Tom Hammond <[EMAIL PROTECTED]> wrote: > Ron: > > >>Is there any reason to use a keying interface between these two? The K2 >>manual says the PA key circuit handles 1 amp at 200v DC. The LK manual >>doens't say what the exact specs are, but from the schematic it looks >>like the LK uses 12V for the TX relay. I'm an appliance operator so sure >>would appreciate advice before I key the amp direct from the rig. > > >Nope, none whatsoever... the MOSFET at the T-R output of the KPA100 is >more than adequate to key just about any T-R line which offers a POSITIVE >DC voltage less than about 200VDC and 5A... UNfortunately, it will NOT >(directly) key some of the older amp T-R lines which offered negative >voltages. > >73, > > >Tom Hammond N0SS
For negative voltage keying I found that using the the circuit by K4IQJ from May 1989 QST, <http://www.arrl.org/members-only/tis/info/pdf/sstrans.pdf> worked well between a Heathkit SB200 and the K2. I built it on a Sunday and the only high voltage P-channel enhancement mode MOSFET available at the local Fry's electronics was an NTE2381 which is overkill. I deleted the zener diode that K4IQJ included to protect the transceiver since the diode protector in the MOSFET of the K2 is rated to handle the full fault current from the SB200 (You should verify this yourself before doing what I did. That is, I believe, [but haven't tried it!] that you can stupidly connect the SB200 to the K2 directly and the K2 will survive.) The circuit is simple; I built it into a small plastic box that sits behind the SB200. The K2 keys (to ground) a 1K ohm resistor connected to the positive terminal of a 9 volt battery whose negative terminal connects to the gate of the FET. A 470K ohm resistor connects from the gate to ground. The source is grounded, and the drain and ground connect to the SB200. K4IQJ included a 15 volt 1 watt zener from the gate to ground, to clamp the voltage on his rig if the MOSFET failed, and suggested using an IRF9610, IRF9612, IRF9620, IRF9630 or IRF9632 for the MOSFET. 73 Kevin w9cf =------------------------------------------------------------- Kevin Schmidt, [EMAIL PROTECTED], http://fermi.la.asu.edu/w9cf Department of Physics Arizona State University, Tempe, AZ 85287-1504 (480) 965-8240 Fax: (480) 965-7954 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
