Agreed. It's good to bring out these things so we are aware of ALL the ramifications of doing things, you never know who's monitoring this channel.
There are some fast, small, non-vacuum relays that can be speeded up with a little circuitry. 73 David G3UNA ----- Original Message ----- From: "Don Wilhelm" <[email protected]> To: "David Cutter" <[email protected]> Cc: <[email protected]> Sent: Sunday, February 15, 2009 1:37 PM Subject: Re: [Elecraft] K3 external qro keying line > David, > > The back emf pulse from a relay occurs when the coil circuit is opened, > and its polarity is opposite that used to operate the relay. A properly > connected diode should 'swallow' the back emf, and a capacitor in parallel > with the coil should reduce the amplitude of the pulse. > Any delay introduced by the diode and capacitor will be on the trailing > edge and will not normally introduce significant delay on the leading > edge. > > Anyone adopting this scheme would not be operating QSK, so any additional > delays introduced will not be significant. > Those desiring QSK operation should consider fast relays (vacuum relays) > or solid state switching devices for their amplifier switching. > > 73, > Don W3FPR > > > David Cutter wrote: >> That's a good thought and provides instant isolation, but have some >> thought about the back emf off the coil - it could exceed the rating of >> the keying transistor. I measured 800V on a very fast scope many years >> ago from a reed relay. Just sticking a diode across the coil will slow >> it down a lot, so, some experimentation with zeners and resistors will >> get the situation optimised. I once used a separate keying transistor >> and relay and found that a small cap from the base to the collector did >> the job quite well by slowing the off rise time, so the transistor >> absorbed a bit more power but gave good control. >> >> 73 >> >> David >> G3UNA >> >> >> ----- Original Message ----- >> From: "Don Wilhelm" <[email protected]> >> To: <[email protected]> >> Sent: Thursday, February 12, 2009 4:00 PM >> Subject: Re: [Elecraft] K3 external qro keying line >> >> >> >>> Terry, >>> >>> For those who prefer not to touch the K3 with a soldering iron, an >>> external 12 volt relay is a good solution. Obtain the power from the >>> K3 12VDC OUT jack and use KEYOUT to key the relay. It accomplishes >>> the same thing and retains the ability to use QSK in the future without >>> 'undoing' the internal relay. >>> >>> 73, >>> Don W3FPR >>> >>> [email protected] wrote: >>> >>>> I've seen numerous posts about the PTT output line on the K3 and using >>>> older amps. Yaesu's, Kenwood's, Icom's all share the same issue. >>>> >>>> >>>> >>>> Unless you are running QSK and need instant keying, I would suggest >>>> adding a small 12v relay inside the K3 that the solid state device >>>> keys and presents the user with a set of dry, isolated contacts that >>>> can handle positive, negative and up to 250v DC or AC. I have added >>>> this to several K3's to protect the switching transistor from eventual >>>> destruction. Once again, if you are using QSK, solid state due to it's >>>> fast switching time is your only option. >>>> >>>> >>>> >>>> Yes, it means touching your K3 with a hot soldering iron, but it's a >>>> "pay me now or pay me later" thing, sooner or later it will blow the >>>> switch if you are hooking up older or HB amps that use other than low >>>> current positive keying voltages. >>>> >>>> >>>> >>>> Terry >>>> >>>> >>>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[email protected] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> ------------------------------------------------------------------------ >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com Version: 8.0.237 / Virus Database: >> 270.10.23/1953 - Release Date: 02/14/09 18:01:00 >> >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
