[1000mp] Real S9

Mon Mar 26 14:20:43 EST 2007

Mike:

I read your message, below, and it occurs to me to remind that the preamp is
not in the circuit on 20m, where alignment usually takes place. Comments?

Garry, NI6T

-----Original Message-----
From: 1000mp-bounces at mailman.qth.net
[mailto:1000mp-bounces at mailman.qth.net]On Behalf Of Mike Schatzberg
Sent: Monday, March 26, 2007 7:35 AM
To: All about Yaesu 1000mp
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.

73 and Happy DXing,

Mike
W2AJI

Chuck wrote:

Hi, Mike,

Oh, I have already installed the mod, and after that, the roofing filter.
Both times I  followed the Inrad suggestions, lowering the 9-1 settings by
1-2 numbers (in my case, the roofing filter didn't change that amount of
compensation);  and both times the resulting s-meter readings agreed
generally with the sub-rcvr. However, I also used my ears and several weak
sigs to establish what I sensed as the best weak-signal s/n ratio. This also
agreed (within 1 number) with the Inrad suggestions. The S-meter STILL seems
quite stingy (both main and sub) compared with other radios. My point is
that, once I had done this, I satisfied myself that further messing with the
IF gain (which would not improve the S/N ratio, but only make all sigs
louder, including the noise) would be a bad idea, and that I should live
with a stingy meter. Either Yaesu's calibration is in error, or we all have
been misled by other radios' overly generous meters. The 50 uV generator is
a great way to give us all a consistent S-9 standard. But Pete's suggestion
to increase the IF gain until the s-meter reads S-9 at 50 uV just reverses
all the good we got out of the IF mod. Remember, the reason for the mod was
to balance the gain distribution by reducing the 70 MHz IF and using the
Inrad amp. to compensate upstream (I think I remember that correctly). I
think it's erroneous to assess the RCVR's performance by looking at the
S-meter. We all installed the mod to make the radio quieter (without losing
sensitivity). Just leave the IF alone, at it's best S/N gain and RECALIBRATE
ONLY THE METER using the 50uv generator as a standard! If I can find the
meter calibration adjustment in the radio, I'll share it.

Yes, if you're referring to the BHI noise reduction system, I've already put
that on my wish list!

Chuck

----- Original Message -----
From: "Pete Smith" <pete.n4zr at gmail.com>
To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
Sent: Monday, March 26, 2007 7:19 AM
Subject: Re: [1000mp] Real S9

> Hi Chuck - well, my logic was that the only thing I had changed was the IF
> gain setting in menu 9-1, and the radio not only sounded a little dead,
the
> main RX definitely had less sensitivity  than the sub-RX.  Given that, I
> felt that getting the S-meter back to reading more or less the same on
both
> with a 50 uV signal would indicate that I had restored the IF gain to
> something like spec.  The XG-1 also has a 1 uV output, and Elecraft also
> makes a highly accurate step attenuator kit if you want to go farther.
>
> 73, Pete N4ZR
>
> At 10:44 PM 3/25/2007, you wrote:
> >Gee, Pete, I'm not trying to start a war here, but it seems to me that
the
> >gain distribution (affected by the I/F gain setting) should be set for
> >max. S/N, not diddled with as a means to correct an S-meter
> >mal-calibration. On the other hand, suggestions have been made that
(after
> >any Inrad mods, etc.) the I/F gain be adjusted until the main RCVR
S-meter
> >indicates the same as the Sub-RCVR reading. That would seem to be a way
of
> >returning the overall I/F gain to its factory setting. This seems fine as
> >long as one assumes that the sub-RCVR setting is consistent with the best
> >main RCVR S/N ratio: a bad assumption, IMHO.
> >
> >Why wouldn't it make more sense to (somehow) establish the best S/N ratio
> >by adjusting the I/F gain and THEN use the 50 uV standard to set the
> >S-meter sensitivity? I've played a little with the I/F menu setting using
> >barely readable sigs to reach a (subjective) optimal setting. That turned
> >out to be fairly consistent with Inrad's suggested compensation when
> >installing their I/F mod kit. My S-meter seems stingy, too, but it seems
a
> >bad trade to give up weak signal performance (and lose the "hiss
> >reduction" we paid for in the Inrad kit) just to get the S-meter right
> >when there's probably a dedicated S-meter sensitivity adjustment
somewhere.
> >
> >What am I missing here?
> >
> >73,
> >Chuck, N4NM
> >(Who's wishing he had one of those VG-1 kits, too :>)
> >
> >
> >
> >----- Original Message ----- From: "Pete Smith" <pete.n4zr at gmail.com>
> >To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
> >Sent: Sunday, March 25, 2007 2:58 PM
> >Subject: [1000mp] Real S9
> >
> >
> >>I just finished building the Elecraft XG-1 signal generator.
> >>
> >>So why am I talking about it here?  Because It puts out a calibrated 50
> >>uv on 7040.  After I built it, the first radio I hooked it to was my
> >>TS-930. S9 right on the button.  Then I connected it to my Mark 5.  S6!
> >>
> >>I had thought for a long time that the Mk 5 sounded "dead" compared with
> >>the 930, but put it down to DSP, etc.
> >>Not long after I got the MK5, I put in the Inrad IF mod, and then a
> >>couple of years later I substituted the roofing filter.  The radio also
> >>has cascaded 400 Hz Inrad CW filters.  In the course of doing all that,
I
> >>guess I had turned the IF gain down too far - anyway, using the XG-1, I
> >>was able to reset it to ~S9 at 50 uV - certainly sounds like the band is
> >>more open!
> >>
> >>I expect the VG-1 is going to prove very useful, anytime I want to check
> >>the performance of my antenna switching or bandpass filtering - and for
> >>$40, I can't imagine a cheaper way to do that.
> >>
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> >>
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