Dan Richardson wrote:

On Wed, 18 Jan 2006 08:24:40 -0500, Amos Keag
wrote:


The Astron RS-35 power supply connects utility power neutral to the
case. It also connects the 13.8 volt return to the case. [This is
commercial common practice but is prohibited in Military Systems
design.]


You've tweaked my curiosity what does the military do?

73
Danny, K6MHE

The general no pun intended Military design requirement is the the
equipment cases carry no intentional or credible fault currents.
[Therefore no inadvertant shocks, in MIL STD terminolgy no personnel
RISK, from a hot chassis]. [RISK is assign for personnel, HAZARD for
equipment]. Accordingly, the cases and circuit returns are isolated
typically by a 500K resistor. There is one system ground point, not a
distributed grounding system.

RF circuit design includes isolation between onbly for the output from
the low level circuits. Coax shields, shielding on shielded
circuits/wires carry no intentional currents and to the maximum extent
possible no fault currents.

Example: the output stages of a 5 GHz telemetry transmitter is on a
circuit board that is physically isolated from the low level stages and
the power source. The isolation may be either capacitive or inductive
coupled; in my last design [c.a. 1986] we used 1/4 wave stubs on the
same board, top circuit to bottom circuit, woking against two separate
returns [top surface base copper versus bottom surface base copper]

In the Nuclear safe environment for example, the primary and secondary
of power transformers MUST be 100% isolated and each winding separately
shielded with the shields connected independently to the chassis.
Therefore a transformer short circuit on the primary cannot propagate
through to the secondary. Or, a primary short to chassis cannot
propagate to the secondary. And the design MUST include 100% absolute
disconnect from primary power in the event of a transformer failure or
power out of spec condition. The requirements go on and on and on ...

Bottom line, equipment cases carry no current, share no current carrying
path [exception is RF output stages only].

So, the ASTRON RS 35 is not suitable for MIL usage. Now the ASTRON
becomes 100% MIL suitable with the removal of just one [1] jumper in the
supply [the connection from 13 volt return to chassis. The secondary of
the PS is 100% isolated from the primary and the regulator circuits are
100% isolated from chassis]. But, the ICOM radios being powered also
violate the MIL requirements and corrupt the system. Remember, HAM
equipment is generally operated in COMMERCIAL circuits and must comply
with local electrical codes.