Anatomy of a homebrew 40m superhet receiver

A look at a simple superhet receiver designed for CW reception. Describes each stage and demonstrates the homebrew crystal filter in operation. A 7 MHz receiver is shown but additional information on how this may be adapted to provide 14 MHz coverage is given as well.
For more information study the circuit of VU2ESE's BitX (available online) and 'Experimental Methods for RF Design' (book).
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[@Ratkill]

Oh man, thanks for this. Plenty of vids on superhet theory, but this is the very first I found detailing an actual build! Cheers m8

[@TheArtofEngineering]

Thanks Peter…. We are both ugly builder fans! 😂 Great video.

[@G4KDXlive]

You have even more amateur band crystals than me!

[@radiofun232]

Beautiful!

[@Alex-nv7cf]

Very interesting! Thanks!

[@raafatalheety826]

Good morning peter .all your circuit is very simple and easy .thank you very much .Yi1HXH Rafat rafat

[@danielstimpson7792]

Enjoyed that..thank you

[@munichman1968]

hi Peter, very good video!!! I use dual gate MOSFETs in the IF stage. That gives me the possibility to use one gate for regulation of the IF amp...by DC voltage provided by a potentiometer at the front of the rig or by an agc stage. 73 de Roberto

[@orvillejones1258]

Very nice tutorial Peter! Your marker board technique is better than PowerPoint!Al, N8WQ

[@Dazzwidd]

Hi Peter, while I was watching this (a great educational video by the way) I waste thinking that instead of narrow bandpass filtering being done in the RF chain, the same effect could be done at audio frequencies just after the detector. As an idea, a 3k center tapped to 8ohm audio transformer could be used in the collector of a 1 transistor amplifier, set up in a configuration much like a Hartley oscillator. The resonating capacitor across the transformer primary is chosen for your desired AF bandpass frequency. Then regeneration is applied to give a dramatic increase in Q. In this way you can very easily bypass the audio filter circuit if you don't want the filter. The regeneration can also be easily adjusted to give the desired bandpass characteristic and in order to set the bandpass frequency you can just apply regeneration until it oscillates. The frequency of oscillation will be it's band pass frequency. Nice and simple, done with a single transistor circuit and a cheap audio transformer which is widely available :)

[@vk3ye]

+Dazzwidd It's possible but audio filtering doesn't suppress the audio image which a superhet with a good crystal filter or phasing rx with a good phasing network will.

[@Dazzwidd]

+vk3ye. Yea okay, I can see that it won't take the signal burden off of the IF stage but I'm struggling to see the implications of doing the processing at AF with CW in a simple transceiver. How will it affect the results from a practical standpoint?

[@vk3ye]

+Dazzwidd Audio filtering will help but your selectivity will still be twice as broad, with responses both sides of centre frequency. No matter how sharp the audio filter you won't fix this. This is the main advantage of a superhet with a narrow crystal filter (like this) over a simple direct conversion.

[@Dazzwidd]

+vk3ye. I think it's definitely worthy of trial on a project radio just to make the comparison. I do see your point though. If other signals produce an audio response that fall inside the passband of the af filter, you will hear them. The af filter is effectively increasing your selectivity however, it's down to how steep and deep the stop band is in the end as to how well it works. If you eliminated your crystal filter in the receiver you demonstrated and left everything else essentially the same, but then used a high Q af filter circuit instead, I would be very interested to see the results. It would be intriguing to be able to have a side by side comparison at the flick of a switch :)

[@ashokdas2070]

Great video Peter, but as newbie i am still in doubt of some parts of design. can you please share the circuit diagram of this. I do not have EMRFD. Its very costly in india approx 20000 INR.

[@diegodelavega1572]

En en mix , t2 falta conexión a chasis. 73 Bs As LW1EUJ