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.