[Elecraft] Data mode and filters

[Joe Subich, W4TV]

> For my measurements, I set the K3 for 100W, recorded the power
> measured by the LP-100A, which we both agree can miss some peaks, SO
> according to your logic, I WAS overdriving the K3.

Yes, you were probably over driving the K3 (KPA3).  You can estimate
the amount of overdrive by using the the LP-100A Peak to Average
function.  With PSK31 "idle", the LP-100A shows the following:

  K3 Power setting   CW Power   Peak    Average    Peak to average
       20W            20.6W     19.5W     7.5W          4.2 dB
       30W            31.4W     29.8W    11.8W          4.0 dB
       40W            40.2W     39.2W    15.7W          3.9 dB
       50W            50.2W     49.1W    19.8W          3.9 dB
       60W            57.7W     58.4W    24.0W          3.8 dB
       70W            66.8W     66.2W    28.7W          3.6 dB
       80W            75.0W     75.9W    33.1W          3.6 dB
       90W            84.6W     83.7W    38.2W          3.4 dB
      100W            97.0W     93.3W    43.6W          3.3 dB
      110W           103.0W    102.4W    50.2W          3.0 dB

The "CW" power is an unmodulated PSK31 subcarrier.  Peak and Average
are measured by the LP-100A.  Note that the Peak to Average only drops
1 dB from 20W to 100W (1dB compression) for the PSK31 idle and the
average power stays below 50W so while you are over driving the KPA3, 
you're not seriously over driving at the 100W (peak) level with PSK.
At least with a stiff 13.8V supply the KPA3 does not seem to reach
1 dB compression until almost 100W (peak) output.

In addition, with PSK31 the 3rd order products are only +/- 45 Hz
from the "carrier", the fifth only +/- 77 Hz, seventh only +/- 108
Hz, etc. - you are not going to measure a lot of width until the
distortion is bad enough to generate really high order products.

Don't try this with the ALC systems in some other rigs - the excess
gain in their IF stages will make a mess well before 100W peak out.

73,

   ... Joe, W4TV


On 2015-05-17 12:36 PM, Jim Brown wrote:
> Joe,
>
> Your logic is still faulty.
>
> For my measurements, I set the K3 for 100W, recorded the power measured
> by the LP-100A, which we both agree can miss some peaks, SO according to
> your logic, I WAS overdriving the K3. Yet, the measured bandwidth is
> quite narrow.
>
> On Sun,5/17/2015 6:38 AM, Joe Subich, W4TV wrote:
>>
>> > No, but they/we can put a calibrated peak-reading wattmeter like the
>> > LP-100A in line with the feed to our antennas.
>>
>> While a peak reading wattmeter like the LPA-100 is a good step, it
>> still does not respond to instantaneous peaks.  Most "peak reading"
>> wattmeters will show peak values that vary depending on the PSK31
>> datastream and never show the true instantaneous peak.
>>
>> > And last I looked, few hams run much power with PSK-31.
>>
>> They have to do that or they would be clipping terribly in the final
>> amplifier stage (or in the transmit IF of some poorly aligned rigs).
>> They certainly can't push the rigs to 100W as your tests would imply.
>
> My measurements clearly show what a K3 does when set to 100W.
>
> 73, Jim K9YC
>>
>> 73,
>>
>>    ... Joe, W4TV
>>
>>
>> On 2015-05-15 12:44 PM, Jim Brown wrote:
>>> On Fri,5/15/2015 9:10 AM, Joe Subich, W4TV wrote:
>>>> The vast majority of amateurs do not have calibrated scopes on the
>>>> output of their transmitter/amplifier to keep the instantaneous peak
>>>> output below the onset of compression in the final stage of power
>>>> amplification.
>>>
>>> No, but they/we can put a calibrated peak-reading wattmeter like the
>>> LP-100A in line with the feed to our antennas.
>>>
>>> And last I looked, few hams run much power with PSK-31. As both my
>>> measurements and K6XX measurements clearly show, IMD in the K3 drops
>>> significantly below full power.
>>>
>>> 73, Jim K9YC
>
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