With a 500 Hz filter, one could / should be able to " see" up to 15+ PSK
signals (31.5Hz) within the passband. I do it this way all the time and
there's no problem.
73
Bob K4TAX
----- Original Message -----
From: "Steve Ellington" <N4LQ@igLou.com>
To: <W8JI@contesting.com>; "tentec reflector" <tentec@contesting.com>; "Carl
Moreschi" <n4py@earthlink.net>
Sent: Saturday, March 16, 2002 9:40 PM
Subject: Re: [TenTec] Carl, Pmni, 756 etc
> The PSK crowd really gets upset when I tell them I'm using a 500hz filter.
> They say stuff like...."You need to keep the filters open wide so you can
> see all the stations on your waterfall." Weird Science!
>
> Steve
> N4LQ
>
> ----- Original Message -----
> From: "Tom Rauch" <w8ji@contesting.com>
> To: "tentec reflector" <tentec@contesting.com>; "Carl Moreschi"
> <n4py@earthlink.net>
> Sent: Sunday, March 17, 2002 2:06 AM
> Subject: Re: [TenTec] Carl, Pmni, 756 etc
>
>
> > Hi Carl,
> >
> > > Let me describe the main receive characteristics of the rx340. I do
> > > not consider the 10 khz dynamic range specs to be meaningless. If you
> > > have ever run in field day with lots of transmitters in the near
> > > field, one of the most challenging things for a receiver to do is
> > > operate on SSB with another transmitter on CW on the same band or
> > > viceversa. Most receivers fail miserably at this.
> >
> > That actually is one of the least challenging applications, and has
> > little to do with how the receiver works with close signal spacing.
> >
> > Only the stages in front of the roofing filter are involved in
wide-split
> > overload. If we look at manufacturer and old ARRL tests and
> > reviews, we see they all like to measure outside the roofing filter
> > passband with 10-20kHz spacing or wider. Almost anything looks
> > good at wide spacing.
> >
> > > That said, if your are inside the roofing filter, you are obviously
> > > limited to the dynamic range of the DSP chip. This is 40 db. So for
> > > signals that are closer than 10 khz to the desired signal, 40 db is
> > > all the dynamic range you have. When an undesired signal is within 10
> > > khz of the desired signal and stronger than 40 db above the desired
> > > signal, the analog AGC will come up some to keep the DSP processor
> > > from overloading. This is done as best as it can be by the rx340
> > > hardware and I find I rarely get into this situation.
> >
> > I don't know what the selectivity ahead of the DSP is.
> >
> > If the blocking or IM DR of the DSP system is 40 dB and if the
> > receiver **can't** use a 500Hz or narrower roofing filter on CW or a
> > 2.5kHz roofing filter on SSB, the receiver would offer poor
> > performance in many real-world situations.
> >
> > It might be fine for casual SSB use (wide filters) in urban or some
> > suburban locations, but stay away from weak-signal CW on the low
> > bands, especially if there are multiple signals in the passband of
> > the roofing filter!
> >
> > As a matter of fact, that DR is about the performance of a typical
> > PSK system. You should hear the PSK folks whine and bellyache
> > about overload when a high power (100 watt transmitter) signal
> > comes on a kHz from them!
> > 73, Tom W8JI
> > W8JI@contesting.com
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
>
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