State of the art
ajp166 at bellatlantic.net
Fri Sep 23 21:08:00 CDT 2005
>Subject: Re: State of the art
> From: woodelf <bfranchuk at jetnet.ab.ca>
> Date: Fri, 23 Sep 2005 17:17:59 -0600
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>> Actually the sound card modes like WJST and PSK31 only need the sound card
>> to aquire the signal at audio baseband then the CPU does the heavy lifting.
>> There is also software defined radio, all modes (AM/FM/SSB/CW) where the
>> CPU after aquiring quadrature baseband does the decode work, the RF portion
>> of a reciever can be simple to the extreme but provide prformance and
>> features at the upper end.
>Call me a old fart but I still like Analog Radio and real music rather
>than digital this and that. I still think the BEST radio's are still
>ones built by hand rather than a mass market product like you see now
>days. While I don't deal in HAM radio I do see ShortWave Radio's now and
>then ranging from $49 to $100 with very few features that I consider
>now to be valuable. State of the Art to me is using the best knowlage
>and best use of components at the time rather than cheapest product as
>it now is. -- mass production of high speed low quality FET's -- is
>today's state of the art for all electronic devices built today.
>DSP is great for getting a signal out of noise like a space probe
>with a watt or two of power but just what is the front end of the
>reciver like? Playing with HI-fi audio I found negitive feedback
>is often mis-used. Non-linear components generate x**n harmonics
>that creates more noise because nobody considers this anymore.
>A valve diode I think is the lowest noise diode but who uses that.
>XTAL radio people have great front ends with a high Q but who uses that?
>All this aside ham radio still needs good people who know the
>equipment rather than some $$$$ product by microsoft-radio-95 so when
>ham people need to be called out for real work saving people with radio
>they can do it be it state of the art or a old transiver that they just
>happen to have kicking around with them at the time.
Then you'd like the 5 tube 75/80m RX I've built. Or maybe the 6m SSB
transceiver using analog phasing techniques.
Thermionic diodes are noisy, much more so than silicon. Tubes at RF
cannot approach the noise figured that cheap transistors can. Though
a 3CX1000 amp is still cheaper than a transistor one and far more
tolerent of mishandling.
Crystal sets could not eliminate WGSM (740am) 3000W and 1 mile
away and allow me to hear WABC 770khz 40 miles away.
Non-linearity it's bad design for some things but useful where
efficientcy counts. Look at Class E trannsmitters and switchmode
power supplies for efficientcy.
I have a tranceiver for 6M/2M that uses IF dsp and it's frontend is
very sophisticated and hears as good as any. To beat that took me
a year using some very good analog technology and it's limited to
6M and needs a digital display for the analog VFO. Great radio BUT,
not significantly better than the commercial one save for a few narrow
things I only care about.
What you should check out is Softrock, uses the soundard and CPU
to do the back end stuff and it's frontend is a 29$ kit.
www.amqrp.org/kits/softrock40/index.html (it's sold out but the
details are there).
So whats this got to do with computers. Well as cpu cycles get cheaper,
DSP can do things that analog had to do but not as well. Things like
brick wall filters that don't ring and phase delays that are frequency
invarient are very hard to do with analog. Right now a sound card
and a leftover 30-400mhz PC is a pretty cheap way to do dsp but,
there are chips out there that coming in cheaper and only require
programming. The difference is the computer can also deliver the
user interface or as pilots call them the "glass cockpit" rather than
a box of knobs and dials.
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