LF: SAQ on 24 Dec. 2007

[Dick Rollema <dickrollema@casema.nl>]

To All from PA0SE

Today I had again good reception of SAQ on 17.2kHz. I used a Wandel &
Goltermann SLM type SPM-12 connected to the aerial system for 136kHz with
26nF extra in parallel with the loading coil.

Replacing the aerial by a one-turn untuned square loop of 1 x 1 m the
signal was sufficiently over the noise to be measured at 0.155 microvolt
(25Hz I.F. bandwidth).

 From this follows a field strength of about 429 microvolt/metre (52.6
dBµV).
On June 30, 2002  I measured 482 microvolt/metre (53.6
microvolt/metre. So the measurements are rather consistent.

This makes it possible to do some speculation as to the power radiated by
SAQ (Effective Monopole Radiated Power, EMRP). 

The coordinates of SAQ are given as 57.07N, 12.24E. Using a computer
program written by Harry, PA0LQ, I find as QTH locator JO67CB. My own
locator is JO22GD. Again using Harry's program yields a distance of
735km.

We can now enter these data into the graphs of CCIR Recommendation 368-7
for ground-wave propagation. This results in:

Type of ground  dielectric constant   
conductivity (mS/m)  EMRP

Perfect ground         
-                                       
-                           
1.4kW

Land                          
40                                    
30                         
3.0kW

Land                          
22                                      
3                         
3.7kW

Medium
dry              
15                                      
1                        
4.7kW
ground

Dry
ground                 
7                                      
0.3                     
5.9kW
ground

If we estimate from these data an EMRP of 4kW then with an alternator
output of 200kW the efficiency of the aerial system is (4/200) * 100% =
2%.

This may not seem impressive but for an aerial at such a low frequency it
is  not too bad I think.

The aerial system consists of six vertical radiators of 127 m high. 
They are fed in phase at the top and each radiator has its own loading
coil and earth electrode (system also designed by Alexanderson) . 
The total horizontal length is 2200 m, which is only 0.13
wavelength.  So the system may have been designed to give some gain
in the wanted direction I cannot see how this could have been
achieved.

It would be nice if someone nearer to Grimeton would measure the field
strength outside the near field area, for instance  at 5 wavelength
distance, or 87km. 
At that distance at 17.2km perfect ground can be assumed for calculating
the EMRP (1kw produces 300mV/m at 1km distance, decreasing in a linear
way with distance).  

73, Dick, PA0SE