[time-nuts] Sinlge ADC multi-band receiver
kb8tq at n1k.org
Sun Apr 9 18:22:18 EDT 2017
> On Apr 9, 2017, at 4:29 PM, Attila Kinali <attila at kinali.ch> wrote:
> On Wed, 5 Apr 2017 08:27:58 -0400
> Bob kb8tq <kb8tq at n1k.org> wrote:
>> Galileo E5 is a bit of a strange case. It’s really E5a and E5b.
>> You can either grab it all as one giant signal or as two separate signals.
>> You may (or may not) care about the data on E5a or b depending on what you
>> are trying to do. Getting the entire very wide signal likely has some
>> interesting benefits when it comes to working out very small differences
>> in location or … errr… time.
> I wouldn't call it strange, but rather neat :-)
> The E5 signal is created as a single, 8-PSK signal(see ), which is
> modulated such, that the positive and negative frequency parts get
> a specific signal structure. This is done in order to allow an extremely
> wide band signal to be demodulated in parts. I guess they feared that a
> receiver for a 50MHz wide signal would be too expensive for the
> commercial market and made it possible to process the signal as two
> 20MHz wide pieces. There is a slight loss in correlation energy in this
> case, but for most applications it should not matter. The bigger issue
> is that the path delays for the two receiver channels would need to be
> calibrated and tracked during operation in order to make full use of
> the E5 signal.
> BTW: I have been told, that using the full E5 signal makes the use
> of any other signal kind of unnecessary as its extremely wide bandwidth
> allows a very fine tracking of the signal. Thus the use of any other signal
> (e.g. E1 OS) would actually degrade the receivers timing performance than
> improve it.
Without a “second frequency” you can’t do local ionosphere corrections. That’s
true regardless of the bandwidth of the signals …..
>> One way to do the E5 signal would be a dual (duplicate) IF ISB downconverter.
>> How practical that turns out to be is an open question. The more conventional
>> approach is to take a monstrous chunk of L band down to a high speed sampler.
> As I have written above, to be able to do this is the reason for the E5's
> signal structure. And apparently the designers thought that this would be
> the way how most users would decode it. I am currently not aware of any
> commercial E5 receiver that is already on the market, so it is kind of moot
> to ask what the common way to decode E5 is.
> BTW: Rodriguez' PhD thesis (which is the basis of navipedia) gives a very
> nice overview of the trade-off's that went into the Galileo signals and
> gives a few hints where future GNSS signals could further improve things.
> Attila Kinali
>  Galileo OS SIS ICD Issue 1 Revision 2,
> Section 22.214.171.124 "Equivalent Modulation Type"
>  "On Generalized Signal Waveforms for Satellite Navigation",
> by José Ángel Ávila Rodríguez, 2008
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