[1000mp] On-Air test for Roofing Filter check ??

[Mike Schatzberg]

Hello Dennis:

I can see how some confusion about some of the improvements of the narrow
roofing filter may occur.  For the casual operator, who does not know what
IMD sounds like on the air, in the midst of a contest or pile up, the
difference on IMD reduction may not even be recognized.

Such an operator should be able to recognize reduction from whiskering
interference from nearby very strong signals, or perhaps reduction in
desense when using the wide 6 khz 3rd IF filter, with no 2nd IF filter (menu
5-0 8.2-455).  Just select this option in menu 5-0, and you will hear the
vast difference, with narrower overall bandwidth with the new 4 khz roofing
filter and the ceramic 6 khz 3rd IF filter.  Now the overall bandwidth is
approximately 4.8 khz, and desense from nearby strong stations far less!  I
use this setting as my ultra low noise set up for very weak stations on 20
meters.  Added selectivity, also with low noise can be added by
superimposing the DSP IF filter, IDBT button, onto the 2nd IF.  This
combination works very well indeed.

As I have stated here before, and my findings were echoed in the recent RSGB
article, I feel the Inrad instructions are not correct in suggesting that
the IF gain setting in menu 9-1 be reset to the factory default value, if
you have had the Inrad IF mod in your radio previously.

The overall gain of the two stage low noise amplifier is apparently higher
than stated by Inrad, perhaps as high as 8 DB.  This permits a reduction of
the gain setting by as much as two to three numbers in menu 9-1.  Therefore,
the filter's amplifier accomplishes the same IF hiss reduction at least as
does the earlier IF mod.  Then, since the filter is narrower, it lets in
less band noise altogether.  I believe the noise floor is indeed at least 10
DB lower after the mod!  This change should be able to be noted as well by
the casual operator.  THERE IS NO NEED FOR BOTH MODS IN THE MARK V.

Even the casual operator will notice how quiet the receiver is, particularly
with the RF gain control set back to the 1 to 2 o'clock position to avoid
overload and to provide best fidelity on stronger signals.

Happy New Year and Happy DXing,

73,

Mike Schatzberg
WB2AJI


----- Original Message ----- 
From: "roofus" <roofus at sbcglobal.net>
To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
Sent: Wednesday, December 29, 2004 8:52 AM
Subject: Re: [1000mp] On-Air test for Roofing Filter check ??


> How interesting, so many have posted how well their roofing filter works
and
> now 1 (one) post saying he is not sure he saw a difference (non contest)
and
> it's "NOT TO ENCOURAGING".  I guess it could be worse, it could have been
a
> new IC7800 he just bought.
>
> Dennis KI8U
>
>
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