HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: makeRF on February 26, 2016, 0423 UTC
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It's been a while since I've had time to do some radio tinkering. I came across an interesting schematic last weekend for a very simple transmitter called the Ten Minute Transmitter. I wrote about it here: http://makerf.com/posts/ten-minute-transmitter
If you buy a store bought RFC and use some capacitors in parallel instead of a variable capacitor, the only 'hard to get' part is the crystal.
I've done some tinkering with it since the initial build and have been able to amplify the signal up to about 9 watts! I'm going to play with it some more and post about it again soon.
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Hey makeRF,
those simple circuits are fun to begin with because they work almost every time on the first try and one gets a feeling of success (and therefore motivation). Since you have a Scope capable of FFT analysis, I think there's no need to point that out: but please have an eye on the RFI emitted. I had saw simple 40m band oscillators that easily managed to generate harmonics on 100Mhz and more due to parasitive capacitive couple between (too long) component legs (primary because the transistor choosen was a type with ft=450Mhz++). So, wehen using a simple Oscilattor it's ueful to install a low-pass on it's output.
Oh, and, mind:
- When building an oscillator: it will amplify like hell, but hardly oscillate.
- When building an amplifier, it will oscillate perfectly but hardly amplify. :)
Kind regards,
Zazzle.
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Yes, for sure! I always add warnings for folks to use low pass filters to clean up the signal and a dummy load for experimentation. The waveform is often not clean, especially when it's on a breadboard. It usually looks a bit nicer when soldered, but even then it typically needs filtering for a clean waveform.