While that accuracy may be good for general tasks around the ham shack it
comes no where near what is needed to do any kind of decent calibration.
When changing from 60 to 70 db attenuators and getting .2 db difference I
would wonder what the error would be at different levels.
If you don't know that your attenuator is any better than .5 db and then you
add that error to the calibration source you are not any closer than a bird
wattmeter again.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Phil & Debbie Salas
> Sent: Monday, December 07, 2009 6:10 PM
> To: amps@contesting.com
> Subject: [Amps] FW: Decent HF directional coupler for RF power meas.
>
> Good point. I just emailed W5BIG (the VNA designer) with this question.
> He
> said that the VNA2180 has been lab-tested with precision calibrated
> attenuators. The VNA2180 was off a maximum of 0.3 dB with a 60 dB
> attenuator, and a maximumn of 0.5 dB with a 70 dB attenuator through 140
> mhz.
>
> Phil - AD5X
>
> > -----Original Message-----
> > From: amps-bounces at contesting.com [mailto:amps-bounces at
> > contesting.com]
> > On Behalf Of Phil & Debbie Salas
> > Sent: Monday, December 07, 2009 12:32 PM
> > To: amps at contesting.com
> > Subject: [Amps] FW: Decent HF directional coupler for RF power meas.
> >
> > "The cable and attenuator errors can be known without error, all he
> has
> > to
> > do is pay a
> > cal laboratory to characterize each at the test frequencies."
> >
> > I've watched the Array Solutions guys calibrate their PowerMaster
> > couplers.
> > They use their VNA2180 to accurately measure their cables and
> > attenuators.
> > So the only inaccuracy is the tolerance of the HP power meter.
> >
> > Phil - AD5X
> >
>
> There is also the inaccuracy of the vna that has to be added in also.
> They
> don't say what that is.
>
> 73
> Gary K4FMX
>
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