Another verification that *all* problems are not the fault of the DUT
(Device Under Test), and can often be a failure of the test equipment.
Do be prepared to check the test gear prior to taking measurements.
While that is not practical in most cases, do be suspicious of your
measurements until you have taken steps sufficient to validate your test
setup.
I do not know how to tell you how to validate your test setup in detail,
because that will vary depending on the equipment used, but what I am
saying is that you should not trust the indication of any measurement
device at face value. Verify that the measurement device is giving
proper indications as the fist order of business - or at least second
order when measurements begin to "look funny".
73,
Don W3FPR
On 11/22/2015 5:46 PM, Robert Harmon wrote:
Thanks for all the info on diagnosing the intermittent problem with my
Bird 43 guys !
I discovered their was a poor connection where the RG58 from the meter
movement
connects to the element. As mentioned there is a tiny spring in the
connector on the end of the
cable. It didnt look dirty visually but I cleaned it with some
contact cleaner and now is fine.
It was mentioned to change over to a BNC connector to eliminate
problems. I assume we mean an
adapter from the bird element connection point to a BNC. Then add a
BNC on the end of the short
RG58 from the meter movement. Anyway it is working now, thanks guys !
73,
Bob
K6UJ
On 11/22/15 2:13 PM, Bob McGraw - K4TAX wrote:
Ron mentions various well taken points regarding the Bird 43 meter
series. This also applies to almost all watt meters as well, and
that is the power calibration is relative to a 50 ohm load only. Any
other load Z will introduce errors in the meter accuracy and indication.
At the same time, the ratio measurement for forward power and
reflected power will always be correct in that each value will be
measured with the same degree of error. Thus using this
information, one can accurately calculate the SWR using the forward
power indicated and the reflected power indicated. Where as, absolute
values will not necessarily be accurate under these conditions.
73
Bob, K4TAX
On 11/22/2015 11:38 AM, Ron D'Eau Claire wrote:
Bird instruments specs a Bird 43 at plus or minus 5% of full scale.
If you have a calibrated 1000 watt slug and meter it will read
within 100 watts of the real power. What many people miss is that
the possible 100 watt error is constant over the range of the meter,
so measuring 500 watts the meter will indicate something between 400
and 600 watts and at 100 watts the reading can be off by a full 100%!
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