Hello all,
This is a big project I have, and I doubt I will get to all the factors in this first post, so bear with me; I'll raise them into consideration as I remember them all.
I plan on getting started with amateur radio, as it would help me not only learn more about electronics but apply it in a practical sense rather than what it is now as a dink-around hobby. However, for someone who doesn't have a ton of experience with electronics, this is a major hurdle and I have literally spent months gathering information, analyzing schematics, drawing my own, researching that, and finding out why they wouldn't work to the point of actually being able to come up with something that's viable.
So here, I'll start with the parameters that I would like this transmitter to have and we'll go from there.
1. I would like it to be a completely valve-driven amplifier. Every step, from audio amplifier to oscillator/carrier amplification to modulator will be valve-driven.
2. Due to temperature-induced frequency stability issues, I would prefer this to be a variable crystal oscillator as opposed to a tuned RLC tank circuit.
3. I am aiming for this to be in the realm of 600-800W, and I will probably construct this in multiple pieces (power supply, oscillator/audio amp/modulator, RF linear amplifier) and combine them later into a rack enclosure.
Now, here are some of my questions:
1. RF Output Transformer
Regarding valve-driven push-pull stages, obviously an output transformer would be used. However, even with months of research and looking into this, I'm still blind as to a manner of calculating the plate-to-plate impedance of the stages. Most RF antennae are 50 or 75 ohms, and while I know the proper formula for calculating turns ratios of transformers based on impedance, first the primary impedance must be known.
Now, obviously impedance varies based on frequency, resistance, inductance, and capacitance of a circuit or component. While for an audio amplifier, the frequency varies, for an AM transmitter running at say, 600kHz constant, is the impedance a definite value? That is, can it be calculated readily?
2. Frequency range of output transformer
I know this is a vague question, and something tells me this one will deadlock more than the first, but do any of you have any considerations for how to determine frequency range? Usually in audio usage this doesn't create much of an issue, but at RF ranges the design must be specific in a manner to reduce capacitances or inductances and other frequency-limiting variables to allow for the higher upper boundaries.
Question is, do any of you know of equations or formulae that help in the design of high-frequency transformers? I haven't been able to come to anything surefire or anything more of sites that acknowledge that there are design considerations for that.
3. Amplification of modulated RF carrier
This is probably by far the most simple question - that is, can a post-modulation RF signal be amplified in the same sense as audio, provided that considerations are made for the high-frequency circuit?
That's all I can think of for now. For awhile now, I've had the issue where as soon as I sit down to ask questions and get answers to my problems, most of the 500 million scenarios I've been pondering decide to wander into the realm of forgetfulness.
Thanks in advance,
solidus
This is a big project I have, and I doubt I will get to all the factors in this first post, so bear with me; I'll raise them into consideration as I remember them all.
I plan on getting started with amateur radio, as it would help me not only learn more about electronics but apply it in a practical sense rather than what it is now as a dink-around hobby. However, for someone who doesn't have a ton of experience with electronics, this is a major hurdle and I have literally spent months gathering information, analyzing schematics, drawing my own, researching that, and finding out why they wouldn't work to the point of actually being able to come up with something that's viable.
So here, I'll start with the parameters that I would like this transmitter to have and we'll go from there.
1. I would like it to be a completely valve-driven amplifier. Every step, from audio amplifier to oscillator/carrier amplification to modulator will be valve-driven.
2. Due to temperature-induced frequency stability issues, I would prefer this to be a variable crystal oscillator as opposed to a tuned RLC tank circuit.
3. I am aiming for this to be in the realm of 600-800W, and I will probably construct this in multiple pieces (power supply, oscillator/audio amp/modulator, RF linear amplifier) and combine them later into a rack enclosure.
Now, here are some of my questions:
1. RF Output Transformer
Regarding valve-driven push-pull stages, obviously an output transformer would be used. However, even with months of research and looking into this, I'm still blind as to a manner of calculating the plate-to-plate impedance of the stages. Most RF antennae are 50 or 75 ohms, and while I know the proper formula for calculating turns ratios of transformers based on impedance, first the primary impedance must be known.
Now, obviously impedance varies based on frequency, resistance, inductance, and capacitance of a circuit or component. While for an audio amplifier, the frequency varies, for an AM transmitter running at say, 600kHz constant, is the impedance a definite value? That is, can it be calculated readily?
2. Frequency range of output transformer
I know this is a vague question, and something tells me this one will deadlock more than the first, but do any of you have any considerations for how to determine frequency range? Usually in audio usage this doesn't create much of an issue, but at RF ranges the design must be specific in a manner to reduce capacitances or inductances and other frequency-limiting variables to allow for the higher upper boundaries.
Question is, do any of you know of equations or formulae that help in the design of high-frequency transformers? I haven't been able to come to anything surefire or anything more of sites that acknowledge that there are design considerations for that.
3. Amplification of modulated RF carrier
This is probably by far the most simple question - that is, can a post-modulation RF signal be amplified in the same sense as audio, provided that considerations are made for the high-frequency circuit?
That's all I can think of for now. For awhile now, I've had the issue where as soon as I sit down to ask questions and get answers to my problems, most of the 500 million scenarios I've been pondering decide to wander into the realm of forgetfulness.
Thanks in advance,
solidus