DDUtil Voltage Reading

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I have carefully checked the output voltage of my new power supply against that of a Fluke DVM - both agree at 13.8v.  However DDUtil reports around 0.4v higher, even if the input voltages is taken down to, say, 13v or up to 14.2v.  It's not really a problem, but I just wondered why this is so.  Anyone else found this?  The power supply has digital readouts of voltage and current (MyDel MP30SW1V), and as the DVM always agrees with it I have to assume DDUtil's method of determining the voltage is slightly wrong?

Jeff - G4IUA
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Jeff - G4IUA

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Posted 4 years ago

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Jay / NO5J

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Yes, I've seen DDUtil read a little on the high side too. Never relly worried me because I have no idea if my VOM is calibrated all that well. PS has a meter on it and reports 13.8 v, DDUtil reports14.0v VOM reports 13.68v. the power supply is adjustable on its front panel so to overcome any voltage sag on transmit I turn it  up to 14.5v on DDutil which moves the PS meter up an notch on the scale and reads at 14.1v on the VOM. on transmit DDUtil sags to 14.3v. VOM shows no difference and neither does the PS. The connection between the PS and the 6500 is just the supplied cord. after rechecking the readings today, I worry less about running the 6500 a little high. it's supposed to be safe to give as much as 16v and is supposed to warn if it's to high. Now I'm pretty sure its not. but im going to lower it down to 14.2v on DDUtil on RX. and remember I've got @ .4v of additional safe headroom. I guess it's all in which meter you want to believe. Power out on my PowerMasterII is within 5-6w lower than SmartSDR reports and goes up by about 5-6w if i bump DDUtil up to read 14.4v Amp only needs 60w in fr legal limit out. So it's not like I'm too concerned about the difference the .4v input is going to matter. Just keep DDUtil in the green and you should be fine. It's better that it reads high, less likely to bump into any warnings from the radio.
Jay - NO5J
(Edited)
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k3Tim

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Very similar readings at the station here.  Supply is Astron 70amp linear with a Fluke 77 VoM reading 14.07v, DDuTil  = 14.4v.  The supplied DC power cord was cut to 10".  On xmit there is no change in PS voltage but DDuTil reports 14.2v.  
I've read on internet that a higher DC voltage reduces xmit 3rd IMD products.  Not sure if that is the case but I'm slowly working on a project using separate SDR and 2-tone test generator to verify.

  _..--
k3Tim
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Dave -- W7IWW

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Similar situation here with SSDR/F6700: Fluke and other digital volt meter reading Astron 35A linear PS or Aston 25A switching PS at 13.8vdc, while DDUtil reading is 14.2vdc. On F6700 TX, PS reads 13.8 and DDUtil reads 13.8. When running PSDR/F5000a, both PS were 13.8vdc and DDUtil also 13.8vdc in all cases.
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Anthony Bowyer

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Watching the increments the voltage display moves by, I suspect the measurement is fairly course. Not sure the resolution, but I suspect 8 bits or less. That means the accuracy of the calculated voltage will be only so accurate.
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Anthony Bowyer

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opps! That should be coarse.....The trouble with spell-check
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Jay / NO5J

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What's trully needed is a misspell-check, I don't need to be told I'm right, makes me feel good but only useful if the spelling checker never makes a mistake. Mistakes keep happening so one of us is wrong. When do we get SmartSpell-Check V1.4?  

Jay - NO5J
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Stu Phillips - K6TU, Elmer

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There are two points in the radio where the DC voltage is measured and reported - one before the fuse, the other after the fuse.  Neither of these meters report the actual input voltage and under read the input voltage by several tenths of a volt in my own experience reading and processing the raw meter values via the Ethernet API.

I believe that DDUtil adds a "fudge factor" that attempts to reconcile the difference in the values reported at the points where the radio measures them versus the actual input voltage to the radio.

Stu K6TU

PS: Measure the input voltage at the PowerPole input with a DVM and that's the metric to use! :-)
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Anthony Bowyer

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Good to know! Since you've looked at this, what is the resolution of the value? Might need to know for the future.


Anthony, NT4X

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Stu Phillips - K6TU, Elmer

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The value is sent from the radio as a floating point number that gets scaled down by 1024 before interpreting the value on the client.  I don't know the resolution of the ADC used to measure the voltages in the radio although typical PIC like ADCs are 10 bits...

Without knowing the resolution of the ADC, or the pre-scaling I can't give you an answer.

Sorry.
Stu K6TU
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Jeff - G4IUA

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Thanks for all the input - I can see I'm not alone in finding this.  As long as we are all aware of this 'feature' there's nothing to worry about.  Two difference means of measuring the power supply voltage both confirmed a stable 13.8v source, despite DDUtil reporting it to be 0.5v or so higher.  


Jeff - G4IUA