Or replace the series diodes with power schottkys.
On Mon, 2008-08-18 at 21:29, Joe Subich, W4TV wrote: > > Alan writes: > > > The obvious solution is just to use the K3 +12VDC output > > connector for all accessories. It's rated for 0.5A which > > should be plenty for most devices. As a bonus it's > > controlled by the K3 ON/OFF switch. > > Unfortunately it's not that easy. The +12VDC "output" is > not +12V - it's somewhat less. There are two series diodes, > one in the +13.8V input and one on the +12V output plus the > FET power switch that adds a variable voltage drop that > depends primarily on the current drawn by the driver. > > In transmit the +12V output is often as low as +11.8V (or > less if the primary supply is lower than 13.8V). If the > accessory is designed with a series diode to protective > against reverse voltage at the input, the supply voltage > can be too low for reliable operation of 12V DC relays. > Eliminating D34 in the K3 would be a big help with the low > output voltage. > > 73, > > ... Joe, W4TV > > > > > > On Mon, 2008-08-18 at 16:47, Joe Subich, W4TV wrote: > > > Tom writes: > > > > > > > Be especially aware that rigs with external 12V supplies can > > > > develop what sounds exactly like RFI from "pin 1" problems. > > > > > > > > This is because the power supply leads of the SSB radio are > > > > current modulated at an audio rate. If the 12V supply has a > > > > ground connection common to the negative lead post on the > > > > supply (or through other gear) the V- lead voltage drop can > > > > cause a "pin 1" issue from dc potential that varies at an > > > > audio rate. > > > > > > This is a particular problem with transceivers that have a > > > single V- lead and only one "pin" for the V- connection (like > > > the K3). ... > > > > _______________________________________________ > > Elecraft mailing list > > Post to: [email protected] > > 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 _______________________________________________ Elecraft mailing list Post to: [email protected] 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
