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First of all, 303's never had noise blankers. So the "blanker
control" at the lower left control position is <i>not</i>
original...Originally, 303's had an "rf attenuator" which, when you
look at the schematic, is merely a 600 ohm linear pot across the
antenna. Now, a bit of history;....when the SB-<i>104</i> came out,
true to Heath tradition, a noise blanker was offered that was
optional....that meant it was sold as an "optional" kit....and that
meant that someone could fit one to a 303'....which was featured as
a QST article "modification"....if you have a NB board, it will be
a 104' board, and you should find it mounted to the left inside of
the chassis, above and to the left of the FSK board. I haven't
been in my 303' in a while, but as I recall, the board is rather
clearly marked, if you have one, and roughly about 2 x 3". Note
this was an "after market" modification, and was never authorized,
much less encouraged by Heathkit. As I recall, the 104' NB mod
simply had an off-on switch, not a control. So I'm not sure exactly
what or how your radio was modified, but if you don't find the NB
board inside your 303', you should be aware that as collectors
started buying up 104's, a number of them didn't have the treasured
NB'er, and, because the 303'-with-a-104'-NB-board was a somewhat
popular modification, it's possible someone subsequently stole the
NB board from your 303' to put it into a 104'....<br>
I personally find the excitement over the NB board to be a bit over
done...remember, NB's were designed chiefly for automobile generated
"pulse" type noise. I don't know if they had any effect on general
backround noise; compared to a modern rig's DSP system, they're like
swatting mosquitoes one at a time as compared to a helicopter doing
an insecticide spraying. This may explain why Heathkit offered
NB's "optionally", as relatively few 104's ended up on the
transmission humps of cars of the 70's and 80's....most were bought
as rigs for home.<br>
<br>
Guy<br>
WA6OQQ,<br>
One of the "hams at Heathkit..."<br>
.<br>
<div class="moz-cite-prefix">On 3/13/2014 10:06 AM,
<a class="moz-txt-link-abbreviated" href="mailto:pbrickey@verizon.net">pbrickey@verizon.net</a> wrote:<br>
</div>
<blockquote
cite="mid:4647788.691071.1394730396973.JavaMail.root@vznit170080"
type="cite">
<pre wrap="">Hi,
My SB-303 has a Noise Blanker control in place of the RF attenuator control, but the noise blanker board is missing. Does anybody have an idea of why Heathkit eliminated the noise blanker and substituted the RF attenuator? Anyone have a SB-303 noise blanker board?
73's,
Peter
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