On 1/10/2014 7:01 PM, Ian Jackson wrote:
In message , Jeff Liebermann
writes
On Thu, 9 Jan 2014 21:08:11 -0800, "Sal" salmonella@food
poisoning.org wrote:

Another experiment I ran (back around 1975) was to take 100 feet of
cable
and measure the loss, then repeat the measurement using a different
100 feet
made from ten different pieces. Yup, the loss was about 3 dB more,
indicative of an average 0.3 dB loss per joint, neatly within the
range you
specified.

0.3dB per connector at what frequency?

This is more fun:
http://802.11junk.com/jeffl/antennas/connector-loss/index.html
Just take every connector that you can find, put them in series, and
measure the loss. In this case, it was done at 2.4Ghz and 450MHz. End
to end loss at 2.4GHz was 2dB for about 25 adapters or about 0.08dB
per adapter. At 250MHz, the loss was about 0.2dB or 0.008dB per
adapter.

I've done similar demonstrations using two wattmeters at the local
radio club meeting. The results are typically that the adapter string
has the same loss as an equivalent length of small coax cable. I had
a surplus of BNC T connectors, so a strung about 50 of them in series
and obtained similar results.

Bottom line: Connectors and adapters aren't as evil as the data
sheets and literature suggest.

I've always assumed that the loss measured through connectors and
adapters was mainly
(a) because they have unavoidable length (ie not a lot), and
(b) because the impedance match through them is less than perfect (ie
not a lot).
The ohmic contact resistance may also be a tiny tad higher than the same
length of coax (even less).

The main loss in a connector is due to the impedance bump at the
connector. This can be easily seen on a TDR (Time Domain Reflectometry)
display.

Some connectors are better than others; for instance, the older F
connectors which are crimped down with a ring are the worst. Next is
the connector where the crimp is a hex crimp - it doesn't give a
consistent impedance around the connector.

The best (and the ones we use) compress the entire base of the connector
evenly, creating a smooth crimp. The end of the coax is evenly covered
by the connector.

The other problem is the technician installing the connectors. I've
seen great ones, and not-so-great ones. There are a lot of chances for
going wrong - for instance, it's easy to screw up the braid when trying
to insert a crimp-on connector under the outer jacket and shield. And
soldering connectors (i.e. PL-259 and N) is almost sure to give you a
huge bump (and loss) because it's almost impossible to solder the shield
without melting the inner insulator to some point. It may not short
out, but that doesn't mean you don't have loss there.

--
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Jerry, AI0K

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