Click on the image for a much clearer view.
It is a thing of beauty. You can see all four stages in there. There is the Bandpass Filter in the upper left. Below that is the VFO. In the center you can see the SBL-1 mixer. Off to the right is the audio amplifier. FB Chuck!
Chuck KE5HPY writes:
Allow me to add an endorsement of the joy and practicality of the DC receiver. Whether XTO, VFO or DDS, ring diode mixer, or Polykov, the DC IF concept is a real winner. They really deliver wonderful audio and clarity that is very satisfying for homebrew builder.
Thought you might enjoy these photos of a 40 m receiver and built 10 or so years ago. The design is straight out of EMRFD. At that time, the Altoid tin craze was in full swing and this is one of several projects I stuffed in a tin. This compact receiver has traveled on lots of camping and kayak trips where it delivered good DX reception using only a 30 foot piece of wire for antenna running back to the tent. It’s fun to hear intercontinental QSOs when you’re in the middle of nowhere. With my 40 m dipole attached at home, I think this little rig can hear anything my Icom hears.
It’s great that you’re promoting this practical technology. Keep up the good work.
Posts
Awesome
ReplyDeleteNice tiny construction! Yes, The DCR reigns supreme for a great sounding receiver. Long battery life,too. That would look great with a matching QRP Tx in a Altoids can.
ReplyDeleteQ: Which EMRFD schematic is that from?
73! WN2A
I think it's a variation of Figure 8.22 on page 8.14. I think the VXO has been changed to a VFO using a varicap and a potentiometer. I'm guessing the audio amplifier after the mixer is an LM386. Overall it's a beautiful little rig. 73 de K3NG Goody
DeleteCorrect, that appears to be a variation of Figure 8.22. We also see that it isn't a BPF that precedes the mixer, but a JFET buffer, with a bandpass response. That helps minimize out-of -band responses, and that high reverse isolation takes care of LO Leakage. The TO-92 transistor is the clue here.
ReplyDeleteThanks for the comments and accurate reverse engineering! The front end is a grounded gate JFET amplifier as WN2A points out and the VFO is indeed varactor tuned as K3NG detected. Unlike Pete, my documentation is lacking. I find published schematics inspiring, but can’t resist mixing and matching different stages from time to time.
ReplyDeleteI'm the same way with picking and choosing stages. I like that JFET stage and I'm thinking of throwing it on the front end of a rig I've been building for a while. I'm wondering if I could vary the 12 volts to make a reasonably smooth/linear gain control.
DeleteWhether operating remote or using a dipole at home, I have found the volume control adequate by itself for gain control. The SBL-1 is able to stand up to strong signals quite well. The RF amplifier only provides 10 dB of gain, and overloading is not a problem.
DeleteChuck -- Don't feel bad about not having a schematic. We often get curt messages from guys who seem offended when we say that there is no schematic, and -- GASP! -- no BOM. As if these docs were some sort of birthright. I have been tempted to say that if you NEED such documentation, you probably shouldn't be building this kind of rig. But that would be mean, and I try to be be nice. 73 Bill
ReplyDeleteThanks Bill. I agree with you. Sometimes it would be handy to have better documentation when I have to go back to repair or modify an older build. The biggest obstacle is once the project‘s working I simply want to use it and don’t spend the time to take full notes and record the mods.
DeleteGreat to see useful modifications made to these designs. Creativity helps us to make our own homebrew rigs more functional. The photo alone is worth 1000++ words. Yes, the schematic is only optional. Having both--better still. If you do a schematic, just a picture of a hand-sketch taken with your cell phone is fine- Pete, many others have done it that way. Schematic capture isn't required.
ReplyDeleteAgreed, no BOM's Why bother; we won't be using your specified parts anyway, we use whatever we have in our junk box.
Gerbers? Naw! Dremels? Oh Yeah!!
Just beautiful.
ReplyDeleteSchematic? There are lots of nice 40m DC receivers out there that might be a 'fit'.
FB RX! 👍
ReplyDelete