Another informative and enjoyable video, thanks! You answer every question that comes to mind, which is satisfying. I had not realised that 9545khz crystals are readily available, that makes a fixed 10mhz AM WWV superhet achievable. In my limited experience AM detectors are not quite as easy as they seem. I've had some success with an infinite impedance JFET detector. I'd like to see you take a look at the AM detector options for homebrewers sometime.
I would like to see more detail on how you selected the RF transformer and also how you calculated the Capacitance need for the frequency of interest. While on that top the same detail would be appreciated on selecting the capacitance around the crystal. Thanks for a very informative video.
There are some issues with direct conversion receivers. The LO will automatically lock to any nearby carrier unless perhaps there is good isolation. The second issue is the high gain in one frequency band (audio) results in oscillations or artifacts of oscillations through power supply coupling. Another issue is every component becomes a microphone. It was a long time ago I built a DC receiver and I didn't have a proper antenna.
Here in Europe we have DCF77 (77.5 KHz). When I was a kid there were first Microcontrollers like 8749 to decode but it was more fun to build transmitters to play with at railway stations for example... The signal is still active in 2023. Hard to receive in the Southern Greece. More and More the GPS is used or simply accessing an NTP server.
I'm curious about your comment on carrier phase vs LO phase and distorted audio. Carrier phase should only be important for amplitude of very low frequency baseband signals. Receiving AM with a DSB receiver is quirky because of tuning error, where the USB and LSB content don't match exactly unless the LO is exactly centered on the carrier, and they interfere with each other.
@@levelupeelab nice, thanks for the followup. By the way, I've fallen in love with your videos. You do such excellent work; thanks for sharing your activities!
It would actually be quite easy to phase lock your local oscillator to the WWV signal by using the DC error voltage , LP filtered from the balanced mixer output. A varicap across the crystal trimmer would suffice., pulling it a few 10s of hertz .depending on the error voltage level.
Once I saw your video on a DC receiver for WWV I was interested. When I saw the Johnson Viking Adventurer in the background like the one I own, I scrolled down and when I also saw the Heathkit RF signal generator which I own I subscribed. Cool video! Oh, I had one question. Given that a doubly-balanced mixer/detector will suppress AM why do AM signals like WWV get passed through to the LM-386 audio amplifier?
Great video. If your local oscillator and input frequency from WWV are at exactly 5MHz , you should get no output from from the NE602 and will hear nothing from the lm386 as the difference of the signal from WWV and your LO will be 0Hz and the sum will too high and filtered out. If you can pull your crystal oscillator 1KHz to pickup an AM side band then the the voice information should be clear. I might build your circuit but use my reference generator to replace the crystal in your circuit and tune for a volume null, then my signal generator should be "exactly" in tune. Thanks for sharing.
I notice in the schematic C2, C4, C8 and C11 values are all 10 nf, which is 0.01 uf. What got my attention was C2 in power supply filter. Most similar PS designs seem to always use a 0.1 uf or 100 nf to filter high frequency noise, along with a 10 uf for low frequency noise. The other two 10 nf in the base band filter most likely are correct. I'm not trying to be picky. C2 and C4 are probably OK as they are of 10 nf. Any word of a new DC superhet receiver in the works for WWV reception?
From myself. In checking the data sheet for the SA612A, C2 is shown to be 10nf, not 100nf or 0.1uF as I thought. However C4 should be 100nF or 0.1uF, not 10nF. So I was half right!
@@levelupeelab Finding a 5 MHz XTAL is hard. If I chose 10 MHz to receive instead, what do think C3, C4 and C16 values would be? 10 MHz XTAL are all over.
