SWR - Numerical Indication

[ANDY DURBIN]

"Those extra digits on your meter may be meaningless."

They may be meaningless or they could be very useful. Finding a peak or null, or looking for any small amplitude change, does not require absolute accuracy but high resolution can be useful.

"A freebie Harbor Freight digital voltmeter appears to have a helluva lot better accuracy than reality."

What is important is knowing what you want to measure and how useful your instrument is for making that measurement. For example I have an LP 100A , spectrum analyzer,  and a digital storage scope but the multimeter I usually use is a freebie from Harbor Freight.  I have quite a few of these and measurements are remarkably consistent between meters.  The only one I found to be bad had a very interesting anomaly.  The display acted as a photo cell and skewed the readings if used in direct sunlight!  Indoors it was as good (or bad) as all the others.

A mistake many seem to make is to assume that something that is calibrated is therefore accurate.  Typically a calibrated instrument is only as good as the manufacturer's specification.  A 20% instrument is still a 20% instrument even if it has a current calibration certificate.  What calibration does is weed out the instruments that no longer meet the manufacture's specification and brings them back to that specification level.

It used to wind me up that at work I was required to use a DVM with a current calibration certificate to check whether a signal was in asserted or non asserted state.  Any instruments that were not in calibration were routinely rounded up by the metrology lab police.  Few instruments suddenly change their properties on the day the calibration certificate expires.  

Andy k3wyc




   
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[Bob McGraw - K4TAX]

What happened to using a Simpson 260 or 270 or Triplet 603? Those are
actually better for finding a peak or null, which in both cases are only
relative.  If one works on HV amps as I do from time to time, you'll
find the life of a DVM to be ........zap.

73

Bob, K4TAX



On 11/30/2018 11:54 AM, ANDY DURBIN wrote:

> "Those extra digits on your meter may be meaningless."
>
> They may be meaningless or they could be very useful. Finding a peak or null, or looking for any small amplitude change, does not require absolute accuracy but high resolution can be useful.
>
> "A freebie Harbor Freight digital voltmeter appears to have a helluva lot better accuracy than reality."
>
> What is important is knowing what you want to measure and how useful your instrument is for making that measurement. For example I have an LP 100A , spectrum analyzer,  and a digital storage scope but the multimeter I usually use is a freebie from Harbor Freight.  I have quite a few of these and measurements are remarkably consistent between meters.  The only one I found to be bad had a very interesting anomaly.  The display acted as a photo cell and skewed the readings if used in direct sunlight!  Indoors it was as good (or bad) as all the others.
>
> A mistake many seem to make is to assume that something that is calibrated is therefore accurate.  Typically a calibrated instrument is only as good as the manufacturer's specification.  A 20% instrument is still a 20% instrument even if it has a current calibration certificate.  What calibration does is weed out the instruments that no longer meet the manufacture's specification and brings them back to that specification level.
>
> It used to wind me up that at work I was required to use a DVM with a current calibration certificate to check whether a signal was in asserted or non asserted state.  Any instruments that were not in calibration were routinely rounded up by the metrology lab police.  Few instruments suddenly change their properties on the day the calibration certificate expires.
>
> Andy k3wyc
>
>
>
>
>      
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>

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[Phil Kane-2]

On 11/30/2018 9:54 AM, ANDY DURBIN wrote:

> Few instruments suddenly change their properties on the day the calibration certificate expires.  

Yeah but...an expired certificate can be a very important part of the
shouting and stamping should the issue wind up in a dispute between
"experts" in litigation for some reason.

(I have two hats - one says "Professional Engineer" and the other says
"Attorney-at-Law".)

73 de K2ASP - Phil Kane
Elecraft K2/100   s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
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[ANDY DURBIN]

"If the holes were closely spaced, but far from the bulls-eye, the  shooter was inaccurate but precise."

I would suggest that this is an indicator of repeatability not precision.  

Andy, k3wyc
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[ANDY DURBIN]

"I had always wondered why the KAT utility reported frequency values that were frequently quite different from the actual transmit frequency. It  turns out that the "Observed Frequency" value displayed in the utility  Operate window is the low end of the particular tuning bin that has been  selected by the selection algorithm. "

I don't think that is correct.  From my experimental observations I believe the last observed frequency (the value returned by the F; interrogation) is the most recent value of F received over the serial interface unless that value has been changed to a more recent RF detected frequency.  RF detected frequency has a resolution of 8 kHz which may or may not match the size of a tuning segment.

(There is an exception to this though - If the last value of F received over the serial interface caused a KAT500 band change then the last observed frequency will be stuck at zero until another F transmission is made or until an RF transmission is made . This anomaly has been reported to Elecraft and it's "on the list")

The behavior of last observed frequency does not change if the KAT500 is in bypass mode where no tuning solution is being selected.

it is my understanding that the KAT500, when connected to a K3, actually tracks the K3 receive frequency not the transmit frequency.  My TS-590 Elecraft interface gives the KAT500 the calculated transmit frequency not the receive frequency which seems to me to be a better implementation. ( I had enough problems with my SteppIR retuning at the start of a split TX to want to play the same games with my KAT500 and KPA500)

Andy, k3wyc


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[ANDY DURBIN]

"As far as calculating bin size, I suspect that K3WYC’s solution of sending FA; response frequencies into the KAT500’s serial port might actually yield a better solution since those frequencies can have 1KHz (or better) resolution. In this case the relays should switch very close to the actual boundary instead of at 8KHz boundaries. What I don’t know is if the KAT500 uses RF counted frequency for its bin determination or if it can use the externally reported frequency. I suspect it is the former."

Not quite how I implemented the frequency interface.  What I do is use the values of IF, FA , and FB to determine the frequency my TS-590 would transmit on if it went into TX at that instant.  This calculation to done each time I get a new value of IF, or FA, or FB.   I send that frequency value to the KAT500 using the F command but I only send it if the calculated transmit frequency differs from the KAT500 last observed frequency by more than 8 kHz.   Sending the raw FA value to the KAT500 is not a useful solution for several reasons - The TS-590 may not be using VFO A for RX or TX;  if the TS-590 is using VFO A then FA alone is not enough information to know if A is the TX or RX VFO for split;  Even if A is the TX VFO, FA does not include XIT offset; FA is not meaningful for memory channel operation; etc. )

The KAT500 follows the TX frequency I send it and sets the proper tuning solution for that frequency with no RF transmission required.   The only issue with my implementation is that RF detection can override the frequency I provided and move it to an adjacent, incorrect or less accurate, value.  The fact that the last observed frequency is changed by RF does not necessarily  mean a new tuning solution will be selected.  That depends on how the 8 kHz increments of last observed frequency overlay the tuning segment boundaries (and other factors that are likely Elecraft proprietary).

73,
Andy k3wyc

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