Well I did say I could be wrong. The TX is intended mainly to work a short piece of wire more than working an external loading coil. As I also said..I don't have a schematic or a unit since I sold mine to a friend's kid.
When I had it, I used it as a "mini marti" transmitter when running remote shows from 2 houses over. I never used it to work a base loaded 3 meter stick because that 3 meter system has a C.CUFF C-QUAM board for the TX.
Be interesting to see how it works on the 160m stick.
RFB
From instructions" "The AMT3000 internal inductors are bypassed, and instead, the external base-loading coil provides the required inductance."
So, if this assumption is correct, can a small amateur radio type antenna tuner capable of 160 meters be used to interface the AMT3000 to an antenna?
"can a small amateur radio type antenna tuner capable of 160 meters be used to interface the AMT3000 to an antenna?"
Now that's an interesting idea. I have an MFJ-900 antenna tuner and added more coil to the inductor to bring it a bit further down and into the MW band to about 1Mhz. It worked sweet being fed by a 50 ohm out low power TX (ASMAX-1) and tuned right up into a 102" CB whip through 15 feet of coax. No loading coil was on the CB whip. I wanted to see if the tuner could tune up the whip without the whip needing a loading coil and it did.
I don't know how it will work from an AMT3K but don't see why it wouldn't.
RFB
Hey, here's a question.
If I hook the AMT3000 to the LPB TCU-30 will anything show up on the coupler's meter?
If I know you, RFB, you will say, "Try it."
No, no, it is so much easier just asking without doing any work.
Yup. Right. My comments are never small.
But I will try.
I disconnected the internal coils in my SS-Tran
completely. Then I wired a connection into the
spot where the coils WERE. Then I made a high Q
coil and connected it into that spot. So the transmitter
was running on a NEW internal coil. But it was outside
of the plastic case. And it was a much higher Q than
those teeny coils on the circuit board. I used a "ferrite"
rod to tune it. (I suppose I could have made a variometer.)
The new coil was very hard to tune up.
This worked GREAT with just a 3 meter ground mounted
copper pipe (no loading coil on the pipe) and a 16 radial
ground system. Really really great.
Why am I telling you guys this?
Because you are looking at all kinds of different ways
to get a 50 ohm output from the SS-Tran.
You guys are way way ahead of me on this thing. Way ahead.
However, if telling you about this mod turns on a light in
somebody's brain, that's fine with me. Maybe a different
kind of coil wired directly to the INSIDE of the transmitter
may achieve something.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
"If I hook the AMT3000 to the LPB TCU-30 will anything show up on the coupler's meter?"
That would depend on the unit's output ability to load up to that 50 ohms. Since the unit was meant to run a short wire and use it's internal inductors, when bypassed with the "mod" or in another form, that changes a few things in the specs designed in the final circuit and may or may not dampen it's ability to transfer the RF energy effectively.
Noting the meter on the TCU-30, it's minimum watt indication is 2 watts. Half of that range would be 1 watt. A TH V5 will indicate just under 1/2 between zero and the 1 watt point on the meter scale, which would be about right for 135mW. Also note that the meter and detector circuit, though designed to measure quite a bit more power than 135mW, the reading won't be nth decimal place accurate, but it does see and indicate that low level RF, and the detector circuit is sensitive enough to even see any reflected on the line side at 135mW when the calibrate control is turned to maximum.
Here are those famous words I like to say all the time....go ahead and try it! 😀
Bruce had the right approach by going around the entire internal inductor set completely. You may want to do the same, bypass the internal inductors and pi network all together and run a coax straight into the TCU. Let the TCU set up the loading. The TCU will isolate that transmitter from any other load influences and the TX will always see that 50 ohm impedance..no matter what.
Those TCU couplers can provide a whole lot more than just a way to couple to the power lines or a long wire. They make great test loads and provide an assurance of a constant load impedance even if the line side of the coupler is left open or completely shorted.
RFB
hi bruce. my initial idea was to do something like this. i was thinking i could bypass the pi-network and install a simple homebrew L or T network to match a 50ohm load.
in my initial post in this thread i asked about adding an L-Network after the pi-network. and use the new network to match the load side of the pi-network to 50ohms.
the only reason i thought to do it this way was to be less destructive towards my amt-3000. i really wish i had a second amt-3000. one for testing mods like this and a second one to use in my station.
this weekend i am going to take down my transmitter (which has been modded for baseloaded antenna operation) and test the output with a 50ohm load and a matching network.
does anyone know the actual efficiency of the final amplifier stage? what actual power output is to be expected from a properly operating amt-3000?
"what actual power output is to be expected from a properly operating amt-3000?"
Dietnews posted some info regarding how much it should output into 50 ohms. See a few posts above this one.
I assume the assembly manual does not have a chart with measured output voltage across a variety of loads?
Perhaps in all the experimenting one can be created for future reference.
RFB
I'm glad to know I might have contributed to
this in a small way.
I am trying to remember some things, and maybe
you can help me.
I had a couple of Panaxis AM-100s years ago.
As far as I can remember, the Panaxis had a
final transistor. Right after that was a DC blocking
cap. And then there was - nothing? Is that right?
I seem to remember that the DC blocking cap went
right to the antenna output on the back of the unit.
The other thing that I seem to remember, is that the
Panaxis AM-100 was said to have an RF output impedance
of around 50 ohms(?) But I suppose that may be determined
partly by the load it is feeding? I don't quite know what
I'm saying, but you may get the general idea.
I'm not an engineer like you guys, I'm just a Dude.
But so, what happened with the Panaxis - it's RF output
design, and how it behaves into a load might be similar
to the idea that you had with the AMT-3000. Like you
said - go around the internal coil array and LC network.
From what I seem to remember then, that would be
right at the output of the blocking cap after the final
transistor in the SS-Tran.
Now, the final transistors of the two different transmitters
(Panaxis AM-100 and SS-Tran AMT-3000) are
not the same. Those transistors will each have a different
output impedance - or should I say output admittance(?)
What does this mean if we are talking about trying to
feed into 50 ohms j0 - or - instead we are trying to
create a suitable LC net to feed the 50 ohm load?
Either the Ramsey FM-25 or FM-10 seem to have a similar
arrangement as the Panaxis, even though they are FM
transmitters. Either one or the other just takes the output
after the final transistor's DC blocking cap.
I understand the Ramsey AM-25 has an output impedance
of around 25 ohms - a low impedance - maybe? I don't
know what it's output circuit looks like, though.
Is there any way you can tie these thoughts of mine together?
Because I'm not sure how well I'm conveying this idea.
Your real answer may be outside of the scope of this board.
I wish I could turn back the clock and take some courses in
all of this stuff.
Do you know that I originally majored in EE? But problems
related to my eyesight got in the way and I didn't make it.
I finally did get a degree, but it was years later in a different
field.
I've been looking at this over and over. I hope it makes some
sense. I would be glad to hear any reply that you or anyone
else has.
Best Wishes,
Bruce, DOGRADIO STUDIO 2
RFB. i am dietnews. 🙂
2.24Vrms into a 50ohm load would be 100mW output. however, i know that the amt-3000 only has 100mW power input into the final transistor and i have no idea what the transmitter's actual efficiency is. i seriously doubt it is close to 100mW unless it is class d or e (which it isnt).
Howdy Bruce!
Your on the right thought track. Yes the active elements, transistors or FET's or even a tube will have it's own internal impedance characteristics at their inputs and outputs Those base spec numbers are what is used to calculate a circuit impedance for input or output. Typically the base specs are high in value, especially with elements like FET's and tubes.
As you already had thought with the Panaxis AM 100 example, that unit simply had a coupling capacitor at the output of the transistor pair. That impedance was high on its own. When interfaced to it's companion AM-5 amplifier, which had a toroid transformer input, it is that input circuit of the AM-5 amp that set up a load impedance different from the base spec impedance of the transmitters finals. And because the amplifier elements also have an input impedance base spec, the toroid transformer was necessary to set up both sides load impedance as well as isolate each. Those toroid transformers could have easily been a tunable matching network. The term "broadband", whereas no tuning required between stages is an example versus stages with variable caps and/or inductors.
The base impedance specs will vary with operating voltage, frequency of operation and temperature. Finding the "window" of operational parameters to what the element will be doing is where all the number crunching comes into play. When that AM 100 unit was designed, Ernie knew that it would be used to couple to a simple wire, or an elaborate 3 meter antenna sporting a loading coil or an amplifier. Thus the unit was left "wide open" to allow for the variety of load possibilities.
When I say "wide open"..that is not an absolute. In other words, the unit does not have an infinite load curve. At some point saturation occurs with any active element. Wide open is just my way of saying it has a large range of potential loading possibilities based on what kind of output network is connected to it.
The pair of transistors in the Panaxis, and others, were selected for their characteristics and operational ranges for the range of frequencies to be worked, as well as the voltages supplying them with power and biasing. The coupling capacitor had very little effect in setting up any load impedance and was there simply to provide the DC blocking job and to provide a way to "tap" that output signal without draining the output down by direct loading.
The Panaxis AM 100 could have been designed for a set output impedance and then that would have limited it to specific loading schemes, which for the Part 15 world limits the unit's application as far as what type of load it can interface with. Again as the load impedance will vary over a wide range between a simple wire to a 3 meter antenna with a loading coil and ground system, it made sense to design the output to interface to a wide variety of load ranges that would be most encountered, making the unit extremely adaptable to those various loads.
When selecting the different inductors in units such as the AMT3K or 5K, all that is taking place is allowing the finals to transfer the signal at the best peak efficiency possible with the load attached. In the case of these two units, mainly a 10 foot piece of wire. The matching network provides a wide range to select from so that maximum RF energy is put onto that wire.
In the case of the Panaxis AM 100, a unit with no matching network, it gives the user the choice to either create a matching network to work with a wire, or a loading coil or a simple loading resistor. In both cases of the AMT units and Panaxis unit, it is the matching network that determines the output operating load impedance characteristic and not the active elements themselves. This is why if you hooked up nothing more than a piece of wire to that Panaxis, the signal was not as strong as it would be if it had a matching network to maximize the transfer of the signal onto that piece of wire.
You can test this by bypassing all of the inductors in the AMT units and just connect a wire to the output junction of the finals, even through a DC blocking cap and see just how drastic that signal weakens off that same piece of wire than if the matching network of inductors and caps were inline.
The bottom line is that a transmitter's output impedance is not determined by the active amplifying element's base characteristics or operating characteristics. It is the matching network that does.
It is kin to a connector like an F or BNC or other connector. The connector itself has no real impacting impedance on its own to a circuit. It is the circuit in front of that connector that determines if that F or BNC connector will have a 50 or 75 or 300 or other impedance.
RFB
"2.24Vrms into a 50ohm load would be 100mW output."
Hi dietnews!
The value given above would be what was measured into a pure 50 ohm load..or a calculated value based on a pure 50 ohm load?
See this is where the dividing line is between the numbers on paper versus the actual measured values under real world conditions of an antenna system built for 50 ohms. No doubt that number will change between a pure 50 ohm load versus an antenna system with a 50 ohm spec.
The efficiency of the transmitter final itself only means how much efficiency the final stages or other does it's job in transferring the signal being sent through that final stage. As to the efficiency of how well the signal gets shot out the tailpipe...that depends on how well the tailpipe is designed..ie the matching network. You can have a high efficiency final amplifying element like that in a Class-E amplifier, but that high efficiency can be trashed so fast by a poor or limited matching network attached to it in respect to how good the signal travels from the radiating device..be it a wire or antenna system.
The transmitter may still measure to have it's high efficiency relating to the operational characteristics of the design and final elements used..but if that output network is of poor design or of limited design to what it can interface with on the matching network output side, then efficiency goes out the window in as far as how good the signal emits off the wire or antenna.
Think of it as a poorly tuned antenna...if not tuned right, the antenna does very little in radiating the signal. As such..if the output matching network is not constructed to be as efficient as it can be, or is limited in what can be connected to it, the efficiency of the finals has very little weight in claim to fame because the matching network is dampening the expected performance from that high efficient final.
RFB
Thank you for your thoughtful
explanation about the transmitter
output impedance issue. I do
appreciate it because I have been
mulling over it for a while. I will
probably have to read over what you
said a couple of times to really get it.
Back in my ham radio early days, all
I had were vacuum tube rigs. For instance -
I had a really messed up Viking Challenger,
then I had a Hallicrafters HT-37, and later,
a Kenwood TS-520S. I also had a few other
miscellaneous tube transmitters, most pretty
low power, that either got parted out, or were
given to other hams. Now the only vacuum tube
transmitters I have are, a 3 watt 6AQ5 homemade
rig, and a Heathkit DX-60A and a DX-60B. The DX-60B,
the newer of the two, doesn't work. The DX-60A works
great. Actually, I have been using the DX-60A on
Friday nights to talk to a good ham friend a few
hundred miles away. Aside from getting on a few
FM repeaters now and then, that is pretty much all
of the ham radio I do. I am using Morse code. My
kids and wife think it is cool because it is so alien
to the technology we have now. And I consider the
code to be an art form of sorts. (I am terrible at
it by the way, but that's OK. After about a year
of operating, I think I'm up to about ten words
a minute.)
A funny thing just occurred to me the other day.
The dummy load that I used with all of those vacuum
tube transmitters was just a light bulb. It was
fun to dip the plate, increase the loading, and watch
the glow from the bulb go from red to orange, and then
bright white. And of course I thought the transmitter
i was tuning up was TUNED CORRECTLY. But it wasn't.
Light bulbs are fun, but they are not 50 ohms.
When I would go to switch the transmitter over to the
antenna, I always wondered why the SWR was 2.5 or 3 to 1!
It was because of the light bulb dummy load. And in
the old days, I didn't have an antenna tuner to help
the situation. (I do now.)
After 41 years of ham radio, I just figured that out
the other day!
With my solid state HF rigs, I would use a resistor
dummy load, and I could always get a very low SWR.
Usually very close to 1 to 1.
Anyway, yup, I'll eventually get it.
Thanks again,
Bruce, DOGRADIO STUDIO 2
"I thought the transmitter i was tuning up was TUNED CORRECTLY. But it wasn't. Light bulbs are fun, but they are not 50 ohms. After 41 years of ham radio, I just figured that out the other day!"
Yep. I bet on that other day 41 years later the light bulb really shined! (pictures the cartoon character when realizing something and the light bulb appears over their head)
I don't remember the exact impedance at RF frequencies that a light bulb is..but light bulb is no different from a wire wound resistor and has the same negative effect using it as a load or as a tuning indicator when connected directly to the output of a transmitter.
If a detector circuit is used and tapping the output, and then feeding a light bulb of much lower voltage, then it can be used as an indicator for maximum resonance and give you a better and more accurate indication of tuning.
In those cases where a small grain of rice light bulb on a 3 meter antenna is used, the light bulb is not being used as a load, thus does not give a negative effect in tuning indication. The light bulb is in series with the antenna and will glow when maximum resonance is achieved. In the other situation where the light bulb is being connected as a load from the center conductor to ground of the TX, that is when the negative effect takes place because the light bulb..at it's very very low resistance, is now serving as a load to the transmitter and your tuning up to that low resistance, and is why when you connected up to the antenna, a proper load, the tuning was way off.
The light bulb can be useful for determining if the transmitter is putting out something in the way of power for troubleshooting purposes or testing. But beyond that...using it as a load for tuning up purposes...it is like using the tongue to test an old unknown if good 9V battery...ever do that and get that semi-burn acid taste?!! A voltmeter does a much better job and no taste testing required! 😉
RFB
hi rfb,
i'm not exactly sure what you mean by this question: "The value given above would be what was measured into a pure 50 ohm load..or a calculated value based on a pure 50 ohm load?"
but i am talking about 2.24Vrms equating to 100mW when using a perfect 50ohm dummy load ( 0.1 = 2.24^2 / 50 ). naturally things will be different when we switch over to an actual antenna and real world conditions but the best we can do is account for ideal conditions on the bench and then account for reality when we move on to a real world deployment.
last night i got a really long and detailed email from phil b regarding impedance issues and antennas with the amt-3000. he provided tons of useful information. if i have time later today i'll go through it really carefully and try to pull out some highlights.