33 - All Analog Direct Conversion Receiver

Nick M0NTV discusses and tests an all analog (and all discrete) Direct Conversion Receiver - with a Glue Stick PTO. Includes on air testing - with some seriously surprising results!
My video on building a bandpass filter is here:
• 16 - The Dark Art of t...
Pete's J310 Product Detector is here:
www.n6qw.com/Simpleceiver_Plu...
My own redrawn schematic is here:
drive.google.com/file/d/1W-36...
My redrawing of Dieter's General Purpose Audio Amp is here:
drive.google.com/file/d/1J8-U...
Farhan's Daylight Again transceiver is here:
www.vu2ese.com/index.php/2022...
My cropped version of just the PTO is here:
drive.google.com/file/d/1ZDrT...
Enjoy and keep experimenting!

[@acestudioscouk-Ace-G0ACE]

Good to see what can still be achieved with discrete components. The glue stick stability is impressive too, bet that was a pleasant surprise.

[@M0NTVHomebrewing]

Certainly was! Thanks very much for watching. 73 Nick

[@alanmacdonald65]

Cracking job mate, I've been waiting for this one since beer night last week!

[@M0NTVHomebrewing]

Cheers mate! See you soon :)

[@Paul_VK3HN]

Never thought a glue stick could be so useful! Well done on all points, it's working a treat. And stable enough for FT8? Excellent stability Nick. 73 and looking forward to next episode.

[@M0NTVHomebrewing]

Thanks so much Paul. I couldn't really believe it myself. Amazing what can be done with simple modules. Hope you are keeping well. 73 Nick

[@tdumnxy]

Impressive. Many thanks for sharing your work and knowledge.

[@M0NTVHomebrewing]

Thanks very much Stephen!

[@gibbywankenobi66]

Great Video! It inspired me to try the glue stick PTO. I built mine with a unknown core off of an old computer motherboard. Its white whatever that means. Not knowing the manufacturer it probably means nothing. It fit perfectly. I didn't even use glue it just press fit in. I used wire off an inductor from an old satellite receiver power supply. I had built a circuit to test crystals using a transistor off of an old dishwasher control board. I plugged the glue stick in place of the crystal along with a capacitor. My ancient frequency counter read I was around 9 MHz. I cheated and used a program to calculate the inductance and capacitance I needed. After taking a turn off the coil and changing the cap I can tune most of the 40 Meter band. I was amazed at how good it worked once warm. I want to build Farhans circuit next but getting started with this was lot of fun!

[@M0NTVHomebrewing]

Very well done! That sounds excellent. My first one was made with random toroids and a lot of guesswork - and it still worked! Keep up the great work. 73 Nick

[@oasntet]

When I finally got my license two months ago, I decided I'd try to DIY as much as possible, rather than plunking down $3k (on the low end!) on an HF shack. I just put together a (tr)uSDX, which is basically the arduino radio you're talking about in kit form, but I've also been watching your Daylight Again series when I have time. Let me back up; at the start of the pandemic, I stumbled across a diy synthesizer channel (Moritz Klein) who does very low-level, explain-every-component synthesizer modules. It's far more gratifying to put together something from scratch when you understand what all of the bits do, and I've been doing just that for a while now. I bring this up because that phrase "the go of it" reminded me of that clear distinction between kits and homebrew. Anyway, I'll likely have my Extra this weekend (going there straight from Tech after much studying) and while I'm sure the (tr)uSDX will be great for QRPing while mobile, I'd really like a receiver that I grok fully, and digital just isn't going to be that, yet. So thanks for all of these videos; hopefully between them and the other resources, I'll be able to build a receiver I actually understand, down to each individual component.

[@M0NTVHomebrewing]

Thank you very much George. All the best with your Extra - I hope you ace it. All the best as well with your future building, learning and experimenting. Have fun! 73 Nick

[@migalito1955]

Cool beans. Actually, if I can ever get past my other retirement projects I am going to in 4 stages and over several months build SolderSmoke's direct conversion receiver that Bill, Pete & others developed for high school students. I really want to pull this off. I've built electronic odds & ends and one very sucsessful Regenerative Receiver 12 years ago but by no means am I an EE but I think it is well worth the effort.

[@M0NTVHomebrewing]

Thanks. All the very best in your own building. 73, Nick

[@jonhoyles714]

thanks again nick for a educational and enjoyable watch will defo have bash nice little project

[@M0NTVHomebrewing]

Thanks very much Jon. Glad you enjoyed it and please do have a go yourself. 73 Nick

[@jonhoyles714]

@@M0NTVHomebrewing cool 😎 just out of interesting what antenna did use ?

[@M0NTVHomebrewing]

Hi Jon, I'm using an End Fed Half Wave which is cut for the 40m band. It is resonant on this band plus the harmonics - 20, 15 and 10. It is configured as an inverted L and uses a 49:1 transformer. All homebrew as you might imagine!

[@JayJay-ki4mi]

Great video, but I've been looking for a while on a video that explains what the discrete components are doing together and why. I owned a 130W FM transmitter when I was a teenager and was always very surprised by its internals. It was DIY, but very stable and good. Eventually I'll recreate it but I'm still in the learning stages. I know this is a receiver, so I'm starting with understanding how these work first.

[@M0NTVHomebrewing]

Thanks Jay Jay. Yes, I think you are right to start simple and work from there. FM is actually a whole different ball game altogether and I've only recently started to dig into this myself. It's all fascinating and as my friend Pete Juliano (N6QW) often says, "When you know stuff you can do stuff!" Wise words indeed. 73 Nick

[@andye2005]

Well done! (Especially the FT8. Andy

[@M0NTVHomebrewing]

Cheers Andy. 73 Nick

[@michaelrogers3078]

I really like your videos. Thanks for the time and effort you spend making them. 73 N4MJR

[@M0NTVHomebrewing]

Thank you so much Michael. That's very kind of you. I'm pleased you enjoy the videos. 73 Nick

[@technishn]

Permeability tuned VFO, BFO, ATU. Remember seeing an RF sig gen with sweep generator. Stood back and the dial moved by itself. Suppose you could use a motor to drive the PTO.. Lol

[@M0NTVHomebrewing]

Hi Kevin, yeah they are more commonplace than you might first imagine. I like the simplicity of the glue stick variable inductor. 73

[@BShocked]

It sounds great! What determines the bandwidth of the signal? I heard a few stations at once when you tuned to someone.

[@M0NTVHomebrewing]

Thanks. Your question is an important one because it cuts to the heart of precisely how a DCR works. Basically there is no filtering (other than the wide RF band pass filter at the front end). This means you will hear (in the case of 40m) a LSB signal of say 2.7 kHz plus an inverted form of whatever lies 2.7 kHz above this - which could well be another LSB signal. Listening on a DCR can be tricky when the band is busy but wonderful when the signals are more spaced out. I have a talk (that I referred to in the video) which explains this in much more detail. You can find it hosted by several Amateur Radio Societies including Trystan's Workbench: kzbin.info/www/bejne/iWLLln-JrZ56fNU Hope this helps. 73 Nick

[@Yunesieh]

i can't believe that stability, I also made many hf oscillators, but none of them enough stable to use in real world :( . good job. 73

[@M0NTVHomebrewing]

That was always my experience too. The FT8 experiment was a bit of a joke really - I never seriously expected it to work! It's tricky to tune in to the precise frequency (without a frequency counter) but the stability is really impressive - for a glue stick! Thanks for watching. 73 Nick

[@R2AUK]

👍❤

[@M0NTVHomebrewing]

Cheers Alex. 73

[@hobbyrob313]

I didn't understand much at first, what will be built now? but now believe it is something with RX and TX???

[@M0NTVHomebrewing]

Hi! I've built a Direct Conversion Receiver but it could be modified and extended to become a Superhet or maybe even a transceiver. I think I'll keep mine as it is - but watch out for the next video where I'll update on the changes I've made to improve this radio. Thanks for watching. 73 Nick

[@TheFretman2]

I built the J310 product detector from your redrawn schematic and there's virtually no input from the RF (antenna). I don't believe it's the transformer. Have you known J310's to be bad? I ordered the batch I have from China. It's not the audio section. If I inject only a 1000hz signal at the LO input, the tone is very loud at the speaker end. Injecting the same signal only into the RF input, the tone is barely audible. The sine wave from the VFO at the 20t side of the transformer is very large, compared to the input. So I think the transformer is doing it's job. Any tips on troubleshooting?

[@M0NTVHomebrewing]

Hi there! The straight answer is yes. I too bought a bag of J310 FETs from a cheap overseas supplier only to find that every one of them was a dud! I will only buy them from trusted sources now. FETs are also very sensitive to static electricity and so depending on how they are handled and stored they can be killed quite easily. Best advice would be to swap out the product detector and see if you can get the radio working with another design - like a double balanced mixer (homebrew or commercial e.g. SBL-1 etc.). Bear in mind it will need at least 7dBm of LO to drive it and you won't have any gain in the process (loss actually) but if the radio works then you know the problem is in your J310 product detector. When it comes to analysing the J310 module I would model it in LTSpice so you can see what the voltages should be around the circuit. Then break out the multimeter and get comparing. This will help to confirm whether your FETs are bad, you've got a solder issue (open circuit or short) etc. Hope this helps. Keep going! I always say that building radios is the easy part - having the persistence and patience to troubleshoot them and get them working properly is the real challenge! 73, Nick

[@TheFretman2]

@@M0NTVHomebrewing Thanks so much Nick. Disappointing that those things have a good chance of being duds. I have some SA602 DBM's and can get that going pretty quickly if need be. Just thought I'd try a different design. I'll simulate the circuit in LTSpice and see what I get.

[@jamesmoffat9754]

Spreading out the turns on the glue stick might slow down the tuning rate.

[@M0NTVHomebrewing]

I think you are probably right James. Thanks for watching. 73 Nick

[@deathstalker7344]

But which frequency receiving cw, am, fm ??? Show full circuit diagram with rf amplifier and local oscillator and mention whicn his carrier frequency

[@M0NTVHomebrewing]

Hi! It's a Direct Conversion Receiver for 40m (7.00 - 7.200 MHz). It will demodulate SSB and CW (but with no filtering CW will be challenging!). I don't produce "full circuit diagrams" because as you'll see from my other videos I build in a modular fashion - stage by stage. The links to the schematics for the Product Detector, Audio Amp and the PTO are all in the description. There is a separate link there to my video on building Band Pass Filters too. There is no RF Amp. You might find my talk about how a DCR works helpful too (kzbin.info/www/bejne/iWLLln-JrZ56fNU) Hope this helps. 73 Nick

[@markusm.lambers8893]

Dear Nick, could you please 'switch on' the sub-titles? Then I can 'translate' them to my 'mother-language' and will understand some things, I will miss, when only hear the 'english comment' ! English is not my native tounge, so please help the 'not so good educated' simple people, ... outside the UK, the USA, or even Australia, ... to learn a little bit more, ... ! 73 es merry X-mas to you, and all your beloved around you, de Markus ; db9pz

[@M0NTVHomebrewing]

Hi Markus! Thanks for getting in touch. KZbin will auto-generate subtitles but it takes a while to happen. All my previous videos except this one currently have auto-generated subtitles. This one will too - you just have to wait a little while longer! Thanks again. 73 Nick

[@BabylonLurker]

Glue stick inductor. I chuckled when I heard it, and I love the idea. Another idea for a simple variable oscillator is using a ceramic resonator and a variable capacitor. Take a look at what VK3YE has done with that, you might like it 73 de OZ9QV

[@M0NTVHomebrewing]

Thanks Jan. I follow Peter's channel and I know he's built some amazing stuff. I'll check that out. Thanks for the tip. 73 Nick

[@G7VFY]

PTO's are super stable, which is why they were used in old car radios, along with the fact that they can be made very small. Old car radios are great for hacking into stable VFO's because of their stable PTO's. G7VFY

[@M0NTVHomebrewing]

Thanks Stephen. Yes, I confess I knew very little about PTOs until very recently but I understand they were to go-to design for AM car radios for a long time. They were obviously on to something! 73 Nick