Channel Phase Shift Measurements and Phase Equalizing Fi

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
Post Reply
stevieboy01
Posts: 1
Joined: Sun Feb 27, 2005 1:01 am
Contact:

Channel Phase Shift Measurements and Phase Equalizing Fi

Post by stevieboy01 » Sun Feb 27, 2005 3:18 am

I am attempting to characterise a phase shift in a channel so that I can compensate it at the receiver end using a phase equalizer. I need a method which produces a phase shift curve with more measurements than a Lissajous method produces. I was thinking possibly a phase shift oscillator may be the way to go with each stage producing a 45 degree shift, but I am unsure how to use this. I want to define the frequency and calculate the resulting shift. Also, I am not sure how to use an equalizing filter. I would probably use an all pass filter but how can I define where the curve goes? <p>Please help. I am mightily perplexed!!!<p>Steve

Ron H
Posts: 360
Joined: Tue Dec 18, 2001 1:01 am
Location: Boise, ID
Contact:

Re: Channel Phase Shift Measurements and Phase Equalizing Fi

Post by Ron H » Mon Feb 28, 2005 9:56 am

To do the analysis, you need a vector network analyzer (VNA). This applies a swept frequency to the input and plots amplitude and phase on the output.
Phase equalization using allpass networks, in my experience anyway, is part science and part art. It would help if you could simulate the equalizer, using the output data from the VNA as the stimulus for the allpass network.
If you can digitize the signal, I think there are equalization alternatives that have no analog counterpart.

User avatar
jwax
Posts: 2205
Joined: Mon Feb 09, 2004 1:01 am
Location: NY
Contact:

Re: Channel Phase Shift Measurements and Phase Equalizing Fi

Post by jwax » Mon Feb 28, 2005 6:48 pm

Can't help you, but I love that term, "AllPass Filter"! Sounds useful. :D

Bernius1
Posts: 349
Joined: Sat Sep 21, 2002 1:01 am
Location: NY
Contact:

Re: Channel Phase Shift Measurements and Phase Equalizing Fi

Post by Bernius1 » Tue Mar 01, 2005 4:48 am

Color TV uses the color burst to sync the local oscillator in phase, against which the remaining line is referenced. If your transmission is packeted data, maybe you can pulse a reference signal between the packets at a different frequency, to a PLL in the recvr.
Can't we end all posts with a comical quip?

Dean Huster
Posts: 1263
Joined: Wed Dec 05, 2001 1:01 am
Location: Harviell, MO (Poplar Bluff area)
Contact:

Re: Channel Phase Shift Measurements and Phase Equalizing Fi

Post by Dean Huster » Tue Mar 01, 2005 5:24 pm

I might point out, Stephen, that the traditional RC phase-shift oscillator shifts 180/n for each RC section where a 4-section oscillator will have APPROXIMATELY 45° shift for each section. The actual shift for each section will be strictly dependent upon the R and C values, their tolerances and their tempcos. To me, that eliminates the RC phase-shift oscillator as any serious contender as some kind of standard for a 45° phase shift unless you used very carefully-matched components with a small tempco. Even then, your final frequency may then be an issue if you have to have both the four shifts and the final frequency to be accurate. Quite a balancing act!<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

Post Reply

Who is online

Users browsing this forum: No registered users and 24 guests