External DDS Dual VFO for the
Drake TR-7 / TR7A
If desired, the DDS VFO Controler can be
packaged in an external cabinet. In this example, the
controller has been placed in a nice new, weighted sloping metal
enclosure. It plugs directly into the Drake's RV7 socket.
No
wiring changes are required for either the TR7 / TR7A or the PS7.
The TR7 provides power to the DDS VFO and receives
the new VFO signal when the remote DDS VFO is switched on. A
separate lead run to the rear of the PS-7 power supply switches the VFO
on transmit of the SPLIT feature has been enabled. Here the schematic. Construction details and an itemized parts listing may be found here.
The red button in the upper left is a
dedicated SPLIT button, and the black button will switch the VFO's,
lock the dial and (if desired) save the current memory contents for the
next power up. The center toggle switch operates the DDS VFO
RIT function whose control is in the upper left corner.
Note: This is just a 10K potentiometer which is not shown on the schematic.
The three LED's across the top
(left-to-right) are for VFO A, SPLIT, VFO B. The LOCK LED was
not provided on this particular variant, although it could easily be - by
drilling
out the face plate. The voltage regulator is heat sinked to the
rear of the chassis and high quality RG-174 miniature coacial cable is used for all
the external connections (3 to the RV7 plug, and one to the PS7 power
supply).
The DDS VFO's R8 has been set to match the level of the
TR7's internal PTO (1 volt, peak-to-peak).
Here are some better pictures of the front, side, rear and inside of this unit:
