venerdì 24 giugno 2016

Se non sono pazzi non li vogliamo - Test di trasmissioni ULF al di sotto dei 3kHz !

Segnalato da Renato Romero : 







DK7FC ha scritto:
BTW, I am now preparing for first tests on ULF, the range between 0.3
>> ... 3 kHz. Tests on 2970 Hz have started. This is a completely new
>> league. 2970 Hz is almost 100x 'harder' than 8270 Hz. It is not easy
>> to generate a high voltage on my wire on that frequency. Transformers
>> saturate and i need 6.1 H of inductance! As a first step i am using a
>> large ferrite transformer with 2 E cores and a coil body. I have
>> wounnd 3000 turns on it by hand! :-) The ferrite material is N27 and
>> it can handle 1V / turn at 2970 Hz without a problem. I took 0.22 mm
>> diameter wire. 15+ layers and each one is isolated by Kapton
>> insulation tape, like the old TV transformers :-) See
>> %206.1H.jpg
>> and
>> %20coil.jpg
>> 
>> I can run just 3 kV, not more. Otherwise the 'transformer' which is
>> just a coil in fact, is risked to flash over.
>> At 3 kV my ERP is about 100 nW!
>> So far i managed 3.5 km to my own remote grabber, you still can see
>> the last races at
>> You still can see last traces from a previous 2 kV test there. The
>> SNR was 25 dB in 424 uHz. But this is just a near field test... The
>> far field starts at 16 km distance. It is a hard way to get that
>> distance. But i have built a portable E field probe and stereo audio
>> recorder with a Raspberry Pi. So i can take a walk in the forest and
>> receive in really quiet places, far away from any electricity. My
>> next plan i to receive my own signal in 7.9 km distance, there is a
>> nice place :-) I have also ordered a second cheap Neo 6M GPS module
>> for pps and NMEA signals on the other channel during the /p
>> experiment. Then this will be a ideal portable monitoring system for
>> post processing with absolute time stamps and even location
>> informations are stored.
>> We will see. I'll come back to you when i think there could be a
>> chance to see a trace on 2970 Hz, maybe in a 1 uHz BW :-) The QRN is
>> MUCH lower there, relative to 8.27 or 6.47 kHz! Maybe this is an
>> advantage that we underestimate now! But the man made noise can be
>> more problematic there, you know. So it is good for people who like
>> to take a walk in the forest and like to install a hidden wire there
>> to mount their portable RX to it and come back a few hours later to
>> bring it home and post process what they got :-)
>> 

>> 73, Stefan

1 commento:

Rodolfo Zucchetti ha detto...

con cosa posso ricevere il segnale, con il mio ampli Hi Fi Musical Fidelity XT100 con risposta in frequenza 20Hz-20 kHz, +0 -0.2dB mettendo un filo in ingresso audio :-) , con Spectran o cos' altro?

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