PTT voltages

[KM3K]

Hello,
I've searched my FT-950 manual and also the Internet for specs on what voltage levels are expected on a PTT-line.
Unfortunately, all I could find out for sure is the FT-950 normally has the line at +5 VDC in a standby case.
So I presume that the line must go near 0 volts to activate the transmitter.
I'm thinking now that there must be specs that are just simply understood to be in effect.
Do all modern day transceivers follow the same convention?
If so, could someone detail what the specs are?
Thanks in advance for any comments.
BTW, I just ordered an ARRL book "Get on the Air with HF Digital" to see what I can find out from there.
73 Jerry KM3K

[WB6BYU]

The convention is that a contact grounds the PTT line to put the rig into transmit mode.
How much voltage there is across the contacts, and how much current must flow to do
so, will vary a lot from one rig to the next. 

Some older rigs could have 100V across the contacts to switch a tube, or require 100+mA
to pull in a relay, but most modern rigs probably run it from 5V or 3.3V logic.  It probably
will key the rig with a silicon diode (0.6V drop) in series, but beyond that you'll have to
measure it for a specific rig.  I know that my old Ten-Tec rigs don't key reliably when
the contacts get at all dirty, even though other rigs will key up just fine using the same
contacts.

[AA4PB]

There are no standards. Each mfg is free to handle the PTT in any way he likes. As said, modern rigs usually use a pull up to the +5V power and ground it for transmit. I've run across some optical isolators that wouldn't pull low enough to ground to reliably key some rigs. Personally, I like to use a FET because it has a very low "on" voltage drop (0.4V or so) and can handle around 60V open circuit (depending on the type) which makes it pretty universal for modern solid state rigs.

[AD6KA]

I've searched my FT-950 manual and also the Internet for specs on what voltage levels are expected on a PTT-line.

Look on Page 14 of the FT-950 manual.
"Interfacing to Other Linear Amplifiers"
Pin 2 of the "Linear Jack" is capable of
handling 30v DC @ 1A
or 60v DC @ @ 200mA.
Pin 2 of the Linear Jack is "TX SEND"
Pin 3 is Ground.

Good luck with your amp setup.
73, Ken  AD6KA

[N4CR]

I've searched my FT-950 manual and also the Internet for specs on what voltage levels are expected on a PTT-line.

Look on Page 14 of the FT-950 manual.
"Interfacing to Other Linear Amplifiers"
Pin 2 of the "Linear Jack" is capable of
handling 30v DC @ 1A
or 60v DC @ @ 200mA.
Pin 2 of the Linear Jack is "TX SEND"
Pin 3 is Ground.

Good luck with your amp setup.
73, Ken  AD6KA

You are talking about keying a linear.

He is asking about PTT. (I think)

Two very different things.

[KM3K]

He is asking about PTT. (I think)

Yes, N4CR, you got it right; it is about PTT.
73 Jerry KM3K