Instructions for modesl DFD1-A/B/S/Hamm/National/Drake/Swan
 

Digital Frequency Display 1                                       DFD1S display

A miniature digital frequency counter designed to display the frequency of operation of HF, VHF, UHF and SHF
superhetrodyne (with an adjustable IF offset) and direct conversion (without offset) receivers and transmitters. Also can be used as a bench top frequency counter or built into other test equipment. Usable to 40 MHz. (8GHz with an external prescaler)

The unit uses a PIC16C71 microcontroller which has a built in A/D converters connected  to 15 turn trimpots. These trimpots are used to input a frequency offset, usually equal to the IF frequency of the receiver or transmitter, and other functions described below.

• DFD1/S (0-16.384 MHz) DFD1-S has S meter in display.
  • Trimpot (1) Fine offset in 1KHz steps
  • Trimpot(2) Coarse offset in 128KHz steps
  • Trimpot(3) Multiply (multiplies frequency and offset by 1 to 256)*
• DFD1A (0-20.971,520 MHz)
  • Trimpot (1) Medium offset in 1280Hz steps
  • Trimpot(2) Coarse offset in 163,840Hz steps
  • Trimpot(3) Fine offset in 10Hz steps
• DFD1B (0-200.971,520 MHz)
  • Trimpot (1) Medium offset in 128KHz steps
  • Trimpot(2) Coarse offset in 163,84KHz steps
  • Trimpot(3) Fine offset in 1KHz steps
• DFD1-Hamm (for Hammarlund Radios)
  • Trimpot(1) Tweek Low
  • Trimpot(2) Tweek High
  • Trimpot(3) Model set
• DFD1-National (for National Radios)
  • Trimpot(1) Tweek Low
  • Trimpot(2) Tweek High
  • Trimpot(3) Model set
• DFD1-Drake (For Drake Radios)
  • Trimpots are not used or provided with the kit.
• DFD1-Swan (For Swan Radios)
  • Trimpot (1) IF frequency of your radio.
  • Trimpot (2)/(3) not used or provided in kit

*(IF and RF resolution is degraded by the value of the external divider N). IF  resolution=N*1000 Hz, RF resolution = N*10/100 Hz.

The unit then measures the Local Oscillator frequency and adds or subtracts the IF frequency offset. The result is a display of the actual receive or transmit frequency.

The unit has two discrete inputs (open circuit or ground) from which the user can change it's function.

• For DFD1/A/B/S
  • Bottom) ADD/SUBTRACT causes the unit to add (jumper off) or subtract (jumper on) the offset from the measured frequency. This input can be remoted from the bandswitch of band-imaging receivers/transmitters to provide correct frequency display in both bands.
  • Top) 10/100 Hz causes the unit to display with 10 Hz resolution (jumper off) or 100 Hz resolution (jumper on).
• DFD1-Hamm/National
  • Bottom) Enable Tweek Mode
  • Top) 10Hz/100Hz resolution
• DFD1-Drake
  • Bottom) R4/TR4 (off for R4, on for TR4)
  • Top) 10Hz/100Hz resolution
• DFD1-Swan
  • Bottom) 80 and 40Mtrs / 20, 15, 10 Mtrs or Normal/Rev depending on radio IF frequency selected.
  • Top) 10Hz/100Hz resolution
• DFD1/A/B
  • MODE is an additional A/D input programmed by and external resistor (or switched resistors) to display an operating mode . The modes that can be displayed are AM, FM, CW, USB, LSB, FSK, FAX or 'blank'.
• DFD1S this input is the S meter. (0-3.5V full scale)  You must provide signal conditioning to meet this range requirement)

The correct RF frequency is displayed regardless of the relationship between LO, IF and RF frequencies. The RF can be above or below the IF frequency and the LO can be above or below the RF frequency.

DFD1 assembly instructions with built-in TCXO

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