[1000mp] Modifying The INRAD roofing filter board.

[Mike Schatzberg]

Here is a rough translation of his posting:

Gilles De VE2TZT:

Hi everyone,

I book information that may be of interest to owners and FT1000 or MK V, I
think especially at Christmas.

For the last WPX CW, I had installed the filter of roofing INRAD (Other
changes Noise Blancker and key clicks already carried out by the front) and
I was rather disappointed by the results (not found any improvement or even
a worsening on the intermodulation signals strong close on 40m especially
when I have a good antenna).  That comment seemed to contradict measurements
made by the ARRL in QST in February 2005.

That is why I was not surprised by falling on a very interesting article on
W2AJI


http://www.va3cr.net/mods/roofingfiltermodmarkV.htm

The day before the CQWW CW, I told myself I need to decide to settle the
issue in order to have the heart test net and true greatness. I still made a
minimum of verification: After delivering the menu 9-1 by the gain of the
3rd IF his factory set (14 for my field MKV) I compared the deviation
S-meter main receiver to the secondary receiver (even and especially same
mode filter (500 Hz) on both) by injecting a carrier with a single crystal
oscillator on 3510 kHz with a length of over 30 cm as a receiving antenna.

The result is self-explanatory, I S-9 on the first and S-8 on the second (2
sticks difference).

>From that moment on, the arguments of W2AJI seemed plausible: the amplifier
filter INRAD has too much gain and more than offset the insertion loss, as a
result, probably, the 2nd too mixer receiving its signal signals
transmoduler starts earlier than expected.

So I made the change suggested (very simple, it is sufficient to replace a
12 ohms with a 15 and a 220 by 150).

Following the first and second receiver have this time that a difference of
1 / 2 to 1 baton following the amplitude of the signal (because of the
problem digit: all or nothing).  It seems to me that on re-enters this time
in the original specifications of INRAD and that, indeed, the modification
decreased the gain of 3dB.

The amplifier is now, as expected, justly compensate for the loss of
insertion of the filter.

So I handed the gain of the 3rd IF at 13 (-1 compared to the factory
setting, and consistent with the doc INRAD) for the same indication on the
two receivers.

This is, of course, very subjective, but at no time during the CQWW CW, I
had the same unfortunate impression choppy noise coming from nowhere that I
experienced during the WPX.

----- Original Message ----- 
From: "VE2FWW" <ve2fww at globetrotter.net>
To: <1000mp at mailman.qth.net>
Sent: Sunday, January 27, 2008 8:38 PM
Subject: [1000mp] Modifying The INRAD roofing filter board.


> Hello
> I wonder if anybody in this group had modified the INRAD MARK V OR FIELD
roofing filter board.
> I read the informations on W8JI website.
> This mod is done to keep proper input impedance  for loading the filter
> There are two resistors to be changed on the INRAD board....R5...which is
a 12 Ohms ...replaced by a 15 Ohms....and R6 which is 220 Ohms...replaced by
a 150 Ohms...
> I would like to know if anybody performed this mod on the INRAD Board....
> I have Inrad Roofing filters in my Fields ...and it would be interesting
to know the difference between the MOD and the NO MOD????
> Any input would greatly appreciated...
> Thanks
> NOEL ve2ryy
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