Message-ID: <50745161.7030406@iup.uni-heidelberg.de>
Date: Tue, 09 Oct 2012 18:31:29 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <50731B6C.2060506@iup.uni-heidelberg.de> <50732867.7070201@telia.com> <5074294B.80807@iup.uni-heidelberg.de> <op.wlwzelqpyzqh0k@pc-roelof> <50743561.9060504@iup.uni-heidelberg.de>
In-Reply-To: <50743561.9060504@iup.uni-heidelberg.de>
Subject: Re: LF: active antenna output termination?
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: quoted-printable
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


Hi Roelof,

So, this is the drawing (fasten your seat belt):=20
https://dl.dropbox.com/u/19882028/LF/DK7FC%20LFMF%20RX%20and%20RXantenna.=
png=20
(2.2 MB)

You see, there are 2 receivers connected to the cable in the shack. So i=20
can monitor LF and MF to the same time. The LF RX provides the DC supply=20
for the probe. The RX is supplied by a normal transformer DC supply=20
which makes a galvanic decoupling. In front of the transformer there are=20
EMC filters and so on, to decouple this from the mains. The output of=20
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=20
should correctly terminate the cable in the shack since both receivers=20
have high inputs, such as a probe of an oscilloscope. However, if=20
looking sharp to the image you will see that there may be a problem from=20
the LF RX That's input short cuts a frequency, depending on the=20
resonance of the 100pF C and the L... Will see...

73, Stefan/DK7FC


Am 09.10.2012 16:32, schrieb Stefan Sch=E4fer:
> Hi Roelof,
>
> In the moment it's just in my mind, not on the paper. I thought it is=20
> 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=20
> but also depend on the local situation. The AFN signal is a good=20
> example. I still don't know why it took so long until i discovered=20
> this strong signal. Another issue is the grounding situation, cable=20
> length and also the frequency response of the input impedance of a=20
> receiver. All this may let a circuit design appear as a nearly perfect=20
> solution in the one location but appers as complete rubbish in the=20
> other location...
>
> Just found another bug: The IM coming a few seconds after adding the=20
> 50 Ohm termination load are coming from a 0.1 A poly switch fuse which=20
> is in the supply path of the RX, which feeds the probe. I should have=20
> switched 1 uF in series to the 50 Ohm, not to apply DC, of course.=20
> First i remembered the fuse but thought that this can't be the problem=20
> because there are still signals shown on the MF RX. The fuse does not=20
> lower the voltage to 0V but to 2V which seems to be enough to produce=20
> 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=20
>> "Fernspeiseweiche"?
>>
>> 73,
>> Roelof, pa0rdt