Key line in a Lincoln II+??

[2NC995]

Can it be done?

I can handle the amplifier end, but no idea where to start on the radio.

The RF keying kind of sucks. Problems show up when the conditions are poor and I’m talking slow...amp unkeys with a short pause, then the next word is cut off. I don’t want to increase the delay, because that has it’s own problems.

I think I’ll be much happier in the long run with a key line.

 

[543_Dallas]

Pick up a small relay and run 12v+ to it from the power socket or the on/off switch in your radio. Connect the negative to the tx pin on the mic socket. This will ground and engage the relay when you key the mic.

Put a small rectifier diode across the neg and pos on the relay with the band to the positive side. This will shunt the voltage spike from the relay when it disengages. The collapsing magnetic field makes a voltage spike that could (unlikely) damage something else.

Then connect your amp relay cable to the relay you just installed. I've done this in a few different rigs to switch a sdr receiver out of line on transmit....rf keying does suck

 

[2NC995]

Pick up a small relay and run 12v+ to it from the power socket or the on/off switch in your radio. Connect the negative to the tx pin on the mic socket. This will ground and engage the relay when you key the mic.

Put a small rectifier diode across the neg and pos on the relay with the band to the positive side. This will shunt the voltage spike from the relay when it disengages. The collapsing magnetic field makes a voltage spike that could (unlikely) damage something else.

Then connect your amp relay cable to the relay you just installed. I've done this in a few different rigs to switch a sdr receiver out of line on transmit....rf keying does suck

Thanks so much for the detailed response. When I get it done, I’ll post the results!

 

[2NC995]

Just ordered a micro relay, and have everything else.

Double checking my plan...lol.

 

[543_Dallas]

Just ordered a micro relay, and have everything else.

Double checking my plan...lol.

View attachment 31892

Thanks for posting that. I'm not sure my original idea will work with the channel up/dn sharing a pin with the tx. I would probably use the rx pin (pin 2). This will have the relay engaged on rx and disengage it on tx. You'll have to use a spdt relay. dpdt will work but have more unused terminals. You will have to find the pins that are normally closed (nc) so that they close and key the amp when the relay is disengaged. For this you might want to find a switched power source in the radio or turn off the power supply when the radio is in use. I'm not sure how easy or hard that will be with a smt rig. With an older radio there aren't so many hoops to jump through.

 

[2NC995]

Thanks for posting that. I'm not sure my original idea will work with the channel up/dn sharing a pin with the tx. I would probably use the rx pin (pin 2). This will have the relay engaged on rx and disengage it on tx. You'll have to use a spdt relay. dpdt will work but have more unused terminals. You will have to find the pins that are normally closed (nc) so that they close and key the amp when the relay is disengaged. For this you might want to find a switched power source in the radio or turn off the power supply when the radio is in use. I'm not sure how easy or hard that will be with a smt rig. With an older radio there aren't so many hoops to jump through.

Thanks. I was worried about that also...but I’m not sure pin two will work either because both 2 and 5 are directly to ground inside the radio.

I bought SPDT relays, so I can go for NO or NC contacts.

For what it’s worth, I’m not using the mic with the buttons. I’d rather not give up the ability, but if it came down to it I’d rather have a key line than channel buttons.

Just don’t want to cook anything figuring it out.

 

[543_Dallas]

Thanks. I was worried about that also...but I’m not sure pin two will work either because both 2 and 5 are directly to ground inside the radio.

I bought SPDT relays, so I can go for NO or NC contacts.

For what it’s worth, I’m not using the mic with the buttons. I’d rather not give up the ability, but if I’d rather have a key line than channel buttons if it came down to it.

Just don’t want to cook anything figuring it out.

View attachment 31901

That's not going to fly either. All I've got at this point is to find a switched voltage or ground source in the radio and use that. Maybe use a 2n2222 to fire your micro relay so you don't put too much load on the circuit you piggyback. You may be able to use a 2n2222 on the tx pin without effecting the channel buttons. If you were willing to lose the buttons you could remove that resistor that connects them to the tx pin.

 

[2NC995]

I can’t see where the PTT is doing anything for the RX.

If pin 2 is grounded inside the radio, then breaking the connection to pin 5 inside the mic doesn’t do anything at all.

 

[2NC995]

That's not going to fly either. All I've got at this point is to find a switched voltage or ground source in the radio and use that. Maybe use a 2n2222 to fire your micro relay so you don't put too much load on the circuit you piggyback. You may be able to use a 2n2222 on the tx pin without effecting the channel buttons. If you were willing to lose the buttons you could remove that resistor that connects them to the tx pin.

Yeah, I’m stuck at the moment. I may try a transistor on the TX pin to trigger the relay and just see how it goes. I don’t believe I have a 2N2222 around, but I think I can make it work with a PNP switching transistor.

Haven’t even been in the radio...but I’m guessing that accessing the mic jack from behind isn’t going to be a cakewalk either.

 

[2NC995]

Here’s my test circuit. I have to measure the ohms on the relay coil to make a guess at R2, and of course I am still very unclear as to whether this may cause issues with the up/dn circuit.

If anyone has any thoughts please don’t be afraid to say so!

 

[2NC995]

May have to throw in the towel on this one. I was thinking that I could isolate pins 2 and 5 inside the radio, and connect the circuit to pin 2. The ptt would keep the circuit grounded, and I would use the NC contacts as opposed to what I had initially planned. What I didn't like is that the left the amp in a default keyed state...radio off = amp keyed, mic problems = amp keyed, any other circuit failure = amp keyed.

At the end of the day none of that matters. The inside of the radio is so tiny and delicate looking that I don't want to mess with it. I will have to deal with RF keying for now as a foot switch might be a tad too much in a mobile

And as much as I hate to increase the value of the delay capacitor...I'm not going to have a choice.

 

[543_Dallas]

I thought we had some electrical engineers around here that could do this in their sleep.

Have you opened the mic up to see if there are any unused contacts on the ptt switch?

 

[2NC995]

No, I sure haven’t.

I’m currently using a D104M6B...which has one of these little buggers in it:

 

[2NC995]

And that little switch is a cakewalk compared to how I felt looking inside the radio...I felt my confidence wither away the moment I lifted the cover, lol.

 

[sp5it]

Relay not needed. Use any NPN transistor.