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- Solid State RadiosOn the old Radioboard the circuit which I posted which had the largest response was a regenerative medium wave receiver using only an LM386 audio amplifier chip. The front end of the LM386 was configured as a Colpitts oscillator using the intrinsic Base-Emitter capacitance of the input transistors and an external 220pF capacitor. The tuning inductor used is a standard MW ferrite rod inductor and the tuning capacitor is a PVC MW 2 gang variable. Because the gain of the LM386 used in these configurations is so large care should be taken to use short lead lengths and a ground plane would be preferred. Using a 9v supply a speaker may be driven to a comfortable volume with the MW version. Regeneration could be controlled in a number of ways. In the simplest version reducing the value of the 1K regen variable resistor increases the audio gain, but reduces the regeneration. Increasing the value the opposite occurs. The three other methods of controlling the regeneration include a 1 mH choke which isolates the RF gain from the audio gain. Audio gain may be varied by adding a 100 Ohm variable resistor in series with the choke. Changing the DC operating point of the LM386 with the regen control inhibits the oscillation. These alternate methods can be tried if the technique used in the simplest versions of both the MW and SW receivers proves to be inadequate. The shortwave version is basically the same as the medium wave version except for the values in the tank circuit and the omission of the 220 pF capacitor. The intrinsic capacitances in the front end of the LM386 provide the proper ratios for Colpitts oscillation at SW frequencies. Using a 9V supply and chips from National or Samsung the SW version functioned well to over 8 MHz which includes the 80 and 40 meter amateur bands. Using a ferrite rod with 20 turns no external antenna is needed to receive a considerable amount of activity on the SW bands. The links below are videos posted by a radio amateur who built an earlier version of the MW receiver. youtube.com/watch?v=-UCACxbQS1U youtube.com/watch?v=PTWd82KI53sLike
- Solid State RadiosI've been thinking about building the LZ1AQ loop amplifier described here: https://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm . Does anyone have experience with one? It seems to get good reviews and looks not too difficult to construct. I'm trying to lay out the parts placement now in Blender for point-to-point wiring. I have a simpler 2-transistor design (M0AYF) built, but the gain on that antenna is a bit too low for my needs. I hope to use the LZ1AQ antenna in combination with my RTL-SDR + HF upconverter, which has been lying idle for a while.Like