Dear Bill,
Please my apologies for my late update on our DCR project. We started with the course in the semester break and once the semester started only a handful of students were able to finish their receiver. A long shelf of shame ....
Here is what we've got so far (those were finished at the end of April already). 3 nice DCRs completely sufficient to copy CW indoors without additional antennas starting from late afternoon. Strong stations can be heard all day. I found that coupling some 6m of wire with one or two windings to the ferrite core can boost the signal dramatically but can also increase noise.
The PTO is based on your design (Bill Meara N26QR & Dean KK4DAS) which was sparked by Farhan (VU2ESE) , except that I've swapped the FET for a NPN. The input amplifier and antenna is from the JUMA active ferrite antenna by Matti Hohtola (OH7SV), the band pass filter is from Hans Summers (G0UPL), the mixer and the headphone amplifier is inspired by Pete Juliano (N6QW), you told me that the diplexer (as well as the whole DCR idea) is attributed to Wes Hayward (W7ZOI) and the perfect schematics of Rick Scott (N3FJZ) where crucial to get me started in the first place. I enjoy keeping track of original sources, as I would do in science. This shows that even little achievements are based on the ideas of many other great people - and this is nothing to be ashamed of.
This was a lot of fun! Thank You!
Best and yours sincerely,
Andreas
Wow, the direct conversion re-engineering of education continues, this time at graduate-school level with biologists in Munich! Amazing.
Andreas points out that his group was also plagued by semester-related problems that caused many additions to the German shelf of shame. Let's hope that someday soon these builders will come to their senses and join the ranks of those who have finished their homebrew projects.
Looking at the schematic (below) of Andreas's project, there are a couple of significant differences from ours:
-- Their AF amp used a transformer-less push-pull design. We had considered this but abandoned it thinking that it would be too complicated to explain the workings of this circuit to our students.
-- Most significant, is Andreas's use of a ferrite rod antenna and an RF amplifier. I think a simple 33 foot quarter wave antenna (with a ground or a counterpoise) might work better. But hey, to each his own! The important thing is that a number of these receivers were successfully built. They look beautiful.
Congratulations to Andreas and the successful Munich homebrewers!
Posts
Typical German build, clean, organized and well executed. :-)
ReplyDeleteThat ferrite-rod antenna is an excellent addition to this project, even though it's not nearly as efficient as a dipole or EFHW. It makes the rig more into what a teenager might expect: a fully-integrated receiver. As we all know, the need to string an antenna can be a real gumption trap. Or am I the only one who feels that way?
ReplyDeleteI'm particularly interested in the use of the bipolar transistor in place of the J310 FET for the PTO. I'm trying to make my receiver from what I have at hand. I don't have that FET that I'm aware of. I had wondered if a bipolar could be used, but lacked the knowledge to know what else would need to be changed. From what I can see, we have R10 going from base to the positive rail and R15 off the emitter to ground is a different value than the source to ground on the FET. So three changes including the transistor. In Australia BC548 and BC547 seems to be more common and from what I read are interchangable with the 2N3904. I just happen to have 30 still in the packets 2N3904 transistors bought a long time ago. From a shop that sold a lot of Tandy and Radio Shack stuff. These transistors were going out cheap so I bought two packets.
ReplyDeleteTrevor
Bill if possible please post a higher resolution schematic. I was wondering about that 100 ohm resistor connected from the audio output to 9 volts.
ReplyDeleteTry clicking on the image -- that gives a higher res image.
ReplyDeleteI did but it's kinda fuzzy for my eyes. Chuck, WB9KZY
Delete@Roger
ReplyDeleteActually my students where from Iran, Australia, Czech Republic, Mongolia and Turkey and neither the construction style nor the project itself was my idea :)
@Todd
Yes the receiver is a bit deaf but it was initially meant for a 80m ARDF project and I wanted it also to function as a novice rig for listening to CW. I will transpose it to 3.5-3.6 MHz within the next months. I also felt, it is rather difficult to convince my students to use a 20 m antenna, because they only know radios with short antennas - I guess their acceptance would have been limited. But an active E-field antenna might be a better choice!
@Trevor
Honestly, I also simply used what I had at hand. The specified max. collector current of the BC547 seems to be considerable lower than that of the 2N3904 but for the receiver this shouldn't matter.
@Anonymous
The 100 Ohms resistor protects a bit from the popping/crackling noise if you plug in your headphones or powering up the DCR, nothing more.
Best,
A.
I was just wondering about the 100 ohm resistor because with dynamic headphones where there is say 40 ohms of resistance per channel don't you have 75 mA going through them all the time (9V/120ohms=.075A) ?
DeleteSorry for the anonymous post, blogger isn't recognizing my login apparently. Chuck, WB9KZY
Dear Chuck, please check the schematic again and you'll discover that the headphones are connected highside to the power rail and low side via a large capacitor (DC blocking) to the push-pull transistor stage, the 100 Ohm resistor is parallel to the headphones. So there's no constant DC current.
DeleteBest and many thanks!
Andreas
Andreas - Thank you for the explanation, that is interesting, so the common connection for the two headphone drivers is not ground but +9V through the 47 ohm resistor, that's unique in my experience - as I mentioned the schematic is kinda fuzzy for me so it's hard to see all these details.
DeleteBest Regards,
Chuck, WB9KZY
And I have shamelessly copied Pete Juliano's design from his great "Let's Build Something" (LBS) SSB Transceiver project https://www.jessystems.com/Images/Arduino/Fig2R1.jpg
DeleteAndreas - Thanks again. I looked at Pete's video
Deletehttps://www.youtube.com/watch?v=8p39-5Qcf3U
and the LBS article (which is in the sample issue of QRP Quarterly
http://www.qrparci.org/qqsample/qqsample.pdf).
Chuck
I'm viewing it just on a phone. Touching it allowed me to expand it and see it clearly. I did send the image over to my tablet for a better look.
ReplyDeleteThe circuit diagram appears to be a KiCAD schematic. Should we build the gerber files to carve the HSR circuit board on Pete's $250K CNC machine? We could mass produce this thing!
ReplyDeleteI can just see Bill choking on his morning coffee as he reads that question (and maybe Pete too). ;)
It doesn't need that kind of help - it is already in classrooms around the world.
Kudos to all who have contributed big and small!
Scott KQ4AOP
P.S. I am almost finished with my build. I am on the last board. It is my first receiver circuit, my first Manhattan build, and my first scratch built circuit. The details on testing each board in the posted Hackaday.io files is limited. I am sure I will figure it out but if I can't, I am posting questions here.