The diodes are not needed in the normal situation where the P3 is
connected to the K3 IF output.
You can use the P3 as a kind of "poor ham's spectrum analyzer" by going
into the menu and setting "Xcvr Sel" to the last item in the list,
labeled "0 Hz". Now the frequency displayed is the actual RF frequency
of the IF input, not the K3 frequency. The "XCVR" RS-232 connector
should be disconnected from the K3 in this case. Tune the frequency
with the CENTER control. (Make sure the "CenterEn" menu item is "ON".)
If you do that you should add the back-to-back diodes in parallel with
the input BNC connector. Standard 1N4148 or similar switching diodes are
fine. If you don't want to modify the P3 you can do what I did: Add
the back-to-back diodes to a male BNC connector and connect that to a
BNC "T" plugged into the P3 IF IN.
There may be some slight degradation of dynamic range. The third-order
intercept of the P3's preamplifier is about +9 dBm (0.6 Vrms). If
you're worried about it you can use two diodes in series in each leg (4
diodes total) to reduce the distortion contribution from the diodes.
Alan N1AL
On 05/19/2014 06:38 AM, Sam Morgan wrote:
It was mentioned to put a couple of diodes across the P3's input to
protect it. Do the diodes need to be 1n34a's or would 1n4148's be ok for
that application?
I had tried repeatedly to ask Don W3FPR this question off list via
direct email, but I guess all my efforts have ended up in his spam
folder?? :-(
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