CB History WAS Johnson Ranger 1 date of manufacture. Demise of Ham 11 meters
 

In article ,
Jon Teske wrote:
Since ham operators had an assignment at 10 meters, and
the primary user of 11 meters (Medical Diathermy) wouldn't be affected,
it probably seemed like the ideal spot: the only commercial allocations
near it were in the 30-50 MHz range, but assigning a new service there
would have meant displacing existing FM licensees, including many local
government users, who were _also_ interested in keeping their radio
costs down.

I remember medical diathermy in the 50's being an important cause of
TVI. They apparently were available for home use by patients. I never
needed one so I really have no idea what they were supposed to do.
To they still exist? Have they been replaced by a different
technology?

Medical diathermy sources come in two kinds: electrocautery systems used
for surgery, and deep tissue heating. The deep tissue heating systems were
the big offenders, since they were often left operating for long periods
of time.

The deep tissue heating systems have most been replaced with ultrasound,
although some RF-based deep tissue equipment still exists. Electrocautery
is still around.

Aside from the reduction in use of deep-tissue heating systems, the RF
characteristics have been improved a lot. Some early systems were just
relaxation oscillators, running more or less in an ISM band with lots of
impressed 60 Hz trash and lots of harmonics. That stuff has all been
cleaned up and modern medical devices are now clean enough that you
could add a key to them and use them on 10M.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

CB History WAS Johnson Ranger 1 date of manufacture. Demise of Ham 11 meters
 

Thanks for anwering my original question.

Jon W3JT

On 20 Apr 2007 11:04:36 -0400, (Scott Dorsey) wrote:

In article ,
Jon Teske wrote:
Since ham operators had an assignment at 10 meters, and
the primary user of 11 meters (Medical Diathermy) wouldn't be affected,
it probably seemed like the ideal spot: the only commercial allocations
near it were in the 30-50 MHz range, but assigning a new service there
would have meant displacing existing FM licensees, including many local
government users, who were _also_ interested in keeping their radio
costs down.

I remember medical diathermy in the 50's being an important cause of
TVI. They apparently were available for home use by patients. I never
needed one so I really have no idea what they were supposed to do.
To they still exist? Have they been replaced by a different
technology?

Medical diathermy sources come in two kinds: electrocautery systems used
for surgery, and deep tissue heating. The deep tissue heating systems were
the big offenders, since they were often left operating for long periods
of time.

The deep tissue heating systems have most been replaced with ultrasound,
although some RF-based deep tissue equipment still exists. Electrocautery
is still around.

Aside from the reduction in use of deep-tissue heating systems, the RF
characteristics have been improved a lot. Some early systems were just
relaxation oscillators, running more or less in an ISM band with lots of
impressed 60 Hz trash and lots of harmonics. That stuff has all been
cleaned up and modern medical devices are now clean enough that you
could add a key to them and use them on 10M.
--scott