Here is a progress report on Direct Conversion Receiver developments.
Dual Tuned Circuit, Diode Ring with Diplexer, PTO VFO from Farhan's Daylight rig, two stage 49 db BJT AF amp with a transformer.
It works very well.
I discuss: Shielding of the VFO -- necessary or not?
Why brass in the PTO?
Do we really need 100db in a receiver, especially with ear buds?
Sourcing the AF amplifier's transformer.
Using W7EL's diplexer. (I think it has solved my Radio Marti breakthrough problem).
Developing a DC RX circuit that can be built by students.
I end with a bandsweep of 40 meters that includes CW, FT-8, SSB, and AM
Posts
1 hour ago
Dear Bill: I have also been revisiting DC receivers recently, and in case you want to eliminate your audio transformer, I am so far liking the Richard Andersen discrete transistor audio amplifier circuit that I was reminded of at the Mostly DIY RF website where they are planning a kit. However, I did quickly burn out the 2N3904/06 final stage, so I replaced them with a heavy duty TIP31A and 32A pair I had on hand. However, if emitter resistors were added to the design to limit the current then the original transistors could probably be made to work.
ReplyDeleteBest Regards,
Walter KA4KXX Orlando, FL
Thanks for the heads-up Walter. I've been following this madness with my own version of the DCR (Bill, letter from my lawyer and invoices from my therapist heading your way soon). I think I'll give it a go due to my lack of a suitable transformer. The only "problem" I see with implementing the KE3IJ amp is it's circa 2004 whereas everything else is sooo last century :)
DeleteNev: Our attorneys at Dewey Cheatham and Howe fear NO ONE! Bring it on! As for the therapist, I understand the suicide hotlines now have an introduction that begins, "If you are calling about a Direct Conversion receiver, press 1." 73 Bill
DeleteNev: Mouser has the transformers: https://www.mouser.com/ProductDetail/Xicon/42TM013-RC?qs=h3Xc2LqAealCgSV7Tuf2oQ%3D%3D&countryCode=US¤cyCode=USD
DeleteThanks Walter. It is amazing how many of us are revisiting the DC receiver. Yes, that circuit is very attractive. I have used it in BITX transceivers, in lieu of the LM386. And I used it in a DC RX. But I think t would be too complicated for high school students. I think for our purposes it would be better to have a simpler circuit, even if it yields a bit less gain and requires some more hard-to-get parts, like the output transformers. There is a great tutorial on how this circuit works here:
ReplyDeletehttps://www.electronics-tutorials.ws/amplifier/class-ab-amplifier.html
73 Bill
If I understand right, incorporating RIT and Zero Beat button allows exactly set the CW tx frequency, and listen on either sideband. Who needs a superhet? Ed KC8SBV
ReplyDeleteRe: pointer/scale: maybe re-purpose a 'standard' dial-cord system, driving the 'drum'(if needed) by the shaft of the knob that also drives the screw-thread (suitably isolated for hand capacitance)? The cord/string will have linear travel.
ReplyDeleteJust re-viewed Nick M0NTV's Glue Stick effort, and wonder where the 'nut/plunger' carrying the cores sits up the tube? Could an appropriate-sized and -placed aperture or slot expose a pointer on the 'nut'?
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