VLF tests

Frank Gentges gentges@itd.nrl.navy.mil
Tue, 21 Dec 1999 14:48:58 +0000 (GMT)


We are working on a lot of various things here for LF with our license at 
136.75 kHz.  I like you eneded up as a "suit" in the front office of the 
Navy but am having a ball now getting back to my roots.  I find I can 
function just fine.  I never wanted to leave the lab but my superiors 
felt different at first and I think they later wished I had stayed there.

Your experience with filters could be helpful.  Some thoughts...

We are looking for narrow audio filters to copy CW at horrendous S/N 
ratios.  It is hard to find 50 Hz bandwidth filters but at that bandwidth 
you can copy CW much better than at 300 or 500 Hz which is more common.  
Several club members have the DSP development kits and at some point 
these should prove to be good and flexible for this.  TI DSPs seem to be 
more general purpose while Analog Devices fixed point processors are more 
optimized for the transversal filter function.  The Analog Devices shows 
up in the TenTec RX320 as the DSP so we have some interest in hacking the 
DSP code to get some narrower filters.  See our LF web page at
<www.amrad.org/projects/lf> for our LF mod for this receiver.

Other LF projects going on include LF receiving antennas and LF power 
amplifiers using common power FETs.

You need an LF signal generator to test those receivers.  Look around for 
an HP 606.  Its pretty good for that and old enough to be reasonable in 

I'll add you to our LF mail reflector so you can get into the mainstream 
of our work.  You also need to watch the LOWFers.  They are doing some 
nifty work with killer restrictions on transmitter antenna's and power 
levels.  Look at <www.lwca.org> and get on the LOWFer mail reflector.

Frank K0BRA

On Tue, 21 Dec 1999, Bob Hicks wrote:

> I'm interested.  Retired engr from Collins/Rockwell.  Have Collins 651S and
> Harris 590 both of which have "some" vlf capability -- unmeasured.  Some
> test equipment, unfortunately most starts at 100 kHz or higher.  Basically
> an RF engineering background with speciality of filter networks -- but like
> most engineers of my age retired in management and tools are a little rusty.
> Good cheerleader.  VLF novice although around TACAMO and Loran C projects
> early in career.
> Bob in plain ole Plano, TX
> w5tx@airmail.net
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