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A.2 AC gain
SR446 400 MHz Programmable Gain Preamplifier
Now that the lock‑in is prepared, disconnect the BNC cable from the
BNC Tee at the "A" input of the SR865A, and connect that to the INPUT
connector of the SR446.
Set the SR446 to
,
50 Ω
1. Set the SR446 gain to 20 dB.
2. Connect a BNC cable to the − Out connector on the SR446 and
connect the other end to the BNC Tee on the SR865A.
3. Press the [Auto Scale] button on the SR865A, and wait at least
1 second.
4. Remove the top cover from the SR446, by removing the black
screws from the left and right sides of the cover. Depending on
the build date of the SR446, there may be one additional screw in
the top part of the cover, or there may be one silver‑colored screw
on the bottom of the amplifier. Do not remove any of the black screws
from the underside of the SR446.
5. With a narrow flat screwdriver, carefully adjust R412 until the
"R" display on the SR865A shows between 99 mV and 101 mV.
If possible, trim as close to 10× the value noted earlier, when
adjusting the SR865A amplitude.
6. Move the BNC cable from the − Out connector to the + Out
connector.
7. This time, adjust R512 to bring the R display to 10× the noted
value.
8. Replace the SR446 cover and re‑install the screws. Ensure the
adhesive foam shield gasket is oriented towards the front of the
amplifier.
,
, and
.
DC
dB
full BW
27
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