DFD4 / DFD4A assembly instructions.

(DFD4A has no offset capability and is for test equipment only)

	Begin by placing solder globs on the four rectangular pads for the surface mount TCXO.
	Carefully Position the TCXO with pin 1 as shown and remelt the solder globs while pushing down on that side of the device until all four pads of the TCXO are soldered.  You can check by looking at the edge view to verify that solder has flowed onto the TCXO terminals.  If later the unit shows only 8 black squares on the display it may be because one or more of these terminals did not properly reflow solder.
	Next mount the IC sockets and display header.
	Next install and solder all resistors and the two back to back diodes.
	Then install and solder all capacitors and the 78L05 voltage regulator.
	Then the two 2 pin headers.  The one next to the 18 pin socket is always installed.  The one next to the 8 pin socket is installed only if you DO NOT intend to use it as test equipment.
	On the back side of the PCB install and solder the 10K contrast control (adjust it fully CCW) and the 25K calibration control. Later when assembly is complete calibration consists of connecting the unit to a known accurate frequency, or by zero beating the TCXO against 20MHz WWV, and  adjusting this 25 turn pot.
	Next install the green 15 turn trimpots.  (these are not included or used with DFD4A). Install the fourth trimpot if DFD4 is NOT going to be used as test equipment.
	Mount the 14 pin female header on the display module soldering only one pin.  Then verify the connector is at a right angle to the module, remelting the soldered pin and adjusting the connector if necessary.  Then solder the remaining pins. Plug the module into the DFD4 PCB.   At this point you can plug the counter board into the module and power them with a 9 volt battery. You should see something displayed momentarily such as "FAST HF" then a frequency.  What you see at this point is not important as some inputs are still floating until final assembly in your enclosure. If so, you are ready to proceed to final assembly in your enclosure. When used as test equipment, wire the unit to the external controls using the connection diagram below.

Setup

MODE

• The mode input is actually an analog voltage dividing the 5V supply into four parts. Each part represents a mode.  The analog voltage is developed by a trimpot unless the unit is configured as a bench top frequency counter. When configured as a bench top counter it is developed by a two bit D/A converter from panel switch contacts.
• The unit displays the mode momentarily whenever it is changed. When using a trimpot, adjust it until the desired mode is displayed and then continue to turn it one additional revolution for thermal stability.

OFFSET

• The offset is input via three 15 turn trimpots which represent a 21 bit number. FINE is bits 0-6, MEDIUM is bits 7-13 and COARSE is bits 14-20. This 21 bit number is multiplied by 1KHz to produce a maximum offset in excess of 2GHz.

• Offset should be setup with the HF input shorted to ground to prevent noise from being counted.
• Jumper between HF input and prescaler output must be removed first.
• Optionally, remove the 74HC4046.
• Start Fully counterclockwise on all trimpots which should be zero offset. Adjust each trimpot for minimum displayed frequency.
• Set COARSE to display the value just below the desired value.
• Set MEDIUM to display the value just below the desired value but closer to it than COARSE could provide.
• Set FINE to display the desired value.
• Set the ADD/SUBTRACT jumper as required by your application.
• This jumper does nothing if the offset is zero for a bench top frequency counter. Adding or subtracting zero does not change the answer.

CALIBRATION

• There are many ways to calibrate a frequency counter depending on available test equipment.
• The simplest is to zero beat a signal generator agains WWV (receiver bfo off) while measuring the generators frequency with the counter.
• Adjust the 25 turn trimpot on the back of the PCB to obtain the WWV frequency (20 MHz) on the counters display.
• Or listen to TCXO on receiver while zero beating it to WWV on 20MHz.

• Any other KNOWN frequency can also be used.

$59.95 (backlit display option add $10)

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