On 10/30/18 7:21 AM, Wayne Kline wrote:
My old gray matter is not 100% recall on an article in QST or CQ regarding
connector loss. The tester uses a spectrum analyzer and a TDR with other lab
equptement.
He had up to 20 barrels ,T. and Pl259’s with short lengths of coax .
And the findings were that @ HF and insertion loss was minimal and the BIGEST
issue was lossy CABLE
This all comes from folks reading data sheets and misinterpreting the
values found there.
A typical data sheet might say "connector loss <0.03 dB"
The 0.03 isn't really a "worst case", it's a "the smallest non-zero loss
we can measure".
In reality, the connector loss is much less, but making 0.01 dB loss
measurements is more art than science.
A paper by Pakay and Torok, "Analysis of insertion loss repeatability of
coax connectors" (in "The Radio and Electronic Engineer, v47, #7, pp
315-319, July 1977) gives a table at the end of the loss for various
connectors. I'll give the loss at 100 MHz to save time:
SMA 0.007
N (stainless) 0.004
UHF 0.028 dB
So that 0.03 for UHF connectors (at UHF frequencies) might not be all
that far off.
The uncertainty in loss (across multiple mates) expressed as standard
deviation is
SMA 0.0003
N 0.0002
UHF 0.0002
(all at 100 MHz)
I note that they cite an earlier 1970 paper by Bergfried and Fischer,
and comment that B&F got bigger uncertainties, but most likely because
their measurement equipment wasn't as good.
You could dig up an earlier paper from Nov 1961 by Sanderson: "A new
high-precision method for the measurement of the VSWR of coaxial
connectors" MTT-9, p 524 for a description of a technique using a
slotted line, and a variety of precision equipment. He doesn't give any
sample data, though, just that he can drive the uncertainty of the
measurement down below 1.0001 to 1.0003 "so a VSWR of 1.001 is well
above the noise level"
Reading his methods and analysis, this was a fairly painstaking and
tedious measurement (esp since he did it from DC to 9 Gc) - he worked
at General Radio, and they had a new connector they were pushing then.
I suspect that the average ham isn't going to worry about whether the
match in the connectors is good to VSWR<1.001.
Precision metrology is an interesting, but frustrating, area...
When you're looking at microBels (0.00001 dB), little things like the
temperature of the connector (much less the cables) have an effect that
is much larger than what you are measuring.
I am always much impressed by this kind of work from the 50s, 60s, and 70s.
Jim, W6RMK
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|