Lenny, Yes, this was a design "oversight" for the K2 - I will not call it a problem, since the focus was for an HF transceiver that would do QSK operation, and do it quite well.
Unfortunately, that goal is not consistent with those who use transverters and mast mounted preamps. The parameters relevant to VHF operators and HF operators are different - and the K2 meets the HF operators needs quite nicely. I would steer those VHF operators who need to operate sequencers to the PTT for CW article on my website (www.w3fpr.com). As far as I know, it is the best solution for VHF operators with external preamps and amplifiers to contend with. The original concept for the K2 being a good QSK CW transceiver for HF operation breaks down a bit when the use of the K2 for an IF transceiver for VHF/UHF operation is added. I think my PTT for CW circuit alleviates some of those problems - but then, I am biased. One "advantage" for my circuit is that it relies on the activation of the PTT input to the K2 and not on a key closure. I believe that any circuit which relies on a key closure will shorten or eliminate the first CW element - yes, my circuit can do that too, but it is much more unlikely since the operator must first initiate the PTT line and then begin keying. 73, Don W3FPR On 12/5/2010 9:34 PM, w2bvh wrote: > I faced this issue just recently with a K2 and my homebrew 2M > transverter when putting a used 550 W dual 4cx250 power amp into service. > > In the long run its best to make the mod to the K2 Don W3FPR outlines on > his web page and I intend to do so some time soon. But as a quick hack > to get on the air I built up a little circuit consisting of a one-shot > and 2 relays that goes in the transverter, > > It works as follows: the relay is interposed between the output of the > power attenuator at the I.F. input of the transverter and the first > stage in the transverter's transmit string (the first stage in this case > is the transmit mixer). > > When the K2's keyline is asserted (low) it triggers the one-shot which > activates one relay for 35 ms, The relay is driven by a general purpose > npn transistor. While the the relay is driven, it puts a 51 ohm resistor > across the output of the the power attenuator and opens the path > between the power attenuator and the mixer. This prevents the K2's rf > from reaching the transverters transmit mixer for the duration of the > one-shot. After 35 ms have gone by (enough time for the power amps tr > relay to engage) the one-shot times out, reconnecting the power > attenuator to the transmit mixer. The keyline signal also goes to a > second relay via a general purpose npn transistor. That relay drives the > keyline of the power amplifier. > > I used an HCF4047 one-shot which happily runs off the 13.5V transverter > power. The relays are a small inexpensive Omron units. > > You could probably do something similar to this scheme but *external* to > your XV144 and get similar results. > > The upside is that the power amp is not hot switched. The downside is > that the around 20 ms of the first element in the first morse character > is clipped off. Additionally that same morse element does not have a > controlled rise time since it *is* hot switched (in my case at > approximately -4 dBm). So you get a slightly shortened first dit or dah > with a single key click for that element. For me it was a worthwhile > temporary compromise. > > It is disappointing that the K2 doesn't have a settable delay for the > onset of rf. A small oversight in an otherwise excellent rig (I've had > mine for over 10 years). > > 73, > Lenny W2BVH > > > > On 12/5/2010 7:00 PM, Bob DeVarney W1ICW wrote: >> Second question. >> I am using my K2 and XV-144 as my EME rig. I take the output of the >> transverter key jack and feed it to my sequencer, which then sends the >> appropriately delayed signals to my amp ( 750 watts ) and my T/R relays >> and preamp at the tower. >> >> My question is this: >> >> Can I slow down the transition from receive to transmit internal to the >> K2? Is there a menu option to do so? I could of course use the ptt >> signal from my computer to key my sequencer, and then have my sequencer >> key the K2, but what if I use the "tune" button on my front panel? That >> appears to be instantaneous. >> The last thing I want to do is wipe out a very expensive preamp or hot >> switch my relays with a 1 kW amp ( in the works ) >> >> >> Thanks in advance, >> >> Bob W1ICW >> >> P.S. I have rediscovered my K2 this year, as a high performance VHF rig >> ! K2s aren't just for QRP HF any more, I've made over 170 EME QSOs with >> my K2, XV-144, 600 watts, and a small ( by EME standards ) array of 16 >> dBd gain on 2 meters. Bravo to the Elecraft team for coming up with such >> a versatile product ! >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
