What's the S22 of an IC-756PRO? With that figure, S22^2 is defined as:
Power reflected from the network output divided by Power incident on the network output.
Better yet, we can then calculate the reflected power dissipated by the IC-756PRO.
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73, Cecil http://www.qsl.net/w5dxp
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Cecil, I havn't the foggiest idea what an IC-756PRO is except that it is something which comes from that excellent manufacturer Icom.
But your extremely brief question is the most hillarious ever asked on this newsgroup. You are still at the best of your form. I can't stop laughing.
The best I could do is ask what is the S22 of a 6J5. One thing for certain, it is not mentioned in manufacturer's data sheets. Yet ARRL simple PA design rules manage very well without it.
Yes for the purposes of the OP's case it is. He is trying to use an existing transmitter design and a hunk of wire. This seems to be the part of my argument that people are missing. I suggested he use a matching network to match the wire to the transmitter's output.
I read in sci.electronics.design that Cecil Moore wrote (in ) about '1/4 vs 1/2 wavelength antenna', on Sat, 26 Feb 2005:
If the FM is what passes for music these days, it's MUCH better IMHO. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
I read in sci.electronics.design that Reg Edwards wrote (in ) about 'Say what you mean.', on Sat, 26 Feb 2005:
You wouldn't expect to use scattering parameters for a 6J5. But change that to 7194 and the question is not so facetious. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
It's been thirty years since I "hammed". I was only interested in the electronics, not the talking, so I dropped out after I got a homemade solid-state 2-meter rig running.
But I vaguely recall a 5/8 wavelength antenna that had a good low-angle pattern.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
No, you've got the concept backwards. Obviously the worst matched is the
1 o=minute case, next would be the 2 minute case and so on up to one which runs for about its MTBF at the connected load. This last case would likely be the one the designer was targeting.
There is very little that is sent in the form of radio waves that is worth the electrical power to send it. The really sad thing is that much of what is send via FM is really "voice grade" material. When FM was new, the material for FM was specially produced to take advantage of the wide bandwidth and large dynamic range.
Unfortunately, the OP (is he still here?) was stuck with a box to short to even fit a 1/4 wave whip. I also think that this box could not be assumed to be resting on the ground
If you squint at the ASCII art below, you will see more or less the radiation pattern of a 5/8 whip over a large ground plain. ................................. .................!............... ...........******!*****.......... ..........*......!......*........ ..........*......!......*........ ...........****..!..****...A..... ........*******..!..*******...... .....***.........!.........***... ...*.............!.............*B
********************************
If you don't have a large enough ground plain, the notch in the side labeled "A" starts to go away and the peak at "B" reduces.
The long and short of it (apropos of your antenna spec), is that your shorter antenna will need a new matching circuit (apropos of the smaller antenna's size) for the related issues of maximum transfer of power. The reasons for matching may vary (and with it, efficiency), but not so you would notice. If you did notice, then your production tolerance (if not customer application) variations will kill you in the marketplace (fact of life in a Kapitalistic world). No amount of armchair philosophies about Thevenin's theorem will replace that loss.
I did the same after putting together a HF setup. The electronics was fun, but the chirping was booorrring.
I didn't know the height affected the pattern that much. IIRC 5/8 wavelength seems to be what the AM stations around here. Though they'd load up a barn if it worked.
Well, it is more accurate to say that you don't, that is for sure. Defining a solution by negative results can fill up a library without any positive accomplishment. Obviously people don't have a nuclear reactor, or lunar lander, or bank account to balance the national debt. The joke of this, of course, is that no one needs a 100 W (or more!) network analyzer, or nuclear reactor, or lunar lander, or bank account to balance the national debt to explain a rather more trivial problem. Which, by the way, has nothing to do with pretending at all.
The suggestion that
does not negate its existence which commonly proves what you choose to dismiss as impossible. I have calibrated this gear (called an artificial or active load), and the gear (called transmitters) it tests and there are no differences in Physics based upon your presumption of low-power/high-power demarcations.
To say
is one of those assumptions forced into the argument. There are any number of ways to do something wrong. Trumping none of these straw men validates another wrong impression passing as theory. This returns us to the imposition of impossibilities to answer a rather mundane concept, eg.
So to return to a common question that seems to defy 2 out of 3 analysis (and many demurred along the way) - A simple test of a practical situation with a practical Amateur grade transistor model
100W transmitter commonly available for more than 20-30 years now:
Presuming CW mode into a "matched load" (any definition will do);
Report the DC power consumed before hitting the key;
Report the DC power consumed while holding the key.
Concurrently note: A. Report Heat Sink Temperature for a previously idle/rcv condition; B. Report Heat Sink Temperature after 10 minute key-down.
For a hypothetical "100W" model (again, a contemporary, common example for Amateur use) available through standard commercial venues:
About 20W - 30W
About 200W - 250W A. About 20 degrees C (or room temperature) B. Well above 37 degrees C (or skin temperature)
Now, if we are to be any judge of efficiency (Thevenin does not have to be invoked, condemned, or venerated); then it runs close to 50% (±10%). Others can invoke their favorite deity to explain.
Now, if we are to be any judge of dissipation (no requirement for advanced degree); then heat as a loss by virtue of less than 100% efficiency is quite evident. Others can invoke photons to describe why.
To forestall any armchair engineers, yes, this efficiency is System efficiency. However, I would be surprised if a practical common Amateur grade transistor model transmitter commonly available for more than 20-30 years now has any configuration that does not apply supply voltage directly to the final transistors; and instead adds a significant current path outside of this load (citations to available schematics would be compelling, but any argument without this would be speculation). It takes very little effort to subtract out the power drain of the receive mode (being very representative of the similar power demand of supporting circuitry for transmit up to the driver stage). Barring such amazing evidence of a significant power drain not found in the finals, it follows that a simple computation of efficiency has its merit and has been met.
It is in the sense that it improves the source match by trying to hold the forward power constant regardless of load. Most SWR foldback systems overreact but a good ALC system, what we called a "leveling loop" in waveguide reflectometers back in the mid-20th century certainly improve the source match.
Just to bring back to the original discussion and reiterate:
S22 is a small signal (linear) parameter, by definition. It does not apply to the large signal environment.
This idea is somewhat related to the idea that power amps should be tuned for "maximum transfer of power," which is a small signal (s-param) issue, and requires conjugate matching. The idea is incorrect because it ignores the practical large signal non-linearity and *any* consideration of DC to RF efficiency (which is prime for PA design). Linear parameters provide *no* recognition of things like DC to signal power efficiency and therefore practical issues like supply rails.
First order matching of an RF PA to a load involves transforming the load to the optimum point on the AC load line (for example, more or less equal positive and negative swing limits for class A). That's what "matching" is for an RF PA. It makes no statement about actual "output impedance" of the source. What is said is that "such and such RF PA will deliver X power into some specifed impedance within some VSWR circle." That's all. The concept of output impedance begins to break down for large signal devices.
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