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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

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)

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  • \$\begingroup\$ Are you trying to construct a direct conversion receiver at 10MHz rather than the more normal superhetrodyne? The difference between AM and AM DSB is that in DSB the carrier frequency is suppressed making it much more power efficient. see en.wikipedia.org/wiki/Amplitude_modulation \$\endgroup\$ – JIm Dearden Jun 19 '13 at 9:24
  • \$\begingroup\$ There is no 'bug with transistors' mentioned at the link you cite. There is no subcarrier in AM. A low-pass filter isn't sufficient to demodulate AM. You need a detector. You should also consider heterodyning like everyone else has for about ninety years. \$\endgroup\$ – user207421 Jun 19 '13 at 9:27
  • \$\begingroup\$ @JImDearden, correct. A direct conversion receiver seems easier. As I'm going to be reading the signal digitally, I don't consider I'll need high quality. I re-read that wikipedia entry, but all I can make out is the power of the carrier wave is reduced. \$\endgroup\$ – Nathan Goings Jun 19 '13 at 16:08
  • \$\begingroup\$ @EJP, It seems there is a comment on the page indicating normal result and rationalized with "for various reasons." Still, this design doesn't seem to simulate. The WWV broadcast format says there is a timecode on a "100Hz subcarrier" \$\endgroup\$ – Nathan Goings Jun 19 '13 at 16:17
  • \$\begingroup\$ There's a comment stating that the circuit doesn't behave exactly as the analysis predicts. There nothing there about it being a simulation bug, or a 'transistor bug' either. \$\endgroup\$ – user207421 Jun 19 '13 at 19:37
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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: -

enter image description here

  • 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.

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  • \$\begingroup\$ Thanks for your answer! Per-link, I discovered it's not an RC circuit that demodulates, it's an envelope detector (I guess you call a diode detector). I've updated my answer to reflect that. I'll look into the mentioned "Q Factor." I was hoping to do more simulations, but I might start purchasing components. \$\endgroup\$ – Nathan Goings Jun 19 '13 at 17:07

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