Tunable Bandpass Filter
in [Design]
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From: ChrisQ on 18 Nov 2009 07:18 Joel Koltner wrote: > "ChrisQ" <meru(a)devnull.com> wrote in message > news:zlFMm.28177$Pi5.25630(a)newsfe08.ams2... >> So what is the current state of the art in sdr, using commodity hardware >> ?... > > For HF work, these guys are popular: http://www.flex-radio.com/ . They use > 192kHz, 24-bit ADCs for sampling, and thereby purportedly have very good > performance relative to traditional analog receivers. > Yes, 24 bits would be enough and quite impressive at a 192Khz sample rate. The technology is moving fast these days :-). Haven't done much radio for years. Still have an old 60's Plessey PR155 radio in the lab, which has an early (1965) quad discreet schottky diode front end up converted to a 37.3 Mhz ist if, with a roofing filter at 15Khz bw. I remember the hp schottky diodes were called 'hot carrier'. Fairly radical at the time and far better than the Racal equivalent radio's, but pretty standard technique now. Current technology is starting to look really interesting, though I think Collins built a digital back end radio over a decade ago... Regards, Chris
From: Joel Koltner on 18 Nov 2009 13:01 "ChrisQ" <meru(a)devnull.com> wrote in message news:eCRMm.661$mC4.267(a)newsfe22.ams2... > Haven't done much radio for years. So what kind of things do you work on these days? > I remember the hp schottky diodes were called 'hot carrier'. John Larkin likes to draw them in a way that suggests their "hot carrier" nature... > Current technology is starting to look really interesting, though I think > Collins built a digital back end radio over a decade ago... Same with the military -- the big change has been that this stuff has become affordable to the average person. I'm surprised how quickly the Flex Radio guys have grown... I remember it being only something like 4-5 years ago where they had one model that was clearly being assembled in some guy's garage. :-) The specs were good though, and they started selling like hotcakes. Given a couple more years I think they (and a few other new companies like Elecraft, and Ten-Tec seems to be hanging on) will start taking a significant bite out of the near-triopoly Kenwood/Icom/Yaesu market that is HF radios. ---Joel
From: ChrisQ on 18 Nov 2009 17:30 Joel Koltner wrote: > "ChrisQ" <meru(a)devnull.com> wrote in message > news:eCRMm.661$mC4.267(a)newsfe22.ams2... >> Haven't done much radio for years. > > So what kind of things do you work on these days? Have been freelance since the mid 1970's. Now getting a bit wrinkly, but manage to stay in work most of the the time. Radio in youth -> electronics -> computing. Currently doing hardware / software design for a client that builds led based highway signs. The biggest ones are 128 pixels high x 192 pixels wide x 2 colours and draw 3-4 Kw power with all the diodes on. Interesting challenges involved w/regard to display timing, update time, self test and other requirements. All the comms is 9600 baud rs485 half duplex, so image data is compressed. Work mainly from own lab these days, but on client site as required. Also have some back burner projects for light aviation using lcd displays. One of those has been so long on the back burner that motorola / freescale eol'd the processor :-(. Am now retargeting to arm 7, as everyone makes them, they are cheap and are more powerfull. Not such an elegant architecture as the Freescale devices though. So what are you working on ?. > Same with the military -- the big change has been that this stuff has become > affordable to the average person. > > I'm surprised how quickly the Flex Radio guys have grown... I remember it > being only something like 4-5 years ago where they had one model that was > clearly being assembled in some guy's garage. :-) The specs were good though, > and they started selling like hotcakes. Given a couple more years I think > they (and a few other new companies like Elecraft, and Ten-Tec seems to be > hanging on) will start taking a significant bite out of the near-triopoly > Kenwood/Icom/Yaesu market that is HF radios. > > ---Joel > Problem is that there really aren't enough hours in a week to cover all the stuff that looks interesting and we all have to earn a living as well :-)... Regards, Chris
From: Joel Koltner on 18 Nov 2009 18:06 "ChrisQ" <meru(a)devnull.com> wrote in message news:dA_Mm.7$3e4.5(a)newsfe27.ams2... > All the comms is 9600 baud rs485 half duplex, so image data is compressed. That's pretty glacial :-) -- is it some protocol standard that's been around forever? > Am now retargeting to arm 7, as everyone makes them, they are cheap and are > more powerfull. Not such an elegant architecture as the Freescale devices > though. I'm planning to try out an AVR32 in the not-so-distant future. It seems to have a nice mix of a regular 32-bit CPU's architecture with "DSP lite" additions. > So what are you working on ?. RF design, mostly military and high-end/lower-volume commercial contracts. (I'm a regular old engineer at a small company.) Much of it is still analog, often with some of the simpler digital protocols (e.g., BPSK) tacked on. A lot of what I do is kinda "block diagram" level board design, using MMIC amplifiers, mixers, etc. moreso than discrete transistor-level circuit design. I have done a fair number of filters over time, and have a good-sized handful of switchmode power supply designs under my belt. I also program when needed -- usually low-level stuff like bootloaders and self-test/PC-based-test code. Mostly C/C++ these days, although still a bit of assembly, and I have used Python for a couple of little projects. It's clear to me that there are people out there who are *much* better than I am at RF design and circuit design (some of them hang out here on SED...). Much of my value seems to be that I have a broader-than-usual set of abilities, even though I'm not an expert in any one particular field. And of course over time I'd like to think my skills have improved; life-long learning is a Good Thing. ---Joel
From: JosephKK on 20 Nov 2009 07:39
On Wed, 18 Nov 2009 22:30:33 +0000, ChrisQ <meru(a)devnull.com> wrote: >Joel Koltner wrote: >> "ChrisQ" <meru(a)devnull.com> wrote in message >> news:eCRMm.661$mC4.267(a)newsfe22.ams2... >>> Haven't done much radio for years. >> >> So what kind of things do you work on these days? > >Have been freelance since the mid 1970's. Now getting a bit wrinkly, but >manage to stay in work most of the the time. Radio in youth -> >electronics -> computing. Currently doing hardware / software design for >a client that builds led based highway signs. The biggest ones are 128 >pixels high x 192 pixels wide x 2 colours and draw 3-4 Kw power with all >the diodes on. Interesting challenges involved w/regard to display >timing, update time, self test and other requirements. All the comms is >9600 baud rs485 half duplex, so image data is compressed. Work mainly >from own lab these days, but on client site as required. Could you interest a manufacturer in a larger roadway application device with array like 100 wide by 24 tall (primarily text)? Other constraints similar. > >Also have some back burner projects for light aviation using lcd >displays. One of those has been so long on the back burner that motorola >/ freescale eol'd the processor :-(. Am now retargeting to arm 7, as >everyone makes them, they are cheap and are more powerfull. Not such an >elegant architecture as the Freescale devices though. > >So what are you working on ?. > >> Same with the military -- the big change has been that this stuff has become >> affordable to the average person. >> >> I'm surprised how quickly the Flex Radio guys have grown... I remember it >> being only something like 4-5 years ago where they had one model that was >> clearly being assembled in some guy's garage. :-) The specs were good though, >> and they started selling like hotcakes. Given a couple more years I think >> they (and a few other new companies like Elecraft, and Ten-Tec seems to be >> hanging on) will start taking a significant bite out of the near-triopoly >> Kenwood/Icom/Yaesu market that is HF radios. >> >> ---Joel >> > >Problem is that there really aren't enough hours in a week to cover all >the stuff that looks interesting and we all have to earn a living as >well :-)... > >Regards, > >Chris |