Going on "holiday"

I just wanted to let everyone know that I’m taking a vacation for the
week
(and won’t be taking my computer with me <gasp!>). I’m sure the list
will
continue to survive and function as usual with the standard amount of
help
and advice given by everyone, so you probably won’t even notice that I’m
missing.

In the mean time, Johnathan C. should be putting out a release
candidate
of 3.5.0 within the next day. We have already moved our master branch in
GNU
Radio to this version, anyway, so if you’re keeping up that way, you’ve
already made the transition. Please continue to report bugs, though,
before
we put out the full 3.5.0 release. This represents a number of big
changes,
so we need eyes on and hands inside the code to make sure it’s working
right. I recommend people submit bugs to the Issue Tracker on our
Redmine
page (you’ll have to log in to create a new ticket, the guest account is
guest:gnuradio), otherwise it might get lost in email.

Thanks!

Tom

http://www.downforeveryoneorjustme.com/gnuradio.org

Tom -

gnuradio.org is down =(

Cheers,
Ben

It actually wasn’t “down,” but I don’t know why it was responding the
way it was. I just rebooted it to fix whatever the problem was. I’m
about at the airport, so I have to pass these problems off to Johnathan.

Sent from my iPhone

I wasnt sure if I should mention it on this forum, but funny the
coincidence.

-Bob

Tom R. wrote in post #1029008:

It actually wasn’t “down,” but I don’t know why it was responding the
way it was. I just rebooted it to fix whatever the problem was. I’m
about at the airport, so I have to pass these problems off to Johnathan.

Sent from my iPhone

On Fri, Oct 28, 2011 at 11:53, Tom R. [email protected]
wrote:

It actually wasn’t “down,” but I don’t know why it was responding the way
it was. I just rebooted it to fix whatever the problem was. I’m about at the
airport, so I have to pass these problems off to Johnathan.

There was some issues with Amazon Web Services earlier today. The
server
instance is running now.

Johnathan

I have a question about software defined radio

I saw a pass band the other day on a screen which prompted me to ask

The Software defined radio has a specific bandwidth ?

Does it “scan” across the band very quickly to form the passband, or is
the
bandwidth already that large it just appears as a chunk of MHz ?

I am trying to make the connection between how a Software Defined Radio
would be different from an analogue system.

For example decoding packet radio using an SDR, is there any performance
degradation due to the way it works ?

Would the SDR “sweep” and miss some of the signal ?

  • Andrew VK4TEC -

On 28/10/2011 5:08 PM, Andrew R. wrote:

I am trying to make the connection between how a Software Defined
Radio would be different from an analogue system.

For example decoding packet radio using an SDR, is there any
performance degradation due to the way it works ?

Would the SDR “sweep” and miss some of the signal ?

  • Andrew VK4TEC -

A typical SDR hardware front-end (just taking the RX view for now) has a
tunable direct-conversion down-converter that converts a swath of
bandwidth at a desired center frequency into a complex (I,Q) baseband
signal that “straddles” from -BW/2 to BW/2,
with “DC” in the middle.

That swath of (analog) bandwidth is sampled by an ADC and FPGA, and then
decimated for delivery of a lesser bandwidth (again, in complex
baseband form) into the host computer for further processing. The
decimation also acts as a filter, so that there is strong alias
suppression
in the delivered bandwidth. It is usually the case that the FPGA
decimator is configurable with respect to the amount of bandwidth
delivered towards the host.

Bandwidths of several MHz into the host are achievable these days, with
all demodulation, etc, happening on the host.

That is not to say that you couldn’t implement a sweeper for doing
SIGINT and spectral estimation, etc. In fact, there are Gnu Radio
applications that do just that.

Thanks Marcus

So you can go outside the useable bandwidth, you just need to understand
that you will loose something as you move to the next chunk of RF ?

I saw an image of several MHz and a little decode window, but I guess
that
is a decoding window, smaller than the SDR sampling window.

I want to use SDR for satellites and packet radio

Does it meet a tnc / analogue radio specs ?

  • Andrew -

----- Original Message -----
From: “Marcus D. Leech” [email protected]
To: [email protected]
Sent: Saturday, October 29, 2011 7:16 AM
Subject: Re: [Discuss-gnuradio] SDR question

On Fri, Oct 28, 2011 at 11:54, Johnathan C. <
[email protected]> wrote:

Well, partially. The disk volume that holds the mysql back-end to the
Redmine website seems borked, causing very slow responses to links on
the
site, but they do seem to work eventually. Other things like the cgit
interface to repositories and pushing and pulling from git seem ok.

I’m looking into it.

Johnathan

On 28/10/2011 5:31 PM, Andrew R. wrote:

Thanks Marcus

So you can go outside the useable bandwidth, you just need to
understand that you will loose something as you move to the next chunk
of RF ?
Generally, the hardware samples at a fixed rate (USRP1 samples at
64Msps, and USRP2/N2XX sample at 100Msps for example). From
the hosts point of view, if the tuned frequency is X, and the
requested bandwidth is Y, your baseband extends from X-(Y/2) to X+(Y/2).
Not sure what you mean by “loose something as you move to the next
chunk of bandwidth”.

I saw an image of several MHz and a little decode window, but I guess
that is a decoding window, smaller than the SDR sampling window.
It is often the case that an actual application will bring in more
bandwidth than it strictly needs–usually because the
application-specific
bandwidth is a little bit smaller than one of the integer fractions
of the samplers input bandwidth. So you typically bandpass-filter in
software
to whatever the bandwidth of your application is, and then possibly
down-sample, or not, depending on the application.

Let’s say your sampler front-end runs at 100Msps, and you really only
want 75Khz of bandwidth.

On a USRP2 or N210, the maximum decimation value is 512, which produces
a sample rate of 195312sps, (100e6/512) since this is
complex-baseband, that 195312sps is also 195312Hz of usable
bandwidth (in a sense, complex sampling “cheats” Nyquist).

So, you’d place a bandpass filter in the signal path to filter it down
to 75Khz, before you did anything else with it in the signal flow.

I want to use SDR for satellites and packet radio

Does it meet a tnc / analogue radio specs ?

An SDR-based platform would have no trouble doing at least the
modulation and radio parts of a TNC, although implementing something
like AX.25 in Gnu Radio is likely a poor architectural choice.

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