Lee de Vries
I have just completed building &bench testing my PHSNA. Packaging is still to be done.
I am using a DDS60 & a Mini Pro. & a level detector board by SV1AFN.
I made a couple of small changes.
a) I did not use a 100 Ohm trimpot as I did not have one on hand. In addition, the output of the AD8307 is very unlikely to exceed +2.5 V (+15dBm), therefor I changed R1 & R2 on the regulator to 510 Ohm's to give me aAVref of 2.534. The code was changed accordingly. After calibration, this gives a slop of 0.1056 approx Ie. more counts/dB That works good.
b)I used a SARK110 to do the calibration using the preset levels of -73.-63,-53,-43,33,-23,-13 & -10dBm
After calibration it is very accurate around the higher levels, but gives an error of about -1.5 dBm at the -73 dBm. level. Why is this so????
c) After calibration , I adjusted the gain of op-amp 1 on the DDS50 board. to give me an output level of -10dBm. All good. I did note that the input into op-amp 1 (190 mV p-p) & the output of op-amp1 (560mV p-p) is quite clean looking (using a Tektronix 100 Mhz. CRO), however, the output of op-amp2 the output is far from sinusoidal (1024 mV p-p). Is this normal. The gain of op-amo 2 is about 4, so I would have expected about 2000 mV p-p and a clean looking sinusoid.
d) I expect to run my gear of my station supply, which is 13.2V, so the regulator on the PHSNA board gets pretty hot. So, I added a DC-DC pre-regulator to drop the V+ voltage to about 8.5 volts, which of course will be the Vsupply of the op-amp. I would not have thought that the op-amp would be saturating at that supply voltage. In fact, increasing the supply voltage made little difference to the look of the sinusoid.
This may help some constructors. In the mean time I would welcome comment on the distortion of the
sinusoid in op-amp2 and the level error near the lower calibration point.