[TenTec] Omni VII - More IF scheme speculation

[Duane - N9DG]

More wild speculation below:

--- Bill Tippett <btippett at alum.mit.edu> wrote:

> N9DG:
>  >I'm 98% sure in the 455 kHz IF. The IF scheme from what I
> can
> tell is very close to the Pegasus/Jupiter with 45 MHz 1st
> IF
> and ~455 kHz second IF. Putting the improved filtering in
> those two spots will improve two areas of weakness in the
> RX320/350, Pegasus, Jupiter, Argonaut V and Orion sub rx.
> 
>          I agree but am left wondering why this is
> not called a Jupiter II rather than an Omni VII?  Perhaps
> marketing reasons.

My guesses are:
1) Because they feel it will equal or exceed the Omni VI in
performance.

2) It will be a "step up" from the Jupiter, the Jupiter will
remain in the product line for the near term holding down
price point just bellow $2K.

>  Here's my guess about the IF scheme:
> 
> 1st IF:  45 MHz with 20 kHz and (hopefully?) 6 kHz roofing

The preliminary info is a bit ambiguous about exactly where
the optional filters would go. However my take on it is that
there will be both 20 & 6 kHz filters at the 45 Mhz(?) 1st
IF. A 6 kHz filter in the 1st IF will make a world difference
because my experience with Pegs have been that it is the
stuff that gets through the first IF is what actually
overloads the 2nd IF and causes the spurs every 12 kHz up and
down the band with big signals. It is even more pronounced if
you've done the infamous IF gain "full clockwise" tweak. 

> 2nd IF:  455 kHz with ? standard and optional 2.5k, 500,
> 300 Hz

My take away from these filter choices at the 2nd IF
(assuming that this is where they are) is that the 2.5 Khz
1st LO synthesizer tuning step used in the RX320/350,
Pegasus, Jupiter, Argonaut V series radios is history. The
1st LO probably tunes to the actual frequency instead of
using the software LO (tunable) in the 3rd IF to compensate
for the 2.5 KHz step of the 1st LO in the older series
radios.

> 3rd IF:  XX kHz DSP

My guess is it will be either 12 or 14 kHz just like the
other TT DSP IF radios. The real question in my mind is
whether it uses the same series ADC of the RX320/350,
Pegasus, Jupiter, Argonaut V, or the AKM AK4524 of the Orion
series. Along with that will it use the same DSP processor as
the Orion (ADSP21065L - 32 bit) or is it a ADSP218x series
part (16 bit). Inquiring minds want to know.

> 
> I could be wrong about the 6 kHz roofing at 45 MHz...it
> could be at 455 kHz instead.  If so, it will only have
> mediocre front-end performance (similar to Pro 3, etc).
> Should the latter turn out to be true, expect Inrad to
> offer a 4-5 kHz roofer at 45 MHz in the blink of an eye!

I've often pondered the feasibility of modifying the Pegasus
(Jupiter, 516 etc.) with a narrower filter at 45 MHz.
Couldn't make it any narrower then about 6 kHz because of the
2.5 kHz 1st steps though because the first 2 IF's are
actually "nominal" frequencies.  

The other main that thing I wonder about is image performance
on 6M assuming that it is indeed a 45 MHz 1st IF. 45 MHz
would only be 5 MHz away from the low end of 6M which would
put a some pretty steep requirements on the front end band
pass filtering for that band.

I have some suspicions about the architecture/implementation
of the Ethernet side of the radio but I'll wait for some more
official details before publicly speculating on that.

In time we will know the answers to all of these questions.

Duane
N9DG

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com