Tom,
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. Years ago, I had a ham that lived
next door to me. Our antennas were only 100 feet apart. We could
never operate on the same band at the same time. Well, I did an
experiment with the rx340 and my tentec delta. On 15 meters,
I setup my delta with a dipole about 100 feet apart from the rx340
antenna. I ran 100 watts on the delta. What I found was as long
as I stayed at least 10 khz away from the rx340 receive frequency,
there were no effects from the delta signal whatsoever. The rx340
is the best receiver I have ever seen for this type of overload.
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.
But when it occurs there is no popping or artifacts generated whatsover.
The desired signal just drops in audio strength a little.
This is the only bad effect I have seen with the rx340. And the Orion
will fix it with its 250 hertz roofing filter. The benefits of the rx340
far outweigh this one weak point. The audio out of the rx340 is
truely something to behold. Amazing clarity on AM broadcast stations
(the sync AM is unbelievable), SSB that allows you to find exactly
the best filter width for maximum fidelity and QRM rejection, and CW
with unsurpassed filter sharpness.
Carl Moreschi N4PY
Franklinton, North Carolina
n4py@earthlink.net
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "tentec reflector" <tentec@contesting.com>; "Carl Moreschi"
<n4py@earthlink.net>
Sent: Friday, March 15, 2002 3:02 AM
Subject: Re: [TenTec] Carl, Pmni, 756 etc
> > First let me say no all DSP implementations are alike. If DSP is done
> > properly, DSP is no different than any other type of filtering. It
>
> Except we probably need at least 12 bits of digitized information
> and a very good low-noise fast A-D convertor to have dynamic
> range that equals that of a conventional crystal filter.
>
> Right now that means it costs much more to have the same
> performance as conventional filters provide, but I expect that will
> change in a few years.
>
> The best solution is to do a good front end with narrow conventional
> filters, and then a DSP system for final selectivity. Of course the
> first filter would be what sets the window for excellent dynamic
> range.
>
> > is just much more flexible. The CW signals through my rx340 sound
> > wonderful and very pure tone. I hear none of the problems that Tim
> > decsribed. I never use my Omni V.9 anymore because the SSB and CW
> > sound so clear and nice in the RX340.
>
> > The design of the RX340 takes great care to never overload the
> > DSP processor.
>
> What is the close-spaced two-tone IM dynamic range, and the
> blocking DR? (None of the useless 10kHz spaced stuff that makes
> the receiver look better than it is in the real world please!)
> 73, Tom W8JI
> W8JI@contesting.com
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