[R-390] Poor man's R389

[roy.morgan at nist.gov]

Quoting DW Holtman <future212 at comcast.net>:

> Hello,
> 
> I have never had a receiver to access VLF. Anybody have any suggestions 
> on inexpensive converters for HF receivers such as the R-390A?

DW,

There have been converters made and published in ham journals. But they
overload, suffer from feedthrough and have other maladies.  Heath made one, and
Palomar Engineering does still, and it appears to be head and shoulders above
the Heath one I have used. Cost is $100.00 
http://www.palomar-engineers.com/VLF/vlf.html

"Many receivers do not cover the VLF band below 500 KHz or, if they do, have
greatly reduced sensitivity there. QST’s reviewer (Jan. 2000)  reported: “the
difference was astonishing. In many cases I couldn’t hear the navaids at all
with the IC-706, but they were clearly audible when received through the
Palomar converter.”

The VLF Converter has excellent sensitivity. It also has a 7-pole filter to
eliminate overload from local medium wave broadcast stations.

It connects between your antenna and the radio. When turned “On” the 10-500 KHz
band appears at 4010-4500 KHz for general coverage radios (Model VLF-S) or at
3510-4000 KHz for ham-band-only radios (Model VLF-A). When turned “Off” the
antenna connects directly to the radio for normal shortwave reception."


FAR Circuits almost certainly has a kit (circuit board and magazine reprint) for
very modest money.  You buy parts and enclosure and build it yourself. Cheapest
way to get one of these converters:


The downloadable catalog http://www.farcircuits.net/FAR_CKTS.pdf lists:
73’s Dec91 VLF SPACE SHUTTLE RECEIVER $7.50
COMM. QUARTERLY Winter94 JOE CARR VLF RECEIVER $6.00
LOW &MEDIUM FREQ SCRAPB00K 9th ED RADIO CORNELL REGEN RECEIVER PREAMP $4.00
POPULAR ELECTFeb95 AAVSO VLF RECEIVER PREAMP BY CARR $6.00
(I see no converter, but the Low and Medium Frequency Scrapbook likely has
one.)


There is a simple "mod" for the R-390A to let it hear below the normal lower
limit of 500 kc: Simply feed your antenna into the radio at one of the test
points in the RF deck *after* the input tuned circuits (through a cap to avoid
messing up any AGC.)

It may overload, suffer from cross modulation and so on, but it gets you started
with zero actual modifying, building, or expense.  A preslector or low pass
filter (or both) may be very useful, depending on your antenna and location.

Roy,
K1LKY

Roy Morgan
7130 Panorama Dr.
Derwood MD 20855