This is a simple subtone encoder that anyone can build, which will generate 123Hz (default), 91.5Hz -or- both at the same time, for convenient repeater access. I have to advise, that I am not sure of the legality of running both 91.5Hz and 123Hz at the same time, but it does work :)
(Reproduced with the permission of the author)
This is a simple subtone encoder circuit to be used in older radio's that do not have an encoder built in already. The advantages of this circuit over other's that I have seen are:
1) Low component count, hence low cost.
2) Very easy to use. The board will generate 123Hz as is, you just have to set the level to suit your radio. A subtone should be <10% of your overall modulation, so for 25Khz channel spacing, we are deviating +/- 5Khz from the center carrier frequency. You must set the subtone level to be between 300 - 500Hz deviation. In a nut-shell, you should be able to trigger the repeater even with a noisy signal, but the amplitude of your tone must be low enough to be inaudible to receiving stations.
3) This unit is somewhat future - proof, in that, it can be re-programmed to generate any audio tone, or multiples thereof, it can be re-programmed to do CW ident at set intervals or behave as a roger beep.
4) Easy to install - just connect P1 to TX 8v in the radio, connect P2 to 0v, and connect P3 via a series resistor of your choosing to the MIC audio in of the radio, -OR- to the VCO control input. The tone encoder is capable of generating over 2V P-P at the output, so the resistor in series is a must! (Hint: 10Kohms as a minimum value is a good start)
Here is the schematic of the unit -
Note: You must use a 16Mhz crystal, even though the source code mentions 32Mhz, I did this to "Trick" the software into producing the 91.5Hz tone. The circuit calls for a 4Mhz crystal, please ignore this and use a 16Mhz parallel resonant crystal.
You'll notice that PIN 5 and PIN 6 of the PIC are not connected, this is because I have used them as inputs. If you pull PIN 6 low, while powering on the unit, it will generate 91.5Hz until power is removed. If you pull PIN 5 low, it will generate both 123Hz and 91.5Hz at the same time! :)
Here is a shot of the unit after assembly
This is a shot of the PCB after install into my DSE K6400 2M kit -
If you want the PCB made, just contact me via the Blue Mountains Amateur Radio club, and we can work something out.
Also, if anyone has the manual for the DSE K6400 radio, I would love to hear from you.
And finally, I have attached the source code for the subtone unit, which is written in Proton Plus. If anyone wants to add to/modify/improve on the code, please feel free, as long as credit goes to the original author :)
Best 73 once again, James VK2TIM
