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
