Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
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page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
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!
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.
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
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!
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
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.