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Programmable 50 MHz
Counter - Resolution 100 Hz
Joachim Münch DF4ZS - Goedeke Michel Str. 27 c - D 26434 Wangerland - Tel.: 04425 - 271002 email
... Tel.: 0049-4421-51777 ...
The frequency counter described here was built up using the "sandwich" construction and uses low cost components. It consists of three standard 0.1" raster pad boards. All ICs – except those placed under the LCD – are mounted on sockets. The counter may be programmed – by means of jumpers – to any intermediate frequency above or below the actual operating frequency. It only shows the „kHz“ and „100 Hz“ digits; all other digits will not be displayed. Refer also to the LCD shown below; it really displays a frequency of .106 600 MHz. You may use this counter as a replacement for an analog frequency scale. The whole counter has been realized using the so called „ugly construction“ with isolated copper wires instead of printed conductors. The pin connectors for the addressing (programming) are equipped with a cover, which serves as an extra mechanical stabilizer. Some components are SMD types. The total component price in Germany is about 20 € (equivalent to about 20 US-$). Skilled amateurs might be able to build this counter within about 40 hours. My offer to you (if you need it!): At a small extra fee, I can build it for you – please contact me via Email.
Circuit Diagram, Programming Scheme, Photos.
Programming the Counter.
1.) The i.f. of your equipment is
10.700 000 MHz. You want a display offset of „700.0“; this has to be converted
into its binary equivalent
(7 = 0111). The remaining jumpers have to be fixed to a binary „0“, which means in this case a ground connection!
2.) The i.f. of your equipment is 12.345 678 MHz. You have to ignore
the „MHz“ digits as well as the two least significant digits.
The binary code for 345.6 then is 3 = 0011; 4 = 0100; 5 = 0101; 6 = 0110
By setting the jumper J00 to „0“ = ground (this means „count up“), the LCD will show the programmed preset value as long as there is no input signal to the counter. No value at all will be displayed, if you set the jumper J00 to „1“ (this means „count down“).
Operating frequency is 7.050 0 MHz and the i.f. is 456 kHz. This would mean a VFO frequency of 7.506 0 MHz. In order to get the „correct“ readout, you have to program the counter as follows:
a.- 1000 – 456 = 544.0 – converted into the binary equivalent: „0101 0100 0100 0000“.
b.- Jumper J00 set to „Count up“ = „Ground“.
Without input signal the LCD will display a value of 544.0.
The operating frequency again is 7.050 0 MHz. The VFO shall work at 456 kHz below this QRG – that means a VFO frequency of 6.594 0 MHz.
a.- Set the programming pins to 456.0 – binary equivalent: „0100 0101 0110 0000“ and
b.- Select „Count up“ (Ground) at J00.
Without an input signal to the counter the LCD will display 456.0.
Operating frequency (F_RX) is 3.650 0 MHz. The i.f. is 9.000 0 MHz and the VFO delivers a signal at 5.350 0 MHz. You have programmed the counter to 000.0 and Count down.
a.- F_RX = 3.500 0 MHz. The VFO has to deliver a signal at 5.500 0 MHz. The LCD would show (correctly!) a value of 500.0.
b.- F_RX = 3.600 0 MHz. The VFO works on 5.400 0 MHz. In this case the „difference“ of 100 kHz would be correct, but the direction of counting were wrong.
Consequently, you had to set J00 to „Count back“, which means that you have to set it to Vcc = +5 V in order to get the correct readout of – in this case – 600.0.
Home return email aktualisiert 13. August 2009