[1000mp] RTTY and the FT1000MP

[Kok Chen]

On Mar 18, 2006, at 11:51 AM, Ted Boerkamp wrote:

> I have used the opto-coupler circuits shown on a few websites for
> this purpose and I am tying into the RTTY jack on the back of the
> 1000MP (original model). When I click on TX in MMTTY, a LED lights
> on the input side of the opto IC, but the 1000MP is not keyed.
> So I know that the signal is getting to the opto-coupler but the
> output doesn't seem to be right to key up the radio.

The problem with the FT-990, FT100D and FT-1000MP series transceivers  
is that Yaesu had opted for a diode wired-OR circuit to isolate the  
various PTT inputs rather than providing a transistor switch for each  
PTT input.

Because of that, you need to key the PTT with a very low impedance  
switch.  The FSK input does not suffer the same malady.

Back in July 2004, George W1ZT did a careful study of it (I-R plots  
and all) and the gist of it is that you need an "on" state of better  
than 0.63 volts at 15.4 mA (or a resistor of about 40 ohms) to  
reliably turn the PTT of a Yaesu FT990/1000D/1000MP on.

Among devices that do NOT work reliably are: 4N33, 4N29A and a  
Silicon diode towards ground.

Any transistor with a guaranteed Vce(sat) of less that 0.6 volts and  
capable of sinking 15.4 mA would work reliably.

I have George's pdf document and if someone wants to post that at a  
web site, please write to w1zt at arrl.net and if George does not have a  
copy handy but agrees to let it be published, I can supply the document.

73
Chen, W7AY