Your capacitors are most likely as marked.? An LCR meter will
show different readings depending on the frequency used by the
meter.? If your meter would use a lower frequency, the capacitance
shown would be higher.? That's a problem when a specific
capacitance or inductance is specified as the value will be
different at different frequencies.? (The lower the frequency the
lower the measured capacitance.)? Unfortunately the frequency for
the specified value is rarely given or mentioned. ? Without
knowing the frequency for a specific value, the specified value is
sort of meaningless.? Frequency for measured value? is just
important to know as the part's tolerance.?? Also, the heat
generated in a capacitor can greatly change it's value and can
cause trouble in tuned circuits.? I suspect the issues in the pi
network of a QCX are more related to capacitance change and losses
due to heat in the capacitor then from capacitor tolerance.?
Lee
w0vt, w5drc
On 8/11/2018 4:40 PM, HF via Groups.Io
wrote:
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Hi all... I've been reading on this forum that there have been
some issues with the bluish capacitors for the QCX low pass
filters.? I recall that the matter is on Hans' list to
investigate, but haven't seen an announcement from him about his
conclusions yet.? I ordered an LCR meter (marked LCR-T5, has a red
PCB with lever socket and buttons marked OFF and TEST) on ebay to
check mine.? I'm now building my QCX (20m version).? The nominally
390 pF capacitors C25 and C26 measure at 368 and 370 pF.? The
nominally 180 pF capacitors C27 and C28 measure at 164 and 172
pF.? The meter doesn't show them as being particularly lossy.? I
don't know the claimed tolerance for these capacitors, so I don't
know if being off by 5-9% is significant, nor do I know whether
this inexpensive LCR meter is capable of measuring to 5% accuracy.
Is this enough information to decide whether to order alternates?
Halden NR7V
