Matt Ettus wrote:
Other than 802.11, there aren't many applications that require more
than 8 MHz of bandwidth. Radio astronomy is one, but you can use
fewer bits per sample with RA. It is not uncommon to use 1 or 2 bits
per sample, which would allow you to cover 128 and 64 MHz respectively.
There is an 8-bit per sample mode in the USRP which will allow you to
get 16 MHz of BW across the bus.
Matt
I tried my radio astronomy application on a 3.4Ghz system from gateway,
and was unable to do more than 8Msps, despite
the fact that the CPU was relatively lightly loaded (30%) at 8Msps.
In radio astronomy, the sensitivity goes up with
SQRT(bandwidth*integration_time). There are practical limits to
the integration time you can use, but bandwidth well beyond 8Mhz is
routinely used for continuum observations.
At the higher radio astronomy frequencies, the "big boys" are now
routinely running their 1 or 2-bit samplers
at 1Gsps (which gives you 1Ghz complex bandwidth)! There are, of
course, practical limits in available bandwidth
at lower frequencies. For example, the area around 21cm only has
27Mhz of dedicated spectrum, but in reality,
that spectrum is being encroached upon both by deliberate
transmissions, and spurious emissions.
That's why places like the Green Bank radio observatory (was there last
week) are in the middle of
100-mile-wide "radio quiet zones". No deliberate radio transmissions
allowed, and no microwave
ovens allowed on-site, etc, etc. There's no cellphone service in that
part of West Virginia for a reason :-)
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