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IC-R20 operators manual

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Duplex Offsets

    
             
 
 
             
Many radio users use not just one frequency per channel, but two. Frequencies are used in pairs in nearly all cases except when simplex operation is in use. 

To learn more about why frequencies are commonly used in pairs, view this explanation of why paired channels are used.

The R20 is able to deal with cases where dual channels are in use although it is not essential to set this feature for  basic listening.  It has no bearing on how the R20 operates until you press the monitor button.

Duplex can be set in VFO mode or saved on a channel by channel basis into memory.

 
           
 
           
 
           
             
Enabling Duplex
    Duplex is enabled from the SET MODE menu.
  • Hold down  [8]  until it bleeps and the SET MODE menu is shown
  • Rotate the tuning dial until the chevron points to >DUPLEX. If you don't see this item in the menu, use SET EXPAND to unhide additional menu items.
 		    
                     
         

IC-R20

          
                     
   

*** SET MODE ***

   
   

   
   

SCOPE AF OUTPUT

   
   

OFFSET FREQ

   
   

>

DUPLEX

   
   

TONE FREQ

   
   

DTCS CODE

   
   

DTCS POLARITY

   
                     
     

COMMUNICATIONS RECEIVER

      
                     
  • Press  [8]  again, you should now see the screen below.
  • Rotate the tuning knob to select a new value.

OFF gives zero offset and is for simplex use. When the associated  paired frequency is lower then -DUP is used. When the paired frequency is higher +DUP is used.

                     
         

IC-R20

          
                       
   

DUPLEX

   
   

 

   
   

>

OFF

   
   

 

-DUP

   
   

 

+DUP

   
   

 

   
   

 

   
   

 

   
                       
     

COMMUNICATIONS RECEIVER

      
                     
When you have made your selection, press  [8]  to return to the SET MODE menu or  [DUALWATCH]  to exit.
Any changes you make on the fly are enacted as you make them and so are effective immediately.  You are not required to confirm your changes at any stage. However, you may wish to re-save your newly changed settings to a previously saved memory channel in order to permanently update its parameters .
On returning to the main screen, you will now notice the appropriate flag, either  -DUP  or  +DUP  in the top left of the display. This indicates that duplex offset is armed.
Setting a duplex offset value
The offset value is the actual difference in frequency between your current frequency and its pair
  • Hold down  [8]  until it bleeps and the SET MODE menu is shown
  • Rotate the tuning dial until the chevron points to >OFFSET FREQ
  •  
                     
         

IC-R20

          
                     
   

*** SET MODE ***

   
   

   
   

SCAN STOP BEEP

   
   

SCOPE AF OUTPUT

   
   

>

OFFSET FREQ

   
   

DUPLEX

   
   

TONE FREQ

   
   

DTCS CODE

   
                     
     

COMMUNICATIONS RECEIVER

      
                     
  • Press  [8]  again, you should now see the screen below.
  • Use the tuning knob to select a new value.
The offset value shown in the example below is 4 Megahertz, 800 Kilohertz and 000 Hertz which is usually expressed as 4.8MHz or 4800kHz.
                     
         

IC-R20

          
   

   
   

OFFSET FREQ

   
   

   
   

4.800.000

   
   

   
   

   
   

   
   

   
   

   
   

   
     

COMMUNICATIONS RECEIVER

      
                     
When you have made your selection, press  [8]  to return to the SET MODE menu or   [DUALWATCH]  to exit.   
Any changes you make on the fly are enacted as you make them and so are effective immediately.  You are not required to confirm your changes at any stage. However, you may wish to re-save your newly changed settings to a previously saved memory channel in order to permanently update its parameters .
 
Common duplex values  in the UK are
Low Band   10MHz or 13.5MHz
VHF Marine (ship to shore)   4.6MHz
VHF MidBand   -4.5MHz
VHF HiBand   +4.8MHz
UHF   +6.5MHz or +5.5MHz
 

 

       
  If you need to calculate a frequency pair, you can download this excellent utility by mainsailman 

 
       
  To use it, you will need to have a spreadsheet application installed on you computer, or failing this, you can download a free Excel reader from Microsoft. The url is on the links page.    
   

 

The sole reason for setting the offset value is to enhance the monitor function. Pressing the  [SQL]  button on the side will open the squelch. In addition to this, if you have assigned a duplex offset, when pressing the  [SQL]  button, the scanners receive frequency will in also change so the R20 receives the mobile transmit frequency. When this happens, you will then for instance be listening to a repeater's input frequency rather than its more normal output frequency.
This can be useful to determine if a mobile unit is nearby or to detect if someone is jamming a repeater in your vacinity. It can be used with Short Term Hire to see if the mobiles you are hearing are going through a repeater or just using simplex.

 


 

       
 

 
       
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