Hi Clemens,
In my application i use it to decouple my 2 orthogonal VLF loops from
the soundcard and do some "matching" of the low output impedance of the
loop to the high input impedance of the soundcard. The levels absolute
signal levels rised arround 10 dB, so it is an improvement. However the
MSKs, especially DHO38 is 10 dB down now since the transformer does not
work on such a high frequency. Anyway, my focus is below 9 kHz and the
levels from 9...25 kHz are still fair.
There is however not really a S/N improvement and mains hum and all the
man made noise in the H field make the loops rather a game instead of a
system suitable to detect weak signals from Dreamers. Seems i have to
change the location of the loops. The old problem...
73, Stefan/DK7FC
Am 06.04.2012 10:42, schrieb Clemens Paul:
Hi Stefan,
I have measured exactly this transformer about a year ago for a friend.
He tried it for a (meanwhile abandoned) soundcard based SDR- TRX project
for HF and failed due to lack of sensitivity.
I connected two of these XMFs back to back and measured in a 50 Ohm
environment
with a VNA from 5-20kHz.
There was plenty of loss,IIRC something *around* 10dB per transformer.
That's not surprising after you have measured the DC resistance (high!).
This may or may not be of importance for your application depending on
your AF level and type of matching (power matching versus voltage
matching).
73
Clemens
DL4RAJ
----- Original Message ----- From: "Stefan Schäfer"
<[email protected]>
To: <[email protected]>
Sent: Thursday, April 05, 2012 4:21 PM
Subject: VLF: Audio transformer test
VLF,
I just checked the amplitude and frequency respose of the audio
transformer i use to decouple my signals between soundcard and
antenna. Just a simple test. They are in use in various applications,
are cheep and small.
Type, Distributor and datasheet:
http://www.reichelt.de/Trenntrafos/NFU-1-4/index.html?;ACTION=3;LA=444;GROUP=C54;GROUPID=3320;ARTICLE=73039;START=0;SORT=artnr;OFFSET=16;SID=32fRwi5qwQASAAACIkJWk502917f27b61570f9f85c5c030e3f831#av_tabdata
Looks they operate down to 5 Hz which is excellent:
http://dl.dropbox.com/u/19882028/VLF/Uebertragertest.png
Also the wide range looks fine up to 20 kHz:
http://dl.dropbox.com/u/19882028/VLF/Uebertragertest_wide.png
In the pictures, the upper SL instance is a frequency generator
driving the headphone output of the soundcard. The lower instance
records signals coming from the Mic input.
As a conclusion i found that the transformer is even suitable for
ZEVS receiving at 82 Hz.
73, Stefan/DK7FC
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