

Antenna wax stops corrosion.


* antwax.JPG (11.38 KB, 209x204 - viewed 952 times.)
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« Reply #42 on: July 23, 2011, 11:26:12 AM »

Don, the copper has to be real thin to affect 160 such as is on RG-6 copper clad steel and the skin depth isnt a concern on 80 and up. Solid copper RG-6 is available. With the commercial rural line cable its more than sufficient for 160, one of my 900' 2 wire Beverages is using it. Heck the others are using a copper/cadmium alloy and none require a preamp even way down at LF.

Since CATV only goes down to 5 MHz what happens lower isnt their concern but Ive measured a 500' hunk of 3/4" at 160 over 20 years ago and I needed a digital meter to measure...its that good.... but is copper over aluminum anyway.


It will be interesting once I get the OWL going, to compare it to the RG-213. I will try to run it as flat as possible @ 438Ω out to the tuner complex at the tower.

When I first installed the antenna years ago I used military grade RG-214, doubly shielded and both braid and inner conductor silver plated. This was in the days when big dish satellite TV systems were in vogue; this same stuff was often used between the LNA at the focal point of the dish and the first stage of the receiver, located at minimum several feet away.  I figured that if it's good enough for microwave, it should be practically loss-free at 160m. I was disappointed when it measured only about 92% efficient.  Running 100 watts input to the line at the transmitter yielded about 92 watts at the other end of the 140' run.  

A few years later I checked it again, and the efficiency was way down, less than 80%.  That's when I discovered that rodents or other critters had chewed holes in the jacket allowing water to contaminate the coax.  I replaced it with direct-burial RG-213.  Again, the efficiency was up to about 92-93%.  A couple of years later, it had dropped to the mid-80s.  I didn't dig the  whole thing up, but did not find any holes chewed in the jacket this time, but looks like water still infiltrated it somehow. So much for running buried coax. I still had some left on the roll, so I replaced the buried run with an overhead run.

But even if OWL is 98% efficient, there is always loss in the matching network or tuner. A figure I have long seen tossed about is that the typical transmatch or tuner runs about 90% efficient (the Johnson KW Matchbox is supposed to be slightly better). The tank circuit in the transmitter should run about the same or maybe even less, since the ATU (tuner) typically runs at a lower loaded Q than does the tank circuit.

That's why I say that most hams have an inflated notion about their power output and the efficiency of their transmitter.  Let's say the final amplifier tube generates exactly 100 watts of steady carrier. The tank circuit losses reduce that to 90 watts. The tuner drops that another 10%, so the input to the feed line is 81 watts. Assuming the OWL is 98% efficient, about 79 watts actually make it to the antenna. The figure would be about the same with coax, if it is fed without a "transmatch", assuming the coax to be about 90% efficient. Using coax with a transmatch, lop off another 10% of the power to the antenna.

Assuming 75% efficiency at the class-C final per the tube data sheets, to generate 100 watts the transmitter runs 133 watts DC input. Therefore, taking into account plate tank circuit losses, antenna tuner losses and feedline losses, the total real efficiency of that same final (DC input to RF input to the antenna) is closer to 60% (54% with transmatch-coax combination), and that is a "best case". In the case of a "leen-yar", assuming 60% peak efficiency at the final tubes, the overall peak efficiency is closer to 48% (43% with transmatch-coax). And that's just at the peaks. The overall average efficiency is much lower, whether running AM or SSB.

Still, with a good antenna, a 20% reduction in power due to network and feedline losses will have a negligible effect on the signal at the other end, so this is largely much ado about nothing.

BTW, FWIW I ran across this article last night. A lot of interesting comments follow, both knowledgeable and clueless.

http://www.eham.net/articles/26162
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« Reply #43 on: July 23, 2011, 12:34:11 PM »

He talked about "Far Field"  Never heard the term before. I guess I could look up what it means but I'll take the lazy approach and see if anyone one on here can tell me what it means?
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« Reply #44 on: July 23, 2011, 01:16:36 PM »

Lots of math and fun can be thrown at this: but basically the Far Field is a point beyond which you are measuring far enough away from the antenna, that the power drops off in an exact inverse square manner with distance. Every time you double the distance between transmitter and receiver (in free space in the far field), you cut the amount of RF power received by four times. This is how you know you are actually in the far field.

In the Near Field, usually less than a couple of wavelengths away, the RF and the probe (or receiver and pickup antenna) are effected by all kinds of STUFF and Effects both known and unknown and it is harder to measure power accurately. Even comparative measurements are hard to make in the near field. This is why people use ammeters in the base of antennas. It is easier to make assumptions on power.

So to measure a bunch of 75 meter mobiles for a shootout, your pick up antenna should be no closer than several hundred feet away and it should be walked around a circle or several antennas should be switched in around a radius to average out effects. A half mile away would be a good distance! 
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« Reply #45 on: July 23, 2011, 02:06:27 PM »

Lots of math and fun can be thrown at this: but basically the Far Field is a point beyond which you are measuring far enough away from the antenna, that the power drops off in an exact inverse square manner with distance. Every time you double the distance between transmitter and receiver (in free space in the far field), you cut the amount of RF power received by four times. This is how you know you are actually in the far field.

Actually, the inverse square law applies to three-dimensional space. Terrestrial propagation is essentially two-dimensional over the surface of the earth, so the drop-off more closely resembles a simple inverse function than it does to the inverse square law.

Ground wave signals propagate along the physical surface of the earth, making ground wave strictly two dimensional.  Sky wave propagation is ducted between the ionosphere and the ground via ionospheric refraction and ground reflection, making it also closely resemble two dimensional propagation, particularly as the distance away becomes large compared to the virtual height of the ionosphere.

Doubling the distance on the average would halve the signal strength, not reduce it to one fourth.  Of course it becomes more complicated than that with multi-path skywave and when skywave and ground wave propagation combine to produce skip zones and fading walls.
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« Reply #46 on: July 23, 2011, 03:07:54 PM »

I doubt if any hammy hambone Class C amp is better than 70% and a Class B linear can reach 65 but 62 seems to be reasonable in a good design. Ole timey claims of 80-85% were due to a combination of assumed measurement accuracy mixed in with a bit of wacky tobacky.

In a pi net an incorrect value plate choke and insufficient C in the plate blocking cap can combine to eat up an easy 5%.

For any long outdoor run going to 50 or 75 Ohm hardline and good connectors eliminates the water migration and critter issue. I'll take my 450' run of 3/4" hardline over an OWL with a tuner any day.
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« Reply #47 on: July 23, 2011, 04:04:16 PM »

The filament, screen, grid power, associated supplies and fans of big transmitting tubes doesn't help the efficiency situation either...

Taking it a step further, I am picturing the QIX-designed class E AM PDM rig.  One thing is for sure - when I run the 4X1 modulated by a pair, the room heats up. At the SAME RF power output, my class E 24 pill MOSFET PDM rig barely has an effect on room temp.  During the summer the e-rig is actually usable. The 4X1 is not. Noisy blowers too.

One obvious reason for less heat when using the e-rig is except for the low level 12V/24V  circuitry, there is no power being burned during standby. I key the HV supply - and there's no fils cooking.  In contrast, the 4X1's and associated supplies probably suck up 600w on standby.

But the other thing that is amazing is the RF output efficiency. I am seeing ~90% RF efficiency and >90% PDM modulator efficiency on the E rig.  The AM antenna on 75M is hardline feeding a 1/2 wave dipole, no tuner, just a coaxial choke - how more efficient can that be?

Should we regard the class E rig as an anomaly here?  Or should we just consider it "alien technology" and be done with it?  Grin     I just love coming into the shack, hitting three toggle switches and keying up a cool AM KW within seconds.  

Still, both rigs are fun.

T
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« Reply #48 on: July 23, 2011, 04:23:09 PM »

That eHam article was readable but the comments reminded me of why I quit reading anything on eHam a few years ago.

Two omissions were (in my opinion) G5RV, and the frequent use of the term "resonance" by hams when referring to a 1:1 VSWR. 
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« Reply #49 on: July 23, 2011, 04:34:27 PM »

Quote
In contrast, the 4X1's and associated supplies probably suck up 600w on standby.

The 3 filaments alone take about 475W. Add in the blowers, HV PS bleeders/equalizers that are always running, the transformer heating even in standby, the other PS in the rack and I bet they add an easy 3-400W more.

Quote
Should we regard the class E rig as an anomaly here?  Or should we just consider it "alien technology" and be done with it?       I just love coming into the shack, hitting three toggle switches and keying up a cool AM KW within seconds

I dont discuss that mode in polite company Grin  Plus I operate all bands and QSY at will on any.

Now if you want cool (and quiet) than use that 3CW triode Ive mentioned; run it linear and scrap the mod deck.
The only difference you will notice is the AC meter outside spinning a little faster and on your bill Grin
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