Sounds like the transistor isn't biased "on" all the way. Could be the series resistor on the transistor base is too high a resistance value or the transistor choice was bad. A 2N3904 or 2N2222 should work OK. If you really want a "hard" low, use a power mosfet instead of the transistor - like a 2N7000 or a VN10LP. In that case, the gate would correspond to the base connection, the Source goes to ground, and the Drain is your connection to the PTT on the radio.
Chuck WB2EDV ----- Original Message ----- From: Vernon Densler To: Repeater-Builder@yahoogroups.com Sent: Saturday, April 18, 2009 6:05 PM Subject: RE: [Repeater-Builder] Re: MASTR II PTT With the simple echolink interace which has a NPN transistor doing the switching the voltage across the PTT line and ground is 7v when the com port is not active and 6.5v when it’s active. So I am only getting a ½ volt drop instead of a total short to ground. Is it because the transistor can’t pull it down far enough? Will a transistor with a higher power dissipation help? Thanks, Vern
