Hi Roelof,
So, this is the drawing (fasten your seat belt):
https://dl.dropbox.com/u/19882028/LF/DK7FC%20LFMF%20RX%20and%20RXantenna.png
(2.2 MB)
You see, there are 2 receivers connected to the cable in the shack. So i
can monitor LF and MF to the same time. The LF RX provides the DC supply
for the probe. The RX is supplied by a normal transformer DC supply
which makes a galvanic decoupling. In front of the transformer there are
EMC filters and so on, to decouple this from the mains. The output of
the RX is fed to the PC via a audio isolating transformer.
The MF is RX is there since a few days and is so far running on batteries.
The 50 Ohm in series with 1 uF is what i will add in a few minutes. This
should correctly terminate the cable in the shack since both receivers
have high inputs, such as a probe of an oscilloscope. However, if
looking sharp to the image you will see that there may be a problem from
the LF RX That's input short cuts a frequency, depending on the
resonance of the 100pF C and the L... Will see...
73, Stefan/DK7FC
Am 09.10.2012 16:32, schrieb Stefan Schäfer:
Hi Roelof,
In the moment it's just in my mind, not on the paper. I thought it is
no good idea to publish anything as long as the problems are not solved.
Of course all the problems are not only coming from the circuit design
but also depend on the local situation. The AFN signal is a good
example. I still don't know why it took so long until i discovered
this strong signal. Another issue is the grounding situation, cable
length and also the frequency response of the input impedance of a
receiver. All this may let a circuit design appear as a nearly perfect
solution in the one location but appers as complete rubbish in the
other location...
Just found another bug: The IM coming a few seconds after adding the
50 Ohm termination load are coming from a 0.1 A poly switch fuse which
is in the supply path of the RX, which feeds the probe. I should have
switched 1 uF in series to the 50 Ohm, not to apply DC, of course.
First i remembered the fuse but thought that this can't be the problem
because there are still signals shown on the MF RX. The fuse does not
lower the voltage to 0V but to 2V which seems to be enough to produce
some signals for the MF RX, which has its own supply voltage.
I'm going to make a drawing...
73, Stefan
Am 09.10.2012 15:50, schrieb Roelof Bakker:
Hello Stefan,
Where can I find the circuit diagram of your probe and also of the
"Fernspeiseweiche"?
73,
Roelof, pa0rdt
|
