Re: {Collins} Receiver test data, Sherwood



Granted that the test must be somewhat time-consuming (so it would be
difficult to expect Rob to undertake as many tests as needed to get a
reasonable statistical result), Gary's point about the small sample size and
unit-to-unit variability is indeed well taken.  The Holmdel ARC (K2DR) at
Bell Labs did something similar back in the late 1970s, making some MDS and
DR3 measurements on receivers owned by members of the club.  We had a
similar experience, lots of unexplained strange results, many probably due
to not aligning the units before the test.  It was fun, though, and
certainly early days not long after Wes Hayward's article in QST on the
matter.  Somewhere I have a table of the results we got, if anyone is
interested I can pass it along.
73
Mike W2IY

-----Original Message-----
From: Collins [mailto:collins-bounces+w2iy=verizon.net@xxxxxxxxxxxxx] On
Behalf Of Gary J FollettDukes HiFi
Sent: Thursday, September 29, 2016 12:05 AM
To: Don Jackson
Cc: Collins CCA Reflector
Subject: Re: {Collins} Receiver test data, Sherwood

Thank you for the response, a well spoken response I might add.

I'll read the referenced article as well.

Gary

> On Sep 28, 2016, at 9:57 PM, Don Jackson <w5qn@xxxxxxxxxxx> wrote:
> 
> Hi Gary,
> 
> Ah yes, Rob Sherwood's receiver data is interesting, and I spoke with him
a couple of years ago before writing the article on dynamic range that
appeared in Q1 2016 Signal magazine. Yes, 2-tone dynamic range has become an
increasingly important differentiator among receivers over the years because
it is a good measurement of how well a receiver performs in a crowded signal
environment.
> 
> Rob did not test many Collins units (maybe only the ones listed), and more
unfortunately, did not record the status of service bulletins performed on
the units. In a nutshell, SB1 and SB2 affect the DR3 performance. SB1
improves DR3 by reducing the gain in front of the IF filter. SB2 improves
DR3 by adding selectivity prior to the mechanical filter, which,
unfortunately, contributes to 3rd order distortion. If you haven't read it,
I recommend that you check out the article, and you will see comparisons of
various S-Line receivers with different combinations of service bulletins.
As well, the article describes how changing to an Inrad mechanical filter
will improve DR3.
> 
> If you have further questions, let me know and I will attempt to answer
them.
> 
> Don, W5QN
> Technical Editor, The Signal
> 
> -----Original Message----- From: Gary J FollettDukes HiFi
> Sent: Wednesday, September 28, 2016 8:46 PM
> To: Collins CCA Reflector
> Subject: {Collins} Receiver test data, Sherwood
> 
> I am always out to learn and the best way to do so it to ask hard
questions and learn from those who have the answers.
> 
> I was just wandering around the Sherwood site regarding receiver dynamic
range ratings (again) and I noticed a curious thing.
> 
> The Collins 75S-3B is rated 6 spots higher than the 75S-3C.
> 
> Now the only difference between the two (of which I am aware) is the
addition of the second crystal board and associated switches for added band
coverage.
> 
> I think maybe this tells you what the "Gauge R&R" (Readability and
Repeatability) is for this test.
> 
> Also, I was wondering how many samples of a given radio are tested, since
there MUST be some degree of unit to unit variation.
> 
> I know there are other things the drive receiver performance quality
measurement but I find it interesting that this one test gets such high
visibility when it can't even produce the same result from two different
versions of the same receiver.
> 
> Even Direct Digital SDR radios get this figure of merit rating even though
they have no mixers! Interesting.
> 
> Gary
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