Excellent audio file of SAQ reception

Andre Kesteloot andre.kesteloot at verizon.net
Sun Sep 25 16:21:12 CDT 2005

Forwarded from the QCWA Chapter 91 e-mail list:
André N4ICK

This is the easy way to listen to the excellent 12 words/min CW  
signal transmitted by station SAQ's Alexanderson Alternator on 17.2  
kHz on 25 September 2005 at 09:30 UTC and 12:30 UTC.  This WAV file  
was recorded by DL4YHF using a LF receiver and an active ferrite  
antenna to capture the signal and a computer program to down-convert   
its modulation to the audio range.

Imagine what it must have been like to copy such a signal back in the  
heyday of the spark transmitter.  It must have been a marvel to those  
that heard it.

For more on this alternator, see


Here's what I found interesting on this web page by Jerry Proc  
VE3FAB, regarding:

RF Signal generation:
"The alternator [at SAQ] runs between 2,500 to 3,000 rpm and needs to  
be set precisely to the correct speed in order that its 300 poles  
will generate the required frequency of 17.2 kHz.  To spin up such a  
monster, a motor in the range of hundreds or horsepower is required."

"In their heyday, most alternators ran on frequencies between 10 to  
30 kHz, although a few ran as high as 100 kHz. Some of these machines  
could be up to 50 feet long and weigh many scores of tons..."

CW modulation:
"With the key up, power is applied across a dummy load; with key  
down, power is sent to the antenna. This is accomplished with a  
magnetic amplifier circuit (also an Alexanderson invention) that  
changes a coupled circuit from being non-resonant in a key down state  
to being resonant at key up state in order to absorb the radiated  
load. If this was not done, there would be speed variations between  
the 'load' and the 'no load states' resulting in frequency excursions".

station SAQ:

"One Alexanderson alternator still remains in operating condition.  
This machine, whose power output is 200 kw, is located at the  
Grimeton Radiostation, 10 kilometers (6 miles) east of Varberg on the  
Swedish west coast.   The antenna at Grimeton is 2,280 meters (1.42  
mi) long."

Dick, KM4ML

More information about the Tacos mailing list