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#40m alignment problem - 90 deg phase shift #40m


Syd
 

Having some problem adjusting R17 and R24 in the phasing circuit.   IC5 pins 1 & 7 show a clean 90 degree phase difference of the signals.   IC5 pin 1 shows a 90 degree phase difference compared to IC7 pin 1.   I think that's correct.   IC5 pin  7 shows a 90 degree phase difference compared to IC6 pin 1. There is no change in phase when R17 and R24 are adjusted while looking at the last two signals per troubleshooting manual. I would think I should see a phase change here when either control is adjusted.  Shouldn't the outputs of IC6 and IC7 match up? 

I'm thinking that the phase of IC5 pin 1 gets shifted 45 degrees, and the output of IC5 pin 7 gets shifted 45 degrees the opposite way to make the I  and Q match up to add together.  If that's true then I have to take a closer look at the phases in the two signal paths to see what is or is not working.  Any thoughts on this are appreciated.
73 wt1v


@CurtisM
 

Syd

If indeed you can visually and audibly peak the trimmer cap, possibly the RF inpu transformer and some circuitry is working, maybe. If one trimmer pot is effective in nulling, I would he a bit more confident.

Carefully check the trimmer pot pins to measure if they are really connected. Measure continuity from bare pin to  further down pc trace. Easy for one of these pins to not he soldered, don't ask how I know. If all these pins are attached, then either improper windings or missing connections are in order, they happen. Hint, use the builtin test source to aid your troubleshooting.

73 curt


Alan G4ZFQ
 

There is no change in phase when R17 and R24 are adjusted while looking at the last two signals per troubleshooting manual. I would think I should see a phase change here when either control is adjusted.
There is a good description of operation in the manual.
The link in the manual leads to here http://www.norcalqrp.org/files/AustinNC2030Presentation.pdf where there is a better description of operation.
Are you checking as instructed? I'm not sure you will see the very fine adjustments on a scope.

73 Alan G4ZFQ


Syd
 

    By comparing the two I and Q signals simultaneously on the scope I should see some sort of phase change!   The T/S manual mentions overlaying these signals by adjusting the two resistors (R17 & R24), and making the signals overlap!   I interpret this to mean that one should see a phase change in the Q signal path!   Although,
as the manual mentions, this is not as exact as using the built in bar graph, but it is a T/S tool.

    So  again there must be a fault in the variable resistors (Q)  filter/amplifier circuit.

   BTW I made a mistake when I said I thought that the 2 signals, I  and Q, might have to have a 45 degree phase shift!  Researching online about  demodulating I  and Q signals, they get added together to produce the audio signal, and the phase matching of the I and Q paths is critical to the demodulation process.

73 wt1v


Syd
 

Since the trimmer is now working, and the outputs at Q5 are good, and there are no adjustments in the I path, but the Q path does, and the signal levels out of both channels are pretty much the same at IC6 & IC7 pin 1, I definitely will take your advice about checking the continuity around both of these pots!!! Won't be the first time I have found some sort of soldering problem in the kit!!


Syd
 

more info on this problem
I measured 90 deg phase difference between IC5 #1 & IC5 #7.
From IC5 #1 to IC7 #1 there is a 90 degree phase shift.
From IC5 #7 to IC6 #1 there is a 180 degree phase shift! Shouldn't this also be a 90 degree phase shift?

Although there still is a quad signal going into R27, I'm still not sure that this is correct!
73 wt1v


Alan G4ZFQ
 

I measured 90 deg phase difference between IC5 #1 & IC5 #7.
From IC5 #1 to IC7 #1 there is a 90 degree phase shift.
From IC5 #7 to IC6 #1 there is a 180 degree phase shift! Shouldn't this also be a 90 degree phase shift?
Syd,

I still think you are looking for a problem that is not there.
In the link I sent before Dan Tayloe shows the final stage of phase shifting. Two complex signals 180° apart which when combined null out the unwanted sideband.

And I'm still doubtful that a scope will show the small fractions of a degree shift when the pots are adjusted.

73 Alan G4ZFQ


Syd
 

I may have fixed it. The board has been a little sensitive to touch, so after prodding around with a plastic tool, I found IC 8 more sensitive. One of the pins looked   a bit funny so I resoldered it, much better, but still a little sensitive to touch. I poked around, especially between the pins with a plastic tool even though I could see nothing, and suddenly things looked a lot better. Checking out the IQ filter circuit with a scope I now have

IC5#1 - IC5#7 = 90 degree phase (I and Q)
IC5#1 - IC7#1 = 90 degree phase (I)
IC5#7 - IC6#1 = 0 degree phase (Q)
IC6#1 - IC7#1 = 0 degree phase (I and Q)

I thought I and Q were added while being 90 degrees out of phase.
I have another 20m kit that I just finished and will be making comparison measurements to finish this project.
73 wt1v


Daniel Curtin KF4AV
 

Syd,

As best I understand from Hans' explanation in the build notes, the resistors adjust the level of the signals, not the phase. They need to be 180º out of phase and close in amplitude to cancel adequately.

73, Dan KF4AV


Daniel Curtin KF4AV
 

The document Alan cites has a great description of how the phase shifts are use to supress one of the sidebands, with beatiful graphs, starting around p. 27.


Daniel Curtin KF4AV
 

Oops. The I/Q Balance adjusts the amplitudes, the other 2 pots do trim the phase for low and high audio frequencies. I need to read more carefully.