Post subject: UHF superhet receiver Posted: Sat Nov
19, 2005 12:31 pm
I was 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!
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
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.
Post 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.
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.