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Small 2M crystal FM design
Hi, I'm looking for a small, 2m FM fixed frequency TX design for a
backup telemetry link on a model craft. I've seen designs based on discontinued Motorolla baby-monitor ICs, but simple varactor/tripler designs seem less common. Weight/size are important, and I'd like output around 1-2W. Duty cycle will be fairly low. There is 4.8V or 12V available already; 4.8V is likely to be noisier, as it drives the servos. 12V is prefered. What I was thinking was ~48 Mhz crystal oscillator with varactor, fed into a tripler, then a bandpass, then into an amplifier (RF transistor?)? I've seen a number oscillator designs floating around (handbook and otherwise), but I don't know how to find out what's most appropriate. Any suggestions, designs I've missed, books to read, etc? Something like the Ramsey FM6 (preraid)? Plan B is to find another HTX-200 or similar, pull out the guts, and use that. :) But I'd rather have something I can lay out myself. Thanks, R C KG4MVB |
Motorola did a number of one chip FM TX ICs, - they are cheap and widely
available and produce about 50mW output which can be use to drive something like a 2N3866 output stage (I only give that device number as I have one in the junk box!) 73 Marcus M3ChB "R C" wrote in message m... Hi, I'm looking for a small, 2m FM fixed frequency TX design for a backup telemetry link on a model craft. I've seen designs based on discontinued Motorolla baby-monitor ICs, but simple varactor/tripler designs seem less common. Weight/size are important, and I'd like output around 1-2W. Duty cycle will be fairly low. There is 4.8V or 12V available already; 4.8V is likely to be noisier, as it drives the servos. 12V is prefered. What I was thinking was ~48 Mhz crystal oscillator with varactor, fed into a tripler, then a bandpass, then into an amplifier (RF transistor?)? I've seen a number oscillator designs floating around (handbook and otherwise), but I don't know how to find out what's most appropriate. Any suggestions, designs I've missed, books to read, etc? Something like the Ramsey FM6 (preraid)? Plan B is to find another HTX-200 or similar, pull out the guts, and use that. :) But I'd rather have something I can lay out myself. Thanks, R C KG4MVB |
Motorola did a number of one chip FM TX ICs, - they are cheap and widely
available and produce about 50mW output which can be use to drive something like a 2N3866 output stage (I only give that device number as I have one in the junk box!) 73 Marcus M3ChB "R C" wrote in message m... Hi, I'm looking for a small, 2m FM fixed frequency TX design for a backup telemetry link on a model craft. I've seen designs based on discontinued Motorolla baby-monitor ICs, but simple varactor/tripler designs seem less common. Weight/size are important, and I'd like output around 1-2W. Duty cycle will be fairly low. There is 4.8V or 12V available already; 4.8V is likely to be noisier, as it drives the servos. 12V is prefered. What I was thinking was ~48 Mhz crystal oscillator with varactor, fed into a tripler, then a bandpass, then into an amplifier (RF transistor?)? I've seen a number oscillator designs floating around (handbook and otherwise), but I don't know how to find out what's most appropriate. Any suggestions, designs I've missed, books to read, etc? Something like the Ramsey FM6 (preraid)? Plan B is to find another HTX-200 or similar, pull out the guts, and use that. :) But I'd rather have something I can lay out myself. Thanks, R C KG4MVB |
It can actually be much simpler these days using a minicircuits vco (50R output) and a pll chip, not a lot else to it really. 10mW would give you a fair old range line of sight. Stick a minicircuits ERA 80mW device (4 legs, 50R in, 50R out) on the output of the vco if you want a bit more umpf. Just as easy on 70cms or the unlicensed 458MHz ISM band, same for 23cms and 13cm or 2.4GHz ISM band. It's SO EASY these days with the building blocks you can get. Clive |
It can actually be much simpler these days using a minicircuits vco (50R output) and a pll chip, not a lot else to it really. 10mW would give you a fair old range line of sight. Stick a minicircuits ERA 80mW device (4 legs, 50R in, 50R out) on the output of the vco if you want a bit more umpf. Just as easy on 70cms or the unlicensed 458MHz ISM band, same for 23cms and 13cm or 2.4GHz ISM band. It's SO EASY these days with the building blocks you can get. Clive |
Can anyone provide some part #'s for these one chip FM TX & RX IC's? I'm
interested too. Marcus Sleightholm wrote: Motorola did a number of one chip FM TX ICs, - they are cheap and widely available and produce about 50mW output which can be use to drive something like a 2N3866 output stage (I only give that device number as I have one in the junk box!) 73 Marcus M3ChB "R C" wrote in message m... Hi, I'm looking for a small, 2m FM fixed frequency TX design for a backup telemetry link on a model craft. I've seen designs based on discontinued Motorolla baby-monitor ICs, but simple varactor/tripler designs seem less common. Weight/size are important, and I'd like output around 1-2W. Duty cycle will be fairly low. There is 4.8V or 12V available already; 4.8V is likely to be noisier, as it drives the servos. 12V is prefered. What I was thinking was ~48 Mhz crystal oscillator with varactor, fed into a tripler, then a bandpass, then into an amplifier (RF transistor?)? I've seen a number oscillator designs floating around (handbook and otherwise), but I don't know how to find out what's most appropriate. Any suggestions, designs I've missed, books to read, etc? Something like the Ramsey FM6 (preraid)? Plan B is to find another HTX-200 or similar, pull out the guts, and use that. :) But I'd rather have something I can lay out myself. Thanks, R C KG4MVB |
Can anyone provide some part #'s for these one chip FM TX & RX IC's? I'm
interested too. Marcus Sleightholm wrote: Motorola did a number of one chip FM TX ICs, - they are cheap and widely available and produce about 50mW output which can be use to drive something like a 2N3866 output stage (I only give that device number as I have one in the junk box!) 73 Marcus M3ChB "R C" wrote in message m... Hi, I'm looking for a small, 2m FM fixed frequency TX design for a backup telemetry link on a model craft. I've seen designs based on discontinued Motorolla baby-monitor ICs, but simple varactor/tripler designs seem less common. Weight/size are important, and I'd like output around 1-2W. Duty cycle will be fairly low. There is 4.8V or 12V available already; 4.8V is likely to be noisier, as it drives the servos. 12V is prefered. What I was thinking was ~48 Mhz crystal oscillator with varactor, fed into a tripler, then a bandpass, then into an amplifier (RF transistor?)? I've seen a number oscillator designs floating around (handbook and otherwise), but I don't know how to find out what's most appropriate. Any suggestions, designs I've missed, books to read, etc? Something like the Ramsey FM6 (preraid)? Plan B is to find another HTX-200 or similar, pull out the guts, and use that. :) But I'd rather have something I can lay out myself. Thanks, R C KG4MVB |
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