Analog, multichannel RF recorder?

I need to record some real-world RF waveforms. All-digital approach
looks *very* disk intensive!

Wondering if there are multi-channel analog recorders adequate for the
job. Pointers to "better" digital solutions are appreciated as well.

Scenario:

I have 8 antennas receiving ~1GHz signals, ~5 MHz bandwidth each
signal.

Each antenna drives 3 RF->IF sections, for a total of 24 IF outputs.
IF is around 75MHz.

IF is undersampled (Fs=60MHz) with 12-bit A/D converters.

60M samples/second * 12 bits/8 bits/byte) = 90 Mbytes/sec

24 channels * 90 Mbytes/sec = 2.16 GB/sec
(That's 129.6 GB/minute or 7.776 Terabytes/hour, and I'd like to record
a full hour of data.)

24 channels is ideal, but 4 channels is absolute minimum.
Could record either the 75MHz IF output, or 1GHz RF straight from the
antennas.

I then need to play these back (4-24 channels in parallel) for testing
my receiver (al RF or just IF).

[Analog in and out is easiest. Digital record/playback approach is OK
(no wow & flutter problem) as long as resolution remains around 12-bits
and there are no artifacts of original sampling, because I need
"authentic" signals coming thru the IF and into my A/D converters for
accurate testing.]

[I could also test my DSP section only, by recording my own A/D
converter outputs, given an affordable disk system with sufficient I/O
bandwidth. With 8 channels at 90MB/s = 720 megabytes/second, I could
record about 6 minutes of data on one 250 GB drive, which is an
acceptable starting point for me.]

Tall order I know, but I'm open to creative solutions. Thanks a ton for
*any* help or references you can provide.

mj

jjohnson@cs.ucf.edu wrote:
> I need to record some real-world RF waveforms. All-digital approach
> looks *very* disk intensive!
> 
> Wondering if there are multi-channel analog recorders adequate for the
> job. Pointers to "better" digital solutions are appreciated as well.
> 
> Scenario:
> 
> I have 8 antennas receiving ~1GHz signals, ~5 MHz bandwidth each
> signal.
> 
> Each antenna drives 3 RF->IF sections, for a total of 24 IF outputs.
> IF is around 75MHz.
> 
> IF is undersampled (Fs=60MHz) with 12-bit A/D converters.
> 
> 60M samples/second * 12 bits/8 bits/byte) = 90 Mbytes/sec
> 
> 24 channels * 90 Mbytes/sec = 2.16 GB/sec
> (That's 129.6 GB/minute or 7.776 Terabytes/hour, and I'd like to record
> a full hour of data.)
> 
> 24 channels is ideal, but 4 channels is absolute minimum.
> Could record either the 75MHz IF output, or 1GHz RF straight from the
> antennas.
> 
> I then need to play these back (4-24 channels in parallel) for testing
> my receiver (al RF or just IF).
> 
> [Analog in and out is easiest. Digital record/playback approach is OK
> (no wow & flutter problem) as long as resolution remains around 12-bits
> and there are no artifacts of original sampling, because I need
> "authentic" signals coming thru the IF and into my A/D converters for
> accurate testing.]
> 
> [I could also test my DSP section only, by recording my own A/D
> converter outputs, given an affordable disk system with sufficient I/O
> bandwidth. With 8 channels at 90MB/s = 720 megabytes/second, I could
> record about 6 minutes of data on one 250 GB drive, which is an
> acceptable starting point for me.]
> 
> Tall order I know, but I'm open to creative solutions. Thanks a ton for
> *any* help or references you can provide.

What if you extract the modulation on the signals, record that, and 
regenerate the original signals by modulating oscillators? Why do you 
need a cycle-by-cycle record of the rf?

--
john

jjohnson@cs.ucf.edu wrote:

> I need to record some real-world RF waveforms. All-digital approach
> looks *very* disk intensive!
> 
> Wondering if there are multi-channel analog recorders adequate for the
> job. Pointers to "better" digital solutions are appreciated as well.
> 
> Scenario:
> 
> I have 8 antennas receiving ~1GHz signals, ~5 MHz bandwidth each
> signal.
> 
> Each antenna drives 3 RF->IF sections, for a total of 24 IF outputs.
> IF is around 75MHz.
> 
> IF is undersampled (Fs=60MHz) with 12-bit A/D converters.

That isn't undersampling if the bandwidth of each IF is less than 30
MHz. If it's really undersampled, you have garbage; find another
project. If the bandwidth is much less than 30 MHz -- which in a 75MHz
IF seems likely -- you can sample at a lower rate, saving data. You
probably need to know only the baseband signal. They can recreate the RF
with appropriate modulators.

> 60M samples/second * 12 bits/8 bits/byte) = 90 Mbytes/sec
> 
> 24 channels * 90 Mbytes/sec = 2.16 GB/sec
> (That's 129.6 GB/minute or 7.776 Terabytes/hour, and I'd like to record
> a full hour of data.)
> 
> 24 channels is ideal, but 4 channels is absolute minimum.
> Could record either the 75MHz IF output, or 1GHz RF straight from the
> antennas.
> 
> I then need to play these back (4-24 channels in parallel) for testing
> my receiver (al RF or just IF).
> 
> [Analog in and out is easiest. Digital record/playback approach is OK
> (no wow & flutter problem) as long as resolution remains around 12-bits
> and there are no artifacts of original sampling, because I need
> "authentic" signals coming thru the IF and into my A/D converters for
> accurate testing.]
> 
> [I could also test my DSP section only, by recording my own A/D
> converter outputs, given an affordable disk system with sufficient I/O
> bandwidth. With 8 channels at 90MB/s = 720 megabytes/second, I could
> record about 6 minutes of data on one 250 GB drive, which is an
> acceptable starting point for me.]
> 
> Tall order I know, but I'm open to creative solutions. Thanks a ton for
> *any* help or references you can provide.
> 
> mj
> 

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Could you not write to a RAID rather than a single disk?

jjohnson@cs.ucf.edu wrote:
> I need to record some real-world RF waveforms. All-digital approach
> looks *very* disk intensive!
>
> Wondering if there are multi-channel analog recorders adequate for
the
> job. Pointers to "better" digital solutions are appreciated as well.
>
> Scenario:
>
> I have 8 antennas receiving ~1GHz signals, ~5 MHz bandwidth each
> signal.
>
> Each antenna drives 3 RF->IF sections, for a total of 24 IF outputs.
> IF is around 75MHz.
>
> IF is undersampled (Fs=60MHz) with 12-bit A/D converters.
>
> 60M samples/second * 12 bits/8 bits/byte) = 90 Mbytes/sec
>
> 24 channels * 90 Mbytes/sec = 2.16 GB/sec
> (That's 129.6 GB/minute or 7.776 Terabytes/hour, and I'd like to
record
> a full hour of data.)
>
> 24 channels is ideal, but 4 channels is absolute minimum.
> Could record either the 75MHz IF output, or 1GHz RF straight from the
> antennas.
>
> I then need to play these back (4-24 channels in parallel) for
testing
> my receiver (al RF or just IF).
>
> [Analog in and out is easiest. Digital record/playback approach is OK
> (no wow & flutter problem) as long as resolution remains around
12-bits
> and there are no artifacts of original sampling, because I need
> "authentic" signals coming thru the IF and into my A/D converters for
> accurate testing.]
>
> [I could also test my DSP section only, by recording my own A/D
> converter outputs, given an affordable disk system with sufficient
I/O
> bandwidth. With 8 channels at 90MB/s = 720 megabytes/second, I could
> record about 6 minutes of data on one 250 GB drive, which is an
> acceptable starting point for me.]
>
> Tall order I know, but I'm open to creative solutions. Thanks a ton
for
> *any* help or references you can provide.
>
> mj

You mention that the signal BW is just 5 MHz. Is the signal center
frequency fixed within the IF? If so, you could digitally downconvert
the signal, with sample rate reduction, and record the baseband.

I would think writing out to multiple disks simultaneously to reduce
the required BW is the way to go.

John

Sorry to have not been more accurate, precise, and clear. First, I
think I should have said "bandpass sampled" instead of undersampled.
IF output is centered at 75 MHz, +/- about 15MHz of signal BW (spectrum
from 60MHz to 90 MHz).

Sampling at 60MHz shifts that down to baseband (0-30MHz) where the DSP
begins. The 5 MHz BW I quoted is after some of the filtering in our
DSP.

I was hoping to capture analog on a multichannel recorder so I could do
repeated playback thru the RF->IF analog chain, and iteratively tweak
components (including my A/D converters), without having the artifacts
of other (possibly inferior) A/D converters corrupting my
"gold-standard" reference signals.

Digital capture also means I have to hook up 24 modulators to replay
the RF. I wanted to avoid degrading my reference signals as much as
possible. Replaying and modulating captured baseband means the next
time I look at the signals in my DSP, they will have been thru my IF
twice, plus somebody else's modulator, which munges things a bit. Thus,
capturing original Rx antenna output would be ideal.

Also, capturing the data will be expensive, as it requires rental of an
airplane for a couple of hours. Swapping disks every 2-5 minutes does
not give me much continuous, uninterrupted data to work from. (I want
to replay an entire flight segment thru certain maneuvers and across a
good strectch of airspace.)

Having said that, if there is an "easy" (affordable, off-the shelf)
RAID solution I can write to from my ADC converters (129.6 GB/minute
for at least 10 minutes), I could use that for replay into my DSP
datapath simulations. Not ideal, but far better than nothing.

Hope this better explains my needs and rationale. But as I mentioned
before, all feedback is appreciated.

Thanks again,

mj

In sci.physics jjohnson@cs.ucf.edu wrote:
> Sorry to have not been more accurate, precise, and clear. First, I
> think I should have said "bandpass sampled" instead of undersampled.
> IF output is centered at 75 MHz, +/- about 15MHz of signal BW (spectrum
> from 60MHz to 90 MHz).

> Sampling at 60MHz shifts that down to baseband (0-30MHz) where the DSP
> begins. The 5 MHz BW I quoted is after some of the filtering in our
> DSP.

> I was hoping to capture analog on a multichannel recorder so I could do
> repeated playback thru the RF->IF analog chain, and iteratively tweak
> components (including my A/D converters), without having the artifacts
> of other (possibly inferior) A/D converters corrupting my
> "gold-standard" reference signals.

> Digital capture also means I have to hook up 24 modulators to replay
> the RF. I wanted to avoid degrading my reference signals as much as
> possible. Replaying and modulating captured baseband means the next
> time I look at the signals in my DSP, they will have been thru my IF
> twice, plus somebody else's modulator, which munges things a bit. Thus,
> capturing original Rx antenna output would be ideal.

> Also, capturing the data will be expensive, as it requires rental of an
> airplane for a couple of hours. Swapping disks every 2-5 minutes does
> not give me much continuous, uninterrupted data to work from. (I want
> to replay an entire flight segment thru certain maneuvers and across a
> good strectch of airspace.)

> Having said that, if there is an "easy" (affordable, off-the shelf)
> RAID solution I can write to from my ADC converters (129.6 GB/minute
> for at least 10 minutes), I could use that for replay into my DSP
> datapath simulations. Not ideal, but far better than nothing.

> Hope this better explains my needs and rationale. But as I mentioned
> before, all feedback is appreciated.

> Thanks again,

> mj

An off the shelf linux box with 4 400GB (~$300 ea) drives configured
as one large disk with linux gets you 1.6 TB.

However, AFAIK the fastest disks around these days have a transfer rate
of 1.5 GB/sec which only gets you 90 GB/minute.

There are some solid state disks around that can do better (but not
much) than that with multiple fiber channel interfaces, but they aren't
cheap.

I know of no computer system you can buy that will directly address
over 1 TB of memory; direct to memory would get you the speed, but
not the capacity.

I think you are screwed in storing this much data this quickly on any
current storage device unless you can do real time compression on
the data.

-- 
Jim Pennino

Remove -spam-sux to reply.

jjohnson@cs.ucf.edu wrote:
> I need to record some real-world RF waveforms. All-digital approach
> looks *very* disk intensive!

Just on general principles, you can beat down the RF signal to video using
quadrature detectors. Record the in phase video and quadrature videos on two
video channels of sufficient bandwidth. In fact, you would be best off using
A/D converter and record digitally. That, and the frequency and phase of the
carrier,  should give you all the information you need. Actual waveforms
could be reconstructed in a computer, if you really need that.

Bill

<jjohnson@cs.ucf.edu> wrote in message
news:1107460901.200754.128210@c13g2000cwb.googlegroups.com...
> I need to record some real-world RF waveforms. All-digital approach
> looks *very* disk intensive!
>
> Wondering if there are multi-channel analog recorders adequate for the
> job. Pointers to "better" digital solutions are appreciated as well.
>
> Scenario:
>
> I have 8 antennas receiving ~1GHz signals, ~5 MHz bandwidth each
> signal.
>
> Each antenna drives 3 RF->IF sections, for a total of 24 IF outputs.
> IF is around 75MHz.
>
> IF is undersampled (Fs=60MHz) with 12-bit A/D converters.
>
> 60M samples/second * 12 bits/8 bits/byte) = 90 Mbytes/sec
>
> 24 channels * 90 Mbytes/sec = 2.16 GB/sec
> (That's 129.6 GB/minute or 7.776 Terabytes/hour, and I'd like to record
> a full hour of data.)
>
> 24 channels is ideal, but 4 channels is absolute minimum.
> Could record either the 75MHz IF output, or 1GHz RF straight from the
> antennas.
>
> I then need to play these back (4-24 channels in parallel) for testing
> my receiver (al RF or just IF).
>
> [Analog in and out is easiest. Digital record/playback approach is OK
> (no wow & flutter problem) as long as resolution remains around 12-bits
> and there are no artifacts of original sampling, because I need
> "authentic" signals coming thru the IF and into my A/D converters for
> accurate testing.]
>
> [I could also test my DSP section only, by recording my own A/D
> converter outputs, given an affordable disk system with sufficient I/O
> bandwidth. With 8 channels at 90MB/s = 720 megabytes/second, I could
> record about 6 minutes of data on one 250 GB drive, which is an
> acceptable starting point for me.]
>
> Tall order I know, but I'm open to creative solutions. Thanks a ton for

As you have
"8 antennas receiving ~1GHz signals, ~5 MHz bandwidth each",
what you might do is to mix the outputs the eight signals
with a quasi-random, time-reference signal
( Perhaps from the GPS system.),
and feed the outputs into nine video recorders.
( One for the quasi-random, time-reference signal.)

A digital computer or optical computer,
could be used to sample any two of the channels
and to determine auto-correlations, cross-correlations,
perform Fourier transforms, power spectral density, etc.

--
Tom Potter

If you have 8 antenna's why do you have to record 24 channels.

Can't you record the 8 signals before they go into the 2 way converters
(whatever those are)?

Saves you a factor of 3.
Mark