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Thread: homebrew single transistor regen (with a stupid resonance question)

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  1. #11

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    OK, yes I think you have a Armstrong regenerative radio there, but it certainly isn't designed for optimum performance, IMO. Still, what you are doing is providing yourself with some wonderful and interesting experiments and it's teaching you many things.

    Yes, I suggest you copy an existing HF design when you go to make up a "real" radio and go from there. However, you do have many of the elements already.

    If you want to continue to experiment, here are some suggestions:
    The way you "couple" (or don't couple) the antenna to the tank circuit won't work at HF unless your antenna is really short because there will be too much capacitance in the circuit. You really need to couple the tank circuit to the antenna using a small value capacitor or (better yet) an antenna coil that is inductively coupled to the tank circuit.

    The way you are controlling the regeneration and tapping off the audio is not really very good.

    In the old days, the regeneration control was called the "throttle" and "throttling" is still best done with a variable capacitor. I would suggest removing R1 and R2 from their present locations, put a 1-2 MH choke coil in where R2 is now, discard R2, put a variable "throttle" cap between the top of the tickler coil and ground for smooth regeneration control and then relocate R1 so it's between the choke coil (opposite the tickler coil) and the battery. Tap the audio off at R1 using the blocking cap C3 as shown.

    Have fun.
    Last edited by WA6TLP; 09-14-2011 at 07:13 AM.

  2. #12

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    Quote Originally Posted by WA6TLP View Post
    The only thing I would suggest (as I state at length in my article), stay away from Mr. Kitchen's so-called "Scout Radio."
    The "Scout Regen" actually is a variant of Kitchin's "High Performance" JFET design using a tickler and throttle cap. Its manual can be seen here: http://www.qrpkits.com/files/Scout_Regen_v1.2.1.pdf . The other design, that you described in your web page as having poor performance, appears to be called the "beginner's receiver" or, in the case of your PC board, the "Scout Beginner's Receiver".

    The high performance regen is also viewable here: http://www.electronics-tutorials.com...o-receiver.htm . That article also has much good advice about proper construction of a regenerative receiver. I followed that article's advice closely and have a good working regen as a result (works even up to 30 MHz).

    Now if you want to go for even higher performance, do visit the regenrx group mentioned already. There was a recent discussion there about using a separate detector stage (placed after the Q multiplier) for increased dynamic range. You can also use varactors for tuning and throttle control, which allows all RF leads to be kept very short (very important in a regenerative receiver).

  3. #13

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    In the old days, the regeneration control was called the "throttle" and "throttling" is still best done with a variable capacitor. I would suggest removing R1 and R2 from their present locations, put a 1-2 MH choke coil in where R2 is now, discard R2, put a variable "throttle" cap between the top of the tickler coil and ground for smooth regeneration control and then relocate R1 so it's between the choke coil (opposite the tickler coil) and the battery. Tap the audio off at R1 using the blocking cap C3 as shown.

    Thanks!, I'll try that. I'm really glad I decided to start with AM broadcast before trying any HF; the signal is lower frequency and much stronger, so it had a better chance of working. I just found this http://www.circuit-projects.com/radi...-polarity.html which is close to what you're talking about. I guess need to get another variable capacitor so I can control regen! (make it 2, since the variable capacitor I have now for the tank is 'junk')


    After reading a lot of the comments, I'm seeing a lot of your guy's suggestions in other circuits, such as coupling antenna to tank circuit through a capacitor, etc.


    I have a million-and-one questions, but I think I'll settle for just a couple:


    - I've noticed, is that I see many AM and shortwave designs with ticklers, but none for FM broadcast with ticklers. Is it just impractical? FM receivers have small coils, so I don't see a 5 turn air core coil next to a tickler really working as well as a 40 turn coil does with AM.


    - How does this design oscillate? http://www.vk2zay.net/article/file/360 I've seen some where the coil is tapped, and some feedback is introduced that way, but I don't quite get how it works here. http://www.ke3ij.com/am-univ.htm is also similar, but the tank is off the emitter instead of the base. (I may end up using KE3IJ's design, since it seems it can scale from AM broadcast up to aircraft, which means maybe I can use the same circuit and just swap out parts of it to make a simple multi-band radio.)

    Again, thanks everyone!

  4. #14

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    Quote Originally Posted by KJ6LRG View Post
    ...
    - How does this design oscillate? http://www.vk2zay.net/article/file/360 I've seen some where the coil is tapped, and some feedback is introduced that way, but I don't quite get how it works here. ...)
    There is enough unneutralized interelectrode capacitance to allow the amplifier to go into oscillation.

    I looked over the links to the "high performance regens" and they are essentially identical to what I built with just some variation in part values and the addition of a biasing diode in my design. These designs are proven to work and if you can get the circuit board instead of having to 'gin one up like I did with a diamond burr, it will be so much easier and may even work better (although mine works just great). If you can get it as a kit - even if it's a little pricy, you will save a lot of time, disappointment and frustration AND money by getting the kit.

    Remember this though, if you do build one of these high performance regenerative radios, you will learn a lot, you will feel a very special kind of well-earned pride, you will gain a lot of satisfaction listening to broadcasts on your own radio and, if you are hard-core enough, you may even use the radio in conjunction with a homebrewed transmitter to make a few QRP contacts on CW now and again. One thing you will never have is a really good ham band radio that works even as well as a 1940 Echophone EC-1.

    Good luck and have fun.

  5. #15

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    If you do go ahead and build a high performance regen, I highly recommend that you not solder the transistors directly into the circuit, but instead place them in plug-in sockets (IC sockets or similar) so you can swap them easily. Regens are rather critical to build and there are many possible sources of poor performance (overcoupling the antenna, too much feedback, parasitic oscillations, stray capacitance, wire lengths, ground loops, mechanical stability, thermal stability, voltage regulation, device bias, etc). Your transistors can also be a source of trouble if you happen to get a noisy or otherwise poorly-performing one. By being able to swap out your transistors easily, you can quickly determine if poor circuit performance is caused by your transistors or not. I spent too long on one regen trying to track down poor perfomance, that turned out to be due to two noisy transistors (RF amp and detector). Since my transistors were soldered into the circuit, it was troublesome to swap them so I instead wasted much time investigating all sorts of other possibilities before narrowing down the problem to the transistors.

    Also, don't underestimate the importance of layout, wire lengths, and physical stability (of tuning mechanism and coil). These become particularly important as you approach VHF.

    Your idea to build a wide-range multi-band radio based on KE3IJ's "universal regen" is something I've also pondered. Do let us know how it goes. You might find it easier to use the alternate design of KE3IJ's "40 meter tweeter" which does away with the emitter choke and basically replaces it with a resistor.

    Here's another possibly interesting design that covers 4.5 through 50 MHz.
    http://www.sparktron.com/pbox.html (see item number 28-110).

  6. #16

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    I've been building transistorized projects since the 2N107 days of the late 50's and I've never had a project fail to work because of a bad transistor nor have I ever wished I had put them in sockets.

    Of course, I've always bought premium quality devices where there was no doubt as to to their actual type.

    The advice on the importance of layout is good. If you lay things out well, the probability of having all the problems mentioned in QRP-GAIJN's post should be minimal when building something as simple as one of these regenerative radios. When I had all my problems with the "Beginner's Scout" radio, perhaps they were do to some of this, but when I changed design to the straight forward Armstrong type regenerative radio, using a tickler coil, but keeping the component layout essentially the same within the same box, everything then worked smoothly and well.

    I guess the moral is: stick with a robust design that is straight forward and does not require hand-picking parts in order for it to work properly. Avoid designs or abandon designs that are "squirreley" where regeneration control is not smooth and you get beeps and hetrodynes where they shouldn't be. If you go with something like Kitchen's "High Performance" radio (my radio is essentially that radio), you can't go wrong. Just be sure you avoid anything like the "Beginner's Scout" radio.

  7. #17

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    Thanks! Yeah, I'll stay away from the scout regen.

    Soon it'll be time to stop tinkering with this on a breadboard and start solding it together. I have seen Youtube videos of FM receivers working on a breadboard, so I may want to try it there first, but I know I won't have solid performance until I move it onto a proper circuit board.

    So, I have another question for you (WA6TLP). You suggested I put a choke between the tickler and the battery. Why? I see the same thing on Harley oscillators as well: http://www.electronics-tutorials.ws/...r/hartley.html (Scroll down to shunt-fed hartley)

    The version of the Hartley that makes more sense to me is 'Basic Hartley Circuit' which is higher up on the same page: The base is biased the same way I'm currently doing it (resistor network between battery and ground), but what confuses me is the resistor and capacitor on the emitter. Do I even need that? The resistor on the collector should limit the current safely. What performance improvement is made by doing that instead of just grounding the emitter?

    In many designs I see a choke put in between RF and audio stages; this makes sense to me. The choke on KE3IJ's radio is right before the output to the 'radio shack' speaker. (Which, BTW is the amplifier I'm using in all my experiments so far! That little speaker is pretty handy. My dad has one I remember from when I was a kid, and I was surprised to see RS still sells them, so I picked one up real quick!)

    This Saturday in the garage is going to be pretty fun!


  8. #18

    Default Regens

    I can certainly suggest Kitchin's high performance regen as a good build candidate, even I managed to get one going some years ago with VERY little electronics experience. I dig it out from time to time, it's a hot performer!

    For FM broadcast band, I can recommend the "Radioshack Special". Google it and don't be put of by the name and inferred quality.

    de VK2HHS

  9. #19

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    "You suggested I put a choke between the tickler and the battery. Why?"

    Hummm, how can I explain this simply and without a diagram?

    FET_RegenS.jpg

    OK start by marking up your schematic as I have suggested or reference my schematic above. Now looking at the schematic you will see that the collector of your NPN (or the drain of my FET) is connected to the bottom of the tickler coil. With me?

    This is so that currents flowing in the collector (or drain) must flow through the tickler and thus affect its magnetic coupling to the tank circuit. OK?

    Now consider this, in order to couple the signal back down to the tank circuit so the circuit can amplify through regeneration or (with enough feedback) go into self-oscillation (for CW and SSB), RF current must be able to flow through the tickler coil (in addition to the normal DC collector current) so that it can be inductively coupled to the tank circuit. OK?

    The amount of RF current flowing through the tickler must be "throttle-able" which means that you must be able to carefully control it and we do this throttling by increasing or decreasing the bypassing that is performed by the throttle capacitor. Think of it this way, without bypassing to ground at the top of the tickler coil, no RF current flows through the coil to ground (DC flows, but no RF). The more capacitance, the more bypassing, the heavier the RF current will be flowing in the tickler, the more will be coupled down to the tank circuit and the more the circuit will "want" to oscillate. Does that make sense?

    Now, without a choke coil in the DC path to isolate the top of the tickler coil and prevent bypassing by the battery (which is an excellent bypass in itself) or by components in the audio circuit, lots of RF current will flow in the tickler and that get coupled to the tank circuit and you won't be able to stop the circuit from oscillating. In effect, the circuit will run wide open and your throttle capacitor just won't do anything, you will have just too much RF bypassing.

    Here's the magic of the choke. The choke blocks all the bypassing by the other circuit elements and the only thing that the top of the tickler coil sees is the throttle's bypassing to ground -- and you can control that. You absolutely need a choke coil right there to block unwanted bypassing to ground by the follow-on circuits. Does any of that make sense?
    Last edited by WA6TLP; 09-16-2011 at 05:15 AM.

  10. #20

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    "what confuses me is the resistor and capacitor on the emitter. Do I even need that?"
    Probably not unless the audio is tapped off there, which it is in many designs. You will see that in my diagram, the equivalent source circuit is where I tap off my audio. Assuming your audio is not tapped there and you are using an NPN bipolar transistor in this circuit, bipolars are notorious for going into "thermal runaway" and thus a conservative design calls for additional biasing circuits in the emitter circuit. You are probably running extremely tiny currents through this transistor with minimal chance for thermal runaway, so my guess is that it probably isn't needed. That's my take on it anyway.

    I hate working with bipolars and love working with FETs. Part of that is because they are so much more like the wonderful vacuum tubes of my youth. Still, in many ways, FETs are easier to work with.
    Last edited by WA6TLP; 09-16-2011 at 05:19 AM.

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