Well, found that a bad scope probe can be a big problem when trying to understand things…LOL. Since replacing the bad probe, I discovered that the LO is working fine, have just over a volt coming out and going to the Product Detector. The RF input section still bothers me but it seems to be working as it should. However, the RF Phase Shift inductor (molded inductor) may be a problem, so after looking at things, I am going to take Mark’s advice and try a torroid. This may help recover some gain I seem to be losing. I get a three fold gain in voltage (317mv input/922mv output) from the RF Amp…but this varies as the input signal decreases in amplitude.
I have thought about incorporating some type of feedback for the RF Amp section to help maintain the RF level from the input to the Product Detector. I can hear a signal with -50 dBm input, but any less than that and I lose all AF going to a speaker/headphone. I should be able to use half that value of input signal and still hear a signal. I am thinking after I try swapping a torroid for the molded inductor, I may switch to a single signal type detector or pop a NE602 in-place of the current front end and see what I get. Since I wouldn’t be able to hear the binuaral effect anyway (due to being deaf in one ear), I might as well move on and try other ideas.
I built a 40 meter NE602 receiver a number of years ago and it was fun and simple. I may use the LO from this project and incorporate that receiver into a single signal receiver. I want to make up one 80 meter LO and one 40 meter LO on separate PCB boards to have on the bench for future use. All in all, this has been a fun and thought provoking exercise. I need to keep a focus on little things that can affect the overall success of the project (Thanks Mark of helping me learn this!), and remember to check my measurement methods to ensure they are sound and accurate.
I will probably have one more update after this and then move on to another project involving a remote terminal for my PHSNA.
