Ron,
Yes, there is a simple test. Turn on the Preamp, do not connect an
antenna, and tap the case of Q21 with something metallic (like a
screwdriver). You will hear clicks along with bursts of sound because
the screwdriver is acting as an antenna (it is important to distinguish
between the two). When you turn on the NB, the clicks should diminish.
Remember that the KNB2 responds to impulse noise only (like automotive
ignition noise or nearby lightning static), it will not make any
difference for noise that has a slower rise time, like atmospheric noise
or other forms of wideband noise.
The way the KNB2 works is to "punch a hole" in the received signal path
- it "blanks" the signal path for a duration selected by the capacitor
time constant. If the time constant is too long, it can create
significant distortion in the received signal. Some have doubled the
value of C11 (solder an additional .001 uF across its leads) and
reported better results, but it really depends on your particular noise
source.
73,
Don W3FPR
On 9/10/2011 12:36 AM, R Thompson wrote:
> Is there a simple way to check if the noise blanker for the K2 works? I
> tried to use it tonight but it didn't seem to make any difference. Then
> I tried turning a switch on a fan on and off, that produced S7 noise
> spikes on the S meter, but the noise blanker didn't seem to make a
> difference.
>
>Ron VE8RT
>
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