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Re: Transystems Modifications



The filter that I am using is the DFC22 series from Murata. They offer about
35 dB of image rejection when used at 2256 MHz. The filter that comes with
the Transystems converter lets 2401 pass through as well as the image at
2111 MHz. What this means is that when receiving on 145 MHz with a 2256 MHz
LO, the converter dumps all of the noise energy from both 2111 and 2401 on
145 MHz. This basically doubles the noise on 145 MHz. Using a filter with
over 30 dB of image rejection can cut this noise by over 2.5 dB.

My question is: Why would you even leave these filter in the converter is
they are not offering considerable image rejection. I understant that they
offer protection from strong nearby signals, but they are also degrading the
NF by being before the first stage. I have not measured the loss of the
first filter, but it should be at least 0.5 dB. I do not have any pre LNA
filtering on any of my converters and I have never experienced any overload.

The specs of the Murata filter can be found here:

http://www.murata.com/murata/weblibrary.nsf/pdf/c10/$file/dfc.pdf

These parts are available in QTY 1 for $8 or $3 dollars a piece.
Link here:


http://www1.future-active.com/results.asp?hidPageName=1&ddCountry=US&ddCurre
ncy=USD&txtSearch=dfc22

These are easy to solder and work great

Pieter N4IP








----- Original Message -----
From: "Douglas Cole" <n7bfs@qwest.net>
To: "Pieter Ibelings" <elpieter@hotmail.com>; <amsat-bb@amsat.org>
Sent: Monday, May 07, 2001 4:04 PM
Subject: Re: [amsat-bb] Transystems Modifications


> Pieter Ibelings wrote:
> >
> > Hi Guys,
> >
> > Yesterday I modified a Transystems downconverter by bypassing the input
> > filter and installing a Murata 2.4 GHz filter at the second filter
location.
> > The results are really really good. The noise is lower and the
selectivity
> > is also greatly improved. The old filter configuration let the image in
> > which would add 3 dB of noise to the converter. A picture of the
> > modification is below:
> >
> > http://www.ozoni.com/n4ip/tsmod.jpg
> >
> > Other pictures at :
> >
> > http://www.ozoni.com/n4ip
> >
> > Now I am in the process of replacing the LO by a 282MHz TCXO x 8
multiplier.
> >
> > This thing will outperform my other homebrew converter if I am not
careful
> > :)
>
> Man , you can sure bang things out fast pieter , took a look at your
> helix/stepper motor movie , that was neat , though I am curious on the
> transystems mod , is the new filter the little salmon colored cube to
> the left of center in the pic' ?
>
> I haven't gotten mine apart yet to look inside , so don't know what it
> looks like un-modified ....
>
> Thanks for sharing :)
>
>
>
> --
> Douglas Cole   N7BFS
> AMSAT#26182 , K2 # 544
> http://www.users.qwest.net/~cdoug3
> Registered Linux user # 188922
>
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