An Improved Superhet for WRMI reception
This, hopefully, will be a "new and improved" version of the simple superhet for reception of WRMI that was previously shown here.
Improvements will include wider range frequency coverage, better image rejection, and improved selectivity, achieved principally by changing from a single down conversion to an intermediate freque3ncy of 455 KHz, to a dual conversion up converting to 10.7 MHz as the first intermediate frequency.
With the use of a simple low pass filter as the front end, reception from the broadcast band to seven MHz or so should be readily accomplished. Images will be in the range above 22 Mhz so unlikely to present any issues, and a crystal filter at 10.7 Mhz will establish the initial selectivity ahead of the second IF.
Construction has begun. The Front end filter, mixer, and second conversion local oscillator are complete.
A TDA1072 again is used as the main device of the…
After experimenting with this off and on, I think the best way to utilize the aspect ratio of the 0.96 inch TFT screen, is a tape rule analog dial. This gives a nice fluid motion of the dial increments and looks right on the short screen.
Sadly my cheap phone does not reproduce the colors well. The frequency readout is a golden yellow, the memory/vfo indicator is Grey. The large ticks are green, the minor ticks white, the fiducial red. The s meter is green up to s9, then turns red about +10. The s meter units are Grey, then red above s9. The s meter has a very nice movement.
This has turned out to be a nice radio; I have been using it on a daily basis and it is well suited for that purpose. It has good sensitivity, good selectivity, good AGC, excellent recovered audio, and enough convenience features to make you feel like you're not driving around in an old econobox.
Win W5JAG