The pulses are transformer or capacitively coupled and shape filtered in
that process which tends to be more repeatable with repetitive pulses.
There's nothing in the analog circuit other than the pulse shaping and
pulse amplification that works on repetition, but that has significant
effect making them more effective on repetitive things like ignition and
power line noise than on random events like lightning. The pulse shaping
circuits usually are not DC coupled so need repetitive pulses to center
the pulses that shut off the gate.
On 7/28/2010 3:24 AM, Ken Brown wrote:
> You may be right about the pulses needing to be narrow and strong in
> order for most noise blankers to work on them. I do not think you are
> correct about them needing to have a regular repetition rate. For
> example the noise blanker in the Omni VI has a detector to trigger the
> generation of a blanking pulse, and a switch in the IF signal path
> controlled by the blanking pulse, which performs the blanking. There is
> nothing in the Omni VI noise blanker that requires repetitive noise
> pulses in order to work. It can blank a single noise pulse as long as
> the pulse is strong enough to trigger the blanking pulse.
> There are noise blanker circuits that are designed to work on repetitive
> pulse type noise, particularly 60 and 120 Hz repetition rate noise
> pulses produced by AC power lines (or 50 and 100 Hz in the other
> hemisphere) These circuits are typically synced to the the AC power
> source using a sample directly from the mains rather than from the
> receiver IF, and can blank the receiver even when the noise pulse would
> not be strong enough to trigger a blanking circuit such as in the Omni VI.
> There are other types of noise blankers which use a whole separate
> receiver, working at a different frequency from the one the main
> receiver is tuned to, to sense noise pulses and trigger the blanking of
> the main receiver. These also do not require repetitive noise pulses to
>> NO ANALOG NOISE BLANKER HAS EVER WORKED ON ATMOSPHERIC NOISE. The
>> noise characteristics its made for are ignition noise and line noise
>> that have a regular repetition rate but are made of isolated narrow
>> but VERY STRONG pulses. Unless you have a thunderstorm close by, you
>> don't get similar pulses from the static crashes and the noise blanker
>> doesn't see big enough or narrow enough pulses to work to cut them out.
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