In another thread ( http://www.part15.us/node/3004) there is discussion of comparing one transmitter to another. There needs to be some agreement on how or if this can be meaningfully done.
In another thread ( http://www.part15.us/node/3004) there is discussion of comparing one transmitter to another. There needs to be some agreement on how or if this can be meaningfully done.
Each transmitter being discussed has it own antenna requirements for optimum range, one requiring an external loading coil, the other not. Forcing both transmitters to use the same antenna system for comparison is like trying to compare the towing capability of a tractor to that of a pickup truck by requiring either the truck to use tractor wheels or the tractor to use truck wheels. In order to assess the desired result each vehicle needs to be considered as a system with the proper wheels installed and the pull of each system then evaluated.
The same thinking applies to the transmitters. Rather than forcing one transmitter to use an antenna system designed for the other each should be equipped with its own recommended antenna system. By doing this the question remains is "Which system gives the best range?" and not "Which transmitter gives the best range?".
This raises another problem, however, and that is how is the range to be measured? Many factors affect the range of a transmission system and these, as well as the detection method, would need to be considered. One way this can be done is to have the comparison performed by the same experimenter using the same transmitting site and detection equipment and range criterion. Otherwise the uncontrolled variables will make meaningful comparisons questionable.
Another approach is to perform a bench comparison using a simulated antenna and ground system where, for example, the power delivered to the simulated radiation resistance can be compared for each test transmitter. This could provide a reasonable basis for comparison with the assumption that the simulated antenna system is realistic and typical of those found in actual installations.
Such a simulated antenna could be a 30 pF capacitor in series with a 30 ohm resistor. For the case of the transmitter requiring an external loading coil a "typical" coil would be required and this choice could affect the results.
Without some controlled experiments perhaps the only thing we will have is a collection of anecdotal reports from users based on their experiences. This has happened with other brands of transmitters and it might give an impression of the comparative performance of the various transmitters.
Neil
Thank you Neil for taking the time to pass on some of your wisdom. You are spot on.
Well I guess I will be the other side of the opinion with comparisons.
I disagree. Now if the antenna system is built properly, peaked and tweaked and all that jazz...then comparing one TX and another on that same antenna system is not futile, but quite helpful in determining not only the matching capabilities of the antenna system to different transmitters, but also finding out how well different transmitters match up to that antenna....which in my opinion, makes more sense to conduct tests with what will be used in the field rather than sit all day at a bench with a piece of wire expecting real world results.
Lab work is one thing, but field work is another whole story. Some might be satisfied with measurements on a bench, but me..the bench only goes so far..literally with the sense that in the end, the TX will be hooked up to a station's primary radiating system which gets that signal to the listeners out there...not the one or two sitting in the lab with you.
Now this analogy of towing tractor vs towing truck is complete nonsense. Why?...Well for one thing, the AMT3K is no tractor, and the AMT5K is no truck, or vise versa. Now if we were talking about comparing the AMT5K to a BE-1, well then your statement may merit some praise in my neighborhood. But we are not talking about major differences in these two transmitters. Both are kits, both are built for low power radio transmission, and both are limited in their capacity to throw power into the air. Oh yes...one has the adjustable power pot....wooopie. Means nothing when it comes right down to it...simply because when adhering to the rule, well that pretty much knocks the power pot right out of the contest and comparisons for real world tests and results.
I don't know about anyone else, but I am interested in how well the AMT5K performs with existing antenna systems so many have spent the time to construct and install into their yards to reach an audience. And that cannot be done at the bench with a simple 10 foot long wire.
How many big boy broadcasters change out their antenna system when they replace that aging transmitter???
Next to none.
RFB
Neil, Radio8z, I'm glad you posted this very rational way of viewing the situation with evaluating the new AMT5000.
As you noticed, I ran into trouble right away trying to compare with the AMT3000 because of my totally non-standard antenna. Even at that, my "test" would have been a drive down the street with a car radio saying, "It goes twice as far," or whatever.
Others have a different stake in the game than I do, in that they actually want to achieve the greatest distance possible. For me, my indoor and outdoor is blanketed with AM and shortwave signal, and I worry about much more distance because there are people who like to report things such as "an unlicensed station."
Another comfort I have in embracing the new transmitter is that I recognize in PhilB someone who has consistently provided a highly reputed first product, and we have his all important contributions to this forum, which always rise above the more romantic ambitions of those of us who are putting bed springs on flag poles. Without a doubt I believe the specifications PhilB attributes to the new transmitter, yet I am in Missouri.
The Missouri slogan, "Show Me," is actually another way of saying "skepticism," and skepticism is, at its best, a first step in scientific inquiry to verify an earlier finding. It is an acceptable and fair position to be skeptical, and I join you, Radio 8Z, in waiting for a set of instructions for conducting proper bench tests.
So we have "people of faith" who believe in the new product, and skeptics who would like to prove it for themselves. Things couldn't be better.
EDITOR'S ADDITION: I remember that many people today use "skeptic" as a substitute for the word "doubt." That is a common mistake, as a skeptic is an open minded person who wishes to see evidence, where as a doubter doesn't think there is evidence. An important difference of words.
The power control is an absolute necessity to allow the operator to always adjust the transmitter for the various current and voltage differences that occur during initial setup with a different antennas.
True, once everything is in place and calibrated, the power control will stay fixed in the correct position, but the control guarantees the operator his full legal signal to the final.
I also had fun today running the transmitter at 1mW just to see what the weakest achievable signal would do. This is one great way to run antenna experiments without having to drive a mile away. If an antenna can be improved while running 1mW, you can hear the improvement fairly nearby.
Maybe the AMT3000 can be modified with a power control?
well comparing it to a hamilton should be easy both the sstran and hamilton have the same audio, power interfaces and are capable of the same tuning methods using the same 118 inch wire antenna. it should just be a matter of hooking up either with the same antenna, power and audio interfaces, tuning each per the instructions on the same frequency and listening to how each sounds and making note of how far each goes using the same radio receiver. barring a FIM and other highly advanced test equipment that even most broadcast engineers dont own there is no real way for any of us to do a real scientific test. since we all know by looking at the design this transmitter was really designed to compete with this other transmitter and would be the one im guessing people are most interested in knowing how it compares too. anything using a base loaded 3 m whip using an air wound coil over an elaborate groundplane is going to outperform the internal tuning coils on both this transmitter and the high priced alternative as well. the reason for the internal toroid is to get around the legal grey area about using traditional base loaded 3 meter whips where the fcc agent may choose to count the length of wire wound on the coil as part of the 3 meter limitation.
"the internal toroid is to get around the legal grey area about using traditional base loaded 3 meter whips where the fcc agent may choose to count the length of wire wound on the coil as part of the 3 meter limitation."
The internal toroid could be viewed as a way around this grey area regarding a loading coil. However I seriously doubt there has ever been any setup using a loading coil getting tagged as a violation.
The same could be said about the internal toroid...after all, it is in effect doing the same thing as an external coil does, electrically increasing the resonant element length. But both do not actually increase the radiating element's physical length. This can be clearly argued in a court.
Since the rules do not specify the 3 meter limit as the electrical length...it is obvious that the rule applies to the physical length. The rules also do not forbid the use of a loading coil and thus again can be argued that the coil has nothing to do with physical length.
Most outdoor setups of a 3 meter system have the transmitter located right at the radiating element, be it a Hamilton or AMT. It can be argued that the transmitter consists of everything up to and including a home made air coil before it all connects to that radiating element, which is external to the enclosure of the whole. What does it matter if that coil is inside the kit case, or inside a weather proof box right above or next to the kit itself? What is the real difference between the two technically other than one is manufactured and one is home built?
None really. Both perform the same function..to resonate a very short radiating element which is no where near the minimum 1/4 length. And to resonate that incredibly short element, both the toroid and external air coil increase that physically short radiating element length electrically.
The comparison can be done by simply using a portable radio and noting the point where reception is weakest with one transmitter, then again checked after another transmitter with greater efficiency is installed.
Agreed this is not a super duper hi-tech method but apparently it seems acceptable in a majority of situations even with field agents who know that most Part 15 broadcasters will not have the top of the line test gear to perform Nth decimal point measurements.
And even though incredibly simple and even to some may be ridiculous and they wont ever be seen using such a technique or hint they would ever do such a thing, it is a way to determine if there is any noticeable difference between an older transmitter with "x" efficiency versus a new one with "improved x" efficiency.
Adjusting the 5K to match the power input of the 3K after maximizing the coupling to the antenna, that is when the real comparison happens. Allowing for a +5% window of power input level seems reasonable to cover most variables that are present in so many different antenna systems out there.
Again its not accuracy we are after, it is reasonable comparable results that can be determined by simple methods as plotting a coverage range between unit A and unit B.
If the transmitter has better efficiency pushing that signal through its circuitry to the output point, that should be measurable enough to see a difference even though the antenna and loading coil has not changed. There may be some re-peaking of the antenna but if both transmitters are operating at the same specifics of power input level, and one has better efficiency transferring this power into the same load, that should be able to be detected even with a simple radio listening for quieting of the signal at a given distance.
RFB
"The power control is an absolute necessity to allow the operator to always adjust the transmitter for the various current and voltage differences that occur during initial setup with a different antennas."
Ok...then how does one apply this to their antenna system or systems with a transmitter not equipped with a power pot?
I agree that the power pot is useful for conducting tests and experiments. But....
"True, once everything is in place and calibrated, the power control will stay fixed in the correct position, but the control guarantees the operator his full legal signal to the final."
Suppose that power input level setting is above the full legal signal limit to the final in order to overcome inherent 3 meter antenna deficiencies? Does this declare the transmitter as being better or having greater efficiency over one that does not have adjustable power?
From my prospective...its cheating..and quite illegal. Again for testing and experimenting its fine..but for actual use and intent of broadcasting legally without a license, the power input limit is clearly defined and we all know what that legal limit is..regardless if there is a power pot or not.
It will be up to each user to adhere to the legal limits no matter how much lure that power pot brings, or how much it can be turned to get the wanted results. When the 100mW point is reached...that's the end of the line and is when the real comparison results can be taken to the bank.
RFB
The tractor/truck analogy was prompted by an attempt to force the same antenna system to be used in the comparison of the two transmitters in the discussion. This analogy would not apply if each transmitter was designed to operate with the same antenna system characteristics such as is the case with commercial transmitters. But this is not the case with the AMT3000 and the AMT5000. They are designed, from the transmitter output view, for different "optimum" antenna systems, the difference being the external loading coil which becomes part of the Z transformation network in the 3K model. While the AMT5000 can be configured to use the external coil this would not be necessary for a comparison since the intended mode is to use the internal coil. The common factor between the two is the radiating system impedance and not the impedance seen by each transmitter at the output. 50 ohms is usually the design target for a transmitter load when the antenna systems can be expected to present this value but in this case the impedance is not well defined and is probably in the realm of 30 - j3500 ohms. This is the load with which to make the comparison whether it is a bench simulation or a real radiator and whether or not the transformation is done internally or externally.
Suppose a bench test was done with two transmitters using a 30 pF cap. in series with a 30 ohm resistor and the measured powers delivered to the 30 ohm resistor are 30 mW and 90 mW. It would be rational to conclude that the unit with the 90 mW power would yield greater range than that of the 30 mW unit with a real antenna assuming the real antenna Z was similar to that of the simulated antenna. Granted, the results of an actual test with a radiating antenna may vary but the data used in this example would be a strong predictor of the comparison results.
A range comparison from a particular experimenter done with a portable radio is fine but it is not rigorously replicable by others. Nonetheless, if this is done it should be a reasonable predictor of the results obtained by others.
Regarding the "power pot", it is not to "compensate for antenna losses" rather it is to set the input power as close as practical to the 100 mW limit. The DC input power for a low efficiency final is less sensitive to load conditions than is the input power with a high efficiency final. Without provision for adjustment the high efficiency design would have to done for the "worst case" antenna anticipated to ensure compliance and may not provide the optimum performance with a particular antenna.
Neil
actually the 3000 has an internal loading coil provision as well to allow use with a 118" wire.
guess the best way is neils way setting both sstrans to 50 ohms and making measurements and setting up the rangemaster with a proper load and taking efficiency measurements.
Good point Robert but I would expect that the internal inductors in the AMT3000 would have much higher loss than that presented by an external coil.
In either case, the test load would not be 50 ohms but would be the 30 - j3500 or similar load since the ultimate output which does the work is that which is delivered to the radiating element.
Neil
ultimately i think we would want range testing to be done in the configurations that a typical end user would use in addition to the scientific lab approach
Range is not the only benchmark in comparing transmitters.
I would consider listenability, or fidelity to be equally as important, if not more so. Now, that is completely subjective.
Plus, what about cost? Even if say, a Rangemaster, has the greatest range, it really doesn't matter all that much to someone whose budget is several hundred dollars.
When it comes right down to it, I don't think a quote scientific unquote comparison really can be made.
Ancedotal information is perhaps the most useful - what is your setup and what happened? When I made my decision to purchase, I listened and read and researched as much as possible. I was lucky in that I had the capability to purchase several transmitters and compare them all in a singular environment. Unfortunately (or fortunately for time reasons), it was the only way I could install a transmitter. I tested the Rangemaster, the AMT3000, the then Talking House, the Talking Sign and the ProCaster. Ultimately, I chose the Rangemaster. It had slightly better range than the Procaster (probably due to the Inovonics 222 I have connected to it) and blew the AMT3000, Talking Sign and Talking House away (again, probably due to my setup of putting it in a box, using the internal tuners with a whip antenna). But what really sold me was that the Rangemaster just plain sounded better with similar sound processing.
Q.E.D.
By the way, factors that will affect range:
1. Soil conductivity
2. Height of installation
3. Length of antenna+ground (less than 10 feet, right?)
4. Nearby objects
5. Not so near obstructions
6. The weather
7. Your exact antenna construction (material, radius, etc.)
8. Your music source
9. Your music processing
10. Your signal processing
11. Your feedline
12. Your transmitter & power source & tuning
13. Interference on your frequency from other stations
14. Interference from other signal sources
15. The receiving radio and all the factors associated with it (many the same as with the transmitter)
I'm sure that there are many more. I think that all this does it to show that what may be 'best' in a laboratory environment may not necessarily hold in the real world.
"what may be 'best' in a laboratory environment may not necessarily hold in the real world."
100 percent in agreement with that. I do however recognize that bench/lab testing provides us with a solid starting point for reference in performing tests in other conditions, such as through an outdoor antenna setup. And the variables with that from one installation to another is very wide. All of those things listed are just the scratch of the surface.
I run two Inovonics 222 processors since my station is transmitting C-QUAM, but I have not found any significant benefit to the carrier itself and its coverage range, only the quality of the audio produced through those processors. It could be the result that my station is a Carrier Current system and not a through the air system.
The example described in the previous post is indication that comparisons between units and results can be observed, even with less than optimum testing methods and equipment.
RFB