Hi Phil,
I designed the KNB2 before the KNB1, and the KNB2 is the more versatile
the two blankers. It also has more dynamic range, compatible with the
K2's receiver.
If your friend wants to use the KNB2 in his own design, he'll need to
substitute discrete control signals for those that are normally decoded
and driven by the KNB2's 8-pin PIC. I think it is clear from the
schematic what the PIC's pins do, but you could also probe them as you
activate the unit from the front panel of the K2, or I can give you
more technical detail as needed. The reason we used a PIC here is so
the blanker could be controlled over the auxBus, like other options in
the K2.
Regarding center frequency: 39 MHz may a little high for the KNB2, so
he may if fact want to mix down to the K2's I.F. (which is 4.914 MHz,
by the way, not 4.014). Still, it may be worth experimenting with
component changes on the KNB2 to make it work at the much higher
KWM-380 I.F. This would certainly be simpler. Also, a mixer could
compromise his receiver's dynamic range unless carefully designed.
The remaining issue is input/output impedance. The KNB2's native
Zin/out is about 150 ohms, which matches the K2's mixer post-amp and
the following crystal filter. I'm not sure what the KWM-380's impedance
is at this point in the circuit, but the KNB2's tuned circuit could be
redesigned to match just about anything. One thing he may want to do is
eliminate the resistive divider at the input to the first tuned circuit
in favor of a capacitive divider. This will improve delay through the
filter, which could help with some types of noise. (I had to use a
resistive divider here in order to preserve the K2's high dynamic
range; the resistors serve essentially the same function as the 5-dB
pad that is removed when the KNB2 is installed in the K2.)
I wish him good luck with his project.
73,
Wayne
N6KR
On Feb 10, 2005, at 8:20 PM, Philip Westover wrote:
Hi Everyone,
A good friend of mine wrote the following to me, and I was hoping I
might get some comments from this list. He is working on
incorporating an Elecraft noise blanker into his old KWM-380....
I'd appreciate any input I could get to help my friend.
- Phil, WA7URV
---
http://www.elecraft.com
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