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Re: Murata/K5GNA PCB Filter Plots..



Hmm.. I'd agree the Transystem is a nice little converter for the price, and 
the Murata filters look good.

I think in some ways from this message and from a personal one I just 
received from K5GNA that they misunderstood some of the comments on my page.

I agree that if you are going to go "simple and cheap" that simply replacing 
the second filter and the LO synth crystal is the way to go.  If you are 
going to use a BBQ grill thats fine and ulimately recommended at this point.

My comments about using a DEM preamp, etc, are for stations who are already 
going to use a bigger (or non BBQ) dish and a helix anyway. In  this case 
the preamp and the CP feed would give you a definate edge...

Bob K5GNA is correct that in most circumstances, and certainly if you would 
use a "Commercial passive feed" that the extra 0.5 dB or so of connector 
losses you'd get would offset the slightly higher NF of the 3033/3733... 
well almost... but certainly if $/fractions of dB were concerned.

However-- unless the first filter is also used for Noise Figure matching of 
the GaAs FET in the front end of the Transystem unit-- which is a 
possibility--- a simple teflon stripline board of that size would have 
minimal losses, maybe 0.1 dB.  This *has* to be better than a comb filter in 
the front end.  Grounding of the FET front end can still be done by a 1/4 
wave grouded stub.  Yup, someone has to build some of these boards, but I 
cannot see how as K5GNA has stated (once in his instructions, and once to me 
personally) the NF would get worse if this was properly designed and 
installed.  Sorry, but I've been there and done that before...

But in any case, the real reason I network analyzed the filters is for the 
experimenters out there to have some quantative data, and be able to make 
"unpopular improvements" if they wish-- and for the rest of you out there to 
see proof that these readily available, inexpensive units ($54), with a 
inexpensive ($12) easy to do modification can work very well on AO-40.  With 
reasonable care in the conversion the performance from unit to unit will be 
very consistant and very good.

I also see for the Drake US people out there (like me-- can't have enough 
downconverter "toys" around) that the PC board/Murata filter combo K5GNA 
sells is probably a better alternative than either getting a filter from the 
UK or (gasp) from DigiKey...

Fred W0FMS


>From: K5OE@aol.com
>To: fspinner@hotmail.com
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Murata/K5GNA PCB Filter Plots..
>Date: Wed, 11 Jul 2001 23:28:28 EDT
>
>Fred,
>Thanks for the quantitative & graphical data.  Let me offer a little
>qualitative observation from installing the K5GNA Murata filter in a TSI 
>3733.
>
>I have been using local MMDS channels to check out various downconverters 
>and
>antennae for a while--more as a "does it work or not?" kind of pass/fail
>test.  I also have used these signals for various kinds of comparison 
>tests.
>The 3733 is a hot little unit for MMDS, noticeably better than a stock 
>Drake
>connected to my now-standard-test-jig (a 16-turn helix pointed at Discovery
>Channel from a second story bedroom window).  After I installed the Murata
>filter, the picture from the MMDS channels (about 2520 MHz) was, well,
>crappy.  It was all snowy and had bad audio.  I immediately realized this 
>was
>due to the sharp roll off of the filter.  The d/c performs very well for 
>2401
>MHz, as I am using it right now to capture telemetry from AO-40 at  62,000 
>km
>(lots of synchs but no good CRC's right now at MA=128).  For those that are
>curious, or perhaps think I am kidding, here's a screen shot that I use as 
>a
>consistent test pattern for my not-quite-the-way-the-professionals-do-it
>comparative analysis:
>
>http://members.aol.com/k5oe/mmds.jpg
>
>73,
>Jerry, K5OE
>
>fspinner@hotmail.com writes:
>
> > It's been awhile since my last insanity.  I decided to check the K5GNA
> >  PCB/Murata DFC22R44P084BHD Dielectric filter.  Also, I editoralized a 
>bit
>on
> >
> >  the page, and overall the filter board looks like a good board for the
>AIDC
> >  3033/3733 and probably the Drakes as well.
> >
> >  Network analyzer plots are at:
> >
> >  http://members.home.net/fspinner/W0FMS/Murata
> >
> >  or as always through the:  http://w0fms.org  "domain-reflector"
> >
> >  Fred W0FMS
> >
> >  _______
>----
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