You need to back up and check things one at a time. Does the master II key when you hard ground the ptt line with a solid jumper wire?
What is the voltage at the resistor in series with the base of the transistor when the interface is active and when it is inactive? When it is inactive the voltage should be real low, when it calls for ptt it needs to be high enough to cause the transistor to turn fully on taking the collector to near ground (.6 above ground typical) The 2n2222 transistor and a couple of resistors (usually 10k in series with the base lead and a 47k from base to ground) are all that are required to key a Mastr II reliably. I have built several. Now if you only have 5 volts at your interface when it is suppose to be keyed you may have to decrease the resistor value in series with the base of the transistor. Please attach a schematic of what you are using for an interface it would eliminate many guesses as to what is your problem. And pencil in the voltages you observe when active and inactive. tom ----- Original Message ----- From: Chuck Kelsey To: Repeater-Builder@yahoogroups.com Sent: 4/18/2009 8:14:30 PM Subject: Re: [Repeater-Builder] Re: MASTR II PTT 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 its active. So I am only getting a ½ volt drop instead of a total short to ground. Is it because the transistor cant pull it down far enough? Will a transistor with a higher power dissipation help? Thanks, Vern
