[Racal] 6790 On VLF

[Dallas Lankford]

In my experience the standard 6790 does quite well down to about 100 kHz =
with a set of VLF EPROMS.  To refresh my memory, I measured the MF / LF =
sensitivity of one of my 6790's again.  For a 5.7 kHz BW (Rockwell =
Collins torsion filter) in AM mode using 30% modulation, a 10 dB S+N/N =
ratio is obtained with 0.6 uV at 1000, 300, and 200 kHz, and this falls =
off to 1.1 uV at 150 kHz.  I haven't listened below 150 kHz.  In CW mode =
with a 300 Hz filter, the noise floor (MDS, et al.) is 0.06 uV at 150 =
kHz.  I use phased (home built phaser) interference (noise) reducing =
antennas (short grounded inverted L's with 9:1 transformer step-down for =
twin lead feed), and hear all sorts of non-directional beacons, and some =
trans-Atlantics from my location in North Louisiana.

But what I really like about my VLF EPROMS is that they provide tuning =
(handy!) steps of 1, 10, and 100 Hz, not the standard (unhandy!) 1, 30, =
1000 Hz of the standard EPROMS.  The 100 Hz tuning step is really great =
for tuning around with the tuning knob.  But be careful!  There are (at =
least) two VLF EPROM sets, one with the 1/10/100 and the other with =
1/30/1000.  The 1/10/100 set does not have AGC return (so you can't set =
up an S-meter with your remote control software), while the 1/30/1000 =
does have AGC return (which is a non-issue in my opinion because I turn =
my computers off when I turn my radios on).

These VLF EPROMS are available from:

Allen Bond
wb4gnt@arrl.net




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