I have been working on a TRF receiver that I posted about in another thread. Figured on starting new thread as the old one was a bit long.
Here's the schematic. The local/distant switch is not present as I doubt it will work. Also the antenna preamp is not completed yet with the antenna connecting to the primary of the first RF transformer.
I hav a problem of low sensitivity using two TRF stages.
I took some measurements last night. I do not have a proper scope probe so I just used a regular wire which could have affected measurements somewhat.
550 KHZ signal at tuning cap of first TRF stage
550 KHz signal at ptimary of second RF transformer
2 MHz signal at tuning cap of first TRF stage
2 MHz signal at primary of second RF transformer
Any ideas as to what the problem could be?
I wonder if maybe I need to use a choke in the source circuit of the FET and just capacitor couple the RF transformers like in the following schematic?
I tried to connect a 6800 uF cap to the 12 volt power wires rto the amp board (where main 12 volt power for whole receiver is connected) and got a low frequency oscillation. I then tried the same capacitor from the regulator output to ground and got oscillation. I am thinking there may be some coupling in the power supply as when I turn up the volume control nearly all the way with no signal being received I get a higher frequency oscillation.
Would it be a good idea to insert a resistor in series with the 12 volt power wire to each regulator and then use a filter cap after the resistor to further isolate each stage's B+?