Joe, I'm not sure some of your suppositions are correct.
First of all, the ADC samples at a significantly higher rate than the
incoming RF (for HF), at 245.76MHz. Then, those samples go through
decimation inside Digital DownConverter (DDC) in the FPGA, and the higher
the decimation, the more the processing gain, and therefore added "bits". I
believe the typical assumption is that you gain the equivalent of approx.
one-half bit (3dB) of dynamic range every time you decimate (divide) the
sample rate by two. This is real gain, not some imaginary trick or magic.
If you start with a 245.76MHz sample rate, and end up with 240kHz (example),
you could achieve a processing gain of an additional five bits, or 30dB. If
my quick math is correct. All without AGC or other games.
Throw away at least one A/D bit, so 15 bits(ADC) plus five bits(proc gain)
yields 20 bits, or about 120dB of dynamic range. I must be a little off, as
I saw one note on the Flex reflector that they think 153dB or so of dynamic
range. Maybe by lowering the final sample rate some more, or not tossing
all of one bit of the ADC. I believe Mitola suggested that 130dB of dynamic
range is adequate for HF, I'm not sure if that includes noise from storms,
etc. BTW, the new software is called SmartSDR.
I have been playing with DDC receivers for a couple of years now, and I
firmly believe they will be the future. I suggest that thorough research of
DDC-based receiver design will alter your perception. It did mine.
I love my K3/P3, and do not plan to replace it anytime soon. It just works
GREAT, and is a nice compact box without requiring a computer to use. But,
I was very tempted to by a Flex 6500. That is, until I saw the $200 per
year charge for the software. Technically, very leading edge. Marketing,
you decide.
Hope this isn't too off-topic.
73,
Terry, WB4JFI
-----Original Message-----
From: Joe Subich, W4TV
Sent: Saturday, May 19, 2012 7:29 PM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] OT: Dayton New Equipment Show
The Flex 6000/6700 is an "on frequency" direct digital conversion
radio - that is a 16 bit analog to digital converter operating at
the "front end" of the radio with no intermediate conversion/IF
and filtering stages. In addition, all of the DSP is contained
in the radio (no more PowerSRD). The new software for the Flex
6000/6700 (reportedly "PowerRX") is essentially a "glass control
panel").
A general purpose computer is required for PowerRX but communication
between the computer and transceiver is via TCP/IP which means the
computer can be anywhere. Audio input and output will be available
both on the transceiver and from PowerRX (interesting for remote
operation scenarios).
The issue will be the severely limited dynamic range of the 16 bit
ADC. Without effective AGC ahead of the ADC there *will* be overload
problems on crowded bands (e.g. 160/80/40) where any transceiver must
deal with many extremely strong ("local") signals while maintaining
maximum sensitivity. With AGC, the strong local signals will cause
"blocking" as the gain is reduced to prevent overflow of the ADC.
The new Flex design is certainly "interesting" but may not truly be
ready for critical "real world" use with the widely varying signal
levels in amateur service.
73,
... Joe, W4TV
On 5/19/2012 3:43 PM, Tony Estep wrote:
> On Sat, May 19, 2012 at 11:53 AM, Edward R.
> Cole<kl...@acsalaska.net>wrote:
>
>> ...website now shows the Flex-6000/6700 newest entry into the SDR
>> market....
>
> ===========
> Said to be digital from antenna connector to output. Their hardware has
> long needed updating, so perhaps this will be it. However, Flex's really
> weak link has always been their software/systems integration, so it
> remains
> to be seen if this does anything to mitigate that.
>
> Tony KT0NY
>
>
>
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