Dear Gary, LF Group,
The problem as I have specified in my e-mails is the low output. Last
night
I checked back to the DDS IC & there are no substantial losses in the
signal
path, even the insertion loss of the LPF is negligable. Here are the
actual
levels into 50 ohm load at the output of the DDS VFO.
137 & 274 Khz - 22mV
....
There should be about 12-13dB of insertion GAIN between the DDS output
and the output of the PCB due to the ERA-1SM modamp. Looking at the
Analog Devices data sheet, and the schematic component values, the DDS
output should be 10mA pk-pk, driving roughly 2 50R loads in parallel,
i.e. 250mV pk-pk. The modamp should bring this up to about 1V pk-pk. The
DC bias voltage on the modamp output pin should be 3-4V. Is it possible
the modamp is in the wrong way round? If it had got turned through
90degrees, the signal would go straight from DDS to output via the 2
ground pins of the modamp.
Cheers, Jim Moritz
73 de M0BMU
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