Re: {Collins} Receiver test data, Sherwood



There is no doubt that he knows more about receivers than just about anyone else. That is why I often look to his information when I am trying to learn.

However, I do make measurements all of the time, of a more critical nature, for my work, and thus I always have the concept Gauge R&R in the back of my head when I see comparisons between something producing a 104 dB reading (for any test parameter) and 105 dB. I would submit that  those two receivers are the SAME and not try to rank them in order. It’s a tie…


Gary




> On Sep 29, 2016, at 12:37 PM, Dave Bottom <ars.kd6az@xxxxxxxxx> wrote:
> 
> Back in 2009 when restoring my 75S-3B I was really pleased with the results except that there was virtually no perceptible difference between Fast and Slow AGC compared with my 75S-1 (from the 1970's) and I ran across some interesting material on the Internet about specifically my issue. 
> 
> I sent an email off to get some further insights, not recognizing Rob's new call sign. It was only after a couple of exchanges and talking with him on the telephone I realized who I was talking with.  
> 
> Rob does indeed own Collins gear, at least an S-3Line when I talked with him and I could tell he enjoys using it. The 75S-3B tested was undoubtedly his own well tuned receiver.  The 75S-3C might have been someone else's and he may have not been inclined to mess with that person's radio, but since he is so approachable, just ask him!
> 
> By the way his input on tweaking my 75S-3B's AGC so it was Slow for SSB and Fast for CW or AM was a huge success.  It was just as I was expecting it to be.
> 
> 73 Dave WI6R
> 
> Sent from my iPhone
> 
> On Sep 29, 2016, at 9:22 AM, Michael Tortorella <w2iy@xxxxxxxxxxx> wrote:
> 
> 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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