Modifications

  
You can add a 10kHz jump mod to the 142gtl.
  
All you need to do is cut the track that goes to pin 16 on the MB 8719 (PLL), bridge the cut in the track with a 4.7K resistor, then  attach a center off type toggle switch directly to pin 16, pin 16 will go to the switches center pin, the top pin can go to pin 18 and the bottom pin will go to pin 9, refer to the diagram below:
  
 Pin 18--------|O|  
  
Pin 16--------|O <--------center off single pole double throw switch.    
  
Pin  9 --------|O|
                          
  
When this mod is used the switch stays in the center (off) position for normal use, to activate the mod just flick the switch either up or down depending on which channel you are on at the time (it will either need to go + or - depending on the binary code produced at the time), here are what I believe they should be for the A channels:    
  

    

      
A channel
      
actual channel
      
switch position (UP/DOWN) 
    
    

      
3a
      
4
      
DOWN
    
    

      
7a
      
7
      
UP
    
    

      
11a
      
12
      
DOWN
    
    

      
15a
      
15
      
UP
    
    

      
19a
      
20
      
DOWN
    
  
  
 
  
Flicking the switch in the opposite direction will not have any effect, as the pin you are switching would be in the same state already (Hi/Low), which means for example that if you where on CH 4 and flicked the switch UP instead of DOWN you will still be on CH4 !
  
 It is possible to just use a plain on/off switch and a relay, which will automatically shift the pin voltage high or low depending on the binary code, but it is hard to describe and I have not tested it yet, although it should work in theory, the channel offset would still occur as well (i.e. 3a is ch4, 7a is ch7, you need to be above some and below others).