[TenTec] Orion - cooling fan

[Adam Farson]

Hi Tim,

ICAS = Intermittent Commercial and Amateur Service, as compared to CCS
(Continuous Commercial Service).

These two service types were first defined in the power-tube industry. The
classical definitions are as follows:

Continuous Commercial Service (CCS)  -  is defined as that type of service
in which long life and reliability of performance under continuous operating
conditions are the prime considerations.

Intermittent Commercial and Amateur Service (ICAS)  -  is defined to include
the many applications where the transmitter design factors of minimum size,
light weight and considerably increased power output are more important than
long tube life. In this service, life expectancy may be one-half that
obtained in Continuous Commercial Service.
Under the ICAS classification are such applications as the use of tubes in
amateur transmitters, and the use of tubes in equipment where transmissions
are of intermittent nature. Intermittent operation implies that no operating
or 'on' period exceeds 5 minutes and every 'on' period is followed by an
'off' or standby period of at least the same or longer duration.

As applied to solid-state transmitters, ICAS does not imply reduced device
life, as unlike vacuum tubes, the RF power devices are not regarded as
consumables. Rather, ICAS in a solid-state environment implies de-rating to
keep the device junction and case temperatures within their maximum ratings.
Thus, ICAS suggests a limited operating or 'on' period followed by an 'off'
or standby period of at least the same or longer duration, whilst CCS
assumes continuous, key-down operation at reduced output (assuming the same
heatsink area and/or fan CFM for both applications).

In this context, "100% ICAS duty cycle" can be a little misleading, since
the very term ICAS implies some de-rating by time (duty cycle < 100%) for
rated power output, compared to CCS for the same PA/cooling assembly. If we
use the tube-industry definition given above, we arrive at "safe operation
at rated power output for 5 minutes transmitting, followed by at least 5
minutes standby". This implies "key-down" CW transmitting (e.g. RTTY). For
SSB, the allowable transmit time will be longer.

Typically, a PA cooling system should be designed to keep the device case
temperature in the range 70 ~ 80ºC (158 ~ 176ºF) at 25ºC (77ºF) ambient, for
a 30-minute SSB voice transmission or a 5- to 10-minute “key-down” CW
transmission at rated output. These are minimal duty cycle values for an
amplifier operating in average amateur service. Longer “key-down” intervals,
necessitating larger heat-dissipating surfaces and greater air circulation,
are required for contest operation or at high ambient temperatures.

I hope this is helpful.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/

-----Original Message-----
From: tentec-admin@contesting.com [mailto:tentec-admin@contesting.com]On
Behalf Of tlogan7@cox.net
Sent: Sunday, January 05, 2003 22:33
To: tentec reflector
Subject: [TenTec] Orion - cooling fan


Hi folks -
The TT info on the Orion describes a 100% ICAS Tx duty cycle with user
supplied cooling fan.  What does ICAS mean and does the Orion have an
internal fan? Thank you. 73/Tim

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