[BC] question for you engineers

[Chuck Lakaytis]

In the early sixties I was a shift maintainence chief of a HF 
transmitter site located in Saran, France courtesy of the US Army.  We 
had quite a few 50 KW Collins transmitters driven in some cases by 5 KW 
AT&T T-409 transmitters.  These were independent sideband, suppressed 
carrier transmitters. The usual operation was for -20 db carrier 
suppression;  if there was severe fading or jamming we reduced the 
suppression to -10 db.  The carrier was used to sync up the receivers, 
important to keep the crypto gear in sync.

Each sideband had two independent channels, four Khz in bandwidth.  The 
transmitters could transmit four independent voice channels, although 
this was not done very often.  Usually we had three data slots and an 
encrypted voice channel.  If the fading got bad we basically simulcast 
the same data and voice on the upper and lower sidebands taking 
advantage of the fact that most of the fading was selective and one 
sideband would stay up while the other one faded. 

It was pretty cool for the time.  I was one of the first techs to be 
trained in the new fangled transistors.

I got a citation once from the commanding officer for fixing a problem 
that the Collins engineers had with new experimental digital codec.  
They could not get the audio levels right, unitil one day I figured out 
the problem and patched an audio amplifier into the circuit, along with 
some limiting from an AT&T "Transocean" audio processor.  So maybe I can 
claim that I did the first audio processing for a low bit rate audio codec!

The coded was a big rack crammed with those new fangled circuit boards.

Here is a picture of the transmitter site courtesy of CSM retired Tim 
Casey, one of the guys in our outfit.

http://www.geocities.com/Pentagon/Barracks/8386/xmitrm.jpg


Lamar Owen wrote:
> On Tuesday 01 January 2008, Bruce Doerle wrote:
>   
>> I think we are talking phone telecommunication in and about the 1930s,  T1s
>> weren't around until the 1960s.  It would have been impractical to build a
>> complex circuit like a codec at that time.
>>     
>
>
> As to putting phone calls over radio, the same equipment that interfaced 
> landlines to microwave relays could be pressed into service to put a landline 
> over a broadcast console; the first trans-atlantic public phone call was made 
> in 1927, over a radio link, if I remember my factoids correctly.
>   

-- 
Chuck Lakaytis
Director of Engineering
Alaska Public Broadcasting, Inc.
135 Cordova Street
Anchorage, Ak 99501
office   907-277-6300
fax      907-277-6350
cell     907-301-4339