[Collins] Split Mode

[Garey Barrell]

Dr. Gerald N. Johnson wrote:

>On Tue, 2006-02-14 at 09:59 -0500, Garey Barrell wrote:
>  
>
>>Henry -
>>
>>This was a common problem back in the 60's.  You were transmitting at 
>>14.040 MHz.  The problem is that with the S-Line you have to remove the 
>>cables and replace the 100 ohm dummy load in the transmitter to operate 
>>split across a bandswitch division.   We used to hear quite a few 
>>Collins stations calling a DX station on SSB, down at the bottom of the 
>>CW band!  None of the other brands (Drake, Heath, etc.) had the problem, 
>>because they had 500 kHz bands.
>>
>>73, Garey - K4OAH
>>Atlanta
>>    
>>
>
>It isn't necessary to remove ALL the cables. Just the crystal oscillator
>cable between transmitter and receiver, and then plug the transmitter
>oscillator internal short cable to the transmitter first oscillator
>jack. That jack is J7 in the transmitter. Its OK to unhook that cable
>from the Jack J1 in the receiver and put in the dummy load but not
>absolutely necessary.
>
>That simple change will let you use separate crystals for transmit and
>receive and to split any amount. But if you switch to transceive on the
>transmitter you probably won't receive and transmit on the same
>frequency because of the differences between the crystals even for the
>same band segment.
>
>  
>
Dr. Jerry is of course correct!  :-)   I didn't recall the specific 
cable, I'm more familiar with the Drake scheme.   As he says, without 
the crystal oscillator cable you are relying upon the two crystals in 
the receiver and transmitter to be on the same frequency for "true" 
transceive. 

This was the downside of the Drake system prior to the C Line.  There 
was a trimmer in the receiver to "net" the receiver crystal to the 
transmitter crystal for transceive.  Only problem was that as soon as 
the temperature changed a bit, the crystals had different T/C curves and 
moved apart, (or not!).  Drake's answer in the late "A" and all "B" 
series was color coded crystals characterized for similar T/C slopes.  
The "letter" at the end of serial numbers (Red, Green, Blue and Yellow,) 
id'd the crystal in each receiver and transmitter and if you had the 
same letter on both, they tracked well enough over temperature.  In the 
"C" line the two oscillators were coupled together with a new cable, 
enabling a sort of phase lock between the two oscillators and solving 
the problem.

73, Garey - K4OAH
Atlanta