Guys from this site "predicted" the test would be biased in favor of the Talking House. Also a reminder, that comments from the "other" site based on threads was biased not only against Phil B. but Keith H. as well.
I also noticed a bit of a difference among two of the test engineers over at happy hobby ... one of them is a Rangemaster dealer, but the other one was snubbed by unresponsive e-mail after repeated attempts, punishable by death in Saudi Arabia.
And in Mother Russia!
How come WDCX has so many pictures of handsome men?
It's impossible to know with certainty what biases were present during the testing.
All you can go by is what actually happened. My biggest problem with the entire test is that to a casual reader, or a newbie Part 15 operator, it would appear that the Rangemaster is the 'best' transmitter. That may indeed be the case, but the Challenge doesn't prove that. It is the 'winner' within the narrow confines of the parameters of the testing, which obviously includes not doing any additional research outside what the manufacturer provides in documentation.
Pretty narrow indeed.
The results of the Challenge are not very useful in the real world of Part 15, where you hopefully do your homework, and may want to use equipment not provided by the manufacturer.
Maybe the next test should be done this way?
http://www.arrl.org/files/file/Technology/Procedure%20Manual%202011%20with%20page%20breaks.pdf
WDCX, the ARRL Lab Test Procedure reads like the 10,000 Volume IRS Code. Why would you post it today?
Any other day would be fine, but why today?
Oh, and, as for Post # 20, that's Evan. I dated her when he was Eva. She didn't look too shabby at night with bad lighting. It was the next day when I realized it was time to reconsider, but I'd been taped to a floor lamp and was worried about tipping over.
Neil, here is my belated reply to your post #13 above. Been doing taxes!
The transistor efficiency is more accurately called "transistor drain efficiency" for MOSFET transistors or "transistor collector efficiency" for bipolar transistors and is a measure of how much of the total input power is dissipated in the transistor.
% drain efficiency = 100*(Pin-Pdrain)/Pin
where Pin = Power-in DC voltage * Power-in DC current
I measure the Pdrain value in LTspice with a .MEAS statement:
.MEAS TRAN Pdrain AVG Vdrain*Idrain
Pin is measured conventionally as the DC supply voltage * DC supply current.
There are a number of inconsistencies in the text of the article. I referenced it only for the schematic and graph (Fig. 5). I wasn't completely impressed with the text, but it's mostly pretty good.
He shows Rloss in the schematic as being part of the antenna model, which would make Rloss the same as the ground loss. The current flowing through the coil is the same as the current flowing through the antenna equivalent, so measuring the coil current with an RF ammeter is a valid way to measure the current to the antenna.
The author doesn't distinguish between transistor efficiency and overall transmitter efficiency. In fact, his opening paragraph says "The Class-E design is a perfect choice for the LowFER or MedFER experimenter due to its simplicity and high efficiency (essentially ~100%)". He doesn't explain how he measured efficiency. His graph (Fig 5) shows near 100% efficiency, so I assume it is showing transistor drain efficiency, or more likely, it is showing output efficiency with no ESR losses in his PSPICE model. His implication that the transmitter efficiency is ~100% is not true. Especially important would be the significant ESR loss of the large 2.831 mH inductor, L coil. The loading coil is by far the single most important contributor to losses in the transmitter once the transistor loss is minimized by Class E.
I have always viewed the "output" of the transmitter as being the antenna terminal, which is the physical output of all transmitters having internal loading coils. This puts the coil loss inside the transmitter. The antenna presents a reactive impedance with reactance equal to the reactance of the antenna capacitance and resistance equal to Rrad+Rgndloss. Since the loading coil cancels the reactance, the load is simply Rrad+Rgndloss, and since Rrad<<Rgndloss, the load can be simplified to just Rgndloss.
The equation for overall transmitter efficiency is:
% transmitter efficiency = 100*Pload/Pin
Pload can be determined from P=I^2*R by using the I = measured RMS output current and R = Rrad+Rgndloss, or just R = Rgndloss for simplicity.
I don't think there is anyone out there that actually knows the value of Rgndloss for their antenna. Rgndloss can be estimated, but actual measurement is difficult.
First, some housekeeping. There is another thread where the Transmitter Challenge is being discussed and this thread is about Class E circuits and is not the place to revisit the Challenge. Future posts in this thread regarding the Challenge will be removed.
Now, thank you Phil for your input on this. You and I appear to be on the same page regarding defining the transmitter efficiency except that I would not count the .MEAS in LTSpice as an actual measurement.
Measuring output power via the loading coil (and antenna system) current fails unless the Rcoil and Rground are known. It would be appropriate, in my view, to simulate an antenna system using your 30 pF and 30 ohm bench load whereby the effect of the loading coil R can be measured under replicable conditions.
I can measure the efficiency of my transmitter with the actual antenna system by using a current transformer at the transmitter output to measure the output current and simultaneously measuring the output voltage to circuit ground (which is also the antenna system ground). The measurements are made with a two channel scope and antenna resonance is set by adjusting the phase angle between V and I to zero. Having previously bench measured the antenna loading coil RF resistance and using the V and I output measurements to calculate the total load resistance the Rground + Rrad can be calculated by subtracting the coil R. Thus the actual power delivered to the radiator plus ground is known.
The 86% number agrees closely with the bench measurement of the transmitter efficiency using only a 29 ohm resistive load and no loading coil.
My transmitter with 100mW DC input delivers 86 mW measured at the input to the loading coil and the coil R is 18 ohms (from memory so it may be off a bit) and a typical total load R measurement is 40 ohms. The efficiency when the loading coil is included as part of the transmitter with these data is (Pout*(Rg)/(Rcoil + Rg))/PDCIN which equals 0.47 or 47%.
Some power is lost because this transmitter has an output filter but using the same numbers for Rcoil and Rg and 100% as the drain efficiency and no output filter the efficiency would be 55% but I have not measured this.
Neil
To test the AMT-5000, a 3 m vertical rod would have to be mounted in close proximity to the transmitter. The antenna mounting is not part of the design, and it would have to be improvised; but that would not be an overwhelming difficulty. Tuning would be done by selecting taps on the internal loading coil and using the internal tuning capacitor (C1) to tune for a DC current peak at the final stage. So far so good. What follows next is what I call "magic." The instructions then say to turn C1 one turn clockwise, which is supposed to tune the transmitter below resonance by an amount that sets up class E operating conditions. Whether this particular tuning step works or not depends on what the ground loss resistance of the antenna installation is. The ground loss resistance for the installation is, of course, unknown, and can vary greatly from one installation to the next; and the operator following the manufactrer's instructions does not know if his transmitter is operating class E or not. But the transmitter will "work" in the sense that it will produce an AM signal even if it is mistuned. What is unknown to the operator is if this transmitter is operating optimally, or "class E." Optimum tuning requires observing and adjusting the shape of the drain pulse on an oscilloscope. Nothing in the instuctions tells the operator to use an oscilloscope or what to look for on the oscilloscope display. That is why I say that this design is best for the advanced experimenter rather than the general user.
As for using an external antenna with a loading coil that is described on the SSTRAN website, the transmitter design allows for bypassing the internal loading coil, but there are no instructions for tuning for a current peak as with the internal loading coil, and then adjusting for class E conditions. This is up to the "advanced experimenter."
You already know, John WDCX, that "Ermi", who knows some about electronics, expresses a chronic prejudice against the SSTran products.
The motivation for this always deprecating position has never been disclosed, but it is always certain that one's attacker has some axe to grind.
In previous postings you have given a positive report about assistance from PhilB at SStran.com, and it would seem more gentlemanly on your part to contact him about your thoughts rather than set flame here.
It might be true that the question you raise is handled at the SSTran website, as are various additional tips about transmitters and antennas.
OK.
So, anyone care to weigh in - Ermi? Phil? - and produce documentation on how to tune the AMT5000 with an oscilloscope and what to look for in the display? Some may have an opinion that it's for the advanced experimenter. Others may have the opinion that the lack of documentation disqualifies the AMT5000 as a viable Part 15 transmitter, period. Me, I'd just like to see the apparent documentation hole plugged.
I believe I understand the thinking that went into the First Edition of the AMT5000 Manual.
I believe the author reasoned that the ordinary kit builder might neither have a scope nor be proficient at using one, so he presented a workable means of achieving Class E tune with a meter alone.
Now we are hearing spurious questions about "how to use a scope for tuning the AMT5000 and how to add an out-board loading coil in place of the resident loading coil." I can figure it out. I have a scope. I didn't need the scope to achieve the right results, so I didn't use it.
Giving advanced lessons in RF engineering is beyond the purpose of the included AMT5000 Manual.
When Rich(F) has tried to present scholarly technical facts the monkeys commenting on other sights called him sarcastic names and called his technical presentations a "paper blizzard."
I am compiling a Part 15 Enemies List and getting all the names who have been using basic hate-speech format to persistently attack a reputable Part 15 transmitter manufacturer and anyone who recognizes what's taking place.
You haters should build a cross somewhere and set it on fire. You'll feel better.
... "Ermi", who knows some about electronics, expresses a chronic prejudice against the SSTran products. The motivation for this ... has never been disclosed, but it is always certain that one's attacker has some axe to grind. ...
Posts having differing points of view easily could result from the learning, experience and/or even the unproven opinions of the posters -- not necessarily because any of those posters has an "axe to grind."
Such posts and their readers will benefit when sufficient proof/documentation is included in those posts to support their conclusions.
Hence my "paper blizzards," to quote Ermi Roos.