On Sun, 15 Aug 2004 18:25:15 -0400, "Leland C. Scott"
wrote in :


"Frank Gilliland" wrote in message
.. .
Mailbox is empty. Did you remove the "nospam"?

I did. In fact I just sent it again just now. It does have a file attached
so if your E-mail program filters out mail with attachments you will have to
turn it off.


I got the file with the pics. Nice work, and I'm glad to see your
acceptance of the fact that solid dielectrics (even teflon) have
dielectric constants that aren't constant with frequency. However,
your description of a UHF-type connector isn't particularly accurate.
If you had ever taken one apart you would have noticed that only a
small part of the conductor (maybe a mm or two) is actually contacting
the insulator. The rest is surrounded by an air gap, making most of
the coupled connection a section of coax using an insulator with a
dielectric constant of 1.

Regardless, I suggested that you -measure- this apparent loss, not
calculate it (.....gee, seems I've said that before.....). Since you
don't care to measure things, I did. The Adler I mentioned earlier is
a 100-watt translator tuned for TV channel 77. I measured the output
to my wattmeter through one 12' length of RG-11 and again through two
6' lengths of RG-11, the difference being that the latter adds a male
and female UHF-type connector to the line. The wattmeter showed no
visible difference. So I did the same test directly to the dummy load
and measured with an RF voltmeter at the dummy load. The difference
was a loss of 0.4 volts, which is slightly less than 1 watt, or about
0.05 dB. Yes, I use teflon connectors and I keep them clean. And no,
the coax wasn't overheated during soldering (it's all about the
technique!).

Feel free to repeat my tests, both for the UHF-type connectors and for
the mag-mounts. Just don't feed me any more calculations cause they
don't mean squat when the facts show something different.


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?

You haven't impressed me with knowing the difference.


It was intended to educate, not to impress.


I was addressing a
capacitance measurement only, exclusively and separate from any other
electrical property. You can't seem to figure out that your impedance
measurement combines capacitance, inductance, and resistance all together.


Yes it does! That's the point! Capacitance, "exclusively and separate
from any other electrical property", is academic and has no practical
value!


If I took a 1000pf vacuum capacitor and connected it in series with a 1000
ohm resistor, placed it in a black box you can't open, and brought out two
leads for you to connect to your Z-bridge then asked you to make your
measurement you would tell me I have a crappy capacitor.


Not at all. You can tell if the reactance is linear simply by changing
the frequency feeding your impedance bridge. If it's linear then the
capacitor is fine and you simply have 1k ohms of series resistance. If
it's not linear then you might have a problem (depending on the
intended application of this 'black box').


Then if I wanted to
give you somthing to think about I can stick a small inductor in series with
the capacitor and resistor to give some strange impedance variations with
frequency. Now try to figure out what's in the box from your Z-bridge
measurement.


Just swing the signal generator up from zero until you dip, just like
you would with a GDO. That's your resistance. If it peaks instead of
dipping then your reactances are in parallel and you must measure
resistance at DC. Then detune to measure reactances.

And at this point I need to make a point: What I just described is a
quick summary of the basic operation of a simple impedance bridge. The
impedance bridge is one of the most fundamental yet most useful tools
in radio. Now you claim to have a degree -and- you are a ham. For you
to even suggest that one can't determine the properties of an unknown
impedance network using an impedance bridge tells me that you have
never used one, or at least not more than once or twice. If you -do-
have a degree then either it isn't in electronics, you missed a lot of
labs, or the school was criminally negligent in it's course of study.
Either way, here's a few links to get you going:

http://www.tpub.com/content/neets/14...s/14193_89.htm
ftp://bama.sbc.edu/downloads/heath/am1/
ftp://bama.sbc.edu/downloads/knight/z-brdg/

And here's a fascinating page on the dielectric properties of organic
tissue that also includes instructions for an impedance bridge. Note
the problems with electrode polarization at low frequencies when
measuring lossy dielectrics (iow, maybe you should take a second look
at your low-frequency DMM method of measuring a capacitor having a
dielectric of epoxy or paint):

http://safeemf.iroe.fi.cnr.it/docs/H...K/chp4-2-1.htm


That's the problem you have with your measurements where the
black box is the mag-mount. Making a capacitance measurenet, or some simple
calculations, would be like peeking inside the black box and saying, Oh now
I see what is going on.


Here's another "black box" scenario: Using the capacitance tester on
your DMM, measure the "pure" capacitance between two high impedance
windings of a power or audio transformer. I can tell you right now
that your measurement will be wrong, and you can't tell what's in the
"box" unless you change the frequency. Same deal for the mag-mount.






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