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:
WB FM detection via delay line & C-loaded transmission line
- 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: WB FM detection via delay line &
C-loaded transmission line Posted: Thu Jun 11, 2009 5:17 pm
Joined: Mon Apr 20, 2009 2:04 pm
I'm still trudging through my video link in a world
that left WB FM behind (sigh...).
Anyway, it occured to me that
an off-the-shelf mixer IC and a 1/4 wave delay would make for a nice
detector. I popped in an SA602 + delay into Spice, and it worked great,
as long as I didn't over drive it. It was extremely linear over 70MHz
Now, I have two basic questions:
1. Has anyone
gotten some experience with this?
2. I don't care to have 3.57ns
of coax laying about in my case, nor do I care for a couple of feet
of meandering transmission line on my PCB. Has anyone had any luck with
distributed C loading along a shorter transmission line. From the equations,
it looks as though I can pepper the line every 1/2 inch with 10pF caps,
and reduce the length to about 6 inches with only a lower Z and some
ripple in the UHF as the cost.
Does this sound rational? Has anyone
Post subject: Re: WB FM detection via delay line & C-loaded
transmission linePosted: Sun Jun 14, 2009 11:32 pm
Joined: Sun Jan 11, 2004 4:44 pm
Howdy Mike form
I've seen FM detectors that used 1/4-wave delay lines
(first time in my college communications book). Those kinds of books
usually dealy strictly with theory and not with actual implementation
like you've got going there. I like your idea about trying to load with
some caps to try to shorten the delay line length to a reasonable length.
The only real requirement is that you get a 90-deg phase shift between
the mixer ports (with minimal distortion).
Check out this patent. It gives component values for you. You might
be able to come up with something better, but at least this shows that
somebody's thought along the same lines.
I'll be interested in seeing your result.