..he is saying something that I already said in an earlier post in this thread... The several jumpers in the AMT5000 are an important part of setup and were not mentioned in the Report.
Ermi goes a step further by claiming that the jumper settings are not described in the manual and this is not true,
Carl, I just read it again and I may have missed it somehow, but I don't see him saying that anywhere. What I see him saying: "Unfortunately, the manufacturer did not tell you.. in the instruction manual anything about needing to select the drain-to-source capacitance of Q1. The manufacturer obviously knows.. because he has provided jumper-selectable options for setting this capacitance. The problem is that he did not tell you what to do to make the proper selection.
It's in my manual.
On Page 22 the function of Jumpers S14 and S15 are described.
On Page 26, under RF POWER OUTPUT, there's a critical sentence explaining the purpose of C7 and C8, which are selected by those jumpers.
What I am able to glean from the manual is that C7 and C8 may not be needed, but in some cases can optimize the E-Class Operation.
In my transmitter I found, by observing the output on a spectrum analyzer, that S14, C8, gave a higher peak.
The same thing could be done with a meter.
If the quality of the ground varies due to say rain, then the transmitter has to be retuned?
WDCX John Dade has asked a question I had not thought of, and I do not know the answer.
When I last tuned-up I have not gone back to re-check the tuning for weeks or months. I can't even remember what the weather was at the time I tuned, although my documents might have at least that much information, since I kept a record at that time which I should look up.
I can tell you this... the area coverage of the signal scares me a little because it goes so many blocks in some directions.
A strange thing is that some days the signal goes a lot farther than other days, and it doesn't seem to be weather related, as sometimes this happens when it's dry or wet or warm or cold.
Here's an interesting thing that's happening right now.
A giant 100-foot-plus tree as big around as Chris Christie is being taken down RIGHT NOW! The tree has stood about 12-feet from the Wintenna where my AMT5000 radiates. Will the tree removal affect tuning?
RF JOURNAL
I still have a few Edit Minutes, so I've grabbed my RF JOURNAL, in which I document technical experience with all my transmitters.
I see that on June 5, 2013 I played with power settings on the AMT5000. I ran for a while at minimum power, which is 12.8mW, then ramped up to maximum power, which is 319.3045mW. On my spectrum analyzer this ranged from 27dBm to 45dBm. No other observations were made at that time. Following the experimentation the power was set for 100mW to the final.
The most recent tuning of the AMT5000 took place on September 6, 2013, 7:50 PM and the conditions "Dark Dry."
If the quality of the ground varies due to say rain, then the transmitter has to be retuned?
The table below shows how the load on a Part 15 AM transmitter is dependent on the values of the loading coil a-c loss resistance, the r-f ground resistance, and the reactance of the antenna system.
The coil loss was set to 15 ohms, which might be typical for the ferrite loading coil used in some modern Part 15 AM transmitters.
The reactance (j value) was set to 10 ohms, in recognition that it is difficult to achieve and maintain zero ohms (perfect resonance) when adjusting the loading coil.
The table shows how the reflection coefficient and SWR of that complex load varies with different values of loss in the r-f ground connection over a practical range for a typical installation, assuming that the transmitter was designed to drive a load of 30 +j 0 ohms.
The reflection coefficient shows what percentage of the transmitter output power is reflected by antenna system for those conditions, returning back to the transmitter and typically dissipated there as heat.
The loss in the r-f ground system (rods, buried radials) can vary depending on the composition, moisture and mineral content of the soil as far away as 1/2 wavelength from the antenna.
| Coil R | j | |
| 15 | 10 | |
| Reflection | ||
| Ground R | Coeff. % | SWR |
| 10 | 20 | 1.5 |
| 25 | 20 | 1.5 |
| 50 | 38.1 | 2.23 |
| 100 | 58.9 | 3.86 |
Rich that is a good look at the situation with keeping a transmitter in tune with its antenna.
I suppose the thing we must decide is whether to allow the changes to average out over time, which is what I guess I'm doing, or set up some kind of schedule for re-tuning.
Is there a recommended practice?
Is there a recommended practice?
AFAIK, the hardware/circuit needed to "tune" a typical Part 15 AM antenna is restricted to adjustment of a loading coil, whether that coil is provided within the transmitter by the transmitter manufacturer, or is external to the transmitter enclosure and provided by the final installer/user/tester.
If the inductive reactance of that loading coil is perfectly adjusted, it can exactly offset the capacitive reactance of electrically short radiating conductors in the AM broadcast band (conductors totaling 3 meters or less, if meeting §15.219) -- which "resonates" that antenna system.
BUT... even with a resonant load, the input SWR of an antenna system still depends on the "real," or non-j term of its impedance. That real term is the sum of the antenna radiation resistance, the loading coil resistance, and the r-f ground resistance.
Antenna system load SWR is a function of the value of that real term with respect to the resonant load value that the transmitter is designed to drive.
So far I have not seen such a specification to be provided by any manufacturer of commercial transmitters marketed for Part 15 AM.
I know of no commercially available Part 15 AM transmitters either certified or not that include the hardware needed to provide a theoretically perfect (loss-free) match for equal power supplied to all antenna system load impedances in the range of 10 j0 ohms to 100 j0 ohms.
Sorry that my recent posts here have been a bit technical, but then that is the nature of this subject.
Rich, your purely technical views provide a good relief from the sometimes emotional uproar, such as I'm about to do.
On Radio Discussions, a third radio forum, Ermi Roos went to work descrediting the AMT5000.
"The AMT-5000 is said to be a Class E transmitter, but the data given in the AM Transmitter Challenge demonstrates that this transmitter does not actually operate Class E"
That's his opening line, and it's a lie. There is NOTHING in the Challenge that "demonstrates not operating Class-E." Not even if you stand on your head and wear google glass. Think axe-to-grind.
The fact that the "other" part 15 site links to THAT and presents it as fact DEMONSTRATES the bias we have suspected from the beginning.
Also consider the many intelligent remarks made HERE regarding the Challenge. Despite the fact that "they" arranged to use this website to amplify their promotional stunt, they have NOT linked to any of what we've said; there's prejudice writ large.
From the very inception the Challenge was a stupid idea, pitting part 15 transmitters in a sports competition. What could be more anti-part 15?
For god sake one of the test engineers is a Rangemaster and Chez dealer! Look which two transmitters came out on top!
We've got to divorce from those people and ban them from using this website for their nonsense.
Rich, if the term value of the antenna system is known, could not a matching network be used to provide the proper match between the antenna system and the transmitter?
Some examples of base loaded antennas ground the bottom of the loading coil. The feed point is tapped at a point above the bottom of the coil where ideally the load can be matched to the transmitter.
The idea being that whatever the term impedance of the antenna system, the impedance at the tap point would equal the transmitter/coax impedance assuming the transmitter output can be designed to match standard coax impedance values.
This would allow compensation for differences in the ground resistance variable.
Carl, that's out of context. Yes, in his opening line he does state:
"The AMT-5000 is said to be a Class E transmitter, but the data given in the AM Transmitter Challenge demonstrates that this transmitter does not actually operate Class E;.."
but you left off the rest of the line:
"..at least not when it is tuned according to the manufacturer's instructions."
If you'll take another look at his entirety of his post(s), the only thing that is stated is that the AMT-5000 was not operating class E during the test, because the provided instructions for tuning method is incorrect.. he goes on to explain how it was wrong and briefly describes the proper method, and also suggest finding a Class E tutorial on the Internet inorder to properly tune the AMT5000.
Now, is he right?? - I dont know for sure, I don't posses such knowledge. But if he is right, then that would certainly explain why the unit performed lower than expected in the test. And that's my whole reason for posting the link to his comments.
It's supposed to be in defense of the AMT5000, not evidence against it.
And the last line of Ermi's post at Radio Discussions:
"Since you got peak efficiency when output power was peaked, this is proof that the AMT-5000 was not operating class E during your test."
No, nothing in the Challenge Report was PROOF of any such thing.
The transmitter may or may not have been operating in Class-E mode. The test doesn't reveal which.
Phil's Manual is not wrong.
From my perspective, I take a look at the emotional responses from that 'other site' (imagine, anyone daring to question any part of the testing by broadcast engineers with over 757 or so years of experience, particularly by the know-nothing scum from this Forum!), and their actions (blocking IP's from accessing the site) and that, more than anything else, makes me question their motives. If they really were attempting to be objective, then they would be far more open to questions and comments than they have been.
And yes, I realize that Consumer Reports, the ARRL and others only use one example during their testing. These examples are generally obtained directly from the manufacturer, and as such are pretty much guaranteed to operate at their best. But the problem with the AMT5000, as I've indicated previously, is that it's a kit, not factory assembled, and so you really don't know what you're getting in a single example. And from what I recall of the shootout (remember, I now can't access it to check due to their blocking IP's), there were other transmitters from non manufacturer sources, such as the Rangemaster, which could also have skewed results, either negatively or positively.
Bottom line - I was surprised by the relatively low ranking of the AMT5000. It doesn't make sense. I don't dispute the measured data, but feel that there may be other factors at play (some of which I've elucidated previously) than just pure signal efficiency; more testing needs to be done before anything definitive should be published, stated, or even theorized. Particularly when there's empirical evidence from actual Part 15 broadcasters that appears to contradict the shootout data.
Anyway, I can't afford the big transmitters.
But even if I could, the performance of the AMT5000 for me is so effective that I am already afraid of a knock on the door for inspection.
There is no way I want to have a stronger signal.
One accurate measurement is worth a thousand expert opinions. 🙂
And three accurate measurements would be worth a whole heck of a lot more, particularly when the one set of measurements don't match with what has been seen in real world use by real Part 15 broadcasters.