[1000mp] Real S9

[Chuck Lewis]

Right on, Mike. That's exactly as I understand it, even to the point that 
the latter batch of roofing (or 'roughing', as one friend insists) filters' 
decreased insertion loss results in a duplication of the I/F mod boost. My 
9-1 settings (roofing filter replacing the I/F mod) are identical with those 
I established with the I/F mod, using the sub RCVR S-meter as a way to 
re-establish overall I/F string gain. I did not have to make any subsequent 
changes to the 9-1 settings; my subjective test for perceived best S/N left 
the 9-1 adjustment within one digit of both Inrad's recommendation AND that 
which produces identical (albeit low) S-meter readings.

So, it would appear that our problem, if any, is that setting the S-meter at 
S-9 = 50 uV either screws up the weak-signal performance (turn up 9-1 until 
the meter reads S-9), or screws up the S-meter linearity (adjust VR8006 & 
8007)!  I'll put up with a stingy meter in favor of a quiet and sensitive 
rcvr. Catch 22. I think we're in agreement!

73,
Chuck, N4NM

----- Original Message ----- 
From: "Mike Schatzberg" <cherokeehillfarm at earthlink.net>
To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
Sent: Monday, March 26, 2007 9:34 AM
Subject: Re: [1000mp] Real S9


> Hello Chuck:
>
> What we were speaking of here is resetting the IF gain after the Inrad
> Roofing filter mod, not the IF Amp mod.
>
> Improved signal to noise ratio is achieved here due to the narrower first 
> IF
> filter and the few dB of net gain
> resulting from the surplus gain remaining after the filter insertion 
> losses
> are eliminated via the module amplifier.
> This is an additional advantage of the roofing filter mod, but not the
> primary objective.  The original design of
> the module amplifier was to be able to compensate for the losses of the
> narrower crystal filter.  Over time, the manufacturing
> process for the filter apparently became more refined, and the filter
> insertion losses deminished.  I wrote to Inrad myself
> suggesting that their instructions for installation might be modified to
> take advantage of this development.  They did
> indeed change their instructions after it became evident that newer 
> filters
> had lower losses.
>
> This change in the filters does more or less let the roofing filter mod
> parallel the performance of their earlier IF Amp mod.  Many people have
> swapped out the older mod for the newer roofing filter.
>
> I have worked here on the bench with the new filter installed, examining
> signal to noise ratio, noise floor with MDS, and the S meter calibration.
> While each radio is different due to component selection and overall set 
> up,
> my personal conclusion has been that the signal to noise ratio is 
> optimized
> generally within a decrease of 1 to 2 integers of the original factory
> settings, and that the S meter readings will not be significantly
> compromized for linearity within this range.
>
> While the S meter readings at S9 (50 uV input) may be correct for small
> reductions in IF gain settings, my measurements indicate that too low a
> setting will result in loss of linearity below S9.  You can then perform 
> the
> S meter calibration which is a two step process; first setting VR8006 for 
> a
> one dot deflection with a +11dBu input signal, and then setting VR8007 for
> S9 + 60 dB with a +100 dBu input signal.  Yaesu does not calibrate the 
> meter
> at S9, please see page 3-3 of the technical suppliment for this 
> information.
> Please note that the IPO lamp is off for these adjustments, meaning the
> preamp is operating.
>
> Regarding the accuracy of other receivers S meters, I would say that there
> are two issues at work here.  One source of error always seems to be 
> whether
> the S meter is calibrated with the preamp on or off, this makes for a 2 S
> unit change alone generally.  Secondly, some manufacturers really haven't
> adopted the Collins standard of S9 equal to 50 uV input, with one S unit
> being worth about 6 dB.  Their S meters are not only incongruent with this
> standard, but they are also non linear.
>
> You just might want to actually measure what you have created once you 
> have
> made a larger change to the IF gain to optimize signal to noise.  I will 
> not
> even venture to guess what might also change in terms of dynamic range and
> BDR with larger excursions from the original factory settings.
>
> Experience still says that downward adjustment of the gain in menu 9-1 by
> one to two units will produce acceptible results across the board.  You 
> will
> also see that the two receivers remain in approximate correlation at S9.