Tunable Bandpass Filter
Guy Eschemann
filter) for a communications application. The middle frequency is in
the range 2..7 MHz, and the required bandwidth is 600 kHz. How do I
get started with this?
Many thanks,
Guy.
Joel Koltner
news:b33af39e-d6b1-44ae...@x31g2000yqx.googlegroups.com...
Couple of questions:
-- Is the entire analog channle also 2-7MHz? Or wider?
-- What power levels are you dealing with?
A few approaches are:
-- Mix your signal with an LO of, say, 19.4-14.4MHz such that the band center
of interest is at 21.4MHz (use a low pass filter so that you don't pick up the
image frequencies above 7MHz). Use a cheap off-the-shelf 21.4MHz IF filter
(probably ceramic) to get your 600kHz passband (this is a Q of
21.4MHz/600kHz=36 -- easy peasy). Mix again with the same LO to put your
center band back where it came from. (High power levels -- much above, say,
0dBm -- start creating intermods and compression problems from the mixers.)
-- Build yourself a bank of switched capacitor and inductors that get switched
in and out as appropriate to "build" a bandpass filter wherever you need it.
(Use PIN diodes or MMIC switches for the switching.) If you need very fine
control you'll end up using a varactor diode (or perhaps a DC bias on an
inductor) to set the exact center frequency. (High power levels here push
your varactor or inductors far enough outside of their linear ranges that get
start getting frequency responses that are functions of power levels as well
as intermods.)
-- Same as above, but use relays for switching inductors and capacitors in and
out and motorized variable capacitors (or slug-tuned inductors) if you need
fine tuning. (Higher power levels are attainable, but you end up consuming a
lot of physical space and tuning is slow.)
If the filter is simple enough, you *might just* be able to get away these
days with an FPGA-based "all digital" implementation: Feed your signal to an
ADC, have the FPGA run a FIR or IIR filter, and spit it back out to a DAC. As
with most things "DSP," there are a lot of upsides, although your signals are
at a high enough frequency you'll probably consume a fair amount of power
running all the multipliers in your FPGA, and it isn't going to be the
"bargain basement price" series of FPGAs that'll have enough horsepower to
pull it off.
---Joel
Jan Panteltje
Eschemann <guy.es...@gmail.com> wrote in
<b33af39e-d6b1-44ae...@x31g2000yqx.googlegroups.com>:
You could mix up to some higher frequency, use a fixed filter at that frequency,
and then mix down again.
And tune the local oscillator.
Jon Slaughter
It would help to know how sharp you need the filtering.
christofire
"Guy Eschemann" <guy.es...@gmail.com> wrote in message
news:b33af39e-d6b1-44ae...@x31g2000yqx.googlegroups.com...
How about visiting a library and reading some relevant books?
Chris
Guy Eschemann
There are 8 non-overlapping analog channels in the range between 2 and
7 MHz. Each channel is approx. 600 kHz wide.
I'm not sure about the power levels yet, but the channel selection
filter comes after the preamplifier and the receiver main amplifier
(AGC), so the amplitude is pretty much controlled at this point.
If possible, I'd like to avoid any mixing up and down. I'm actually
considering a mixerless approach (bandpass sampling) to translate the
channel of interest down to DC, so it would be really annoying to mix
the signal up and down just for filtering.
Also, I don't want to use a digital filter at this stage. This would
require sampling the band of interest at something like 30 MHz, which
is bad for power consumption.
Thanks for your help!
Guy.
> Couple of questions:
>
> -- Is the entire analog channel also 2-7MHz? Or wider?
ChrisQ
I remember seeing an article years ago about a dual mixing technique
that used two minicircuits sbl1 type balanced mixers in cascade with a
common variable local oscillator and a crystal filter interspersed
between the two mixers. Draw it out on paper and do the sum /
differences to see how it works.
You don't say how many db/octave at the edges, but a crystal filter can
provide a very sharp rolloff. The 600Khz passband may be better handled
by an lc or active filter with fast opamps, depending on requirements.
Otherwise, how about using fast opamps in a byquad or state variable
configuration ?...
Regards,
Chris
Joel Koltner
news:nvGdnUeJQYfUXZzW...@bt.com...
> How about visiting a library and reading some relevant books?
I'd love to hear it if you could point to any book that has a large amount of
text specifically devoted to *tunable* filters. I have plenty of filter books
(including many of the "classics"), and most give little more than passing
mention to them. (I suppose because -- other than the "mix it up to a fixed
frequency with a good filter" method than Jan and I mentioned -- most
implementations I'm aware of are some variety of the "brute force" method
anyone would think of, so perhaps there's not a whole lot to say...)
One approach I forgot to mention: I have seen people build active filters with
multiplying DACs as the tuning elements up to better than a MHz, but I think
7MHz would be quite a stretch (the DAC's parasitics start to eat you alive).
I've messed around with gyrators occasionally, and while you can build them to
tens of MHz with fast op-amps, tuning is still tricky -- the last time I went
down that path I convinced myself a way to make it work might be to bulid a
set of two filters with matched tuning elements, have one be the "real"
filter, and the other servoed to it via its twin that's constantly seeking to
peak a synthesized signal (from a DDS or whatever) that's going through it.
Alas, this approach is best for small signals and an IC implementation.
Speaking of which... the IEEE has plenty of articles on tunable filters, but
most are oriented towards IC implementations. Too bad the standard membership
fee of $176/yr (!) doesn't get you *any* on-line access to the them...
---Joel
Guy Eschemann
> It would help to know how sharp you need the filtering.
Ideally: -60dB within the 80kHz guardband.
Joel Koltner
> There are 8 non-overlapping analog channels in the range between 2 and
> 7 MHz. Each channel is approx. 600 kHz wide.
For 8 channels I think I would just build 8 lumped-element filters and switch
them in and out. -- It's easier to get decent repeatibility using, e.g., 2%
inductors and capacitors when each component only influences one frequency
band rather than a single "switching" filter where multiple inductors and
capacitors may interact and their tolerances then build on one another.
Depending on what order filter (how sharp) it needs to be, 8 filters can still
be pretty compact.
---Joel
Tim Wescott
(top posting fixed)
You're kind of painting yourself into a corner, and the corner is called
"eight non-overlapping band-pass filters".
Or consider that you're already on the wrong side of some active
electronics, so you've already levied most of the disadvantages of a
superheterodyne receiver against yourself. Why not just go the rest of
the way and make it a superhet? Upconvert to something convenient like
that 21.4MHz, filter, then use a fixed downsampling scheme.
The whole reason that Armstrong invented the superhet was to dodge the
difficulty of trying to make a good agile filter at RF -- here you are 75
years later struggling with the same problem, yet the answer may still be
the same one.
Tim Wescott
>> It would help to know how sharp you need the filtering.
>
> Ideally: -60dB within the 80kHz guardband.
You need a superhet.
ChrisQ
> On Mon, 16 Nov 2009 13:32:59 -0800, Guy Eschemann wrote:
>
>
>>> It would help to know how sharp you need the filtering.
>> Ideally: -60dB within the 80kHz guardband.
>
> You need a superhet.
>
and a crystal filter, unless you mix down to baseband + a low pass filter.
There are probably mobile radio ic's that would do the job, but not
really my field. Silicon Labs, Broadcom and others...
Regards,
Chris
ChrisQ
Thinking again, plug 'software defined radio' into google...
Regards,
Chris
Joel Koltner
news:C2kMm.7618$Gn....@newsfe26.ams2...
> Thinking again, plug 'software defined radio' into google...
Yea, but a very real problem that SDRs have is that while, sure, you can get
beautiful, near-vertical skirts around a filter, if there's a strong
interferer nearby, you have to filter it prior to digitization or at best you
lose SNR for the intended signal (desensing)... and at worst that SNR goes
negative!
Although you probably know this. :-)
Tim Wescott
Baseband + lowpass will be difficult. Normal I/Q downconversion with the
carrier "off to the side" probably won't give you 60dB of rejection. You
could get that rejection by using the Weaver method, but only if you
could tolerate the DC bias in your baseband signal squatting right in the
middle of the signal that you're trying to decipher.
OTOH, if you _could_ deal with the DC bias, then it may work quite well,
and fit well into your preferred downconversion scheme.
ChrisQ
From analog radio days, yes, but have no experience of sdr at all. Just
something i've been reading about in the last few months. From what I
can see, it doesn't get round the need for a low phase noise lo to
prevent filter washout, irrespective of how the filter and processing
are implemented.
A crystal filter is still hard to beat on cost and performance, even now
:-)...
Regards,
Chris
Joerg
> "christofire" <chris...@btinternet.com> wrote in message
> news:nvGdnUeJQYfUXZzW...@bt.com...
>> How about visiting a library and reading some relevant books?
>
> I'd love to hear it if you could point to any book that has a large amount of
> text specifically devoted to *tunable* filters. I have plenty of filter books
> (including many of the "classics"), and most give little more than passing
> mention to them. (I suppose because -- other than the "mix it up to a fixed
> frequency with a good filter" method than Jan and I mentioned -- most
> implementations I'm aware of are some variety of the "brute force" method
> anyone would think of, so perhaps there's not a whole lot to say...)
>
For ultrasound engineers and Radar guys it's routine, except that we
call them tracking filters. They consist of a fixed lowpass and a
highpass that's tuned downwards while echoes are received. The challenge
is to make them reproducible in production without any alignments. Many
tricks there, such as servo or pilot tones, but that's as far as I am
allowed to speak in public.
> One approach I forgot to mention: I have seen people build active filters with
> multiplying DACs as the tuning elements up to better than a MHz, but I think
> 7MHz would be quite a stretch (the DAC's parasitics start to eat you alive).
>
> I've messed around with gyrators occasionally, and while you can build them to
> tens of MHz with fast op-amps, tuning is still tricky -- the last time I went
> down that path I convinced myself a way to make it work might be to bulid a
> set of two filters with matched tuning elements, have one be the "real"
> filter, and the other servoed to it via its twin that's constantly seeking to
> peak a synthesized signal (from a DDS or whatever) that's going through it.
> Alas, this approach is best for small signals and an IC implementation.
>
The challenge with that would be to find matched tuning elements. It'll
be almost down to PIN diodes which can be had as duals and dual FETs but
those aren't so hot when you need a spiffy shape factor because they are
resistive elements.
Then there's the old scheme of having several resonant filters spread
apart like it was done in the old tube-era TV sets. 2-7MHz is feasible
but that's close to the reasonable limit. 600kHz BW at 2MHz will be a
real stretch with a resonant scheme.
Quite frankly, I'd consider a DSP here.
> Speaking of which... the IEEE has plenty of articles on tunable filters, but
> most are oriented towards IC implementations. Too bad the standard membership
> fee of $176/yr (!) doesn't get you *any* on-line access to the them...
>
Don't get me started on that ... it is the reason I have stopped writing
for IEEE.
--
Regards, Joerg
http://www.analogconsultants.com/
"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Jim Thompson
wrote:
>Joel Koltner wrote:
>> "christofire" <chris...@btinternet.com> wrote in message
>> news:nvGdnUeJQYfUXZzW...@bt.com...
>>> How about visiting a library and reading some relevant books?
>>
>> I'd love to hear it if you could point to any book that has a large amount of
>> text specifically devoted to *tunable* filters. I have plenty of filter books
>> (including many of the "classics"), and most give little more than passing
>> mention to them. (I suppose because -- other than the "mix it up to a fixed
>> frequency with a good filter" method than Jan and I mentioned -- most
>> implementations I'm aware of are some variety of the "brute force" method
>> anyone would think of, so perhaps there's not a whole lot to say...)
>>
>
>For ultrasound engineers and Radar guys it's routine, except that we
>call them tracking filters. They consist of a fixed lowpass and a
>highpass that's tuned downwards while echoes are received. The challenge
>is to make them reproducible in production without any alignments. Many
>tricks there, such as servo or pilot tones, but that's as far as I am
>allowed to speak in public.
>
>
[snicker]
Probably the same way I do sonar ;-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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If you wanted a President with balls why didn't you elect Hillary?
christofire
"Joel Koltner" <zapwireD...@yahoo.com> wrote in message
news:lxjMm.225580$ua.1...@en-nntp-05.dc1.easynews.com...
> "christofire" <chris...@btinternet.com> wrote in message
> news:nvGdnUeJQYfUXZzW...@bt.com...
>> How about visiting a library and reading some relevant books?
>
> I'd love to hear it if you could point to any book that has a large amount
> of text specifically devoted to *tunable* filters. I have plenty of
> filter books (including many of the "classics"), and most give little more
> than passing mention to them. (I suppose because -- other than the "mix
> it up to a fixed frequency with a good filter" method than Jan and I
> mentioned -- most implementations I'm aware of are some variety of the
> "brute force" method anyone would think of, so perhaps there's not a whole
> lot to say...)
The statement 'The middle frequency is in the range 2..7 MHz, and the
required bandwidth is 600 kHz' suggests something similar to the front end
of an HF or VHF receiver, about which a great deal has been written. I
don't have my own library to hand (I use the IET in London) but I daresay
Google knows the names of some the relevant books
(http://books.google.co.uk/books?ei=v-sBS6KNOYSNjAeUhOGbCw&ct=result&q=RF+tunable+filter&lr=&sa=N&start=10).
Of course, a great deal of filtering (!) of the resulting 978 returns is
then needed, but that would be a task for the OP.
I think the statement 'How do I get started with this?', in the absence of
any evidence of effort spent learning the basics, deserves the the response
I gave.
Chris
Joerg
Yup. Superhet and then one of these puppies, under a buck:
http://media.digikey.com/pdf/Data%20Sheets/Murata%20PDFs/CDSCB10M7GA085-R0.pdf
http://www.abracon.com/Filters/SAW%20FILTERS/AFS315E.pdf
Joerg
> On Mon, 16 Nov 2009 16:38:34 -0800, Joerg <inv...@invalid.invalid>
> wrote:
>
>> Joel Koltner wrote:
>>> "christofire" <chris...@btinternet.com> wrote in message
>>> news:nvGdnUeJQYfUXZzW...@bt.com...
>>>> How about visiting a library and reading some relevant books?
>>> I'd love to hear it if you could point to any book that has a large amount of
>>> text specifically devoted to *tunable* filters. I have plenty of filter books
>>> (including many of the "classics"), and most give little more than passing
>>> mention to them. (I suppose because -- other than the "mix it up to a fixed
>>> frequency with a good filter" method than Jan and I mentioned -- most
>>> implementations I'm aware of are some variety of the "brute force" method
>>> anyone would think of, so perhaps there's not a whole lot to say...)
>>>
>> For ultrasound engineers and Radar guys it's routine, except that we
>> call them tracking filters. They consist of a fixed lowpass and a
>> highpass that's tuned downwards while echoes are received. The challenge
>> is to make them reproducible in production without any alignments. Many
>> tricks there, such as servo or pilot tones, but that's as far as I am
>> allowed to speak in public.
>>
>>
> [snicker]
>
> Probably the same way I do sonar ;-)
>
Sonar? In Arizona? You guys don't even have an ocean :-)
Joel Koltner
news:7me9k9F...@mid.individual.net...
> For ultrasound engineers and Radar guys it's routine, except that we call
> them tracking filters. They consist of a fixed lowpass and a highpass that's
> tuned downwards while echoes are received.
What frequency ranges and how steep are the skirts though?
And what is the tuning mechanism?
> The challenge with that would be to find matched tuning elements.
Yep.
> Don't get me started on that ... it is the reason I have stopped writing for
> IEEE.
Did you have much luck with their insurance offerings?
---Joel
Tim Wescott
> Joel Koltner wrote:
>> "ChrisQ" <me...@devnull.com> wrote in message
>> news:C2kMm.7618$Gn....@newsfe26.ams2...
>>> Thinking again, plug 'software defined radio' into google...
>>
>> Yea, but a very real problem that SDRs have is that while, sure, you
>> can get beautiful, near-vertical skirts around a filter, if there's a
>> strong interferer nearby, you have to filter it prior to digitization
>> or at best you lose SNR for the intended signal (desensing)... and at
>> worst that SNR goes negative!
>>
>> Although you probably know this. :-)
>>
>>
>>
> From analog radio days, yes, but have no experience of sdr at all. Just
> something i've been reading about in the last few months. From what I
> can see, it doesn't get round the need for a low phase noise lo to
> prevent filter washout, irrespective of how the filter and processing
> are implemented.
Yup. Not to mention that the dynamic range of most ADC's is a huge
restriction. The more you can control the bandwidth before conversion
the better off you'll be.
> A crystal filter is still hard to beat on cost and performance, even now
> :-)...
Or a ceramic one, depending on your app.
Joerg
> "Joerg" <inv...@invalid.invalid> wrote in message
> news:7me9k9F...@mid.individual.net...
>> For ultrasound engineers and Radar guys it's routine, except that we call
>> them tracking filters. They consist of a fixed lowpass and a highpass that's
>> tuned downwards while echoes are received.
>
> What frequency ranges and how steep are the skirts though?
>
Typical ranges are 4-6MHz, 6-9MHz, 11-15MHz, 17-22MHz and similar. The
steepness isn't that great, something like 8MHz at -6dB and -60dB at
9MHz, for example. If the OP needs stellar channel rejection he has IMHO
only two options, superhet or DSP.
> And what is the tuning mechanism?
>
Varicaps, usually. However, purchasing duals in order to be able to
servo has become a bear. And one has to remain friends with the
purchasing department since those are the guys who get all the Christmas
bonbons :-)
>> The challenge with that would be to find matched tuning elements.
>
> Yep.
>
>> Don't get me started on that ... it is the reason I have stopped writing for
>> IEEE.
>
> Did you have much luck with their insurance offerings?
>
Nope, they couldn't do it :-(
Joerg
> On Mon, 16 Nov 2009 22:53:17 +0000, ChrisQ wrote:
>
[...]
>> A crystal filter is still hard to beat on cost and performance, even now
>> :-)...
>
> Or a ceramic one, depending on your app.
>
It almost has to be. I don't think you can buy 600kHz wide crystal filters.
Jim Thompson
wrote:
>Jim Thompson wrote:
>> On Mon, 16 Nov 2009 16:38:34 -0800, Joerg <inv...@invalid.invalid>
>> wrote:
>>
>>> Joel Koltner wrote:
>>>> "christofire" <chris...@btinternet.com> wrote in message
>>>> news:nvGdnUeJQYfUXZzW...@bt.com...
>>>>> How about visiting a library and reading some relevant books?
>>>> I'd love to hear it if you could point to any book that has a large amount of
>>>> text specifically devoted to *tunable* filters. I have plenty of filter books
>>>> (including many of the "classics"), and most give little more than passing
>>>> mention to them. (I suppose because -- other than the "mix it up to a fixed
>>>> frequency with a good filter" method than Jan and I mentioned -- most
>>>> implementations I'm aware of are some variety of the "brute force" method
>>>> anyone would think of, so perhaps there's not a whole lot to say...)
>>>>
>>> For ultrasound engineers and Radar guys it's routine, except that we
>>> call them tracking filters. They consist of a fixed lowpass and a
>>> highpass that's tuned downwards while echoes are received. The challenge
>>> is to make them reproducible in production without any alignments. Many
>>> tricks there, such as servo or pilot tones, but that's as far as I am
>>> allowed to speak in public.
>>>
>>>
>> [snicker]
>>
>> Probably the same way I do sonar ;-)
>>
>
>Sonar? In Arizona? You guys don't even have an ocean :-)
Oh, yeah! We have farm-raised shrimp ;-)
George Herold
> > It would help to know how sharp you need the filtering.
>
> Ideally: -60dB within the 80kHz guardband.
Ouch! You mean six active elements? That makes the fast opamp
solution a lot harder.
George H.
amdx
"Jim Thompson" <To-Email-Use-Th...@My-Web-Site.com> wrote in
message news:h1v3g51o5g1kdsdds...@4ax.com...
Farm raised shrimp, aren't they rubbery and bland. Buy only wild caught
Florida shrimp.
http://www.wildamericanshrimp.com/main.html Click on ad in lower right
corner
http://www.underwatertimes.com/news.php?article_id=81003524697
http://www.fl-aquaculture.com/videos/flash/Florida_Wild_Caught_Shrimp_TV.htm
Mike
Jim Thompson
>
>"Jim Thompson" <To-Email-Use-Th...@My-Web-Site.com> wrote in
>message news:h1v3g51o5g1kdsdds...@4ax.com...
>> On Mon, 16 Nov 2009 16:47:34 -0800, Joerg <inv...@invalid.invalid>
>> wrote:
>>[snip]
>>>
>>>Sonar? In Arizona? You guys don't even have an ocean :-)
>>
>> Oh, yeah! We have farm-raised shrimp ;-)
>>
>> ...Jim Thompson
>
> Farm raised shrimp, aren't they rubbery and bland. Buy only wild caught
>Florida shrimp.
Farm grown shrimp are excellent.... and _disease_free_. (Artificial
salt water lakes... a giant version of my aquarium ;-)
They're working on a similar concept for oysters.
>
>http://www.wildamericanshrimp.com/main.html Click on ad in lower right
>corner
>
>http://www.underwatertimes.com/news.php?article_id=81003524697
>
>http://www.fl-aquaculture.com/videos/flash/Florida_Wild_Caught_Shrimp_TV.htm
>
> Mike
>
qrk
wrote:
>Jim Thompson wrote:
>> On Mon, 16 Nov 2009 16:38:34 -0800, Joerg <inv...@invalid.invalid>
>> wrote:
>>
>>> Joel Koltner wrote:
>>>> "christofire" <chris...@btinternet.com> wrote in message
>>>> news:nvGdnUeJQYfUXZzW...@bt.com...
>>>>> How about visiting a library and reading some relevant books?
>>>> I'd love to hear it if you could point to any book that has a large amount of
>>>> text specifically devoted to *tunable* filters. I have plenty of filter books
>>>> (including many of the "classics"), and most give little more than passing
>>>> mention to them. (I suppose because -- other than the "mix it up to a fixed
>>>> frequency with a good filter" method than Jan and I mentioned -- most
>>>> implementations I'm aware of are some variety of the "brute force" method
>>>> anyone would think of, so perhaps there's not a whole lot to say...)
>>>>
>>> For ultrasound engineers and Radar guys it's routine, except that we
>>> call them tracking filters. They consist of a fixed lowpass and a
>>> highpass that's tuned downwards while echoes are received. The challenge
>>> is to make them reproducible in production without any alignments. Many
>>> tricks there, such as servo or pilot tones, but that's as far as I am
>>> allowed to speak in public.
>>>
>>>
>> [snicker]
>>
>> Probably the same way I do sonar ;-)
>>
>
>Sonar? In Arizona? You guys don't even have an ocean :-)
But he had a customer in Santa Barbara.
ChrisQ
>
> Yup. Not to mention that the dynamic range of most ADC's is a huge
> restriction. The more you can control the bandwidth before conversion
> the better off you'll be.
>
A average analogue hf comms radio probably has a dynamic range of 0.5uV
to 1v or better at the antenna terminals and it would take a pretty
special fast adc to get near that.
So what is the current state of the art in sdr, using commodity hardware
?...
Regards,
Chris
Joel Koltner
Joel Koltner
> 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.
They are many others out there... another popular one is the TAPR "HPSDR"
(high performance SDR) kits.
---Joel
Joerg
Ok, that counts. I've tried to get away from ultrasound because it's
mostly been medical and there is no more liability coverage available in
the US. But it always snags me back, like a couple weeks ago and now it
seems I'll be right back in there.
ChrisQ
> "ChrisQ" <me...@devnull.com> wrote in message
> news:zlFMm.28177$Pi5....@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
Joel Koltner
> 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
ChrisQ
> "ChrisQ" <me...@devnull.com> wrote in message
> news:eCRMm.661$mC4...@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
Joel Koltner
> 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
JosephKK
>Joel Koltner wrote:
>> "ChrisQ" <me...@devnull.com> wrote in message
>> news:eCRMm.661$mC4...@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.
ChrisQ
>
> Could you interest a manufacturer in a larger roadway application
> device with array like 100 wide by 24 tall (primarily text)? Other
> constraints similar.
Do you have more details, quantity, delivery etc ?.
Take this to email if it's easier.
sysengatgfsysdotcodotuk...
Regards,
Chris
JosephKK
Caltrans (California DOT) currently uses signs like this:
http://www.dot.ca.gov/hq/traffops/elecsys/reports/CMS_2009.pdf
They are looking into LED based signs.
They are also looking onto LED equivalents to their standard 200 W HPS
and 310 W HPS roadway luminaries.
This has the typical isofootcandle patterns:
http://www.dot.ca.gov/hq/esc/oe/project_plans/HTM/stdplns-US-customary-units-new06.htm#electrical
Joseph