[TenTec] Hello Orion Users

[Carl Moreschi]

Bill,

The Orion DSP filters are NOT audio DSP filters.  They are IF DSP filters
with the 100 db of AGC action in the DSP alone.  They are much better than
anything else out there.

Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <tentec at contesting.com>
Sent: Monday, May 05, 2003 9:05 PM
Subject: [TenTec] Hello Orion Users


> N4PY wrote:
>  >Why not just go with the tentec 250 hertz filter?
>
>          Carl, I've had cascaded 250 Hz filters in my MP
> for over 6 years and I find I seldom use them.  250
> Hz is too narrow, especially in contests, because you
> will miss many guys who call +/- 500 Hz from your
> frequency.  Even dual 500 Hz filters are often
> too narrow and my normal mode of operation is with
> shifted 2.0 kHz filters which give an effective BW
> of about 1 kHz (this is on 10 meters...not 160 where
> 500 Hz is about all you can get away with in a contest).
> The only place 250 Hz filters are very useful for me
> is for extremely weak signals in noise, but often I
> actually can hear those better with a wider BW and let
> my ears do the DSP filtering.
>
>          Inrad's roofing filters have the following bandwidths:
>
>                  BW at -6 dB        BW at -60 dB       Shape Factor
>
> "400 Hz"        455 Hz  955 Hz  2.1
> "250 Hz"        315 Hz  700 Hz  2.2
>
> http://www.qth.com/inrad/ and click "Performance Curve"
>
> There is actually only about 140 Hz difference between
> them so I think the 400 Hz is a nice tradeoff.
>
>          Regarding Mark's question about the relationship
> between the crystal roofing filters and DSP bandwidths,
> The way I understand Orion works is as follows:
>
> 1.  When you select a DSP BW, the next higher roofing
> filter that is enabled is automatically selected.  However,
> these MAY be over-ridden.  For example if I had the optional
> 500 Hz roofing filter installed, and set my DSP BW to 400 Hz,
> I could manually choose any roofing filter above 400 Hz, i.e.
> 2400 Hz or 1000 Hz or 500 Hz.  Why would I want to do this?
> To make the combination a little sloppier to catch those guys
> who call off frequency.  Off-frequency signals would be a bit
> weaker but should be more readable than if I used the narrowest
> roofing filter possible.  I don't see anything in the manual
> about adjusting the DSP shape factor, but that might also
> be desirable for some cases.  I'm sure the manual is very
> basic at this time so it may be possible and I may be simply
> missing whether shape factor can be adjusted or not.
>
> 2.  Orion assumes a 500 Hz filter is in the 500 Hz roofing
> filter position when enabled.  If my Inrad filter is actually
> 455 Hz, I probably want to make sure the DSP BW is not set to
> more than 450 Hz.  I'm not sure if there would be any artifacts
> (false signals) of setting DSP wider than the actual analog
> bandwidth (roofing filter) but there could be.  Maybe someone
> at Ten Tec will comment.  Remember that the DSP BW's are
> continuously adjustable from 300-6000 Hz in 10 Hz steps.
>
> 3.  The simplest way to think about Orion's filtering is two
> distinctly separate stages: analog roofing filters at 9 MHz
> followed by DSP filters at audio frequencies.  The analog
> roofing filter does the heavy lifting by first removing
> unwanted signals outside its passband and then the DSP filter
> goes to work with fine tuning what's left.  The combination
> is the best of both worlds of analog and digital filtering.
>
>          I don't have my Orion yet but this is the way I understand
> Orion's filtering scheme works.  Of course I could be all
> wet so hopefully someone from Ten Tec will straighten me out!
>
>                                                  73,  Bill  W4ZV
>
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