07-10-2017, 11:00 AM
Yes it may seem a little strange to be going a more complicated route, but there are several reasons which influence me going this way (in no particular order and probably not exclusive):
1: I have not got a great many crystals, especially around these frequencies. I know they are readily available but other reasons deter me from going this way. Most of those I have are on fixed MHz points, except for a few oddities.
2: I have a number of these glass low frequency crystals. I tend to collect them. They have a more vintage look about them .
3: Part of the reason for doing this project is not just to get a useable pantry Tx, but to learn quite a bit about different types of circuitry. I feel it more sensible to do this at low powers particularly with these valves than at a possible future higher level. Multipliers and harmonic issues, to me, are a big thing to learn. It is Ok in theory, but my brain tends to wander, multiplying and adding frequencies almost like a mathematical puzzle to get to a particular (at the time) frequency in mind. Practical experience will help me to understand what is reasonably possible and how to do it. To some extent I have a mathematical mind, and have realised it is possible to design with mathematics and implement the result. It might be a bit 'nerdy' but it's powerful and I have found, in at least one occasion, almost the only possible way.
4: Perhaps less of a reason, and maybe one against, is that I am thinking about microcontroller timer generation of squarewave frequencies and filtering the squarewave to extract, principally the fundemental, but possibly a higher harmonic. I know there are chips specifically for this but I do tinker with programming as well. Although not strictly crystal controlled maybe an Arduino Nano with suitable output filtering would be more useful as programmable for a wide range of frequencies, especially when the lower (higher amplitude) harmonics are taken into account?
5: With the components I am using the 7th harmonic is within the range of tuning and is also within the MW band, from my initial checks, at a quiet spot. I could obtain a crystal of this or nearby frequency and probably avoid the need for a buffer but I am happy at the moment with progress. I have other experiments I have tried which, if implemented and successful, may be interesting.
1: I have not got a great many crystals, especially around these frequencies. I know they are readily available but other reasons deter me from going this way. Most of those I have are on fixed MHz points, except for a few oddities.
2: I have a number of these glass low frequency crystals. I tend to collect them. They have a more vintage look about them .
3: Part of the reason for doing this project is not just to get a useable pantry Tx, but to learn quite a bit about different types of circuitry. I feel it more sensible to do this at low powers particularly with these valves than at a possible future higher level. Multipliers and harmonic issues, to me, are a big thing to learn. It is Ok in theory, but my brain tends to wander, multiplying and adding frequencies almost like a mathematical puzzle to get to a particular (at the time) frequency in mind. Practical experience will help me to understand what is reasonably possible and how to do it. To some extent I have a mathematical mind, and have realised it is possible to design with mathematics and implement the result. It might be a bit 'nerdy' but it's powerful and I have found, in at least one occasion, almost the only possible way.
4: Perhaps less of a reason, and maybe one against, is that I am thinking about microcontroller timer generation of squarewave frequencies and filtering the squarewave to extract, principally the fundemental, but possibly a higher harmonic. I know there are chips specifically for this but I do tinker with programming as well. Although not strictly crystal controlled maybe an Arduino Nano with suitable output filtering would be more useful as programmable for a wide range of frequencies, especially when the lower (higher amplitude) harmonics are taken into account?
5: With the components I am using the 7th harmonic is within the range of tuning and is also within the MW band, from my initial checks, at a quiet spot. I could obtain a crystal of this or nearby frequency and probably avoid the need for a buffer but I am happy at the moment with progress. I have other experiments I have tried which, if implemented and successful, may be interesting.
