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Re: [Discuss-gnuradio] Question regarding the DBSRX frequency range and

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] Question regarding the DBSRX frequency range and bandwidth
Date: Wed, 27 Jun 2007 11:47:36 -0700
User-agent: Thunderbird (X11/20070326)

Trond Danielsen wrote:
> Hi,
> I have a small question regarding the frequency range and bandwidth of
> the DBSRX daughterboard from www.ettus.com. According to the
> daughterboard datasheet [1] the frequency range is from 800 to 2400
> MHz, and the adjustable bandwidth is from 1 to 60 MHz. However, the
> datasheet for the MAX2118 [2] states a frequency range from 925 to
> 2175 MHz, and the adjustable LP filter BW is 4 to 33 MHz.
> If someone could provide some information that would enlighten me on
> these matters I would be most grateful.

Frequency Range:
    The MAX2118 datasheet says that it covers 925 to 2175 MHz.  They
spec that because it is the range that their typical customer needs (for
small satellite dish IFs).  However, I have never found one which
doesn't work to the larger 800 MHz to 2400 MHz range.  Maxim guarantees
925 to 2175, I guarantee the larger range.

    When Maxim states that their maximum LPF bandwidth is 33 MHz, they
mean one-sided bandwidth (i.e. 0 to 33 MHz).  Since it is used in a
direct conversion IQ system, that actually gives a 66 MHz bandwidth (-33
MHz to +33 MHz).  Since that is beyond nyquist for our ADC, I spec to 60
MHz (+/- 30 MHz).
    On the low end, they specify 4 MHz, which is really 8 MHz (+/-4 MHz)
of RF bandwidth.  The filter is actually capable of going to a much
narrow frequency, but it is outside of Maxim's specs, since nobody in
the small satellite dish market cares about less than 8 MHz of BW.  So I
spec that it goes down to 1 MHz wide.  It should be noted that when you
go below 4 MHz wide (2 MHz in Maxim-speak) that your noise floor will
rise a bit and phase noise may also rise.


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