[TenTec] Carl, Pmni, 756 etc

[Carl Moreschi]

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 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.  The design has  an 80 DB analog AGC implementation
ahead of the DSP and 40 DB of AGC in the DSP unit itself for
a total AGC range of 120 db.  This design works wonderfully.

Carl Moreschi N4PY
Franklinton, North Carolina
n4py@earthlink.net
----- Original Message ----- 
From: "Tim and Nancy Logan" <cyr999@extremezone.com>
To: "tentec reflector" <tentec@contesting.com>
Sent: Thursday, March 14, 2002 1:54 PM
Subject: [TenTec] Carl, Pmni, 756 etc


> Hi folks -
> I'm aiming this comment/question to Carl, but would like to share it
> with all. Carl has the benefit of owning a truly great TenTec DSP rig
> which he commented about yesterday as being the best receiver he's had.
> With that in mind I'd like to share some somewhat confusing observations
> and see if Carl has had similar experiences. Carl also still has, I
> believe, an OMNI V.9 (I could be wrong).
> 
> After operating the 756PRO for a few weeks, I fired up my OMNI next to
> it last night. A/B testing is tuff with these rigs, but I THINK the
> following is about right (hard to know if I'm tricking myself:
> 
> 1) - The OMNI has a smoother more pleasent sound to it's cw; the 756 has
> a slighly more "percussive" sound to it. Normally not a huge issue but
> see number two.
> 
> 2) - In high noise conditions the 756PRO seems to have a few pops and
> crackles associated with keying. The OMNI V.9 does not. I believe this
> may have something to do with AGC but I'm no techno wizard. A small
> percentage of the time it can be a bit quite annoying. It's possible it
> could be from RFI - but I'm still checking this out.
> 
> 3) - If you want to tune out background noise by turning back the RF,
> you have a greater range and sensitivity to do this  on the OMNI. The
> 756 has a much shorter range before the RF gain completely hides the
> signal as well as background noise.
> 
> 4) - The 756 seems to be able to hear weaker signals a bit better.
> 
> 5) - When there are a number of signals close together, the 756 seems to
> have a harder time sorting them out so that you just hear one. Part of
> this is getting used to being willing to use its tighter filters - so
> that for instance you might have the OMNI at 250 and the 756 at 150. It
> also might be that the 756 is hearing more signals than the OMNI - since
> sometimes I cannot locate these other signals on the OMNI. This is an
> area where it gets confusing. It is a no-mans land between understanding
> the noise floor, the best way to use DSP controls, selectivity, etc etc. 
> 
> I would be interested in hearing Carl's experiences and observations as
> he went from crystals to DSP. Did he have similar questions and
> solutions?
> 
> As I say, when you try to be objective - and are not depending on lab
> tests - these are two different beasts and hard to compare. I thought
> you all might find this interesting and, if Carl has time to respond,
> his comments will likely be much more interesting!
> 
> Have a good day all!
> 
> 73/Tim Logan KB7OEX
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