I’ve listened to the SolderSmoke podcast for quite a while, and you’d think I would have availed myself of Bill’s sage wisdom. He’s previously made mention of the endless fun and rapture he’s had tinkering with crystal radios, carried away to the sounds of heavenly lutes (okay, I’m extrapolating here). But he’s also mentioned that he’s had considerably less fun with regeneratives: indeed, proclaiming that they must come from the place where all the solder smells like brimstone.
SolderSmoke Daily News: Crystal Radios from Heaven, Regens from ?
You think I would have listened. But no: I had to try to tinker together N1TEV’s Ultra Simple W1AW Receiver. I’ve now got the all the worst features of regeneratives:
- Hand capacitance: the oscillator wavers and even halts when I touch the regenerative control.
- The oscillator starts and stops unpredictably. If you adjust the regeneration control until the oscillator starts, you can back up and it will stay running until it suddenly clicks off.
- Gain is pretty low. I can just barely hear W1AW, along with some of the digital signals within the band. I installed the optional volume control to boost the level, which helps some, but it’s not brilliant.
- Antenna loading seems to do odd things to the antenna too.
- Touching anything in the circuit seems to quench oscillation.
I did gain a few bits of knowledge in doing this project, but frankly, it’s annoying. Perhaps in the light of day, when the clerics of electronics have said their prayers for my salvation, this thing will seem worth investing time in debugging. I have no doubt that if I lived only a hundred miles from W1AW, this would work, but it’s not inspiring me to greater investment of time.
I think I’ll convert to the Direct Conversion faith for my next project.
I warned you. You should have listened. But I’m sympathetic, because even I find myself lured by the siren song of the regen. It promises simplicity and high gain, and DX, all with a few little parts…
Yea, DC would be better.
Most of the regenerative receiver designs to be found on the internet are more or less junk and that includes N1TEV’s designs.
1/ You are going to have to address the mechanical design issues first and foremost. You are not going to get anywhere without shielding and having slow smooth tuning. That applies even to Direct Conversion receivers.
2/ The gain verses amplitude curve of the amplifier used to provide the regeneration is very important. The gain should decrease very slightly with increasing amplitude. This is nearly impossible to provide with a single BJT unless you run it at such high current levels that it’s gain starts to decrease with increasing CE current. A BJT long tailed pair will give better results as that gives a precise tanh gain/amplitude curve. MosFet’s and thermionic tubes/valves may give better results in that regard.
3/ Changes in voltage across semiconductor junctions cause changes in the capacitance across those junctions resulting in a loss of selectivity that cannot be compensated for by increased regeneration. You should use a circuit design that minimizes the effect of junction capacitance on the LC resonator circuit. Again thermionic tubes/valves can be better in that regard however they are not perfect. The grid – cathode capacitance can change by up to 10% due to space charge effects with increased grid voltage.
4/ Regenerative receiver designs that use a separate AM detector circuit are better. A FET based “infinite impedence” detector might be one of the better types. Simple diode detectors are usually very bad.
Hi Mark –
I’m wondering how I missed this post of yours before. By now, you’ve probably moved on far beyond the realms of regen receivers. I am still stuck on them and, judging by the pace at which I progress, might be moving onto superhets in a decade or two, if I’m lucky!
I have read of a few people having problems with N1TEV’s simple regen for beginners. I’m wondering if it’s anything like the design you had problems with? The guy in this link tells the story of all the problems he had, and how he solved them by changing to an FET detector – http://www.geojohn.org/Radios/MyRadios/RegenSW/RegenSW.html
Anyway, I can tell you from experience that the right circuit, solidly constructed, can give really pleasing results. I have built 2 WBR’s now, both with good results. The second one was a bit deaf, but there is a mod for that, which solved the sensitivity issue, but resulted in breakthrough from a strong local AM broadcaster. A simple BC band trap solved that and now I have a delightful regen for the 31M SWBC band (my other one tunes the 40M amateur band). I am now planning the build of a general coverage regen with plug-in coils. It might be a Kitchin design – I will at least use the AF stages of his design in the Feb 2010 issue of CQ magazine (drop me a line if you need a copy of the article).
I notice from the Yahoo regen group that Alan VK2ZAY was helping you out, so I’m sure with his experience, you have already reached regen enlightenment 🙂
73
Dave
AA7EE