From f2c90ec111a8fd8964fdd21f36e5768b0fd34398 Mon Sep 17 00:00:00 2001 From: Bill Somerville Date: Sat, 23 Sep 2017 22:02:24 +0000 Subject: [PATCH] Minor additions to MSK144 phase eq docs git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8117 ab8295b8-cf94-4d9e-aec4-7959e3be5d79 --- doc/user_guide/en/measurement_tools.adoc | 91 +++++++++++++----------- 1 file changed, 49 insertions(+), 42 deletions(-) diff --git a/doc/user_guide/en/measurement_tools.adoc b/doc/user_guide/en/measurement_tools.adoc index 1deb5f8f2..d783700b3 100644 --- a/doc/user_guide/en/measurement_tools.adoc +++ b/doc/user_guide/en/measurement_tools.adoc @@ -76,64 +76,71 @@ Wait for about a minute and then hit the *Stop* button. A file named === Phase Response and Equalization -*Measure phase response* under the *Tools* menu is for advanced -MSK144 users. Phase equalization is used to compensate for group-delay +*Measure phase response* under the *Tools* menu is for advanced MSK144 +users. Phase equalization is used to compensate for group-delay variation across the passband of receiver filters. Careful application -of this facility can reduce intersymbol interference, resulting in -improved decoding sensitivity. -If you use a software-defined receiver with linear-phase -filters there is no need to apply phase equalization. +of this facility can reduce intersymbol interference, resulting in +improved decoding sensitivity. If you use a software-defined receiver +with linear-phase filters there is no need to apply phase +equalization. After a received frame is decoded *Measure phase response* generates -an undistorted waveform whose Fourier transform is used as a +an undistorted waveform whose Fourier transform is used as a frequency-dependent phase reference to compare with the phase of the -received frame's Fourier coefficients. -Phase differences between the reference -and the received waveform include contributions from the -originating station's transmit filter, the propagation channel, and filters -in the receiver. If the received frame originates from a station known -to transmit signals having little phase distortion (say, a station known -to use a properly adjusted software-defined-transceiver) and if the -received signal is relatively free from multipath distortion so that the -channel phase is close to linear, the measured phase differences will be -representative of the local receiver's phase response. +received frame's Fourier coefficients. Phase differences between the +reference and the received waveform include contributions from the +originating station's transmit filter, the propagation channel, and +filters in the receiver. If the received frame originates from a +station known to transmit signals having little phase distortion (say, +a station known to use a properly adjusted +software-defined-transceiver) and if the received signal is relatively +free from multipath distortion so that the channel phase is close to +linear, the measured phase differences will be representative of the +local receiver's phase response. Complete the following steps to generate a phase equalization curve: -- Record a number of wav files that contain decodable signals from your chosen -reference station. Best results will be obtained when the SNR of the -reference signals is at least 9 dB. +- Record a number of wav files that contain decodable signals from +your chosen reference station. Best results will be obtained when the +SNR of the reference signals is at least 9 dB. - Enter the callsign of the reference station in the DX Call box. - Select *Measure phase response* from the *Tools* menu, and process -the wav files. The mode character will change from `&` to `^` while _WSJT-X_ -is measuring the phase response and it will change back to `&` after the -measurement is completed. The program needs to average a number -of high-SNR frames to accurately estimate the phase, so it may be necessary -to process several wav files. The measurement can be aborted at any time -by selecting *Measure phase response* again to toggle the phase measurement -off. -When the measurement is complete _WSJT-X_ will save the measured phase response -in the *Log directory*, in a file with suffix ".pcoeff". The filename will -contain the callsign of the reference station and a timestamp. -For example: K0TPP_170923_112027.pcoeff +the wav files. The mode character will change from `&` to `^` while +_WSJT-X_ is measuring the phase response and it will change back to +`&` after the measurement is completed. The program needs to average a +number of high-SNR frames to accurately estimate the phase, so it may +be necessary to process several wav files. The measurement can be +aborted at any time by selecting *Measure phase response* again to +toggle the phase measurement off. + ++ + +When the measurement is complete _WSJT-X_ will save the measured +phase response in the *Log directory*, in a file with suffix +".pcoeff". The filename will contain the callsign of the reference +station and a timestamp. For example: K0TPP_170923_112027.pcoeff - Select *Equalization tools ...* under the *Tools* menu and click the *Phase ...* button to view the contents of the *Log directory*. Select -the desired pcoeff file. The measured phase values will be plotted as discrete -circles along with a fitted curve labeled "Proposed". This is the -proposed phase equalization curve. It's a good idea to repeat the -phase measurement several times, using different wav files for each -measurement, to ensure that your measurements are -repeatable. +the desired pcoeff file. The measured phase values will be plotted as +discrete circles along with a fitted curve labeled "Proposed". This is +the proposed phase equalization curve. It's a good idea to repeat the +phase measurement several times, using different wav files for each +measurement, to ensure that your measurements are repeatable. - Once you are satisfied with a fitted curve, push the *Apply* button -to save the proposed response. The red curve will be replaced with a -light green curve labeled "Current" to indicate that the phase equalization -curve is now being applied to the received data. Another curve labeled -"Group Delay" will appear. The "Group Delay" curve shows the group delay -variation across the passband, in ms. +to save the proposed response. The red curve will be replaced with a +light green curve labeled "Current" to indicate that the phase +equalization curve is now being applied to the received data. Another +curve labeled "Group Delay" will appear. The "Group Delay" curve shows +the group delay variation across the passband, in ms. Push the +*Discard* button to remove the captured data, leaving only the applied +phase equalization curve and corresponding group delay curve. + +- To revert to no phase equalization, push the *Restore Defaults* +button followed by the *Apply* button. The three numbers that are printed at the end of each MSK144 decode line can be used to assess the improvement provided by equalization. These numbers