On Sun, 15 Aug 2004 16:26:51 -0400, "Leland C. Scott"
wrote in :


"Frank Gilliland" wrote in message
.. .
Measure it. If you actually find this impedance "bump", maybe you can
explain why impedance is so significant for these connectors

You checked your E-mail? You have the detailed answer there in the attached
zip file.


Mailbox is empty. Did you remove the "nospam"?


while
impedance will "unnecessarily complicate things" for mag-mounts.

You have "unnecessarily complicate things" because you don't understand the
difference.


Now that's an interesting answer..... the difference between impedance
and capacitance is that I don't understand the difference?


Are
you saying that impedance is important for connectors but not for
antenna grounds?

See the file I sent to you.


Checked again. Still empty.


Why not fall back to your "pure capacitance" excuse
where UHF connectors are concerned?

Why don't you explain it.


Alrighty.....

Any capacitor is basically a network of capacitance, inductance and
resistance. The circuit can't see the "pure capacitance" without
seeing the inductance and resistance, hence the necessity of measuring
a capacitor as an impedance since impedance = resistance + reactance.
And because frequency is directly related to reactance, impedance
changes in relation to frequency. The other issue to consider is the
dielectric of the capacitance, which will affect the frequency
linearity (Z/f curve) of the device. For all practical purposes, only
vacuum and air capacitors are linear in this respect -- all others are
not. This means that as the frequency changes, so will the resistance
and/or 'pure' capacitance, or both. And this is why you -must- measure
impedance at the operating frequency.

As far as connectors are concerned, both N-type and UHF-type
connectors are low-impedance coaxial designs, so unless the wavelength
is a few cm or higher there will be little or no reflection due to
impedance mismatch (assuming there -is- an impedance mismatch). With
that out of the way, the insulation is the other cause of concern. It
is effectively the dielectric of the capacitance between the center
conductor and the shield. So in this respect, the quality of the
connector depends on the quality of the insulation. Cheap insulation
will have poor high-frequency characteristics, while.... well, you get
the idea. So if there is power loss it will be due to poor insulation
properties (cheap materials, contamination, etc.). And -that- is why
the N-type connectors are preferred for UHF and up since it is (or
rather, it's -supposed- to be) a sealed connector, thereby preventing
humidity and other crud from contaminating the dielectric (or
corroding the contacts) and therefore causing power loss.

There you have it. It's ironic that while impedance is the primary
factor in both these issues, you have misunderstood both from totally
opposite ends of the spectrum. But hey, nobody's perfect.


Funny why "N" connectors and other "constant
impedance" connectors are used at UHF almost exclusively.

Make up your mind, Leland. What's important -- impedance or 'pure
capacitance'?

Its very clear to me Frank. What is also clear is you don't.


Checked again. Mailbox is still empty.





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