activation (and hence signal peak clipping) is not occurring. As Rich
what the transmitter is capable of delivering in CW or RTTY mode. An
fine. I do not have a K3, but with my IC-7000 I use this method,
> 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
>
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