________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Gray,
David
Sent: Wednesday, July 29, 2009 10:23 AM
To: Ken Javor; [email protected]
Subject: RE: [PSES] Mil-Std-461F 41" rod Ferrite & Cable query?
Hi, I use a Fair-Rite P/N 0443665806 clip-on ferrite core at the center
of
the cable.
The issue I have with this test setup is with the system check section
with
the 10pf capacitor. According to my understanding of figure RE102-8 the coax
shield from the signal source cannot connect to the rod antenna ground and
counterpoise. This is backed up with the wording in the test procedure that
“commercial calibration jigs or injection networks shall not be used”
(These networks have a capacitor mounted inside a metal enclosure with BNC
connectors at each end.) This creates a problem of the signal leaking or
radiating from the coax cable from the signal source into the preamp. Thus the
physical placement of the coax cable changes the system check reading on the
receiver by up to 10dB. This is not a very reliable system check.
Has anyone experienced this?
Thanks
David Gray
TUV America
The active rod that I use has a Type N coax fitting on the top surface of the
pre-amp case. The body of this connector is bonded to the metal housing of the
pre-amp. When the 41" rod is inserted attached, the rod's male N connector
mates with the Pre-amp's female N. The rod is connected only to the center pin
of the male N connector.
I was assuming that the best way to connect the calibrating signal was to use
a coax tee, connecting a 50-ohm load on leg 2 and my 10 pF capacitor on leg 3.
My 10 pF capacitor is contained in a small housing, about 1 cm by 1 cm by 5 cm
long, with a BNC coax connector at each end. The BNC connector bodies and the
walls of the capacitor housing are all common, and keep the 10 pF capacitor
almost in a coaxial cavity.
It seems to me that this replicates the stray capacitances of real life as
closely as possible. I also assume that accepting some odd stray capacitances
is better than the "open wire" method defined in Figure RE102-8.
As usual, the simplest of things appear to require more discussion, with much
further study needed. <g>
Ed Price
[email protected] <blocked::mailto:[email protected]> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
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