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Old October 30th 03, 12:50 PM
Frank Dinger
 
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I'm interested in measuring the velocity factor of some coax I have (more
of
an exercise than necessity). In order to do this, the MFJ-259 Operations
manual states that the "stub" to be measured should be attached with a
50-ohm noninductive resistor in series to that center conductor of the
Antenna connector on the analyzer.

What would be a good way of making this connection? I've thought about it
quite a bit; the best idea I've come up with so far is to have a small

metal
enclosure w/ two SO-239's mounted. The resistor would go from center
conductor to center conductor of each SO-239. But this requires too many
extra connections & lengths. Is there a better way to do this? Would

love
to see anyone else's experimental setup, particularly if there are

pictures
or details on the web.

===============
Since no power is involved the non-inductive resistor can be very small .
If accuracy is a point ,get a 50 Ohms , 1% metal film resistor or select a
near 50 Ohms resistor from a batch of standard 5% resistors with an accurate
Ohm meter .
Cut the leads as short as possible but adequate for insertion and soldering
into the SO 239 coaxial socket.
You now know the minimum distance between de 2 SO 239 sockets and can make a
suitable enclosure from bits of scrap plain printed circuit board ( in
Europe available at amateur radio fleamarkets and often sold by the
kilogramme)
With the enclosure completed and holes drilled for the SO 239 connectors
,fit one connector with the resistor soldered and subsequently fit the other
connector and solder it to the resistor.
The result is a resistor in between the 2 SO 239 connectors with hardly any
wire visible.
Finally finish the enclosure by soldering a cover of the same PCB material
or keep the cover removable by means of soldered nuts inside the enclosure
and matching screws.

Frank GM0CSZ / KN6WH