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...
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My Hobby Website:
LC duplexer - 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: LC duplexer Posted: Sun Aug 07, 2005 9:22 am
i would like to design LC duplxers consist of HPF and LPF
in an eagleware software i got influence between the two filters and
i dont get the needed performance when combining the filters
i would like to know the right way to design it, or to model it in eagleware
or an application note regarding the subject
Post subject: Posted: Wed
Aug 10, 2005 1:04 pm
Joined: Sun Aug 03,
2003 2:02 pm
Location: Erie, PA
It has been a while since I have designed a diplexer, but if memory
serves me correctly, the way to go about a LP/HP combination is to design
with an input impedance of 1 ohm and an output impedance of whatever
you system impedance is (50 ohms?). Then, tie the two 1 ohm inputs together
as the common input.
The theory behind it is that between the
LP and HP filters, the input will "see" the system impedance spanning
in frequency across both filters. At least that's the way I remember
- Kirt Blattenberger
RF Cafe Progenitor &
Post subject: LC DiplexerPosted:
Wed Aug 10, 2005 5:55 pm
In designing an LC Diplexer, it's important
to have the right kind of filters for the HP and LP filters. Neither
should start with a shunt element. (Use Tee filter sections instead
of Pi sections for the first stage).
Otherwise, each filter will
"short out" the signal in its stopband, with disastrous results.
If I remember correctly, you design both filters at the system characteristic
impedance (usually 50 Ohms). That way, the return loss stays (more or
less) constant over both bands.