[JRC] NOT the usual NRD-525

[Phil Atchley]

Hi.
Like myself, many listeners have an JRC NRD-525 receiver, either as their
primary set or among their stable of receivers. Personally I feel that this
is one of the finest solid state receivers that I've ever owned, and I've
had probably WELL over a hundred including Icom R-71A's, Kenwood R-5000's
etc.

HOWEVER!  It does have one particular weakness that is known to most long
term users and is a major detractor to many.  That weakness is "ultimate
selectivity" and it shows up whether you are using a narrow 300Hz CW
bandwidth or the "wide" AM bandwidth or anything in between.

This weakness shows up in two ways.  The first is interference or QRM from
strong signals off to the side and out of the normal bandpass of the
selected filter.  The other thing it shows up as is a high "hiss" level when
listening to weak stations, particularly in the AM mode.  The latter
annoyance is due to the high gain 3 stage IF amplifier that follows all
filter selectivity.  It is simply TOO WIDE for normal use.

Here are the fixes that I did to my NRD-525 and, simply put, IT IS NOT THE
SAME RECEIVER!

1.  On the CFH-36 Filter Board.

   A.  I replaced the first 455KHz filter (LH-12,  12KHz wide) with a Murata
CFW455IT filter.  This is the same mod that many people have done to their
set and it  makes a big difference in ultimate selectivity.
   B.  I bought a 300 Hz Collins Filter for the CW "Narrow" slot.  This was
from Sherwood Engineering and they provided a number of resistors to replace
various resistors/inductors in the filter selection area.  This provides
better impedance matching to ALL the filters and eliminates the inductors
that can couple signals around the filters.   (NOTE, you are replacing SMT
components and it is NOT for the soldering iron impaired folks out there).
   C.  I then installed a CASCADED PAIR of Murata filters, the CFJ455K5 AND
the CFJ455K13 filters in the "AUX" filter "FL-6" slot.  This provided a nice
bandwidth that falls between the "Wide" and the "Intermediate" filter
bandwidths. Makes for full sounding SSB OR sharper AM selectivity than the
"Wide" position does.  Especially useful for listening to Shortwave
Broadcast Stations in the USB/LSB modes.  I used them because I had them!


The above changes resulted in somewhat better ultimate selectivity but the
wideband hiss from the Wide IF remained on weak signals and I felt that
selectivity could also still be improved significantly!   The following
cured this COMPLETELY...

2.  On the CAE-182 Board.

    A.  This mod ADDS an additional filter between the 2nd and the 3rd IF
amplifier.
    B.  Remove resistor R-52 (100 Ohm SMT) that is between Transformer T-3
and Transistor Tr-3.  A Murata CFW455HT was installed, connected to the pads
where the resistor was connected (pads are, Gate of Tr-3 and Secondary of
transformer T3).  The filter ground pins were grounded to a nearby pad.
Then a 2.2K-Ohm resistor is connected from the pad that connects to the Gate
of Tr-3, the other leg of this resistor connects to the OTHER )common)
secondary lead of transformer T-3.  This provides a 2.2K-Ohm load to the
filter AND a DC path for the gate of transistor Tr-3.  Secure the filter
from dislodging with a dab of adhesive.  NOTE. When the board is installed
the filter just fits nicely between the back of the circuit board and the
sheetmetal divider.

CHECK YOUR WORK CAREFULLY FOR SHORTS WHEN FINISHED!!!  I suggest you wear a
grounded wrist strap while working to prevent static damage.  I will not be
held responsible if you break your radio....

THE RESULTS.....

As I said before, this is NOT the same receiver that left the JRC factory.
Some may find that the strong selectivity of all those cascaded filters is a
little TOO NARROW for Program Listening of the stronger Broadcast stations,
but as an Avid DXer I've always preferred narrow bandwidths.   Whether you
are listening to Shortwave broadcasters in AM wide or "utes" in the LSB/USB
modes, you will find that the background is much quieter due to less "monkey
chatter" from off frequency stations and greatly reduced high frequency
"hiss".

WHERE TO FIND PARTS:  I didn't have to look very far.  I had all the filters
that I needed and which had been removed from junked out CB Radios, old
receivers etc.  (SOME CB radios use the smaller 455H filters, not sure if
they are as good as the larger 455HT filters) In retrospect, I would
probably use two Murata CFW-455HT filters, one each to replace Filter FL-2
on the filter board and to add to the IF strip. (the HT filter bandwidth is
a little wider at the nose but has a better shape factor)  But if you have
to buy them look for Murata Filter distributors in a Google.com search.

73 de Phil  KO6BB

********************************************************
*  Chasing NDB's (Non-Directional Beacons)with ...     *
*  RECEIVER 1: JRC NRD-525 W/300Hz Collins filter.     *
*  RECEIVER 2: Homebrew Longwave CW receiver.          *
*  AUDIO FILTERS: Datong FL-3, Heathkit HD-1418.       *
*  30dB Gain Low Noise Tunable Preamp as needed.       *
*  ANTENNAS:                                           *
*    Coil Loaded 18.5 Meter Long Sloper.               *
*    30 Inch long Active Whip, 7 Meters high at base.  *
*  LOCATION: Merced, Central California.               *
*  COORDINATES: 37.18N  120.29W  CM97sh.               *
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