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K2 Performance Measurements with and Without Buffer Amplifier

I've completed a suite of tests on my K2 (SN 05689) assembled by Frank, W6NEK, with and without a prototype buffer interface amplifier installed. My K2 has the following options:
- SSB option
- 100 watt power amplifier
- Noise blanker

Rather than post several dozen spectrum analyzer plots and other data points, I'll summarize the results and show an illustration or two.

The results are:
1. The buffer amplifier produces no meaningful change in the K2's performance; and
2. My K2's performance is similar to the ARRL's measured performance (better in some respects, never worse) and meets all relevant FCC rules and regulations for spurious emissions.

 

The following shows the main configuration for testing intermodulation and transmitted spurious and harmonics. Generally, I used an HP 8558B spectrum analyzer, with a home made A/D converter and software to capture the data in a form amenable to computer publishing.

During the tests, a prototype Z91 was connected to the buffer amplifier output and ran in normal scan mode.

 

 
 
   
The spectrum analyzer plot at the right shows the stock K2, operating at 100 watts, CW mode, 7.1 MHz.

The strongest spurious response is -58 dB below the transmitter output power.

 
The plot at the right shows the K2, with the buffer amplifier board installed, otherwise operating identically with the plot shown above.

(The bottom plot has an extra 20 dB series attenuation, so the reference levels are 20 dB different to compensate.)

The strongest spurious response is -62 dB below the transmitter output power.

There are very slight difference in the emitted spectrum, but these are not significant. In both cases, the levels are far below the FCC's -43 dB limit.

 
   
Received and transmit phase noise are unchanged after installing the buffer amplifier.