I am using one of these for a repeater transmitter, how can I make the
Transmitted PL tone come on and off with the COR/COS, rather than
full time with the transmitter, I have heard there is a way to do this
without adding a separate board.
GM300 Transmitted Audio Tone Help ?
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W3ZR
- was K3BM
- Posts: 20
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- What radios do you own?: MICOM 2/IC7200/FT897
GM300 Transmitted Audio Tone Help ?
73,
Bob, W3ZR / VE3AO / WQZG526 / PG00047486 & T000000033 + RADAR
Bob, W3ZR / VE3AO / WQZG526 / PG00047486 & T000000033 + RADAR
I just did this with a MaxTrac/Radius which is basically the same radio. The PL tone is generated by the microprocessor using two lines through two high value resistors that feed an op-amp. This op-amp has a 27k feedback resistor (yours may be different) and the output is a stairstep representation of a PL tone. This feeds a three-pole low-pass filter that turns it into a nice sine wave.
I took a 2N2222 (probably any ordinary silicon NPN will work) transistor and connected it as follows: emitter to the output pin of that first op-amp, collector to the input pin of that first op-amp. The transistor goes across the 27k feedback resistor. Run the base through a 4.7k resistor to the outside world (I used one of the spare lines that goes to the mike connector). With the line grounded or floating, you get PL like always. Raise the line to something greater than 5v and the transistor turns on, effectively shorting out the feedback resistor and lowering the gain of the op-amp to a level that kills the PL tone from this op-amp. If your receiver's COR signal goes low with a valid signal, just connect the end of the 4.7k resistor to the COR line and it might work just fine. In my case the COR line goes low with signal and is pulled to +12 with no signal so a direct connection is all it takes.
I plan to implement this on my repeater but will add a small RC delay network on the PL control line so the PL remains on for about 3 seconds during the controller's hang time, thereby letting me hear at least part of the CW ID. If there was a way to make the MaxTrac lengthen it's reverse burst timing via code-plug hacking, that would eliminate the need for the external delay.
I'd imagine you could use a PNP instead, such that a ground on the base would disable the PL, and letting it float or raising it to somewhere around +5v would let the PL come through.
I saw no change in transmitter frequency with the PL enabled or disabled using this method. Remember the entire radio is DC-coupled so any level shift will affect the modulation which will affect the transmitted frequency.
Hope this is useful. I can't think of anything simpler than one transistor and one resistor !
Bob M.
I took a 2N2222 (probably any ordinary silicon NPN will work) transistor and connected it as follows: emitter to the output pin of that first op-amp, collector to the input pin of that first op-amp. The transistor goes across the 27k feedback resistor. Run the base through a 4.7k resistor to the outside world (I used one of the spare lines that goes to the mike connector). With the line grounded or floating, you get PL like always. Raise the line to something greater than 5v and the transistor turns on, effectively shorting out the feedback resistor and lowering the gain of the op-amp to a level that kills the PL tone from this op-amp. If your receiver's COR signal goes low with a valid signal, just connect the end of the 4.7k resistor to the COR line and it might work just fine. In my case the COR line goes low with signal and is pulled to +12 with no signal so a direct connection is all it takes.
I plan to implement this on my repeater but will add a small RC delay network on the PL control line so the PL remains on for about 3 seconds during the controller's hang time, thereby letting me hear at least part of the CW ID. If there was a way to make the MaxTrac lengthen it's reverse burst timing via code-plug hacking, that would eliminate the need for the external delay.
I'd imagine you could use a PNP instead, such that a ground on the base would disable the PL, and letting it float or raising it to somewhere around +5v would let the PL come through.
I saw no change in transmitter frequency with the PL enabled or disabled using this method. Remember the entire radio is DC-coupled so any level shift will affect the modulation which will affect the transmitted frequency.
Hope this is useful. I can't think of anything simpler than one transistor and one resistor !
Bob M.
TX PL strip
Can't one of the pins on the accy connector be programmed for strip TX PL for paging applications? This could be connected to the cor/pl line os the rx.
Josh
Josh
It's my impression that the pin on the accessory jack must be set (PL or no PL) prior to transmitting. I don't believe it will actually turn the PL on or off while the radio is already transmitting. But I have no actual experience using this control line, so if someone else contradicts me, then we've all learned something.
My solution does, unfortunately, require a rather simple modification to the radio, but it does exactly what I, and I'm sure others, want it to do.
Bob M.
My solution does, unfortunately, require a rather simple modification to the radio, but it does exactly what I, and I'm sure others, want it to do.
Bob M.