K5SYN - With the gracious permission of George N2APB, and AmQRP, we've been allowed to use pictures and other information from their website. Copyright is reserved by George N2APB, and AmQRP.org.
A Replacement for the Original VFO
We suggest visiting the makers of the DDS-60 at AmQRP.org to obtain the most up to date information and to order this item.
|DDS-60 Top||DDS-60 Bottom|
- Power requirements: 8-12V DC at 130 ma (typical).
- RF Output – fully adjustable to +16 dBm, or about 4V p-p into a 50-ohm load.
- Output signal not affected by varying +V supply voltage – great for battery operation. |
- Near-constant output level from 1-60 MHz. (1.8 dB droop due to sinx/x sampling theorem)
- Good signal purity – harmonics down approximately 40 dB from the fundamental.
- Pin-compatible with the original DDS Daughtercard module
- Only few changes needed in existing AD9850 software drivers
TAK-40 DDS 60 Interface
Here's how the TAK-40 firmware drives the DDS-60…
The DDS-60 uses a 32 bit tuning word and a clock frequency of 180 MHz
which gives us a native tuning step of 180 MHz / 2^32 or .04191 Hz
which is a bit fine for most ham radio applications.
I decided to keep the least significant byte set to 0 which means the
TAK-40 takes .04191 * 256 or 10.729 Hz steps. The TAK-40 keeps track
of 15 bit tuning words so the tuning range is 10.728 * 2^15 or about
352 KHz, a mice match for the 40 meter band.
So in the ISR the TAK-40 increments or decrements the current tuning
work as required then sets the update bit. Once back in the main loop
the update bit is noticed and the subroutine to send the current
tuning word to the DDS-60 is called the subroutine adds the bottom of
the 40 meter band (4409000 Hex) (~2.990 MHz). Since the LSByte is
always 0 and the MSByte is always 04, 15 bits won't cause 4090 Hex to
carry, the TAK-40 only has to do a 16 bit add (tuning word + 4090
Hex) then send the resulting 32 bit word to the DDS-60.
The tuning subroutine also decides whether or not to add the 2's
compliment RIT offset to the tuning word. I don't check for
overflow/underflow so if you crank the frequency all the way down
then turn the RIT all the way down it may pop to the top of the band.
I haven't tried it.
To connect the AMQRP DDS-60 to the TAK-40 you will need to make
this cable to go between the DDS-60, J105 and U103 on the digital board.