Quoting Duane - N9DG <[EMAIL PROTECTED]>, on Tue 20 Nov 2007 08:56:38 AM PST:
> > --- Jim Lux <[EMAIL PROTECTED]> wrote: > >> Actually, terms like SDR get bandied about quite a bit with >> different >> people meaning different things. Here's some background. >> <flame suit on.. this gets controversial> > > For me personally, Joe average(?) ham, I'm not really that > concerned with all the hair splitting definition semantics of > what SDR is or isn't. To me it all really comes down to > simply this: > > "It's all about the 'S' in 'SDR'. And the if the 'S' isn't > routinely changing the 'D' significantly, then all you have > left is just 'R'". > > So for me most of my future radio dollars will be directed > toward radios with lots of mfg. > supported/encouraged/permitted activity in the realm of the > 'S' & 'D', the 'R' will then take care of itself. A lot of > ham radios that do fit the typical definition of 'SDR' are > failing miserably when it comes to my stated position above. > > And I'm finding it increasingly difficult to even consider > radios that have large HW constraints to their SW > define-ability. > You're not alone. There are some practical problems.. sometimes the hardware constraints come from some performance reason (however, semiconductors are getting better every day..20 years ago, a 10 MHz A/D with 10 bits was really awesome. Now you can get 14 bits at 1GHz). We're probably a ways from the HF nirvana of the 30 bit converter at 125 MSPS where you hook an antenna to the A/D, and you're done. Likewise, high power amplifiers have their idiosyncracies that are not all entirely compensatable in software. Probably a bigger issue is the legal one. Hams are a small volume market compared to radios in general. The radio in general market has regulatory restrictions on just how flexible that radio can be to prevent users from just loading up a version of the software that radiates out of band or receives where you're not supposed to be listening. So, a manufacturer that is trying to leverage commercial radio designs for the ham market (since the ham market can't support huge R&D budgets) winds up building radios that inherently are not-user-modifiable. And, there's the Part 15 rules, too. (having the software in mask rom or OneTimeProgrammable PROM makes it easier to pass FCC muster for ham rigs.) It's instructive to look at all the hoops that Icom had to jump through to get the IC-7000 approved.. their filings are on the FCC website. Think of the complexities in modern autotuning HF amplifier designs.. they have little microcontrollers that sense the RF frequency and turn the amp off if you're out of band, and you can bet that microcontroller isn't something you can easily modify. We're faced with a real challenge.. It's easy to build a software radio based on a PC and a simple LO/QSE/QSD like the Flex or SoftRock that has instantaneous bandwidth of over 100 kHz. Even if you put (closed non-modifiable) firmware into the DDS control that restricts the DDS frequency to the ham bands, you could receive and transmit 50 kHz outside the bands. Historically, this hasn't been a big problem (transmitting) because the radios were inherently narrow band. Even if you were set on LSB, and tuned the VFO to 7.0000 MHz, the most you could do is transmit something at 6.995 or so. So the regulators have guard bands between the allocations and spurious emissions requirements to accommodate this. The last thing we want the regulators to do is mandate hardware frequency limits (e.g. filters). Nor do we want them mandating nonmodifiable firmware/software to achieve the same thing. Jim, W6RMK _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
