[Heath] SB-303 Noise Blanker Schematic

[Guy Giacopuzzi]

Well, it took about 30 seconds for the engineers to substitute in the 
303's rf attenuator--it's simply a 600 ohm pot with the antenna on one 
side and ground on the other...I think the input to the rf amp is 
connected to the pot's wiper...as I recall...
Guy
On 3/16/2014 12:40 PM, Brian Wood wrote:
>
> An RF attenuator is not the same as an RF gain control. RF Gain is 
> actually IF gain (or even more appropriately, IF attenuation!), and is 
> inside the AGC control loop. An RF attenuator is outside that loop, at 
> the same place as the bandpass filters (or preselector) and any RF 
> preamps, i.e. close to the antenna. It's useful to attenuate strong 
> signals before they get into the radio.
>
> It IS, however, pretty obvious that something was amiss. I also have 
> the '71 catalog, and it clearly shows "NOISE BLANKER" text carefully 
> scratched out so as not to be all that noticeable. Very cool! A 
> mystery! Having designed a noise blanker, I can attest to how hard it 
> is to get the dang things to work the way you want them to. And of 
> course there is the popular misconception that they reduce broadband 
> noise. They only reduce impulse noise, such as from electric fences or 
> car ignition. True NR is a DSP thing.
>
> Brian, W0DZ
>
> *From:*Heath [mailto:heath-bounces at puck.nether.net] *On Behalf Of *Guy 
> Giacopuzzi
> *Sent:* Saturday, March 15, 2014 9:07 PM
> *To:* pbrickey at verizon.net; heath at puck.nether.net
> *Subject:* Re: [Heath] SB-303 Noise Blanker Schematic
>
> Coool....now, does anyone have an SB-104 schematic handy so that a 
> comparison could be made?  I'm betting that Pete's 303 blanker is 
> unique to the 303'...and now the big question remains, why didn't they 
> develop this on the 303'?  I know the answer to one question 
> though....The question, is why does a 303' have an rf attenuator in 
> the first place?  It's kind of stupid, and it doesn't do anything that 
> an rf gain control can't already do.  Soooo, I bet this "rf 
> attenuator' was the cheap answer to "What do we fill that spot with?" 
> that the engineers had to answer when they couldn't get the noise 
> blanker to work.  At least, that's my theory...
>
> Guy,
> WA6OQQ
>
> On 3/15/2014 2:30 PM, pbrickey at verizon.net 
> <mailto:pbrickey at verizon.net> wrote:
>
>     Hi,
>
>        I have had quite a few questions about this, so I thought I would send out the schematic that is in my SB-303 manual.
>
>     It is attached.
>
>        73's,
>
>                    Peter
>
>
>

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