Thursday, November 19, 2015

Simpleceiver ~ Part 13

Second Generation Simpleceiver

This post is to let you hear how the Second Generation of the Simpleceiver sounds in operation. What I have done is to mate the front end of the 1st generation Simpleceiver consisting of the RF Amp Stage, homebrew Double Balanced Mixer, Post Mixer Amp and three pole Crystal Filter. Using this part it was "haywired" to the new J310 Product Detector, J310 BFO and the NE5534 + LM380 Audio Amp. Ahead of the 1st generation board sandwiched in between the RF Amp and the homebrew DBM, I installed the new Band Pass Filter. Take a listen how quiet it is between stations.
I did make a modification of the interface between the J310 BFO and the J310's that are connected in Cascode. On Gate #2, I have added a 22K resistor to ground and connecting the two modules is a 100 NF cap. A revised schematic is shown below as well as the plot of the output. These changes were made to accomplish two things: 1) the BFO loading is improved and the BFO now reliably oscillates every time the power is applied and 2) the overall gain of the Product Detector is improved. I found a condition that you need to tweak the BFO trimmer cap so that the signal was placed properly on the slope of the 3 pole Crystal Filter. But once you powered the circuit down there were cases where upon application of power the BFO Oscillator would not oscillate. This now has been cured.
Special Note: In the hardware configuration a Broad Band Matching Transformer is connected to Gate #1. The primary is 3 Turns and the secondary is 20 Turns on a FT-37-43 Ferrite Core. The 3 Turn winding is the input and the 20 Turn winding is connected directly to Gate #1. If we do the math the Z in is 50 Ohms and the input to Gate #1 is forced to 2.2K. 2.2K/50 = 1:44. The match is based on the turns ratio squared. 3^2 =9 and 20^2 = 400. 400/9 = 44.44. This this is a close match.

Pete N6QW