Since building The Sproutie a few months ago I have had a great deal of fun with it. It is only the 4th regen I have ever built, but it is the best one so far. One of my main motivations for building it was to own a “serious” regen. I have long thought that the main reason this type of receiver is not taken more seriously nowadays is because they are rarely taken seriously when being built – and perhaps even designed. Kit designers are forced to make severe compromises because, well, who is going to pay hundreds of dollars for a high quality regen kit? A few of us would, but probably not in large enough numbers to make such a kit economically viable.
As an example of taking things seriously when building a regen, take a look at this build of NR5Q’s “Ultimate Regen” by Jim K4XAF. Now that is a receiver any avid SWL would be proud to own and operate.
To make a long story short, I wanted to prove to myself that a regen could serve as a useful and valuable listening tool. I was mainly concerned with SW AM broadcast stations as my main station rig, a K2, doesn’t have general coverage receive. For AM shortwave listening, The Sproutie is indeed very usable, and definitely more than just a novelty. I had spent very little time or effort listening to SSB and CW, and my initial impressions were that CW reception was fine, but SSB reception was occasionally good and occasionally not. I didn’t really think about why, and thought that perhaps it was something to do with the design that I didn’t understand.
Recently, I spent some time with The Sproutie on the ham bands, and the obvious finally occurred to me. It works fine on SSB but when the input signal is too strong, the oscillator pulls, resulting in FM’ing of the signal. In order to overcome this, the best way to operate The Sproutie when listening to SSB is to run the AF gain at, or near, maximum volume, and use the RF gain to set the desired volume. This will ensure that on strong signals, the RF gain is kept down. This is counter-intuitive to anyone who is used to operating a modern receiver with a product detector, where the modus operandi is usually to keep the RF gain at, or close to max, while using the AF gain to control the volume. However, if you got your start with SSB by using an older receiver that had a diode detector and was primarily designed for AM, you’ll remember that controlling the amount of BFO injection was fairly important in resolving the SSB signals well. With one of my first radios, a British R-107 WW2-era military receiver, I was taught to keep the AF gain turned up, and to control the signal-to-BFO ratio by adjusting the RF gain. On strong signals, I quickly learned to keep the RF gain down so there wasn’t too much input signal for the amount of BFO signal. With The Sproutie, the principle is the same, except you are also limiting the amount of input signal so as to not cause the oscillator to pull. Those who have built and operated a number of different regens will be able to comment on this, but my sense is that this is a very common issue with them. Perhaps some designs minimize the effect of oscillator pulling. Can anyone more experienced than me comment? (Note – qrpgaiijin did. Please see his comments below this post on the reasons for oscillator pulling in regens. Input from experienced builders is very valuable so if you’re interested, please do take the time to read.)
Also note that another technique you can use to prevent oscillator pulling on stronger signals is to increase the amount of regeneration. On weaker signals, you might want to reduce the amount of regeneration closer to the “critical” point of onset of oscillation. At that point, sensitivity is greater, which will help with the weaker signals. Of course, all these adjustments will affect the tuning, so you will need to adjust for that. It’s all part of the fun of operating a regen!
To sum up, The Sproutie does indeed resolve SSB signals well, but it requires much more attention and input from the user than other receiver architectures do. The “sports car with a stick shift” analogy works well here. When tuning the bands for SSB signals, you need your hands on the controls on a much more regular basis than when tuning AM signals. Listening to a QSO with stations of vastly different signal strengths can be an exercise in user attentivity and engagement.
By contrast, listening to AM stations on this receiver is much easier. If the oscillator pulls a few 10’s of Hz on strong AM signals (which it almost certainly does), you’re not going to hear the effects. It’s still a good idea to run the AF at a high gain setting so as not to overload the detector, but the need for this is nowhere near as critical. In fact, listening to AM stations on this little gem isn’t much more work than doing the same thing on a superhet. Although the precise regeneration point varies with frequency, you don’t need absolute maximum sensitivity when scanning the band for signals. When casually tuning a SW BC band, I can tune several hundred KHz before roughly resetting the regeneration control. Only when I find a signal I want to investigate further do I take the time to set the regeneration more precisely. It’s a process that becomes second nature after a while. I can almost imagine the diehard regen users in the 1930’s deriding owners of the newer superhets, as they were too easy to use and “not real radios”. What’s the betting that happened?
So here’s the deal – The Sproutie does indeed receive SSB just fine, but you’re going to have to put a bit of work into it. It is, after all, a sports car with a stick shift, and not a luxury sedan with an automatic transmission:-)
NOTE – I just read the original article in Electric Radio magazine, describing NR5Q’s “Ultimate Regen”. There is, of course, no definitive word on whether it is indeed the best regen out there, but I took heart from the following quote by Bruce,
“Before we go any further, if you are a SSB operator you may be wasting valuable time. While I listen to SSB all the time on my ‘regens’ I would not want to try to operate a SSB station using nothing but a homebrew regenerative radio – that would be an exercise in futility.”
The above quote comes from a gentleman who built over 60 regens and authored many articles in the pages of Electric Radio. His words mirror my experience with The Sproutie, and further cements my belief that, as far as regens go, this one is pretty darned good. I love listening to AM on it, really like listening to CW on it, and although I can listen to SSB on it with little difficulty, I’d rather listen to SSB on a superhet with a product detector.
9 thoughts on “Does The Sproutie Regen “Work” On SSB and CW?”
Four practices can minimise oscillator pulling in regens:
1. Maximise tank capacitance at the desired reception frequency by reducing L and increasing C as far as possible (however, if tank C is too high, oscillation will not be possible). This minimises the effect on the resonant frequency of varying parasitic capacitances (see below).
2. Couple the tank to the active device as lightly as possible. This minimises the amount of parasitic junction capacitance that the tank “sees”. Light coupling can be done by connecting the active device not to the top of the tank but instead to a low-impedance capacitive or inductive tap.
3. Use active devices with low junction capacitances like VHF or UHF devices.
4. As you’ve already discovered, limit the signal amplitude in comparison to the oscillation amplitude to inhibit phase-locking.
Thank you qrp-gaiijin. Your input is always welcome and much appreciated,
Another interesting possibility is to use automatic gain control in the RF stage to automatically reduce the RF gain on strong signals. This should theoretically automatically reduce the frequency pulling. Here are some links if you want to pursue this method:
Very nice article, Dave. I have only built one Regen (TenTec 1253) but it was an enjoyable process, and I found the same thing as you – different bands/modes require varying the AF settings. Haven’t gotten good with it because I only use it occasionally, but you are inspiring me to pull it out and play a bit – good project for the new year!
Just a quick note to thank you for the ceramic resonator info and circuit. I did buy a few, and look forward to playing with them. Thank you for sharing this with us. Hope you will have some more time to get on the air this year.
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Rob – I still think of you as KD7KAR – the call you had when we had those QSO’s in which you were using your FET regen as the receiver. I loved those contacts – the magic of knowing my signal was being received by an MPF102 and a handful of discrete components. It was magic. Hope you’re doing well, and have fun with those resonators. Hope we hook up on the air again soon. I need to forsake the SW BC bands for a while and get back to the ham bands!
Nice read. I built my version of the NR5Q Ultimate getting on for 10 years ago. My second regen effort after a Kitchin SS type. Much effort went into the mechanical construction of The Ultimate, and it tells. Rock steady.
Henrik – thanks for commenting. I am curious about the NR5Q Ultimate Regen and have a question for you about it. I’ll e-mail you soon (assuming that your gmail address on QRZ is current).
Thanks Dave, I enjoy your blog. The recent postings on regenerative receivers reminded me of the radios my father, an early 1930’s radio technician, used to make for me when I was an impoverished student. I think they also used to transmit a weak am signal which my landlady didn’t enjoy. I still remember the balancing act of achieving maximum performance just before it broke into screaming oscillation (and an irate landlady). I have had some success with hanging DC receivers off the VFOs of QRP transmitters I have made. The performance was never as good as that of my main station RX but you could offset that with the warm glow of satisfaction of knowing you had designed and built it all yourself. Regards. Tony G (VK3CAB)