Daniele, Warren,
I don't know the inspire kit but my own grabber is a broad band
receiver too and it seems to work. You can see on the 'wideband window'
that i am receiving from 0...24 kHz without extra filtering (sure,
there is a lower cut off frequency due to the design), so the wideband
window shows what the soundcard input 'sees'. As long as there occurs
no saturation due to high levels in the soundcard input (e.g. @ 50 Hz
or 60 Hz in USA), all the filtering can be done in SpecLab. It is even
necessary to cover some kHz since the noiseblanker has to 'see' the QRN
to blank it then.
Also a BFO can be easily arranged in SpecLab. It is no problem to
listen to a CW signal on VLF like SAQ in some weeks :-) There is a
mixer and a VFO where you can type the desired frequency, like 16500 Hz
if you want to listen to SAQ at 17200 Hz on 700 Hz. Also you can choose
a desired CW filter bandwith from 0...100%.
And Markus/DF6NM already mentioned that it is easily possible to 'lock'
the soundcards samplerate to a military VLF transmitter, so you have
quasi atomic clock accuracy. Therefore it is useful to receive up to
above 20 kHz since most of these transmitters are operating there. A
signal decrease due to a filter by 20 dB is no problem there since the
signal levels are very high, usually, depending of the RX location.
I am monitoring the Russian Alpha transmitters RSDN-20_1 which is an
atomic standard frequency at 11904.7619xxxxxx Hz. The grabber window
for that (attached screenshot) shows that the transmitter is currently
active (useful for people who try to optimise their RX, since the
Alphas are OFF sometimes) and it shows that my grabber windows are
accurately sample rate drift compensated. You can see that the drift is
quasi 0, means < 0.001 Hz which is OK for up to QRSS/DFCW-6000 and
above. No need for extra fans and/or keeping the window closed during
the transmissions ;-)
On saturday we saw that Jacek received the signal with best S/N with a
short E field antenna! So my hint for Daniele is to try such an antenna
as an alternative to the loop antenna. Maybe the local H fields are
causing more QRM than the E fields. Jacek (and me) is living in a city
as well! So if Daniele can arrange that the antenna is higher above the
house, it could be an advantage. And those antennas are cheep and small
:-) If possible, it would be nice to have almost no filtering except a
low pass filter at 15...25 kHz. This is surely useful since the LF/MF
bcd stations have to be attenuated. This can even be done before the
first FET stage (if FETs are used) by using a series resistor which
forms a RC low pass filter with the gate capacitance.
There are several sulutions. Wish you fun to arrange your best system
:-)
73, Stefan
Am 05.10.2010 16:09, schrieb Warren Ziegler:
Daniele,
The Inspire kit is a broadband high gain audio amplifier with a very
high input impedance - generically its a 'whistler receiver'.
Whistler receivers like Inspire are good for listening to whistlers,
tweeks, dawn chorus etc but it would be completely useless for
listening to amateur VLF experiments - its broadband, has no 'bfo' to
detect a carrier and would be difficult to interface to a sound card.
--
73 Warren K2ORS
WD2XGJ
WD2XSH/23
WE2XEB/2
WE2XGR/1
On Tue, Oct 5, 2010 at 4:43 AM, Daniele
Tincani <[email protected]>
wrote:
Hi VLF,
any opinions about the Inspire VLF-3 receiver kit?
Thank you in advance for your feedbacks.
Regards
Daniele
|
RSDN20F1.jpg
Description: JPEG image
|
