On Thu, Dec 1, 2011 at 4:01 PM, Michael Tondee <[email protected]>wrote:
> I know this subject has been covered before but I'm reading a couple of > pieces of conflicting info on the web so I want to be clear so I don't > smoke anything on my rig. I have a homebrew 50 watt amplifier built from a > PCB/ parts kit. The amp appeared in QST several months back as the winner > of the 2nd Homebrew Challenge. It has a COR circuit which I have been > using successfully but I want to go to hard PTT control by the rig. The amp > keys by grounding the PTT. I have a switch wired in to select between > the COR circuit grounding the PTT or an external source doing it via a 1/8 > inch phone jack. I just need to wire pin 3 of the Flexwire connector to > the center of the phone jack, correct? Or do I need to add another relay in > the circuit? I also see mention of a diode, where would this go, across the > 1/8 inch phone jack? > It is probably OK. That being said, what is getting keyed? A relay? A transistor? A FET? A big-assed power contactor? The key points (pun intended) are the open-circuit voltage that appears on the keying circuit, and the closed circuit current. If the load is a relay then you need a clamping diode to prevent the inductive flyback pulse from taking out the keying transistor in the 1500. So, take your multimeter, set if for volts, and place it across the PTT input on the amp. That will tell you open-circuit voltage. Switch the multimeter to current and connect to the PTT input on the amp again. This will key the amp. Read the closed-circuit current. Compare these values to the specs for the 1500. If either the voltage or the current exceeds the maximum allowed for the 1500, you will need either an additional transistor buffer or a relay between the 1500 PTT output and the PTT input of the amp. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 [email protected] +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List [email protected] http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
