[Aavso-sid-list] SID receivers

[ChrisAtUpw at aol.com]

In a message dated 19/02/2006, fsteyn at worldonline.co.za writes:
 

I am using a homebrewed received based on a SEA  receiver from the early 
seventies. This receiver consist of two tuned ferrite  pot cores around an 
opamp,then into a two diode detector followed by a DC amp.  Antennas are DIP switch 
tuned amplified loops with a 75cm  diameter

Hi Francois,
 
    There are variable capacitance opamp circuits  available. You use a 
variable resistor to set the exact capacitance. The  gyrator II uses a simulated 
inductance and a fixed capacitance.

I am getting very good results from NWC on 19.8  kHz (9363 km) and good 
results from  NAA on 24.0 kHz (11461 km). But the  question that came up in my mind 
is : now that solar activity is down and the  easy flares are gone as well, 
is it possible to come up with  a "new"  design that will still be technically 
possible, even in a far-off country like  mine ? I am trying to get reception 
from VTX3 in India at 7555 km or possibly  LeBlanc,France at 9100 km. Will I 
get "better" results if I tune to a more  distant station or to a more local 
one ?

    To get the longest daylight reception time, free of  night and dusk / 
dawn effects, try receiving stations on about the same  longitude, 18 deg E. The 
German or Italian stations may be the best for  you, but there is a station in 
France and two in the UK.
 
    Frequency band, kHz Transmitter   18.20 - 18.40 Le Blanc, France, 46:37N 
1:05E   19.48 - 19.68 Anthorn, UK 54:54N 3:18W    22.05 - 22.15 Skelton, UK, 
54:42:24N 2:53:06W   23.30 - 23.50 Burlage, Germany, 53:05N 7:37E   20.19 - 
20.34 Tavolara, Italy, 40:55N 9:45E
 
    I suggest that you look at _http://www.abelian.demon.co.uk/_ 
(http://www.abelian.demon.co.uk/)  for  some very useful reception tips.
    One problem with VLF receivers lies in getting  sufficiently narrow band 
reception to minimise both noise and adjacent  channel reception. One way of 
doing this is to use a phase lock loop and  coherent detection. The gyrator II 
does need polystyrene foil capacitors to  get a sufficiently high Q. One way 
of removing the effect of diode  temperature drift is to use a precision 
rectifier circuit driven by two opamps.  Signal diodes drift by about 2.5 mV / C 
Deg. This can be sigificant, depending  on the receiver location.
 
    Regards,
 
    Chris Chapman
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