I've read a vast amount of information on this topic.
I'm trying to prototype in a circuit simulator and it seems that there is a bug with transistors. Hit the reset button to mess it up. Even when I build one from several sources it gives a similar odd signal. — I'm trying to building a transmitter so I can virtually demodulate it in the simulator. (Tomorrow I'm going to try this with a 555 timer instead of common emitter AC amplifier)
What I'm looking for
- A very simple AM (DSB) receiver — eventually for the NIST WWV station.
- Preferably 10Mhz.
- Made of simple and irreducible components.
What I'm not looking for
- Reducible components such as op-amps and 555 timers kinda scare me.
- High fidelity – I'm fairly certain that I can program around noise on my Arduino.
What I know
- The signal is received on an antenna and frequency resonated on an LC circuit tuned to 10Mhz. This "filters" out the unwanted frequencies. The output from this is a carrier wave.
- The carrier wave is put through an
RC circuit (parallel low pass?)Envelope detector to demodulate it into the output to decode on my Arduino.- 440Hz, 500Hz, 600Hz, 1000Hz, and 1500Hz for tone markers
- There is a 100Hz "subcarrier" that continuously broadcasts "date" information (Year, month, day, hour, minute, and DST to name a few)
What I do not know — Links & explanations greatly appreciated!
- Do I need any special length for my antenna?
- Can any inductor/capacitor combo be used that meets the LC resonance frequency equation? (C=100nF, L=50.3uH, should resonate at 10Mhz)
- I'm guessing this is tied to the output voltage or current of the antenna. How would I calculate this?
- Would amplification between any step be useful for final input on my Arduino? (Antenna->LC->Envelope->output->Arduino)
- Would I run the output into another LC->RC circuit tuned to get the sub-carrier?
- Does an LC->Envelope circuit even work for dual-side-band? (I honestly couldn't find a difference between normal AM signals and AM DSB)
Bonus: Is there any good free simulation software? (I can't seem to get circuitlab to output any useful simulation graphs, unlike Falstad's "View in Scope" or scope-probe)
Best Answer
A lot of questions but if you are looking for a WWV receiver design here is one and below is one of the circuits contained on the link: -
YES but it's probably not too critical if you are receiving a decent signal. A quarter wave dipole at 10MHz is optimum but this will be 7.5m long so try a couple of metres.
NO, you need to tailor the inductance capacitance ratio to give a decent Q factor but not be susceptible to parasitic components. Try for a resonant circuit that uses no less than 50pF - 50pF and 5060nH resonate at 10MHz - if you half C, double L for same resonance at an improvement in Q of 2:1. BTW it's "M" not "m" in MHz
Tricky, suck it and see
See design linked to for best guess at what you should be aiming for.
WWV uses up to 100% modulated AM (or normal DSB) transmission. Use a diode detector (as per link) to produce the demodulated waveforms.