Building an AM receiver for 10Mhz (NIST WWV)

Question

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.
  • I've solved the LC equation for both the capacitor and inductor using wolframalpha.
• 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)

Answer 1

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: -

• Do I need any special length for my antenna?

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.

• Can any inductor/capacitor combo be used that meets the LC resonance frequency equation? (C=100nF, L=50.3uH, should resonate at 10Mhz)

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

• I'm guessing this is tied to the output voltage or current of the antenna. How would I calculate this?

Tricky, suck it and see

• Would amplification between any step be useful for final input on my Arduino? (Antenna->LC->RC->output->Arduino)

See design linked to for best guess at what you should be aiming for.

• Would I run the output into another LC->RC circuit tuned to get the sub-carrier? Does an LC->RC circuit even work for dual-side-band? (I honestly couldn't find a difference between normal AM signals and AM DSB)

WWV uses up to 100% modulated AM (or normal DSB) transmission. Use a diode detector (as per link) to produce the demodulated waveforms.