[TenTec] Inrad #352 Filter for Orion

[Bill Tippett <btippett@alum.mit.edu>]

        Rob Sherwood NC0B of Sherwood Engineering recently
made some IMD measurements of the Inrad #352 650 Hz roofing
filter (inserted in Orion's 1000 Hz position) that several of us made
as a special order in January.  Here is a summary of Rob's results:

> > At 5, 10 and 20 kHz, there is no significant difference between the
> > stock 1.0 kHz Ten-Tec filter and the Inrad filter.
> > At 2 kHz spacing, the improvement is on the order of 6 to 7 dB.
> > At 1 kHz spacing the improvement is closer to 10 dB.
> > There is some strange hysteresis of a couple dB, as you change the level
> > around.  The IMD does not act exactly as one would expect.
> > I am guessing the digital AGC is doing strange things, causing the
> > hysteresis.
> >
> > The insertion loss of filters #2 and #3 are identical to the Ten-Tec 1.0
> > kHz filter.

        The bottom line summary is that the #352 allows Orion to retain
its 20 kHz spacing IMD performance of ~96 dB all the way down to
1 kHz for the modest cost of about $40 if you are willing to warm up
your soldering iron.  Rob's summary below includes only 1000 Hz filter
data but you can calculate performance numbers for the #352 using the
above data:

http://www.sherweng.com/Dayton_2004/Dynamic_Range_Data.pdf

More info on building these filters is at the site below:

http://users.vnet.net/btippett/inrad_.htm

Barry N1EU also has a site on building the filter using NPO disc
capacitors instead of the supplied surface mount caps, but qsl.net is
down at the moment and I cannot bring up the URL.

                                73,  Bill  W4ZV

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