Re: [TenTec] First DSP IF Corsair II?

["Tommy" <aldermant@alltel.net>]

Really NEAT!! Ham radio is alive and well at Duane's QTH. Congrats 
on the 'playing'...could be very interesting!

Tom - W4BQF

----- Original Message ----- 
From: "Duane Grotophorst" <n9dg@yahoo.com>
To: <tentec@contesting.com>
Sent: Saturday, December 04, 2004 5:02 PM
Subject: [TenTec] First DSP IF Corsair II?


> I don't know if any one else has done this before but
> I have created a DSP IF Corsair II, well sort of. The
> experimental lash-up that I'm playing with took all of
> 15 minutes to setup and get going. All that I did was
> connect the antenna input of the Flex Radio SDR-1000
> through a capacitor/tap to connector #73 of the Xtal
> Filter Board (81252). This is the RX output side of
> the 9 MHz 1st IF filter of the Corsair II. This first
> IF filter then essentially becomes a 2.4 kHz roofing
> filter for my little experiment, sort of like an Orion
> :).  The SDR-1000 was then tuned to 8.999800 MHz to
> hear the IF signal coming through the Corsair II I 9
> MHz IF filter. Tuning around the bands is accomplished
> with the Corsair II's VFO, the SDR-1000 is run in USB
> mode for all bands except 17M which is opposite, this
> is necessary for the same reason you must use SB-R to
> operate SSB on that band normally. With the SDR-1000
> tuned to 8.999800 MHz the frequency display of the
> Corsair II is exactly on when the audio pitch of the
> RX signal is correct in both receivers. Since I'm only
> tapping the 9Mhz signal off of the RX path of the
> Corsair II I can actually listen to both the Corsair
> II and SDR-1000 simultaneously; so making performance
> comparisons is easy.
>
> Some impressions and observations:
>
> 1. Much quieter and cleaner recovered audio.
> 2. Incredibly sharp "IF" filters in the SDR-1000, they
> can be set to as little as 10 Hz and you can still
> copy CW FB at this bandwidth, and no ringing.
> 3. Automatic notch filter, the Corsair II did not have
> that before, the SDR-1000 now provides it.
> 4.  The SDR-1000's DSP processing does add ~100 - 200
> ms of delay to the audio (pretty much excludes ever
> using QSK CW with this configuration).
> 5. The Corsair II alone does have a slight edge in
> absolute sensitivity from the tests I've done so far
> (but I haven't calibrated the SDR-1000's settings very
> carefully yet).
>
> The SDR-1000 is no slouch for dynamic range all by
> itself but coupling it with the RX RF filtering and
> low phase noise 1st LO and 2.4 KHz IF filter of the
> Corsair II does make for an extremely pleasant
> listening experience. By tapping into the first IF
> output of the Corsair II I avoid all of the mixer
> noise contributions by the additional mixers needed
> for the Corsair II's PBT functions. It also bypasses
> the Corsair II's product detector and all of its
> low-level audio stages and AF filtering (all of which
> are rather noisy by today's standards).
>
> Since the Corsair II is essentially running normally
> it provides most of the AGC action to prevent
> overloading the SDR-1000. Even so with 2-3 roughly
> equal and strong CW signals inside the Corsair II's
> 2.4 IF filter the SDR-1000 still does not suffer any
> blocking effects that I can tell from my tuning about
> the bands so far (I even tested it a bit during the
> 160M contest last night). You can easily pick out
> pretty weak signals between two strong signals <200 Hz
> away, and you also get a panadapter display for a 2.4
> KHz slice of the spectrum that is defined by the
> Corsair II's 1st IF filter (so I can tell when those
> strong signals are there).
>
> All in all a fun little experiment that did not take
> long to set up, I will play with it a bit more to see
> if it is truly useful from a practical standpoint or
> not. Either way there are many other fun things to try
> with SDR-1000 that I haven't gotten around to messing
> with yet. This experiment has also confirmed my
> suspicions about where most of the internal RX noise
> of a Corsair II actually comes from.
>
> Duane
> N9DG
>
>
>
>
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