Message-ID: <51432AFB.1070302@iup.uni-heidelberg.de>
Date: Fri, 15 Mar 2013 15:06:51 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: simple 475 kHz BPF
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Hi Dimitris,

Am 15.03.2013 02:20, schrieb Dimitrios Tsifakis:
> Hi Stefan,
>
> Opperman is great, they will sell to VK and I can pay via Paypal.
> Thanks for making me aware of this shop and the filter.
>    
Nice to hear and know :-)

> So, are you using this filter in a DC receiver front end?
Yes i do. My MF grabber 
(http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_MF_Grabber.html) 
uses a DC RX with that filter. The input- and output impedances are 
critical. You have to align the component values to the individual 
filter values.
I'm using this circuit: 
https://dl.dropbox.com/u/19882028/MF/MF%20Filter%20schematic.png
Looks like that in a prototype: 
https://dl.dropbox.com/u/19882028/MF/Mechanical_filter_with_source-followers.JPG
Later i changed the input to the yellow wire and replaced the 18k 
resistor on the input by a 500R resistor. This up-transformation gives 
you roughly 6 dB more output signal level. The input Z is very high and 
the output Z is measured to be close to 50 Ohm. So this may be even 
useful as an active antenna (630m band only) frontend in combination 
with a longer 50 Ohm coax cable and a usual RX.

My RX is using an SBL-3 as the mixer, also with a 50 Ohm input. This all 
fits well together :-)

I also use that filter in my MF TX converter!

>   I want to
> make a simple DC receiver because I want to set up a RX station at the
> top of the heavy ion accelerator building, at work. That will put the
> RX antenna at the top of a 50 metre tower, which may produce
> interesting results. I can also use a simple low power DC receiver at
> my block. It's amazing how low the QRM is over there, but of course, I
> don't have mains power.
>    
Calls for solar modules! I'm amazed how cheap they are these days.


73, Stefan/DK7FC