[1000mp] W8JI INRAD roofing filter measurements

[Lou]

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