Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
UHF superhet receiver - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
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.