Elecraft 2T-Gen - Manual (Page 5)

5
In recent years, a much more convenient measuring device has become available at reasonable prices. A
used spectrum analyzer can be purchased at flea markets and used test equipment dealers for very reasonable
prices. Several PC-based spectrum analyzers have been designed and published also. The relationship
between the desired sidebands and those produced by IMD can be observed in real time using a spectrum
analyzer for a measuring device and performance can be easily related to the measurements of IMD
published by the ARRL as part of their equipment reviews.
Most transmitters will produce different output power from equal level audio input at 700 Hz and 1900 Hz.
This can be the result of audio shaping networks in the transmitter microphone input circuit or from ripple in
the SSB filter or both. The Balance control is provided account for this difference by adjusting the ratio of
the tone outputs over about a +/- 3 dB range. The first step in using the 2T-gen is to adjust the Balance
control to account for this difference in the transmitter under test. This is easily done by connecting the 2T-
gen as shown and keying the transmitter and adjusting the transmitter microphone gain or the 2T-gen
Output Adj for a convenient output power. If you are using a spectrum analyzer as a measuring device,
next set the 2T-gen Balance control for equal level the two outputs resulting from the 700 Hz and 1900 Hz
tones.
If you are using an oscilloscope or receiver as a measuring device you will not be able to view the transmitter
outputs resulting from the two tones simultaneously. In this case use a power meter and set the transmitter
for some convenient output. Then disable one of the two tones with JP1 or JP2. If the Balance control is
set correctly the output power will decrease to half of the original reading. If this is not the case, adjust the
Balance control until the power output with both tones is twice the power with one tone. This is an
interactive adjustment and will have to be repeated several times to achieve the desired result. It may be
necessary to repeat this procedure for the opposite sideband because the transmitter SSB filter characteristics
may be different for the upper and lower sidebands.
After completion of the balance adjustment, the transmitter microphone gain or 2T-gen Output Adj control
is adjusted so that the output power produced by each tone is 6 dB below, or 1/4th the rated PEP output of
the transmitter. This setting will result in the rated PEP output power when both tones are present. This is
easily done by disabling each tone in turn with the jumpers on JP1 and JP2.
The drawings below illustrate examples of a spectrum analyzer display and the corresponding oscilloscope
display.