[Elecraft] OT: Bird Wattmeter "meter failures"

[briancom]

Good point Don.  Would like to point out that some commercial scopes these days come with probes that are inadequate for the bandwidth of the scope they are connected to.
The scopes might be rated foe 100 MHz but with the supplied probes the system is lucky to make 50 MHz.  Tektronix was an exception.  Their bandwidth specs were met with factory probes.   Unfortunately the only way to know is to test the entire systems response with a calibrated generator.   One bargain sampling scope I bought was not such a bargain after buying several sets of probes to find ones meeting bandwidth specs.  Even then the best match probe had to have its ground lead shortened a bit to flatten the response.  

Developing a trust in ones test equipment takes effort and time.
73 de Brian K3KO
Sent from my iPad

> On Nov 21, 2015, at 10:58 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:
> 
> Harlan,
> 
> That is correct - improper test leads are often a 'culprit'.
>  For instance trying to measure an HF signal with a 'scope.  The 'scope may b rated for 200 MHz, but if you try to us a "hunk of coax" for a probe, the frequency rating may diminish to 2 MHz (OK, that is just an example).  You need to consider the whole measurement system.  A scope's frequency rating must also be coupled with the frequency rating of the probe.  The use of 10X probes is necessary to keep capacitance loading of the circuit under test to a minimum.  And those probes have a frequency rating too.  Take the entire setup of the test equipment into consideration when doing measurements.
> Make certain that every part of the test equipment being used is suitable for the frequency involved.  A simple coax probe may be OK for AF frequencies, but it is not adequate when the frequency is increased.
> 
> A 'scope can show proper RF voltage amplitude, but the frequency rating of the probe and the 'scope should be taken into consideration.  For instance, a 35 MHz scope will only show a signal that is 3 dB down at 35 MHz.   I would suggest that valid RF voltage measurements be made at 1/10 of the 'scope's frequency rating (and that goes for the probe too).
> 
> Again I state, trust no measurement equipment until its accuracy has been verified.
> 
> 73,
> Don W3FPR
> 
> 
>> On 11/21/2015 10:09 PM, hsherriff wrote:
>> I'm the supervisor of a metrology lab and that is one of the first things I ensure a new technician understands. And many times it isn't the test equipment that is at fault, nor the unit under test, but the methodology of using that test equipment.  Not using the equipment "guard" correctly,  induced voltages, improper test leads for the job.... and many many more.
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to alsopb at comcast.net