Why is it that the sstran input power setting is multiple volts and few hundred milliamps for 100mw versus the Hamilton where one volt at one hundred milliamps equals 100mw?
Why is it that the sstran input power setting is multiple volts and few hundred milliamps for 100mw versus the Hamilton where one volt at one hundred milliamps equals 100mw?
For instance a reading of 2.2v at .455 volt equals 100mw according to amt5000 manual where with range master it would be 1.00 volt at .100 volt for 100mw also with toroid in ground lead it works slightly better than without it. I have a three and half meter ground lead going to a two foot ground rod with ferrite core near tx ground lug wrapped three times with ground lead and a 3 meter wire antenna. Sstran goes about 2000ft to a little grundig portable before disappearing into noise floor. I did retune between no toroid and putting one in line. Also getting a carrier current effect within my apartment building only but not others.
The operating V and I depends on the impedance the final device sees at its collector or drain. This varies mostly with the output network and the load impedance presented by the antenna system. This effect is especially noticeable with high efficiency circuits where the input power is determined primarily by the load.
The transmitter I use operates at about 2.2V and 44 mA for the final driving a 29 ohm resistive load. If the load R is increased, the voltage goes up and the current goes down in the final.
Neil
I'm presently at 2.21 x .495 on input power couldn't get it dead on 100mw input
That ".495" figure I presume is the voltage measured across a resistor to give the current. I had difficulty setting the power input when the transmitter was installed at the base of my outdoor antenna since if I was close enough to do the measurement and adjustment then I was also close enough to detune the antenna. What I finally settled on was to measure the feedpoint R of the antenna and set the transmitter power using the equivalent dummy load resistance on the bench. This is the most accurate way I could think of to get it set correctly.
Neil
The voltage to the AMT-5000 final stage is measured directly, and the current is measured by measuring the voltage across a 10-ohm resistor in series with the power supply to the final stage. .455 V represents .455/10 = .0455 Amps. 2.2 X .0455 = .1001 Watts, or nearly 100 mW.
"This effect is especially noticeable with high efficiency circuits where the input power is determined primarily by the load."
One of the drawbacks to attempting Class E amplification, the high sensitivity to load characteristics which in turn equals a very narrow window of tolerance to maintain that efficiency.
Simple wire, or elaborate 3 meter outdoor antennas are inherently sensitive to external inductive influence already. Put a transmitter with a sensitive output subject to load variances and that ends up shifting even more so than other designs such as Class C or D. But even those will swing too.
Adding isolation between the output and antenna input will only rob that efficiency, and the isolation probably won't do much considering the sensitivity factors of the TX output design.
It's a trade off between obtaining maximum transfer efficiency vs effective stability over periods of time and influences on the load during that time. A balancing act like walking a high wire, the larger the counter balance the easier it is to stay up there, the shorter that balancing rod is, it takes more effort to stay on that thin wire.
In this case, your balancing on a high wire with a very short balancing stick, thus a bit harder but not impossible to maintain maximum effective signal transfer.
RFB
Since first installing the AMT5000 and getting it successfully tuned into my antenna, I have only once reinstalled and re-tuned it, finding at that time that it didn't need re-tuning. Everything had remained stable for months, and it is still completely in tune regardless of weather or time.
To me the engineering behind the AMT5000 is tailor made to the realities of 15.219.
It is intentionally designed to work most efficiently with a 3-meter antenna. That is the most basic and conventional form of part 15 AM broadcasting.
As with any transmitter some form of grounding is required, no transmission system is complete without a good ground, be it a water pipe or buried radials.
The criticisms as may get voiced toward the AMT5000 don't seem to be based on actual experience with one of the units.
"The criticisms as may get voiced toward the AMT5000 don't seem to be based on actual experience with one of the units."
Ahh yes, but your setup is indoors, away from things like strong winds and nearby swaying tree limbs or brush or occasional tumble weed drifting by.
I bet it's a bit different when that's installed in your future outdoor system, where it will be subject to the elements of surprise by mother nature. I doubt the stability will be affected by a large amount, but given the sensitivity of Class E designs which are inherently sensitive to loading, if that loading swings any amount by external influence, it won't necessarily be noticed by a receiver's S meter (given AGC action by said receiver), but by constant monitoring of that final stage current.
RFB
I have been monitoring the field strength produced by the outdoor ground mounted system and the only significant change I observed happened late this summer when the drought broke and the antenna system resistance decreased significantly with increased ground moisture. Since then, we have had "normal" precipitation and the antenna tuning is quite stable as evidenced by periodic readings of the antenna voltage, current, and phase angle. You may recall that the system is located on the edge of a woods and with the leaves now gone there has been no change in performance. It even survived an encounter with a curious deer!
Lab bench tests of this transmitter showed expected change in the input power as the resistive dummy load was varied but the efficiency (power out/power in, not "collector efficiency") stayed above 80% over the range of 29 to 110 ohms with slight variation. Though this transmitter is efficient it is not operating in true Class E mode since there is some overlap in the V and I waveforms so these observations may not apply to a true Class E amplifier. Simulation predicts about 10% of the power is being lost in the 5 pole output filter and this filter loss may provide some buffering from antenna changes.
As long as the antenna system is resonant there is not much change over time in the transmitter output. Long term resonance seems to be stable with periodic readings at the feedpoint showing the phase angle variance to be about +/- 15 degrees around zero. This swing represents only a 4% loss in power transfer (using VIcos(theta)) so it is not causing problems.
In summary, the transmitter and antenna system used here is stableover time in the field strength produced.
Neil
I am curious...during the surprise antenna inspection, were you on the air monitoring the FS as the Deer Agent was taking a nap or when it stood up to pose?
When tree squirrels decide to park and wag their tails across my 219 system, the auto-tuner would go nuts and dance with the dancing tails of the tree squirrels!
Became pointless to operate that system on a regular basis thus was decided to use it as a stand-by system for CC maintenance or repairs. It's been unused now for over 3 years.
RFB
True, my AMT5000 is snugly indoors, but the antenna is a metal window frame which faces outdoors and the top two feet of the 3-meter length is a vertical wire outdoors from the top of the window frame.
Therefore my antenna, at least, is exposed to rain, ice, wind, heat...
The transmitter doesn't seem to care. None of the physical impact of the elements on the antenna can be observed in transmitter consistency, which is solid.
The signal is monitored 36' away on a spectrum analyzer, and it holds to 50dBm at all times.
i measured 2.21 x .495 /10 = 109 mW
RFB,
The transmitter was on but there was no audio going out during the deer visit. I did check the FS when he had his nose against the coil housing and it was up about 1 dB. Don't know what to make of that.
It seems he has adopted my back yard for his own since he spent the night here and was here until about 8:30 this morning. City deer are strange creatures, in the country you can't get within a couple hundred yards unless you sneak up on them. Here you can approach to within 15 feet before they bolt. I try to stay away because I know what they can do to people if they get aggravated.
Neil
"One of the drawbacks to attempting Class E amplification, the high sensitivity to load characteristics which in turn equals a very narrow window of tolerance to maintain that efficiency".
I'll give everyone a break and skip to the bottom line. The AMT5000 is NOT highly sensitivity to load characteristics and it DOES NOT have a very narrow window of tolerance. Read on only if you want to know why.
The AMT5000 does not have any sort of unusually high sensitivity to load characteristics. This is a myth being perpetrated only by those who misinterpret the theory published on Class E amplifiers.
The AMT5000 is optimized for maximum transistor efficiency of 98% with a 30 ohm antenna ground-loss resistance. The transistor efficiency changes at other load resistances, BUT NOT BY MUCH! The transistor efficiency never falls below 96%+ for load resistances in the 1 to 60 ohm range. Above 60 ohms, it falls off gradually to 89% at 100 ohms. This is without any tuning changes.
Of course, the transfer efficiency to the antenna (overall transmitter efficiency), does vary widely with ground resistance because it is a function of the ratio of the fixed coil loss resistance and the load resistance, which are in series. But, this is independent of the class of the amplifier.
As for variations in the antenna capacitance, the AMT5000 is no more sensitive to this than a class C or class D amplifier. Any good part 15 AM transmitter will be quite sensitive to variations in antenna capacitance. This is the inevitable result of using a high Q loading coil. The tuning peak is very sharp. Sure, you could reduce the sensitivity to capacitance variations by using a lower Q coil, but only at the expense of lower overall transmitter efficiency. It's not really so hard to tune these transmitters with a meter. After each tuning adjustment, just stand away a couple feet before observing the meter.
The AMT5000 has a sharp tuning peak due the the coil Q, but it isn't sharper than other transmitters with good coils. As regards class E efficiency relative to the tuning peak, the transistor efficiency curve actually flat-tops at 96%+ efficiency over variations of capacitance around the optimum tuning point. The result for small variations of capacitance (<1pF) is that the high Q resonant circuit has more effect on the power delivered to the antenna than does the variation in class E transistor efficiency.
RFB: see my last post. Once again you're passing out your "expert" advice on a technical subject you know nothing about.