[Lowfer] A Newbie's thanks, and a note on using Linrad for LF work.

[Roger Rehr W3SZ]

Thanks to all for your help to a newbie.

Yesterday evening after work I finished the K0BRA active antenna and put it
up in the attic with a wire about 50 feet long.  I am not yet ready for an
outside antenna, although I know that will help a lot.

This afternoon I was able to log some better DX than the RD beacon 2.7 miles
away including

IUB	404	Baltimore MD
CLB	216	Wilmington NC
RNB	363	Millville NJ
JF	373	New York NY ... see below for this one...only found with Linrad

plus 10 Pennsylvania stations, closer to home; all confirmed by the NAVAID
frequency assignments you all so kindly showed me how to find.

My main problem with these low frequencies is all of the noise (even though
the FT1000's noise blanker removes a LOT of noise), and separating and
seeing the signals among the noises.  Fortunately, the NDB's have a
characteristic signature on waterfall displays, as you know.  So using a
waterfall, which I am sure many of you do, makes finding them easier.  The
problem is that if a waterfall is used with a conventional receiver, the
swath of spectrum that can be examined at one time is limited to the SSB
bandwidth of the receiver.  For EME I have used a homebrew receiver with
Leif Asbrink's Linrad software to detect signals too weak for me to find
otherwise, and I thought the same thing might be very helpful for this
Lowfer stuff.  The way I have Linrad set up, I can see a 40 KHz (yes, 40,000
Hz!) wide swath of the spectrum at once.  I thought this would make hunting
the NDB's much easier.  And it did.  Its easy to immediately see the NDB's
among the various noises on the waterfall display by using Linrad in this
manner.  And with Linrad, you just have to click on the signal in the
waterfall to immediately hear it.  No tuning of the receiver is required to
hear signals within the Linrad display.  You only need to retune the
receiver to go to the NEXT 40 KHz wide swath of spectrum.

To test this and demonstrate Linrad used in this way I tuned the homebrew
receiver down to the 4000 to 4500 KHz band, setting it to 4389 KHz.  My
AMRAD converter has an output of 4000 to 4500 KHz, so this set the center of
the passband received (and put the center of the Linrad display) to 389 KHz.
With the receiver tuned in this manner, 389KHz received frequency appears as
22000 KHz on the Linrad display.  The low end of the display, labeled as
5000, is (389 - 17) 372 KHz.  The top end of the display, labeled as 45000,
is 412 KHz. I put a gif file of a screen dump of the Linrad screen as it
looked when I did this this afternoon at
http://www.qsl.net/w3sz/lowfer1.gif  .  The details of the Linrad screen as
shown in the gif file will be explained below.

Each NDB has a characteristic signature, as you all know;  a central carrier
with two dashed lines spaced equally on either side of the central carrier,
which represent the CW sidebands.  If you look at the waterfall at the top
of the screen in the gif file, you can see

JF centered at 6000 (373).  CW sidebands are at 5000 and 7000.  I could not
detect this without Linrad, and didn't even know it was there till it
appeared on the waterfall.  It was however Q5 copy with the Linrad filter
set at 20 Hz

NXX centered at 21000 (388).   CW sidebands are at 20000 and 22000.  By
initially setting the receiver frequency to 4389 KHz, I had centered the
receiver on the 22000 cw sideband.

AB centered at 33000 (400).   CW sidebands are at 32000 and 34000.

IUB centered at 37000 (404).   CW sidebands are at 36000 and 38000.  Only
the one at 38000 is easily seen and heard, secondary to noise.

So I was able to see 4 beacons spread over a span of 32 KHz at once, and
just had to click with the mouse on each signal to instantly hear it. WIth
Linrad, I picked up a beacon (JF) I had no idea was there with my
conventional setup (FT1000MP with the same converter, etc plus Spectran
audio filter). I saw it on the waterfall, and clicked on it, and there it
was Q5 copy with Linrad's filter set at 20 Hz, which is where I usually run
it.

Linrad can also be used with a conventional receiver with smaller
bandwidths, but to me its real power for lowfer use is seeing these wide
swaths of spectrum where the beacons just jump out at you off of the
waterfall.

For more information on Linrad you can go to Leif's site
http://ham.te.hik.se/homepage/sm5bsz/linuxdsp/linrad.htm
Linrad runs under Linux.


or to the part of my web page with my experiences with Linrad
http://www.qsl.net/w3sz/SM5BSZ1.htm  which is a branch off my DSP page
http://www.qsl.net/w3sz/start.htm

My very simple computer controlled HomeBrew receiver is briefly discussed at
http://www.qsl.net/w3sz/FAQ.htm#5a and there is a schematic at
http://www.qsl.net/w3sz/HBreceiver.gif

Thanks again, all!

I am happy to answer any questions / criticisms.  I hope the above is of
interest to the list.  If not, I apologize.  I will write up a small web
page that combines what is in the email above with the gif file sometime
soon.  For now just a bit more:  below the waterfall is the broadband
spectrum.  Below that the 'red' window near the center of the screen is the
high resolution display; the NDB 'IUB' is centered in the passband.  The
'green' window to the right is the filter window.  The yellow bars show the
filter shape and width, which can be changed just by dragging the mouse over
it.  You can again see IUB centered in this window, in the filter, and you
can see the keying sidebands. Below that you see the amplitude is 18.8-19.1
dB

73,

Roger Rehr
W3SZ   FN20ah
2 Merrymount Road
Reading, PA  19609-1718
http://www.qsl.net/w3sz