At 12:50 AM 3/3/2012, you wrote: Hi Rich,
A very thoughtful response. PSK31 is one of my favourite modes. I have used several different xcvrs ... at the moment I am using a Kenwood TS-50 and I have setup another xcvr (an old Ten Tec) as a monitor. As you point out the signal must be kept below S9 in the monitor rcvr in order to get an accurate read on the IMD of the transmitted signal. I did the tests into a dummy load. The TS-50 is primarily designed as a mobile SSB xcvr ... however I find it provides excellent IMD (in the -30db area) when I set it for full power and set the PSK31 audio level that produces 15 watts RF output. Beyond the level the IMD figures drop rapidly. I generally operate in the 10-15 Watt output level and I seem to be able to work anyone I hear ... including a lot of DX (with my rotatable dipole at 16M height). I expect the KX3 will work vy well at 5 watts output. When the KXPA3 comes out I would expect to be able to generate a clean signal in that 15-20 watt range.. Jim, VE3CI >The question and response below only consider thermal limitations. There >are also signal quality limitations in some data modes, PSK31 in particular. > >PSK31 is very intolerant of non-linearity. The "crest factor" of >PSK31 can be up to 2, i.e. the peak power can be twice the average >power. Since it is clipping of the peaks that causes splatter or IMD, >with most transmitters you need to keep the output power below one-half >the rated maximum in order to ensure linearity. Linearity is not nearly >as much of a problem in RTTY, but it matters in PSK31. > >If you have the means to measure IMD of your transmitted PSK31 signal, >you can test this. A couple of years ago I did some tests using a >"PSKmeter" (a device that monitors a transmitted PSK31 signal and >reports the level of IMD products in the signal) observing the output of >my K3 in PSK31 with the K3 in DATA A mode. What I found was that IMD >levels were low at powers below 5 watts (KPA3 not in line) and at powers >above 12 watts but below 50 watts (KPA3 in line), but as the power was >increased above the 5 watt or 50 watt level, the measured IMD started to >increase quite rapidly. The reported IMD at full power (10 watts without >the KPA3 or 100 watts with the KPA3) was high - much higher than I would >consider acceptable. > >I did not do similar tests in the K3's PSK D mode, but I have no reason >to believe they would be better. See W7AY's measurements of PSK31 >quality in PSK D vs. DATA A (for power levels below 5W and 50W) at ><http://homepage.mac.com/chen/Technical/K3/Digital/digital.html>. > >I would suggest to anyone who plans to transmit PSK31 at powers greater >than the recommended 5 watt (one-half full power) level that they should >monitor the quality of their transmitted signal to ensure that the >signal quality is acceptable. The simplest "low tech" way to do this is >to have another station report IMD figures for your signal at various >power levels. Note that the other station should be located such that >the signal they receive from you is neither too strong (a very strong >signal can produce IMD in the receiver) nor too weak (the signal must be >well above the noise level for the reported IMD measurement to be >meaningful). > >In RTTY such precautions do not appear to be necessary. Qualitative >observations of the spectrum of my K3's RTTY signals in both FSK D and >AFSK A modes did not show a significant observable difference between >the signals at 50 watts and the signals at 100 watts. > >73, >Rich VE3KI > > >Wayne Burdick wrote: > > > Jim Dunstan wrote: > > > >> The KX3 specifications indicate a nominal 10 watts output. When > >> operating a mode such as PSK, which presents a continuous output, > >> what is the recommended power output? > > > > We recommend using 5 W for data modes and keeping transmissions > > reasonably short. However, you can definitely use full power (up to 12 > > W) if the duty cycle is low, such as during hunt-and-pounce in a > > contest. Of course as the duty cycle goes up, so will the PA and case > > temperature, and eventually the KX3 may automatically roll back your > > power output. > > > > I just did a test using the built-in PSK-D mode, alternately > > transmitting and receiving for 20 seconds each (simulating short > > contest contacts). At 12 watts (20 meters), the temperature never got > > high enough to roll back power during ten minutes of this. > > > > I then tested the KX3's high-efficiency TX mode, which reduces current > > drain by roughly 50% for a given power level. This mode kicks in at at > > 5.0 W or less in CW/FSK-D modes, and at 3.0 W or less in all other > > modes. So I set power to 3.0 W in PSK-D mode, which is amazingly > > effective given the S/N ratio of PSK31, and transmitted continuously. > > After 5 minutes the PA temperature was still increasing slowly, but > > I'm guessing I could have gone on for another 5-10 minutes. > > > > The lesson, here, is to let the other station transmit once in awhile :) > > > > Wayne > > N6KR > >______________________________________________________________ >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
