Good point, I guess the transverter was designed to work with the FT290.
I should have explained a bit more in context!
My MML 144/30-LS, which is the only MM amplifier I have experience of, requires a nice ground connection on its PTT line to operate a relay. While it is waiting on receive, it is putting out an open circuit voltage of around 13.8V.
Now, the FT290 doesn’t provide a simple “grounding” PTT output as some radios do, eg a relay contact or open collector transistor, it shares its internal PTT line.
This is good in some ways, as it can be used to control external equipment, or to control the FT290. The downside is that it is a bit fussy about what you connect to it.
On transmit the PTT line is indeed grounded, but on receive it sits at around 6.8V (mine is a bit lower, something else to investigate one day maybe). Now, connecting that line to the amplifier PTT with its 13.8V is likely to problematic - though it would be quite easy to build a suitable interface.
Actually… I think I have a spare mic connector knocking around, so I could build a PTT switch that fits the mic socket (which allows me to keep the Standby connector to transverter PTT socket connected).
Of course, it won’t work if it doesn’t have a suitable name. Something like the MicPTTturbo GTXLi 2025 Edition…
Ah yes, another good point! The 6.8V to the centre contact of the relay also feeds the collector of Q2011 (through the relay coil). That explains why my radio has about 4.4V on the PTT line on rx, coming from the emitter of Q2011. I still wouldn’t choose to connect it directly the MM amp.
There’s a capacitor and diode in series with the amp PTT. A resistor holds the keying trx base high turning it on and the PTT to earth through the diode pulls the base low turning off.
