Topband: "synchronous noise blanker"

[Tod-ID]

Tom sent me this directly and I thought I would put it on the reflector so
there is a wider awareness of his experience with synchronous blanking
circuits from some time ago. He notes also that electric fences are not
directly synched to 60Hz and would not be 'cured' using control pulses timed
to 60 Hz. 

I thought about that and I suspect that the timing of electric fences is
regular and perhaps based upon some RC charging time. That might make them
able to be addressed using an external blanking circuit with an adjustable
time base which is not tied to the 60 Hz peaks of the power line. 

Tod, K0TO

> -----Original Message-----
> From: Tom Rauch [mailto:w8ji at contesting.com] 
> Sent: Tuesday, February 13, 2007 5:52 AM
> To: Tod-ID
> Subject: Re: Topband: "synchronous noise blanker"
> 
> > The parts and circuitry look simple to acquire and 
> fabricate. I would 
> > suspect that it would work excellently to remove electric 
> fence pulses 
> > from beverage inputs and other RX antennas that we employ, 
> as well as 
> > perhaps removing other significant spikes that plague us on Topband
> 
> I've tried systems like that years ago when I lived in noisy 
> areas, and the problem is noise from multi-phase power lines 
> can have all sorts of odd patterns. Insulators or hardware 
> can arc on the voltage rise, the voltage fall, negative peaks 
> or positive peaks only, it can ring, and it can be on any 
> combination of this on any of the wires representing phases 
> that are 120 degrees apart from what you have at the outlet. 
> My own problem was a 69 kV three phase line about
> 1/2 mile from my house in Sylvania Ohio, and a 345kV line a 
> mile away in my S. Amherst QTH. Then there is the time delay 
> to compensate for, and the only way I could generate a 
> reliable timing pulse was to do a voltage detector trigger 
> that looked at voltage near zero crossing and then fire 
> variable timers (I used NE-555 timers and 74 series TTL
> logic) to blank.
> 
> Of course it can't do a thing for an electric fence or 
> anything else, since it is only synchronized to the power line.
> 
> The problem I had was arcs were never consistent in timing so 
> I had to blank an extra wide window that included good times. 
> This meant unnecessary off time with substantial time-loss of 
> input signal. This also  caused the blanker to modulate 
> everything with a hum of 60 Hz for each polarity and 
> multiples of 60Hz for each phase.
> 
> 73 Tom 
> 
> 
> 
>