God Morgon Attila,
On 04/09/2017 10:28 PM, Attila Kinali wrote:
On Tue, 4 Apr 2017 17:58:11 -0700
jimlux <jim...@earthlink.net> wrote:
The beauty of the system would be that you don't need a SAW filter
at all. If the input stage (LNA + mixer) has a high enough dynamic
range, then the (first) IF filer alone can remove all those out of
band interference. And at the same time, because the IF frequency
being low, you don't need any specialized filter components that
might not be available in a couple of months.
Of course, this doesn't really work that way when significantly
wider signals (E5) have to be caught together with "narrow band"
signals (L1 C/A or L2C).
You got it backwards.
You need to protect your LNA and mixer from other signals, not to be
blocked out by out of band signals which is strong. That's why you have
SAW filters to start with. This has become a larger issue these days.
So, considering that you already have them, then what good do they do
for the different scenarios.
Unfortunately, the AD9361 does not offer the IF bandwith necessary.
Even though it has a high sample rate and can offer high bandwidth
capture of signals, the zero-IF nature of its design doesn't work
for this design approach. The IF of the AD9361 has a low pass filter
of at most 56MHz, ie it offers to capture a bandwith of 56MHz of
frequency space (using both I and Q channels). But the above approach
would need an IF of >200MHz, but it would be enough to only have a
single channel.
Only if you *need* the Galileo E5.
I looked up the prices for the components and figured that the prices for
mixer and IF amplifiers are actually quite low (a 2-4 USD per IC) so it
isn't that much more expensive to build such a system than using a 3 tuner
approach (eg using MAX2120 as Peter Monta did with the GNSS Firehose).
Cheers,
Magnus
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