[1000mp] Improving the Close Spaced IM3 DR on the Mark Vwith Inrad Roofing Filter Mod

[Mike Schatzberg]

Hello Pete:

In general, I think most of the filters have lower insertion losses than the
original prototype designs.  This means that the on-board amplifier has in
general about 3.5 db beyond what is necessary to compensate for the
insertion losses.

If you do not find agreement between your two receivers with the factory
original settings in menu 9-1, and find the main board S meter readings
higher than the sub receiver, you probably have too much  1st IF gain.  This
will lead to the poor IM3 DR results as reported by W8JI with the closer
spacings.  Lowering the IF gain in the menu does not solve the problem,
because it lowers the gain in the 3rd IF which is too late.  The intermod is
created in the second mixer.

73 and Happy DXing,

Mike
W2AJI
----- Original Message ----- 
From: "Pete Smith" <pete.n4zr at gmail.com>
To: <1000mp at mailman.qth.net>
Sent: Sunday, January 27, 2008 10:05 AM
Subject: Re: [1000mp] Improving the Close Spaced IM3 DR on the Mark Vwith
Inrad Roofing Filter Mod


> Perhaps I missed it, but I did not see anything in the article about how
to
> determine if your particular roofing filter has the excessive gain.  I
> tried mine (a fairly early one) with an Elecraft XG-1 signal source, and
> adjusted the IF gain for S-9 at 50 uV, which required a setting of 12.
I'm
> not sure now what the original default setting was, because before the
> roofing filter I had the Inrad IF mod in there.
>
> I have not noticed the IMD deterioration that Mike talks about.
>
> 73, Pete N4ZR
>
>    At 08:46 AM 1/27/2008, cherokeehillfarm at earthlink.net wrote:
> >Improving the Close Spaced IM3 DR on the Mark V with Inrad Roofing Filter
Mod
> >
> >Hello 1000MP Fans:
> >
> >I came across an interesting posting on the Contest Group of Quebec
website.
> >The posting is from November 26, 2007, from Gilles, VE2TZT.
> >
> >Although written in French, it appears that Gilles had quite a problem
> >during contesting with the new Inrad Roofing Filter installed in his Mark
V.
> >You can see his posting here:
> >
>
>http://contestgroupduquebec.com/index.php?option=com_simpleboard&Itemid=41&
func=view&id=528&catid=2
> >
> >My rough translation of his problem is as follows:
> >
> >"For the last WPX CW, I had installed the roofing filter INRAD (other
> >modifications Noise Blanker and key clicks already carried out with by
> >before) and I had been rather disappointed by the results (not found an
> >unspecified improvement, to see even a degradation of intermodulation on
> >strong close signals in particular on 40m where I have a good antenna).
This
> >observation appeared to me in contradiction with the measurements taken
by
> >the ARRL in the QST of February 2005."
> >
> >So basically he says that he didn't see any improvement advantage after
> >installing the Inrad filter, and he even experienced a degradation of the
> >resistance to intermodulation products on 40 meters where he has a
> >particularly good antenna.
> >
> >His article concludes that performing the simple modification to the
Inrad
> >Roofing Filter board as suggested on the VA3CR website, fixed the
problem,
> >and he has now no issues while contesting.
> >
> >For those of you that are interested in addressing the same issue, you
may
> >read about this modification here:
> >
> >http://www.va3cr.net/mods/roofingfiltermodmarkV.htm
> >
> >73 and Happy DXing,
> >
> >Mike
> >W2AJI
> >
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