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FSK Receiver - RF Cafe Forums
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| richas
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Post subject: FSK Receiver
Posted: Wed Jun 08, 2011 5:06 pm
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Joined: Wed Jun 01, 2011
9:36 pm Posts: 2 |
Hi, I am trying to design an FSK receiver with
a high data rate. (1 Mb/s) The operating frequency
is 978 MHz. I have found a transceiver IC that will
handle that rate but the frequency range is 900-928
MHz. I have a reference design for that IC.
It goes as: Antenna -> SAW Filter ->
LNA -> IC Can I add a mixer to the chain
to downconvert to, say, 900 MHz? Perhaps:
Antenna -> SAW -> LNA -> MIXER ->
IC The mixer would have to be capable of
producing a high frequency IF. I could use a 78
MHz LO to produce 900 MHz and 1056 MHz and hope
the IC's bandpass blocks the high side. Or perhaps
I would have to put another SAW filter after the
mixer? I appeal to the experts. Rich
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IR |
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Post subject: Re: FSK Receiver
Posted: Thu Jun 23, 2011 2:02 pm
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Joined: Mon Jun 27, 2005
2:02 pm Posts: 373 Location: Germany
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Hello, It should be stated in the IC data
sheet what is the out of band rejection around the
carrier. If it is not mentioned, then it is better
to use an additional filter. Take into consideration
the losses of the mixer (Conversion loss) in your
chain. In addition, a for the LO source a driver
amp. is most probably required.
_________________ Best regards, -
IR
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ashishbondia |
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Post subject: Re: FSK Receiver
Posted: Wed Jul 06, 2011 7:48 am
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Joined: Wed Aug 16, 2006
8:20 am Posts: 23 Location: India
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It should not be difficult to find transceivers
at 978 MHz.. 978 MHz is generally used in Airborne
communications.. I am not sure about the data rate...
Since the IC you have has input range of 900-928
MHz it should have good rejection for the 1056 MHz
signal.. also if you use a down conversion mixer,
the 1056MHz at the mixer outpurt would be highly
attenuated. Check the level of this signal at the
mixer output.. you may save some money by using
a simple LPF instead of an expensive SAW filter
if the 1056MHz signal is small
_________________ Ashish Bondia, Design
Engineer- RF
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richas |
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Post subject: Re: FSK Receiver
Posted: Wed Jul 06, 2011 12:57 pm
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Joined: Wed Jun 01, 2011
9:36 pm Posts: 2 |
Ashish, Yes, it is hard to find a transceiver
that supports that data rate. RFMD makes one.
I have not heard of using a simple LP filter
at these frequencies, it has been a hassle finding
SAW filters, basically we have to spend $$$.
Right now the design will use a mixer to down
convert to an IF that will feed an IF SAW filter
and then a Quadrature demodulator. This,
of course, may change. Thanks Rich
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biff44 |
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Post subject: Re: FSK Receiver
Posted: Tue Sep 06, 2011 6:39 am
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Joined: Wed Apr 08, 2009
11:07 am Posts: 33 |
I would take something like a CC1101 or ADF7023,
run it at 433 MHz, and down/upconvert your band
to there. TI makes a chip with a LNA and transmit
amp built into the same chip with a cheap switch
to share the antenna that you could use as a front
end. Analog devices has some PLLs with onboard
VCOs that could be the LO, or you could use another
one of those transceiver chips just as a cw LO.
The only tricky thing is the input bandpass
filter, as it is not a common band. maybe make a
simple lumped element BPF since it is not a hard
reject band for image suppression. |
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Posted 11/12/2012
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