Introducing 2B2C, the story of a dual-band 2 channel QRP CW transceiver
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- เผยแพร่เมื่อ 27 ก.ย. 2024
- 'SP-2B2C' is a project to design, build and document in a video series the design and construction of a two band (40 and 20m) crystal locked (channelised) QRP CW transceiver.
The rig is entirely scratch-built, from 'borrowed' designs, circuit elements and ideas. It is a compact, neat pocket rig that will provide more than adequate service as a simple parks and portable rig, but it comes into its own for SOTA where the crystal-locked channels will not be a major impediment to making contacts.
Frequency control is provided by separate dedicated and trimmed 7MHz and 14MHz crystal oscillators with buffers and with a fixed transmit offset.
The receiver is a conventional Direct Conversion design with strong band pass filtering and an SA612 mixer, followed by a dual op amp for audio filtering and gain, and an LM386 for headphone or speaker listening. It has ample gain both in the shack and on a windy summit.
The transmitter duplicates a significant part of the popular QCX and MTR radios using a high speed logic gate as a digital driver, to three BS170 FETs in parallel for a full 5 watts on both bands. Keying for a straight key is done using discrete components.
The receiver draws about 50mA and the transmitter up to 0.8A on key down. Band switching is done with two miniature telecom relays.
Schematic: vk3hn.files.wo...
Part 1 - Concept
Part 2 - Receiver PCB
Part 3 - Receiver Band Pass Filters
Part 4 - Receiver build & test
Part 5 - Tx PCB, keying, pre-driver, LPFs
Part 6 - Transmitter driver
Part 7 - Transmitter PA and tests
Part 8 - Case assembly and field test
Looking forward to this series! Earlier this year I scratch built a 40 meter crystal controlled qrp transceiver. Your smd construction is way smaller than my dead bug/Manhattan style!
But the two rigs are probably very similar. There are a surprising number of design challenges in a CW transceiver. Thanks for commenting.
Brilliant stuff as always Paul! I'm looking forward to this series. We're moving house in a couple of weeks so sadly it'll be a little while before I'm melting solder again but I'll certainly enjoy seeing you design, build and test. Thank you for sharing your creativity with us. Take care. 73 Nick M0NTV.
Hello Nick, I heard your news in a recent video on your channel. Moving is a big deal, so take your time and I am sure you will be itching to get back to hobby projects after you settle. Let me know how you like this project as it rolls on. Part 1 tomorrow, then one part or maybe 2 each week, depending on interest! Stay well.
Looking forward to the next video
Thanks Chris, looking forward to your insightful commentary.
Fine business. Eagerly awaiting for next video
Coming soon, in fact in about 8 hours, then once or twice a week, depending on how interest goes. 73 Praveen, tnx.
This sounds AWESOME, Paul! I've recently come upon your TH-cam channel, and you have captivated me with your builds. I'm well on my way to my first complete transceiver, and have found some of your designs truly inspiring. I've subscribed and hit the bell... looking forward more than might be healthy to the next one!
Brilliant thanks Yakov. Thanks for your very nice comments. Happy to hear that you are a fellow home builder of transceivers. There's a lot to learn and every step brings fun and insights. Let me know how you like this project in the comments as it proceeds. Part 1 tomorrow, then once or twice a week after that. 73 de VK3HN SK
You earned another subscriber! I always love build videos.
Welcome aboard! Thanks Kacy, let me know in comments how you like it.
Nice.... Watching from the U.S.
Thanks for watching Joe.
🥳 looking forward to future videos!
Hi Alex, good to hear from you, let me know how you like this project in the comments over coming days! Part 1 tomorrow, then one part or maybe 2 each week, depending on interest!
@@Paul_VK3HN Sure! I have an upcoming video too. It will be published on Monday and going to present a new radio I've made. Some feedback from you would be very much appreciated!
@@R2AUK I'll look for it Alex.
Hi Paul. While re-examining the schematic of 2B2C I noticed something odd about the power amplifier. The input of 74HC00 PA driver is DC-decoupled and pin 2 is grounded. It means that the input will be, for instance, +/- 3V and is going to be compared by NAND gate with logical 0. This is odd because 1) negative voltage is an illegal input for a logical gate 2) X NAND 0 equal 1 for any X in {0, 1}. I think pin 2 should be actually connected to the 5V bus.
Alex, so good to read your comment that evidences a careful reading of my schematic. Few take the time to do that, and it demonstrates your interest and skill. Give me a moment to check my schematic and my sources, (QCX and KD1JV to name a couple). Your analysis sounds correct. However I know that the Tx produces 5 watts on 40 and 3-4 watts on 20, so the NAND gate driver must be working. In this design the first NAND gate is driven by a bipolar buffer stage, so it might be true that the drive is swinging above 5v, I recall thinking this,was a potential issue with this arrangement. A more likely option is that my schematic is wrong.
Hi Paul, The fault finding /testing will be what I will be interested in . vk2jcc
There's a bit of that. More testing than fault finding. Because I bring up each block in isolation, as much as possible, the faults get caught early. A fair bit on using the Scalar Network Analyser on the filters, and a session with the SDRPlay RSP1A spectrum analyser.
Looking forward to this! de WA3MCK
Thanks, Part 1 tomorrow, then one part or maybe 2 each week, depending on interest!
NIce. I got into that -- building tiny radios -- pretty seriously before essential tremor took the joy out of building things. Inspired by the MicroMountaineer and Howard Batie's designs in Ham Radio Magazine in the 70s and then by Wayne Burdick in the 90s, I managed to build a couple tiny flea-powered radios with xtal control. Then along came the MountainTopper rigs from LNR. The new Arduino-controlled SDR sets are very interesting too. But building your own is always more fun; it's what ham radio's all about, at least to me.
. . . You've done a beautiful job with all these little radios, Paul. Hope to meet you on the air some day. (If we didn't have this damn plague going on, maybe we could meet at the Dayton Hamvention one of these years.) Stay safe & healthy! 73 de W8IJN
Gday Nils. Thanks for commenting, very thoughtful of you. I read your qrz.com story, there are some similarities.
I also studied the Mountaineer and Optimal QRP Transceiver designs in the ARRL handbooks in my youth, but a lot of the American designs were not that easy to reproduce for me, as we did not have a supply of many of the transistors (2n2222s and 40673s) or the toroids (there were unobtanium in my youth). I was too naive to realise that I could have substituted with success. I had plenty of general purpose transitors capable of working at 7MHz and ferrite in other forms.
I eventually got onto those metal can Neosid formers and then, I moved forward. Some of my early projects worked only with a bit of luck, as my Grid Dip Oscillator was primitive and gave misleading dips! I had a long absence from making things, but when I returned, I found out how good the clock generators and microcontrollers had become, and how Chinese manufacture had made accessible things I could only have dreamed about, like VNAs and digital oscilloscopes, to an average experimenter on a budget. That, plus the power of video to share information and inspiration, has made what we enjoy today possible.
Good luck and stay safe, enjoy QRP and experimenting, 72, 73 Paul VK3HN.
Dear Paul….. The cobbling together of Frankenstein rigs is a learning experience! I am building the Alva (Swedish Pixie)…. With a VXO using Ceramic resonator C/O Alan Yates. Heard a VK3 CW (I’m VK2 land) but volume is VERY low. With the VXO disconnected the audio “hiss” is ok and LM386 sounds clean but when the VXO is coupled signals are their but rig is VERY low on audio (almost subliminal). … any thoughts?? Ps thanks 🙏 for these vids
Buen trabajo!!,73.👍
72 73 44 GL Antonio