[1000mp] W8JI INRAD roofing filter measurements

[Billy Cox]

Quite interesting ... does anyone know for certain
that the "one resistor" change is also true for the
older original MP series <not the MK 5 or Field>???

TU!

73 de Billy, AA4NU

-----Original Message-----
>From: Lou <louandchop at sbcglobal.net>
>Sent: Apr 25, 2007 3:12 PM
>To: wa0kds at yahoo.com, 'All about Yaesu 1000mp' <1000mp at mailman.qth.net>
>Subject: RE: [1000mp] W8JI INRAD roofing filter measurements
>
>In the MkV, the NB is in the hardware, not the DSP software. The DSP is
>really more of an audio DSP than an IF DSP as it works at an 11kHz IF after
>all other IF filtering.
>
>Here is a quote from the www.W8JI.com page explaining the issue:
>
>"The NB Problem
>The worse thing about the receiver in any of the FT1000 series radios (I'm
>sure this carries over to other Yaesu models ) is the noise blanker. The
>noise blanker, even when OFF, causes deterioration in the close-spaced IM
>performance of the FT1000MK V.
>
>1.) All signals inside the wide roofing filter (70 MHz) BW of the MK V are
>applied to the IF input of the IF unit. 
>
>2.) They immediately go through a very good balanced mixer (Q2020 and Q2024
>in push-pull). This mixer has very little distortion and very good strong
>signal handling.
>
>3.) 70MHz signals are converted to 8.2MHz .
>
>4.) The 8.2MHz signals reach the gate of Q2009 through C2043 (darkened line
>on schematic). This point precedes all narrow 8MHz IF filtering--allowing a
>rather wide swath of unwanted signals to reach the gate of Q2009 along with
>the desired signal. 
>
>5.) Q2009 is left operating even when the noise blanker is turned off and
>can have substantial gain depending on bias voltages at TP2001. Bias
>voltages at TP2001 can be varied by changing menu settings for NB gain, but
>even the lowest NB gain settings never fully turn off Q2009!
>
>6.) Q2009 acts like a mixer, creating unwanted mixing products of desired
>and undesired signals. Accumulated level of all signals reaching the gate of
>Q2009 produce a large net voltage at the drain of Q2009. This voltage (and
>resulting net current) causes overload and distortion by driving Q2009 and
>2010 into distortion.
>
>7.) The unwanted distortion products feed right back down the same
>connection into the 8.2MHz IF."
>
>This is a one resistor mod on the back of the IF board.  It's very easy to
>get to and perform, much easier than accessing the RF board for performing
>the all important TX clix mod.
>
>Lou W7HV
>
>-----Original Message-----
>From: 1000mp-bounces at mailman.qth.net [mailto:1000mp-bounces at mailman.qth.net]
>On Behalf Of Ron
>Sent: Wednesday, April 25, 2007 11:49 AM
>To: All about Yaesu 1000mp
>Subject: Re: [1000mp] W8JI INRAD roofing filter measurements
>
>I was wondering is the NB  DSP  ?   I find it  hard to believe that a  
>narrow filter  would have any effect of the NB.   I could see how the NB 
>could be removing  IMD  if  it is DSP
>
>Ron  WA0KDS
>
>
>
>
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