For these measurements the bandpass on the TS-2000 was set to 300 - 2800 Hz. The X axis scale on Visual Analyzer seen in Figure 3 is set to range 0 - 5000 Hz. The only criteria I used when setting the Y axis was to allow for a modest centering of the graph over a range of signal condition changes. Note: The graphs display distortion figures THD and THD+N. I have not analyzed the significance of those figures in this discussion.

The Kenwood TS-2000 is typical of most modern transceivers in that it provides in addition to the normal speaker/phones audio output which is controlled by the volume control, a line audio out circuitry which is also adjustable but which is inedpendant of the speaker/phones output. The line output level, once adjusted remains independant of any changes made to the speaker/phones output. The range of adjustment of the line output is in steps 1 through 9 with 1 being the lowest level.

Figure 3

I have the TS-2000 line output level set to Level 1 for the graph seen in Figure 3. The peaks seen above the passband floor represent PSK31 signals of varying strength. The rest is noise, both atmospheric and internal receiver noise. If I increase the line out level to the next higher increment, Level 2 as seen in Figure 4, no significant difference is observed. The level of signal into the sound card has increased as evidenced by the higher amplitude of the passband.

Figure 4

There is a little more amplitude to the noise to the right side of the trace between about 4.1 kHz and 5 kHz as the line output level is increased. In this graph, it may seem of no consequence and just looking at the two graphs, Figure 3 and Figure 4, it would be of no real significance. Differences in signals seen within the passband and just the irregularity of noise could cause seemingly random spikes. If there is cause to question the presence of suspicious noise above the passband in frequency, the next graph will confirm that the suspicion is warranted.

Figure 5

Figure 5 is with the line output level set to 4. The increase in gain is obvious due to the further increased passband floor amplitude. Now look at the noise outside of the passband. Even when we're not dealing with overload caused harmonics showing up in this area of the graph, the increased signal level gain setting is resulting in an amplification of the noise which resides in this area. It appears to me that this area which is higher in frequency and outside of the set passband of the receiver is also outside of the AGC loop. The level of noise on the floor of the passband does not appear to vary with the increased level setting suggesting that it is being "controlled" by the AGC along with everything else within the passband.

Go to Home Page | Go Back | Next, Too Much of a Good Thing

Custom Search

Questions? Comments? Contact me