Hello John,
I realise that my description was very basic and could benefit from
filters, amplifiers etc.
For anyone wanting to just look at audio frequencies the oscillator
could be on 10.7 MHz
and the output of the mixer could be put through a crystal filter
from an ex PMR radio
etc. This could eliminate the osc' feedthrough and remove the
unwanted sideband.
A suitable amplifier could be set to give the same level output as
the audio input and
then attenuated to suit the SA.? Although the shape of the filters
pass band would have
some effect.
73 Ken g8beq
On 21/12/2022 16:13, John Cunliffe W7ZQ
wrote:
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Thanks Kenneth,
Nice descriptions of the fundamental. This particular up converter
uses an external 10Mhz oscillator that ideally should be
synchronized to the spectrum analyzer for best accuracy.
It takes the low frequency input signal between about 10Khz and 2
Mhz and mixes it with the external source. It then applies some
basic filtering and level adjustments and then outputs a signal
above 10Mhz that mirrors the input signal in amplitude. So a 0dbm
signal in equals a 0dbm signal out and a -100 dbm signal in equals
a -100dbm signal out. It tracks pretty good within +- 1-2db above
30khz. Below that the sensitivity / dynamic range fails but is it
still usable.
I use the 10Mhz cal output of the tinySA as the external
oscillator. The signal as is, is too low so I added what I
believed to be a 20db amplifier but it turns out is actually close
to 30db on 10Mhz. That puts the 10Mhz signal right around 0dbm,
perfect for the box and since it is derived from the internal
clock of the tiny it is naturally synchronized to it.
Using the up converter I can now observe low frequency signals in
the 50-150khz range (my interest) using the full dynamic range of
the tinySA . The specs say it works up to 2Mhz but I have not
tested it there.? Eric made a nice video about the performance of
the tinySA on lower frequencies. This up converter gets around
some of the performance issues.
John
