On Thu, 24 Apr 2003 17:18:10 -0700, Roy Lewallen
wrote:

By all means, the slide rule is fine.

To measure the common mode impedance of a choke balun, simply wind a
piece of wire on the core with the same number of turns as you'll use
for the actual balun. Connect one end of the wire to the center
conductor of the antenna analyzer connector and the other to the
connector shell. Read the impedance at the frequency of interest. Or if
you prefer, you can wind it with a short piece of the actual coax you'll
be using. Connect the two coax conductors together on each end of the
winding, and measure as you would with a single wire. If the impedance
is out of the analyzer's range, you can use a different number of turns
and the relationship that the impedance is proportional to the square of
the number of turns.

Use the same method to measure a W2DU type balun (ferrite cores slipped
over a coax line). If the measurement is out of range, measure a
different number of cores and extrapolate -- the impedance is directly
proportional to the number of cores.

Roy Lewallen, W7EL

Brian Kelly wrote:
Roy Lewallen wrote in message ...

500 - 1000 ohms is a good rule of thumb for a reasonably matched
antenna. You can find the impedance of most cores at the Fair-Rite web
site, or you can measure it with an impedance meter or antenna analyzer.


OK, I'll shoot for 750 ohms. Some day I'd like to understand how one
measures the impedance of a choke balun with MFJ analyzers but for now
I'll diddle the slide rule, buy the cores and get on the air.

Tnx.


Roy Lewallen, W7EL


w3rv

Would this method give meaningful results if used at 70 cms using the
UHF range on something like a MFJ antenna analyser?

I could pop various beads onto a short piece of coax and determine the
relative effectiveness, but how good would this be for absolute
results?

Thanks

MikeN ZL1BNB