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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...<br>
Guy<br>
<div class="moz-cite-prefix">On 3/16/2014 12:40 PM, Brian Wood
wrote:<br>
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<p class="MsoNormal"><span style="font-family:"Comic Sans
MS";color:windowtext">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Comic Sans
MS";color:windowtext"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Comic Sans
MS";color:windowtext">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Comic Sans
MS";color:windowtext"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Comic Sans
MS";color:windowtext">Brian, W0DZ<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Comic Sans
MS";color:windowtext"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
Heath [<a class="moz-txt-link-freetext" href="mailto:heath-bounces@puck.nether.net">mailto:heath-bounces@puck.nether.net</a>] <b>On
Behalf Of </b>Guy Giacopuzzi<br>
<b>Sent:</b> Saturday, March 15, 2014 9:07 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:pbrickey@verizon.net">pbrickey@verizon.net</a>; <a class="moz-txt-link-abbreviated" href="mailto:heath@puck.nether.net">heath@puck.nether.net</a><br>
<b>Subject:</b> Re: [Heath] SB-303 Noise Blanker
Schematic<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">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...<br>
<br>
Guy, <br>
WA6OQQ<o:p></o:p></p>
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<p class="MsoNormal">On 3/15/2014 2:30 PM, <a
moz-do-not-send="true" href="mailto:pbrickey@verizon.net">pbrickey@verizon.net</a>
wrote:<o:p></o:p></p>
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<pre>Hi,<o:p></o:p></pre>
<pre> 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.<o:p></o:p></pre>
<pre>It is attached.<o:p></o:p></pre>
<pre> 73's,<o:p></o:p></pre>
<pre> Peter<o:p></o:p></pre>
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