ANTENTOP- 01- 2010, # 012

Some Thoughts on Regenerative Receivers

Note from Wiki: The Hartley oscillator was invented by Ralph V. L. Hartley while he was working for the Research Laboratory of the Western Electric Company. Hartley invented and patented the design in 1915 while overseeing Bell System's transatlantic radiotelephone test. It was awarded patent number 1,356,763 on October 26, 1920.

Figure Credit Line: Wiki

3. Smooth regeneration. This is the hard nut to crack. There is no really good answer here, in my opinion. This , plus the interaction problem was one of the major reasons for the decline in popularity of the regenerative receiver, as well as reduced component costs which made superhetrodyne receivers practical. However, a well regulated power supply to the regeneration stage helps a great deal. A Zener or comparable regulator in transistor circuits, or gas discharge tube for vacuum tubes will work well. I note that one commercial regenerative receiver simply uses a separate 9 volt battery for the detector, and a second for the audio amplifier.

Now, keeping in mind the "simplicity" issue, we can see where these fit into our design process.

The decoupling of the tuned circuit from the antenna serves two purposes. First, it reduces the interaction of your antenna with the detector tuned circuit. If you have ever hooked an antenna analyzer to a random wire antenna, the impedance is all over the place. Investment in a good antenna tuner, such as the MFJ-16010 is money well spent. Of course, a home-brewed tuner is also feasible, either built-in to the receiver, or as a separate unit. Any of the the "QRP" designs will do the trick. The coupling of a resonant antenna into the detector can often lead to "dead" spots in tuning. Hence, the advantage of isolating the antenna from the detector with a "front end."

There is no need to have this front end tuned, but just to keep the antenna interactions from the detector, and reduce or partially prevent radiation from the oscillating detector from producing QRM for other radio users in the vicinity.

When running in "oscillation" mode, or close to it, a regenerative detector is its own little QRP transmitter! For domestic and neighborhood tranquility, the isolation amplifier greatly reduces radiation back into the antenna. It is not perfect, and my two commercial kit regenerative receivers make an impromptu signal generator in the ham shack when needed. An "RF" gain control can be easily introduced to reduce the strength of incoming strong signals, such as some of the major SW stations, like Radio Havana, or the PRC stations.

Along with the simplicity issue, the design for convenient band switching of the detector's tuned circuit is a hassle. If the "tickler" design of the classic Armstrong set is used, then there are either two or three coils that have to be switched. This means at least a three-pole n-throw switch if there is a "primary" coil to the antenna. Three of the six coil points are "ground" for RF, so only a three pole switch is needed. If a coupling adjustment capacitor is placed on the primary side to ground, then at least four points are "hot" for RF. These switches are not only complex, but they are expensive and add a large measure of complexity and increased size to the receiver. There are at least two common alternative solutions:

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