Forum: GNU Radio Resistance? Capacitance? Inductance?

Dear GNU Radio aficionado's-

Whatever happened to resistance, capacitance, and inductance?
When I joined this thread I was hoping you would once in a while
talk about ways of using the software in the computer to modify
the resonant circuit in the hardware radio by making adjustments
to the resistors, capacitors, and inductors.

Am I just dreaming? Am I on the wrong page? Is there any hope?

http://staff.washington.edu/jon/gr-mrfm/

USRP and GNU Radio controlling micromechanical oscillators for Magnetic
Resonance Force Microscopy (MRFM).  Does that count?

-John

On Tue, Feb 26, 2013 at 04:10:55PM -0600, Joel Mayer wrote:
> Dear GNU Radio aficionado's-
>
> Whatever happened to resistance, capacitance, and inductance?
> When I joined this thread I was hoping you would once in a while
> talk about ways of using the software in the computer to modify
> the resonant circuit in the hardware radio by making adjustments
> to the resistors, capacitors, and inductors.

Oh, one of my favourite topics :)

I'll have to point out that I'm completely biased here:
When I started playing around with radio, the thingy between antenna and
the computer was a total black box, just producing the bits and bytes I
needed. In fact, that's what got me attracted to the SDR world, because
I could already program, but those Smith charts... but that's not the
point.

First, I'll give you a practical answer: This mailing list is about GNU
Radio, which is in a sense very hardware-independent. So there you go.

But it's also very important to understand that Software Radio is not
about modelling hardware. Using software allows the use of DSP, which
means we can do stuff like linear-phase filters etc. (good luck tuning
your R/C/I to do that), and we can create transceivers for digitally
modulated signals very easily, which is really awkward in discrete
hardware (although analog modulations are also easily coded).

So, perhaps I just misunderstood your question. But despite not knowing
how you would modify an inductor through software, this wouldn't help in
building a transceiver that, upon sensing a change in the radio
environment, would reconfigure itself and change the waveform used--
which is one goal of GNU Radio. Of course, this comes with some
abstraction, which means that changing the resonant circuit of my USRP
is nothing more than a library call to set_center_frequency() or
whatever it's called.

MB

--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

On Tue, Feb 26, 2013 at 5:10 PM, Joel Mayer <joelm_armillary@msn.com> 
wrote:

>
Resistance? As in "uprising"? Ah a  DSP counter revolution!! :-)

Are you referring to the stuff in the black (err... white) box known as 
the
USRP?

On Wed, Feb 27, 2013 at 3:04 AM, Martin Braun (CEL)
<martin.braun@kit.edu> wrote:
>
> But it's also very important to understand that Software Radio is not
> which is one goal of GNU Radio. Of course, this comes with some
> abstraction, which means that changing the resonant circuit of my USRP
> is nothing more than a library call to set_center_frequency() or
> whatever it's called.
>
> MB

On the other hand, one of the major areas of work that we are still
pursuing lies in the RF front end. We have wideband systems. Ettus has
produced a number of daughterboards that cover multiple GHz of
spectrum, which is fantastic. But through that, we suffer a bit on the
amplifiers and filters needed for some kinds of communications tasks.
What Ettus has done is produced very good IP3s, NFs, gains, etc over
these large bandwidths, but that doesn't exactly compare to having a
filter and amplifier specific to a small bandwidth for something like
cellular communications. Or even, for that matter, antennas for
various waveforms.

Even today's wideband RFICs tend to have a lot of tweakable/tunable
parameters to meet specific needs of different areas of spectrum. Are
there software solutions that could be used to automatically adjust
these parameters? Or an RLC matching circuit? Some of this, I know,
requires advances in the materials and components to make any sense,
in other cases the feedback loop could be a bit long to make any
significant impact. But it's fun to think about. Goes back to my
dissertation days, actually :)

Tom

On 27/02/13 10:08 AM, Tom Rondeau wrote:
> various waveforms.
> Tom
>
In some sense, what we're talking about here is the difference between
Software *Controlled* Radio, and
  Software *Defined* Radio.

A chain of DSP blocks applies a series of mathematical transforms to a
digitized signal, in similar ways
  to the way a series of R/L/C/Gain components do to an analog signal.
One can think of the R/L/C approach
  as performing rough *approximations* to a transform that is defined in
strict mathematical terms.  The DSP
  approach, in general, is able to achieve a higher "fidelity" of those
transforms with a higher degree of
  flexibility and reconfigurability than could possibly be achieved with
analog hardware. Although, at some
  considerable cost--a simple FM demodulator chip is $0.35 in bulk,
whereas the amount of compute-gear you
  require to do the same thing is considerably more costly.  But DSP/SDR
doesn't require that you break out
  the soldering iron and parts bin every time you want to
tweak/repurpose things.

Now, having said that, the notion of having some kind of "tracking"
filtering isn't a bad idea, the problem comes
  down to implementation, and the cost trade-offs involved.
Considering things like daughter cards covering
  30Mhz to 4.4Ghz, exactly how many "cuts" across that bandwidth do you
make, and how much are people
  willing to pay for additional dynamic range implied by band-limiting
at the RF end of things?  The technology
  is mostly there -- GaAsFET RF switches, LTCC filter modules, saw
filters, dielectric filters, etc, are all out there.
  But almost any "hard" decision made by the manufacturer in such things
is likely to be "wrong" in enough cases
  that perhaps all of that should be done externally to a daughtercard,
with provision for a generic switching
  interface (like the existing GPIOs on many Ettus daughtercards).

In an ideal world, you wouldn't need much front-end filtering.  Your
gain stages would be uber-linear up to ridiculous
  input powers, and you'd have a 24-bit ADC sampling at several Gsps.
We aren't anywhere near there yet.





--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

On Wed, Feb 27, 2013 at 11:38 AM, Marcus D. Leech <mleech@ripnet.com> 
wrote:
>> cellular communications. Or even, for that matter, antennas for
>>
>   as performing rough *approximations* to a transform that is defined in
> tweak/repurpose things.
> filters, dielectric filters, etc, are all out there.
>   But almost any "hard" decision made by the manufacturer in such things
> is likely to be "wrong" in enough cases
>   that perhaps all of that should be done externally to a daughtercard,
> with provision for a generic switching
>   interface (like the existing GPIOs on many Ettus daughtercards).

Well said.

> In an ideal world, you wouldn't need much front-end filtering.  Your
> gain stages would be uber-linear up to ridiculous
>   input powers, and you'd have a 24-bit ADC sampling at several Gsps.
> We aren't anywhere near there yet.

Yeah.... that's a hard one to swallow. The near-far problem in some
bands makes even what you're considering here problematic. ~140 dB
dynamic range does sound pretty good for most things, though :)

There are other proposed solutions out there that take this concept
even farther but require much greater investment in hardware cost
(we're talking multiple ADCs, DSP units, etc.).

But we're still going to need front end filtering and amplifiers for a
while longer. Oh, and let's still not forget the antenna, though there
are decent solutions for narrowband signals over large bandwidths
(that is, good performance over a large bandwidth with varying group
delays along the way, so you can only get away with narrowband signals
or clever correction algorithms).

Tom

On Wed, Feb 27, 2013 at 11:52 AM, Tom Rondeau <tom@trondeau.com> wrote:
>>> filter and amplifier specific to a small bandwidth for something like
>>> dissertation days, actually :)
>> One can think of the R/L/C approach
>>   the soldering iron and parts bin every time you want to
>>   is mostly there -- GaAsFET RF switches, LTCC filter modules, saw
>> gain stages would be uber-linear up to ridiculous
>
>> --
>> Principal Investigator
>> Shirleys Bay Radio Astronomy Consortium
>> http://www.sbrac.org


For those interested, this DARPA project was pointed out to me:
https://www.fbo.gov/index?s=opportunity&mode=form&...

Here's a brief write-up that summarizes the effort (apologies for the
in-your-face ad at the top):
http://www.militaryaerospace.com/articles/2012/08/...

Tom

On 27/02/13 05:45 PM, Tom Rondeau wrote:
>
Some of the commercial broadish-band tuner chips already have some of
this with switchable 3rd-order
 filter networks on-chip (or partially on-chip).  The E4000, R820T,
TDA18272, and others have some of this,
  targetted at the DVB-T/ATSC markets.



--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org