I was replying to member 'Part 15 Engineer's post about his station plans, but decided starting a new topic was warranted..
Oh wow. you're one of the few people who own an AMT5000. I'm curious about that design. I understand that tuning the output of the final in that transmitter can be a bit tricky if you want maximum efficiency. Shame that Phil B is no longer around to help out.
Let us know how it goes!
I've asked and commented before about this, but dont think ever got an answer...
Why is it, considering that in 1970 manufactured Class E part 15 AM transmitters were the preference, such as those used in Yellowstone and by Hwy departments (Info-Systems DTI brand transmitters), why didnt the trend of manufacturing and/or building of Class E part 15 transmitters continue? Yellowstone's Park 1970s documentations clearly state that they performed much better than any other part 15 transmitters they used.. So why is it all manufactures since have opted to manufacture the less efficient Class D?
I presumed it must be because they are more complicated to install and tune, but that theory doesn't really add up when you consider Yellowstone park staff who installed them were not particularly technically adept in electronics or anything, they simply drove a ground rod and powered them up.
Also, what's interesting to note is their range was usually stated as "about a mile", why that's interesting is because Yellowstone NP shows a ground conductivity of only 2 - which is about as bad as it can get.
My primary question is why is it Class D Part 15 AM transmitters seems to have always been the norm, whe Class E Part 15 transmitters have a clear history of being much more efficient and likewise capable of achieving much better range?
On a related note, the following is highlights I found interesting from the original 2011 thread at https://www.part15.org/formal-comparison-test-amt5000-3000 /
This was from Carl's second test, both had employed his "wintenna" for testing...
FORMAL COMPARISON TEST AMT5000 / 3000
October 17, 2011 by Carl Blare
AMT3000 received with grade A signal to a point 435 feet from transmitter;
AMT5000 received with grade A signal to a point 643 feet from transmitter;..
~~~
Ermi Roos says
October 17, 2011 at 9:59 pm
Analysis of the results
Taking Carl’s results at face value, the range ratio between the two transmitters is 643/435 = 1.478. Range is roughly proportional to field strength, and power is proportional to the square of field strength. The AMT 5000 has a little more than twice the RF radiated power output from the antenna as the AMT 3000. From these results, the AMT 5000 is roughly twice as efficient as the AMT 3000.
~~~
PhilB says (key points truncated from several post) October 20, 2011 (and after)
Carl,
Something is very wrong with your comparison results, but I don’t know what. I don’t particularly doubt your measurements. Maybe the discrepancy is wrapped up in your unique antenna and ground situation. Your results show only a 47% range increase over the AMT3000 (using the internal inductor tuning). The AMT3000 internal tuning inductors are extremely inefficient and were originally intended for a compact and easy solution for in-home broadcasting. By comparison, the AMT5000, with its class E efficiency and internal toroid coil, will result in about 15 times the “power” The field strength will be about 4 times higher or 400% higher...
...The AMT5000 with internal tuning outperforms the AMT3000 with the base-loaded antenna... Since your results show only a 47% range increase instead of predicted 1500%, there is something else going on. Whatever it is, I cannot say, but it simply doesn’t add up...
This is one possible explanation for your results. Whether or not it is on the money depends on too many unknown variables. Unfortunately, I don’t think this particular comparison really proves a whole lot, other than the range of the AMT5000 is better than the AMT3000 with internal tuning. At least that is one good result!
Seeking reasons for Carls performance discrepency
I believe Carl’s comparison is valid for comparing the AMT5000 to the AMT3000 with internal tuning. I am seeking the reason why the range increase was only 47% vs 400%..
Bump. Still wonder why Class E part 15 transmitters never took off considering that they're so much more efficient and capable. The AMT5000 is the only one I know of since the original DTI transmitters in the early 1970s (which had used a standard whip).
Along the same lines.. Something I always found peculiar about the 1970s part15 transmitrs at Yellowstone, even after the FCC forced them to ground mount them, and the only option park personnel could come up with to keep bears from tearing the xmtrs apart was to install them inside of bear proof trashcans! It was neccessary to cut off a few feet of the whip so it would fit within the can (steel??). Those trash cans where situated about 300ft from the roadways they served and their range were described as "about a mile".
They were manufactured Class E transmitters. Their broadcast were on 620, and they got "about a mile" in Yellowstone, and they had a shortened whip, and were inside a trash can. How crazy is that? How did it achieve a mile radius?
Right after that he FCC added the ground lead into the rules AND made it mandatory for all manufactured part15 transmitters receive prior Certification before marketing.
But they did not outlaw Part15 Class E.
Which brings us back to the original question.
Oh! and I forgot to mention, as I said Yellowstone was using 660hz, presumably because Class E is more efficient at lower frequencies..
http://www.classeradio.com/theory.htm&source=gmail&ust=1753033225996000&usg=AOvVaw22BbA1xrWbAkSzMxj6GuT t"> http://www.classeradio.com/theory.htm
"..The efficiency will drop dramatically as the frequency is increased. In class E, the output network values are chosen such that the output capacitance is part of a total resonant circuit."
also confirmed at https://antiqueradios.com/forums/viewtopic.php?t%3D354147&source=gmail&ust=1753033225996000&usg=AOvVaw19-Pba_bZs_HGNHfyoPwR -"> https://antiqueradios.com/forums/viewtopic.php?t=354147
DeFelice over at Hobbybroadcaster continues to defend his non review 'review' of the SSTran 5000 Class E transmitter, and, implicitly, its shoddy and unscientific treatment in the AM Transmitter test.
It is true that it is more difficult to properly tune a Class E amplifier under some conditions - that's the hole that they fell into with the AM comparison testing.
But when it is properly tuned, it has superior range to Class D, as many users of the AMT5000 have discovered during its deployment in the field.
Here is a link to an article on one way to optimally tune such an amplifier. There are others.
If there is one thing SSTran can be faulted for, it's the overly simplistic documentation on tuning the SSTran 5000, which assumes that you have a decent ground (and not the one used during the AM transmitter test).
What of this about Class E performing better on the lower frequencies like 600? as appears was common when Class Es were in operation.
Or am I completely misinterpreting what the above linked sources say: "..The efficiency will drop dramatically as the frequency is increased.."
The more old charts and graphs of the late Rich Fry's that I revisit, the more evident it becomes is that he always calculated data of Class E transmitters -never the Class D transmitters..
If he had chose to calculate the common Class D type transmitters most use, then all the range potentials of a mile or mile and a half estimates provided (dependant on the frequency) would have displayed a much lower field strength.
My point is that Fry intentionally always provided such graphs that displayed the very highest range potentials of a part 15 AM, even though Class E is very uncommon today. Had his charts been Class D then those range potentials would have been considerably less, and more realistic. - I find that interesting.
In the 1970s the Hwy Depts an National Parks exclusively used Class E, none of them were Class D. It was the Class Es superb efficiency that had prompted the FCC to begin altering and almost abolishing the 15.219 rule.
HB may preach Class E as impractical, but numerous case reports and their history of use paint an entirely different picture.
I guess if Bill can't properly tune one, then it stands to reason that Class E can't be properly tuned.
@richpowers Just an opinion, if it is difficult to properly tune a class E amp it may not be desired as much as a "normal" amp like the Procaster which is simple to use just by peaking a meter without extensive know how and fiddling with a class E amp may not be what all would want to do.
@richpowers R Fly's use of Class E in his charts makes sense. You have to live in precisely the right area with good ground conductivity, and work hard to get even close to a mile range with commonly available transmitters (that use Class D).
I've only been able to achieve that with one installation out of many, and that was due solely to where I lived, with great conductivity, and getting the antenna in the clear. More common is 1/4 to 1/2 mile (and who knows what the listenability is at that point).
Sometimes I think that those claiming mile+ ranges excuse the fact that they are using things such as long ground leads; because that kind of range is theoretically possible, it makes their dubious installation legal.
@richpowers Just an opinion, if it is difficult to properly tune a class E amp it may not be desired as much as a "normal" amp like the Procaster which is simple to use just by peaking a meter without extensive know how and fiddling with a class E amp may not be what all would want to do.
I agree with that. However if the prime objective is maximum legal range, then Class E is the optimum option.
@richpowers ...You have to live in precisely the right area with good ground conductivity, and work hard to get even close to a mile range with commonly available transmitters (that use Class D).
I've only been able to achieve that with one installation out of many, ...
Sometimes I think that those claiming mile+ ranges excuse the fact that they are using ....
I achieved a mile semi-consistently with a 10ft ground lead to boot in Ellabell Ga. But I could only hear it, it was only "listenable" maybe a little more than a half mile.
Claims of mile+ ranges are, I surmise, 99% of them are simply not compliant. But I do believe there's a 1% that are.
In a wide open totally unobstructed area, like park lands, yes, I have no doubt mile+ is achievable