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Re: [softrock40] Re: Divider stage tests

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  • Cliff Kalfaian
    Thank you both Bob and Robby for getting back to me. I was beginning to suspect my inexpensive DMM might have been reacting oddly. Now that you have pointed
    Message 1 of 4 , Apr 28, 2010
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      Thank you both Bob and Robby for getting back to me. I was beginning to suspect my inexpensive DMM might have been reacting oddly. Now that you have pointed out that the voltage at the junction of R44 & R45 is actually a square wave rather than DC, I suppose I might get a different reading on my true RMS reading Fluke. Yes, I do have the CMOS version of U7, and U8 is not installed, nor is R43, and jumper is in place. I guess I should have mentioned all that the first time around. Thanks again,


      On Apr 28, 2010, at 10:19 AM, R R Robson wrote:

      Just out of curiosity, what version of the Si570 were you using in your kit: the CMOS version or the LVDS version?
      If you have the CMOS version, then I assume you did NOT install R43 and U8 (FIN 1002) and you DID install the CMOS jumper. 
      Bob is right about the approximate nature of these voltage measurements in the presence of all that square AC wave activity on the LO output..
      Another double check you might want to do is to measure the divider IC's voltages at the pin on the ic AND at the pad.  One can often see soldering issues pop out when getting anomalous voltages in the tests. 
      However, if you are seeing solid clocking waveforms at the correct frequencies on the divider outputs, you can be fairly well assured that you have met the objectives of this stage.

      tx es 73 de robby wb5rvz
      What happens in the shack stays in the shack!

      From: g8voip
      Sent: Wednesday, April 28, 2010 1:14 AM
      Subject: [softrock40] Re: Divider stage tests


      Hi Cliff,

      As you can hear and measure the outputs of the divider stages, all must be working correctly, so nothing to worry about.

      It is very 'hit and miss' trying to measure a 'voltage' with a DVM or analogue meter which in fact is a high frequency square wave. The assumption being made is that it will read the average of the waveform, hence the 2.5V, but in practice it is totally dependent on how the meter reacts.

      If you have the equipment available to make a more meaningful measurement, do that. 

      The 'DC' voltage approach is designed for those with minimal test gear. Really that test should be to check for either 0V or 5V showing the divider is not functioning and stuck at a static logic state, or a nominal voltage indicating activity on the IC pin.

      Good luck with the rest of the build.

      73, Bob G8VOI

      --- In softrock40@yahoogro ups.com, "n2gyi" <cliff@...> wrote:
      > Hello all,
      > I have just finished and tested the divider stage and I am getting a good square wave signal on my scope, and frequency is 1/4 the output of the LO according to the frequency counter when measured at the proper test points. I see signals on all bands at the proper frequencies (depending on switch configuration) . All would appear normal and working fine except for the following:
      > Problem is that when setting the DIP switches to the 0100 configuration for 7.046, the voltage measured at the junction of R45 & R44 is only around 1.2 volts, rather than the described voltage of 1/2 the 5v rail. This is true for several different switch configurations, while many configurations do show the expected 2.4 volts.
      > This is not directly related to any one specific switch, but to various configurations.
      > All readings on U6 are perfect, showing that all switches are functioning properly.
      > Resistor values for R44 & R45 voltage divider are verified correct at 10K.
      > 5v rail measures 4.85 on my DMM. 3.3v rail measures 3.24v.
      > Total current draw is 72mA with switches at 0000, 77mA with 0100, and 100 mA at a switch setting of 1111.
      > Since the divider is working on all bands, should I be concerned about this voltage?
      > Thanks,
      > Cliff
      > N2GYI

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