[1000mp] W8JI INRAD roofing filter measurements

[Pete Smith]

For those who are interested, W8JI had the following to say (on Topband) 
about the noise blanker in various FT-1000 models back in 2004:

"I've tried to make it commonly known the FT1000 family (and other Yaesu's)
suffer from an engineering oversite. They have an FET amplifier hanging off
the IF amplifier before the narrow filters, and they don't turn that FET's
gain down when the NB is not used. What this does is deteriorate close
spaced IM performance a substantial amount when the FET has maximum gain,
even when the NB is OFF.

In the FT1000 and D, this occurs ALL the time. You have to make a change
inside the radio to stop the problem.

In the FT1000MP, you can cure almost all of it by turning the front panel NB
gain control to zero when not using the NB. No change is needed.

In the FT1000MP MK V, you have to go into a menu and change a NB setting to
reduce NB gain. The only reason the MK V tests so much worse than other
top-end Yaesu's for narrow spaced signal performance is the menu setting of
the NB. Moving one resistor to a new location eliminates the need to get
into the hidden menu to change NB gain."

73, Pete N4ZR

At 12:52 PM 4/26/2007, you wrote:
>All,
>
>I email Tom Rauch (W8JI) about the INRAD and NB mod and, with his
>permission, here's what he said:
>
>" Hi Lou,
>
>... I'm not sure if the variation in results is due to variations in noise
>floor in the later IF stages or other characteristics such as the noise
>blanker gain setting or the gain of the IF amplifier. I've only looked at
>eight or ten radios for a limited time, but maybe I'll revisit my own
>FT1000's (I have one MP, two MP MK V's, and a FT-1000D) again soon.
>
>73 Tom"
>
>I hope Tom can get to this in the near future.   In the interim, we're on
>our own in terms of evaluating the relative merits of the various mods.
>
>We've heard from many who extol the INRAD roofing filter mod.  Has anyone
>here other than me done the W8JI NB mod and can report on their results?  As
>a reminder this consists of a very simple one resistor mod (or 1 resistor
>and three diodes on the 1000 and 1000D) that greatly increases IMDR(with NB
>off and at lowest setting).  Also, according to Tom's measurements, the NB
>mod does not negate the salutary effects of the INRAD roofing filter.  It's
>the INRAD filter that negates the improvements of the NB mod.
>
>I should add I'm not entirely clear on the NB mod with respect to the
>straight MP series.
>
>Lou W7HV
>
>
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