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Contents UNESCO World
Heritage Site Grimeton Radio The Software
Defined Receiver: SAQrx First Steps
Preparing for Reception Listen to World Heritage Grimeton
Radio (SAQ)
Grimeton
Radio is the last transmitter in the world generating rf
power without any electronic parts. No tubes, no semiconductors, only an
engine driving an AC generator. Receiving Grimeton
Radio (SAQ) on 17.2 kHz is as easy as the sketch below depicts:
You only
need to connect some aerial wire to the sound card of your PC and to install SAQrx, a software defined VLF receiver by SM6LKM
for the VLF band below 22 kHz. To protect your sound card from damage and for
amplifying weak signals, it is recommended that you use a simple amplifier
(SAQ preamp) between wire and sound card input. UNESCO World Heritage Site Grimeton Radio
(SAQ)
Grimeton
Radio (SAQ) is the last transmitter in the world preserved that generates VLF
radio frequencies with an alternating current generator (alternator), i. e. a machine that nowadays is only known to produce AC
current with frequencies below 100 Hz – electric power. After its inventor, a
Swedish engineer, this type of transmitter is called Alexanderson Alternator
(see Fig. 2 below).
From the late 1860s to 1930 about 1.2 million
unemployed people left Sweden to seek good fortune in the big cities of
America. Grimeton Radio with the call sign SAQ was
built in the 1920s to maintain communication between the Swedish emigrants
and their home country. For years the transmitter was operated as a
transatlantic telegraphy link to the RCA transmitter Radio Central in Long
Island, New York, USA. After
World War II with the advent of tube transmitters and rising knowledge of
worldwide propagation of short waves, VLF transmitters became less important.
Grimeton Radio was adopted by the Swedish navy to
communicate with submarines for the next decades and so could survive until
the end of the 20th century. It was finally put out of service in
the year 1995 – fully operative with 200 kW output and the last of its kind
in the world. As early
as 1996, Grimeton Radio was declared to be a
national heritage of Sweden and in the year 2004 it became a UNESCO World
Heritage Site.
Grimeton
Radio (SAQ) is activated in cw transmission by the Alexanderson Society at least two times
a year, at the beginning of July around the Alexanderson Day and on christmas eve (look out for skeds). These are
the rare moments, when US swls and hams have the
opportunity to prove that the old lady in Sweden still can be copied at the
east coast of the USA. Reports (from everybody, not only US hams!) are
rewarded by qsl cards. Hear the
roaring sound of the Alexanderson Alternator in the first minutes of this video
by a German TV station and decide for yourself if it might be an exciting
experience to listen to Grimeton Radio on 17.2 kHz.
The Aerial Wire
Don’t
waste much thought on creating a resonant antenna – the half wave length at
17.2 kHz is 8700 meters, much too long for your garden. And don’t think your
aerial wire is meant to last forever with a King Kong approved fastening and
measures for lightning protection. You just
need the antenna for half an hour two times a year, so clamp a wire into your
shack window or to the radiator beneath and get the other side attached to a
tent peg in the ground or to a tree or elsewhere (see Fig. 1
above). Make it as long as you can. Maybe you
want to try a ferrite rod antenna. Our ancestors used it with great effort
for long wave reception. Antennas
successfully used by US stations reach from a 4 foot loop portable on Port
Mahon Beach (Dover, Delaware) to a 100 meter long zepp
at 22 meters height at Marietta, Ohio. Find your own solution and don’t give
up after the first try! The Software Defined Receiver: SAQrx
SAQrx
is a sound card based receiver software by Johan Bodin, SM6LKM, covering 0-22 kHz and running under
Microsoft Windows. The filter bandwidth is selectable in three steps, 300,
1000 and 2400 Hz. It requires a sound card capable of full duplex at 44 kHz
sampling rate (satisfied by most of the onboard PC sound cards). Please note
that extremely cheap USB sound cards (sticks) often provide sampling rates of
only 24 kHz. If you don’t use the built-in sound card of your PC, please make
sure that the sound card chosen is registered as the first by the operating
system. Once you
have unzipped saqrx06.zip and started SAQrx.exe, you will have a panoramic
view of the frequency band between 0 and 22 kHz decoded by your sound card
(see screenshot below). Press [Help] to learn how to
tune the receiver and change the bandwidth. You can download the files needed
from SM6LKM’s web site, or – if not reachable – from this site:
The
SAQ preamp
There are three good reasons why you should
include a preamplifier between the antenna and the sound card:
To meet all these necessities, you can use
the following simple three-stage transistor amplifier:
Fig. 5:
Simple preamplifier doing both impedance matching and signal
amplification Semiconductors
used are common US transistors with noise figures below 4 dB. As well
suitable for the JFET T1 is the European type BF 245, for example. The
bipolar transistors T2 and T3 may be replaced by 2N 2219A,
2N 2222A, BC 109 or any low noise transistor meeting the general
requirements. (Please note: the
transistors have different pin connections!!) The
preamp can be powered with any supply voltage between 8 V and 14 V DC. The input
impedance is determined by R1 as part of the JFET input stage. With 3,3 M chosen here, any weak signal detected by your random
sized VLF antenna will be preserved for further amplification. The next
stage, implemented as a grounded emitter circuit, will give a 2- to 20-fold
gain controlled by PT1. Finally, the emitter follower output stage provides a
very low output impedance of 20 R suitable for any sound card input type.
Choose freely either the microphone or line-in jack for best performance with
your antenna. The
coupling capacities, C1, C2, C3 and C5, correspond to a cutoff frequency of 1
kHz to protect the sound card from overloading by power supply hum and other
QRM. If you
would like to produce a pcb, please feel free to
download the schematics and the board file (you may use a free version
of CadSoft Eagle). There are some boards left
here, so write an email to sabine+++dl1dbc.net if
you would like to get one. First Steps Preparing for
Reception of SAQ
For a
first test, you should try to find a military transmission somewhere in the
band pass of SAQrx. In Europe, there are several
navy stations between 18 kHz and 22 kHz transmitting a constant FSK idle
signal. On weekdays, you may find them transmitting information using a
two-tone or multi-tone FSK mode. Even at parts of the spectrum being quiet on
other days, you may discover data transmissions. From time to time, there is
a RTTY signal (? 45 baud) on 18.1 kHz, maybe transmitted by UFOE, a
Russian navy station. If you
want to make a simple test of your preamp and sound card arrangement, you can
use a test signal generated by the sound card itself with the help of free tone generator software
from NCH software. Connect
the headphones/speakers output of the sound card with the antenna connector
of your SAQ preamp and start NCH Tone Generator and SAQrx.
Always reduce the internal gain of SAQrx to 0 dB to
avoid interference. Please note:
it is not possible in all cases to use the same sound card for SAQrx and tone generation. If you recognize an extremely
high noise floor with the NCH Tone Generator connected, you should better use
a second computer to generate the test tone. If you
want to check the overall performance, activate “white noise” (see Fig. 6) and click “PLAY”.
Fig. 6: Testing the sound card’s
frequency response with white noise Note the
poor frequency response of the internal sound card of the Asus Eee PC I used for the tests (see Fig. 6): above 18 kHz there is a steep
decrease of sensitivity. Below the cutoff frequency of 1 kHz, gain is reduced
rigorously to prevent the sound card from overloading by power line hum. For
testing the gain of the SAQ preamp or in case of troubleshooting you may
choose a sine wave tone at 17.2 kHz. Activate the features depicted below and
set values by double-clicking and editing the “frequency” and “relative
amplitude” sections. Choose the amplitude in a way not to overload the sound
card with full gain of the SAQ preamp. Don’t forget to click “PLAY”.
Fig. 7:
Testing the SAQ preamp’s stages and gain with a single 17.2 kHz tone
(internal sound card of an Asus Eee PC) If you
would prefer to have a hardware oscillator solution, maybe you would like to
use a simple RC oscillator with four Op Amps stages called the Bubba
oscillator (see Fig. 8 below). With the parts chosen, it
will generate a stable frequency output around 17.8 kHz. You can adjust the
voltage output with PT1 in a 30 dB range to meet your needs. Adding a short
antenna wire to the output, you can take it outside your shack to test the
whole rig. Use a 9 volts battery for the portable one. If you
like it, you may use the schematics and board file in CadSoft
Eagle format.
Fig. 8: Bubba oscillator for testing
the SAQ rig Troubleshooting
If you
are using a laptop computer on batteries, the reception may be affected by
interference. Try to connect the RFGND jack to an rf
or a power line ground connection. If you
are in doubt of the performance of the SAQ preamp, please check the
preamplifier with the help of the NCH Tone Generator or with the Bubba
oscillator (see section above). The FET input stage is sensible against
static electricity. I killed several FETs touching the housing (!) after
rolling back my office chair in a low humidity environment. The spark-over
was one of heavy “ouch!” quality, so don’t be overcautious handling the
preamp. |
