[R-390] The R-390A, a GREAT LF rig!

[Philip B Atchley]

Hello all.
Well, here we go again, "I'm trying to stir the pot".

I'm an avid Longwave Beacon chaser (NDB'S).  It's no mean feat to copy a
25 watt Longwave beacon at 2000+ miles or a obscure beacon in Brazil at
6500+ miles (I've done both).  It does put GREAT demands on both receiver
and antennas, especially if you live in a 2 by 4 lot in a mobile home
park with all kinds of computers, dish receivers and other RFI generating
trash from China.

Lately I've been using a homebrewed longwave converter with internal low
pass filter, antenna tuner/40dB pre-amp with a Hallicrafters SX-71A
receiver.  In times past I've used IF filters as narrow as 125Hz and
audio filters as narrow as 12.5Hz (modified DSP).  At this game
selectivity and frequency stability is EVERYTHING (Some NDB's with
duplicate ID's are within hundreds of Hz or less of each other).
Unfortunately the Halli does NOT have good frequency resolution, even
with calibration charts.  

After I put the R-390A in the listening position and used it the past
couple of nights I figured that it would make a GREAT receiver for my
purposes, the limiting factor was now my homebrewed LF converter which
used a NE602 mixer, known for poor dynamic range.

So, I dug up the Longwave modification for the R-390A, put it on a small
perf board and stuck it alongside the 1st mixer tube.  I installed a
solder type BNC jack in place of the IF output jack for the longwave
antenna.  This entire thing is a no holes drilled, no solder into the set
modification, and I'm pleased to say it works very, very well.  As it
couples into the cathode of the first mixer it doesn't appear to affect
operation above 530kHz at all.

When I connected my 60 foot loaded sloper antenna (the one I use for
longwave) to the LF antenna jack I was able to copy many of the daytime
NDB's, though gain was obviously way down do to no RF amplifier.  

I then modified my Longwave converter, pulling the NE602 out of it's
socket (good reason for using IC sockets).  I added one more BNC jack to
the two already on it and connected that to the output of the converters
pre-amp section (this is a Tunable pre-amp with sharp selectivity
itself).  The unit was set up top ground the HF antenna jack of the
R-390A when the pre-amp is on.  This in effect switches the antenna
between the LF and HF antenna jacks of the receiver when the LF pre-amp
is turned on.  

Does it work???   I'LL SAY IT DOES!  I have a better signal/noise ratio
on longwave than I ever had through the converter itself.  The 40dB gain
of the pre-amp more than makes up for the lack of an RF pre-amp in the
R-390A on longwave.  Signals are strong and clear.  If the RF gain is
wide open FCH-344 in Fresno (65 miles) pegs the R-390A RF meter, yet
there doesn't appear to be any IMD at all (due to the selectivity of the
pre-amp).  With the converter I used to hear a "ghost" of FCH-344 behind
MO-367 and a couple other places.  They are no longer there!

AND, for the "purist" the best part of it is the fact that the
modification can be removed in about 5 minutes, putting the original IF
output jack back in and pulling the wire out of the tube socket.   

73 de Phil  KO6BB
Loving home provided for wayward Boatanchor Receivers
ko6bb@juno.com
Merced, Central California
37.18N  120.29W  CM97sh

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