[Elecraft] Dummy Load recommendation

[CUTTER DAVID]

I agree with all that has been said and suspect a lot of responders on this list are or were engineers who are used to using precision equipment.  I think it can be misleading to look at some instruments built into a transceiver for instance, but it never seemed to matter, until Elecraft came along.  I did my calibration with a Bird power meter and a Bird 500W load but I have no idea when they were last calibrated, so, what value do I put on the measurements?  Well, it's good enough for me. But calibration is a special case and I'd never heard of amateurs calibrating for power before Elecraft.  Accurate power meters are costly to buy and maintain if you are in business, but for me now I'm retired it doesn't matter so much because I'm not doing it for a paying customer.  I think we are misled by the easy precision of the digital multimeter which for a few £ or $ is ten times as good as what we previously thought were good analogue instruments.  In short, I think technology can cause us to bite our finger nails unnecessarily.  10% or 20% power error is hardly noticeable to the guy on the other side of the world.  

David G3UNA


> On 23 July 2019 at 16:16 Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:
> 
> 
> Yes a calorimeter is the better way to measure power.   Not inexpensive however. 
> 
> Bob, K4TAX
> 
> 
> Sent from my iPhone
> 
> > On Jul 23, 2019, at 10:07 AM, W2xj <W2xj at w2xj.net> wrote:
> > 
> > If you really want precision, use a water cooled load. Measure the flow rate and input and output temperature. You can precisely calculate power. 
> > 
> > Sent from my iPad
> > 
> >> On Jul 23, 2019, at 9:38 AM, Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:
> >> 
> >> Since power meter systems are calibrated at a known impedance {usually 50 ohms}, and they are voltage sensing devices, any deviation from the calibration value will introduce an error in power indication.  It just depends on how precise one prefers to be with power measurements.
> >> 
> >> 100 watts into 50 ohms is 70.71 volts
> >> 
> >> 100 watts into 55 ohms is 74.16 volts
> >> 
> >> 100 watts into 45 ohms is 67.08 volts
> >> 
> >> 73
> >> 
> >> Bob, K4TAX
> >> 
> >> 
> >>> On 7/23/2019 5:43 AM, CUTTER DAVID via Elecraft wrote:
> >>> I often wonder just how useful a precision dummy load really is in the amateur service.  I picked up home brew dummy load at the club the other day.  It measured 57ohms dc and comprises 4 wire-wound resistors attached in a cluster across the end of the coax.  After lots of disparaging remarks I put it on the VNA and it didn't look at all bad out to 30MHz: nothing over 1.5:1 and no spikes or dips to indicate resonances. I'll have to do it again and make a print-out for posterity.
> >>> I've heard that salt water in a bucket works after a fashion.
> >>> So the question is: how good do you need it to be?
> >>> David G3UNA
> >>> 
> >>> 
> >>>> On 22 July 2019 at 23:58 "hawley, charles j jr" <c-hawley at illinois.edu> wrote:
> >>>> 
> >>>> 
> >>>> Used Bird Attenuator is a good deal.
> >>>> 
> >>>> https://nm3e.com/AttenuatorSampler.htm
> >>>> 
> >>>> Then you’ll have a sample to plug into your counter or scope
> >>>> 
> >>>> Chuck Jack Hawley
> >>>> KE9UW
> >>>> 
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