Hi Lex,
Thanks for adding to the information about the FRU-7 display. I have previously contacted you off list about buying the unit.
I gave to much credit to the 70's technology in my first post. The MHz digits could be derived by subtracting 3 from the H.GEN MHz signal.
Looking at the Block Diagram on page 8 of the FRG-7 manual. The FRU-7 must be counting the 3 - 32 MHz output of the H.GEN and subtracting the VFO frequency. Then the counter circuit must have a preset of .455 MHz that adds to the sum above. For example when tuned to 10 MHz:
H.GEN output is 13 MHz and the VFO is 3.455 MHz (13 - 3.455 = 9.545). Then add the IF frequency of .455 MHz to the above and you have 10 MHz. The FRU-7 doesn't display the MHz digits and shows .000 on the LED's.
It should be a more accurate display, on the upper bands, because the 1 MHz crystal doesn't have a calibration trimmer and any inaccuracy will show up as you increase the receive frequency. For example if the 1 MHz is off by 100 Hz the H.GEN output would be off by 300 Hz on the lowest band and 3,200 Hz on the highest band. Because the FRU-7 counts the H.GEN and VFO frequencies and the VFO can correct for the H.GEN offset the FRU-7 should show .000 when tuned to WWV.
73
Roger VE7LB
