[1000mp] Real S9

Mon Mar 26 10:17:06 EST 2007

I have to agree with Chuck.  The proper way, from a technical perspective, 
would be to optimize the receiver and then calibrate the "S" meter.  Higher 
IF gain does not equal higher receive sensitivity.  It might give the 
appearance of that due to the higher noise level and audio level, but at the 
expense of weak signal performance.  My experience has been that in most 
cases the opposite is true.  The lowest possible IF gain setting before 
actual sensitivity reduction, results  in the highest signal to noise ratio. 
Internal noise is the sensitivity limiting factor in most receivers not lack 
of gain.  I know that sounds crazy but it's true.  In some receivers (not 
the FT-1000 series) I have actually measured the receive sensitivity to be 
the highest with the IF gain set to the lowest setting....problem is you run 
out of usable audio amp power to take advantage of it so it is a trade off.

Pete I would be concerned about the health of your Roofing filter 
module....the reason the IF gain is reduced after the installation of the 
Roofing filter is to compensate for the gain associated with the active 
components on the Roofing filter card as I understand it.  Installation of 
the roofing filter bumps up the gain in one stage and you adjust it back 
down in another with the software which is suppose to result in an improved 
S/N ratio and resulting receiver performance by redistributing the gain more 
evenly across the various stages of the receiver.  A quieter receiver should 
be the result....and yes signals as registered on the "S" meter may be lower 
as well.  But here is the payoff....you will most likely be able to detect a 
signal that won't even move the "S" meter off it's stop where with a higher 
internal noise level, from higher IF Gain settings or poorly distributed 
gain, you wouldn't be able to even hear that signal.

This is all verifiable on the bench with a decent signal generator or 
probably with the XG-1, the step attenuator and a couple of good cables.  A 
decent Analog RMS voltmeter is handy as well. (HP-3400 is great)

Pete in your case I would pull the covers on the radio and lay it up on it's 
side and check the noise level and performance with the Roofing filter mod 
in and out of the radio...if you don't see a noticeable noise level increase 
with the installation of the Roofing filter and no IF gain setting changes 
it has a problem.  Same goes for the Inrad IF Amp mod board if one is using 
it instead of the Roofing Filter mod.

I have seen more than a couple of posts here about problems developing with 
the roofing filter board.

Just some food for thought...

Hope it helps...

Cecil Acuff
K5DL
----- 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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>>
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