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Post subject: UHF superhet receiver Posted: Sat Nov 19, 2005 12:31 pm
hoping somebody could give me some advice on an upcoming RF college project. I have to design and construct a
simple superhet receiver to pick up an aircrafts pulse modulated transponder signal operating at 1.09 Ghz. At this
stage I just have more questions than answers!
How selective should my bandpass filters be, would passive
LC filters work at such a high input frequency?
Should I consider using active pin-programmable digital
filters instead, would the necessity of an onboard clock be worth the effort? Would power consumption be
acceptable? (Device needs to be portable)
For the VCO, should I look for an IC with an external resonant
tank or one where it is included?
What kind of intermediate frequency should I be aiming for? Hoping to
have the option to drive both audio earphones and input to laptop through parallel port.
recommend a good company with a wide range of RF components?
Any information would be greatly appreciated,
even if it's just point me in the direction of some decent literature.
subject: SuperhetPosted: Sun Nov 20, 2005 2:16 am
Bandwidth needs to be enough to handle the pulse
modulation - what's the PRF and the duty cycle? That'll give you a starting point on BW.
LC filters are
getting a bit "iffy" at that frequency - try using transmission-line resonators or cavities. Microstrip would also
do - but there are whole books on THAT subject!
You won't find a digital filter with a center frequency of
1 GHz that anyone other than the government can afford...
Pulse systems are usually not picky about
close-in noise, so either internal or external tank VCO's should do.
For chips, try National Semi and
Analog Devices for PLLs, RF Micro Devices for various parts, Sirenza, and the old groups from Motorola (Freescale
and On Semiconductor). There are a whole lot of specialized suppliers. You find them by Googling.