My Pic-A-Star's first QSO - 25th May 2007
(Double click these photos for high res version)
Front view - Built on a piece of old pine shelving - some bits screwed down .. blu-tack for the rest.
Chris Honey bipolar PA on left (Bought
as an old unopened Cirkit kit on eBay April 2007)
3rd order IMD -30dB at 20watts with 13.2V supply( -23dB at 20watts on 12.6V supply)
Some big coils of wire - 17way cable from
DDS unit to timer unit has PCB connectors on both ends
I will eventually cut this in half and may be route it out of the DDS compartment via feed through caps
DDS unit - unsing Agilent rotary encoder (eBAY!) - interfaced using a 74HC74 - works fine.
74HC74 on left and cable to rotary encoder.
200Mhz oscillator unit at bottom - Pletronics LVDS o/p & LVCS to 3.3v CMOS logic convertor (=LVDS line receiver)
Regulators with brass shim heatsinking (3.3v for osc and 5v for DDS unit)
Rear view - audio out and phono to switch linear on left
LPF unit - Note seven LPFs - separate for
30m and 40m.
Three small relays: two to switch 20dB attenuator. one to ground Rx input on transmit.
Note use of wire wrap wire for relay control signals.
Tx LPFs left RF BPFs right
Magic roundabout bottom centre. Timer board bottom right. Diode logic and stereo PA beneath coiled wire
PA driver amp - underside
PA driver amp MAX2611 chip - has 18dB gain
- so has 5dB input pad. Operated with 8v supply from
78L08 regulator and Id = 37mA. (I initially tried 25mA ... but increasing to 37mA reduced 2nd harmonic
from -37dB to -45dB.
Transformer rather than just the suggested choke in the output
- Primary 6t secondary 4t <br> this halves the current swing as we are exceeding Idmax on peaks?