[Premium-Rx] Military gear

[Gary Geissinger]

Guys,

Michael made some excellent points, but there is another crucial concern
with ex-military gear.

Although the gear arrives in new condition, field repairs are done in
haste using whatever resources are available.

During the Vietnam war I remember the things we had to do to keep the
planes in the sky with working gear.  Most of the time, but not always,
we had acceptable substitute parts.  We seldom had exactly the right
test equipment; we had to be a little creative.  

While I wouldn't mind, for sentimental reasons, owning some of that
gear...I would never power it up without a serious going over!

I've noticed some the same thing with government surplus Harris, Racal,
and Watkins-Johnson gear.  Given a choice of like items (swapfests, etc)
I've been trying to get them with out any repair or rework.  I figure
sometimes a slightly busted radio in mint condition may be a better bet
than one that works but has obviously been "worked on."

One last comment.  On the other hand I remember working with military
technicians who could perform major repairs on units that looked like
new when they were finished.  Those radios would the cats meow to own!

73's,

Gary WA0SPM

-----Original Message-----
From: premium-rx-bounces at mailman.qth.net
[mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of Michael
O'Beirne
Sent: Thursday, July 10, 2008 1:55 PM
To: Premium-Rx
Subject: [Premium-Rx] Military gear

Good evening guys,

I am not sure whether Larry has worn green camo kit and a steel helmet
and 
spent miserable hours in a muddy trench awaiting an "enemy" dawn attack,
but 
I can tell him that some military gear suffers physical and RF abuse
that I 
would be most reluctant to inflict on any amateur gear.

For those who like numbers, here is an extract from an MOD catalogue of 
about 1978 for the Clansman VRC353 VHF transceiver.  The environmental
spec 
is based on British Def Spec DEF133 Table l3 for tactical gear:

Frequency stability
TCXO maintains the selected operating frequency within 5 ppm at any
ambient 
temperature down to - 40 deg C.

Immunity to interference
The extremely high selectivity and low temperature radiation allows the
set 
to be separated in frequency by only 5% and with antennas 2 metres apart
to 
be operated on full power with negligible mutual interference.
[Typically 
two sets in the same LandRover].

Receiver protection
No damage will be caused by a signal on the antenna terminal of 50V emf
via 
50 ohms continuously at any frequency within the tuning range, or 100V
for 1 
second.

Environmental spec
Ambient working temperature from -40 deg C to +55 deg C.
Designed to meet operational conditions in wheeled and tracked vehicles,

travelling on surfaced and unsurfaced roads and open country, and
transport 
by land, sea and air.
Withstand operational shocks in armoured fighting vehicles due to the
impact 
of non-penetrating shells on the vehicle armour and delivery by normal 
parachute techniques.
Capable of operation under conditions of heavy driving rain, salt spray,

high wind, driving dust and snow and humidity in excess of 95%.
The equipment can be operated and stored at altitudes of 2,500 metres
and 
can be transported in unpressurised aircraft at 8,500 metres.
Can withstand immersion to a covering depth of 1.6 metres for at least 2

hours.
Is immune to the corrosive effects of acid spray from secondary
batteries 
and is unaffected by severe contamination by fuel oils, hydraulic oils
and 
lubricated fluids.

I remember operating full duplex FSK HF links on about 5 MHz with a
Tx/Rx 
frequency separation of around 200kHz, a Tx output of 250W and an
antenna 
separation varying from about 30 metres to about 8 metres, and working
the 
links too, albeit with old valved gear designed by Marconi initially for

ships with lots of analogue pre-mixer selectivity.
73s
Michael
G8MOB


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