Re: [IRCA] SP 600 /R390

[Charles A Taylor <MWDXer@xxxxxxx>]

At 10:02 AM 5/6/2007 -0700, you wrote:
>Bob,
>
>I never knew that. Then the R-390 does have an honest Noise Blanker and
>not a Noise Limiter as the SP 600 had. Now that is interesting. I wonder
>what kind of circuit the R 390 uses? Anyone know? That diode set up in
>the SP-600 never did anything much except distort the audio as you
>mentioned. That was the only reason I sold the SP 600. It was one great
>receiver and netted me a lot of great DX through the years. One thing I
>really miss is the crystal phasing. I wish the crystal filters in the
>SPR4 had phasing.
>73,
>Patrick
>Patrick Martin

Patrick,

AFAIK, the R-390's NOISE LIMITER is essentially the same as the R-390A's
NOISE LIMITER. Neither are noise blankers in the proper sense of the
term. All they do is chop off the audio at a predetermined level as set
by the operator by adjusting the LIMITER pot. Like the SP-600, they tend
to distort the audio.

The R-390A is the result of a cost-reduction contract written by the US
Army Signal Corps with Collins Radio Corp. The R-390A was a great deal
cheaper per unit than the R-390. But the R-390A has the mechanical
filters, and THAT, sir, is the important difference! Every receiver, w/
the exception of the R8B, that I have owned I've had to supply either
a crystal lattice filter or a mechanical filter to supplement the
selectivity characteristics.

The lack of a good product detector and a good noise blanker are the
prime drawbacks of the R-390 family.

And the noise blanker of the R8B is "finicky" in that, if the incoming
signal is above a certain level, the NB ceases to operate. I think
that's because the R8B's NB has an AGC input to the NB.

Now go climb a tree!

Kindest regards,

Charles


Charles A Taylor, WD4INP
Greenville, North Carolina 


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