Description Of The A7 Board - HP 35601A Operating And Service Manual

Model 35601A
Service
SERVICE GROUP SIX
A7 BOARD: ARMSTRONG MODULATOR
6-84. DESCRIPTION OF THE A7 BOARD
One input to the Armstrong Modulator is a + lOdBm 10MHz which comes from the A6
board (10MHz Switching). The output of the Armstrong Modulator is either AM modulated
10MHz or PM modulated 10MHz. The modulating signal is the -hp- 3582 noise source,
which has a flat frequency response to 25kHz.
Upon entering the A7 board, the 10MHz is quadrature-split into two signals. One 10MHz
signal drives the mixer while the other 10MHz signal goes through a 29dB pad to a power
combiner.
The other input to the Armstrong Modulator is the -hp- 3582 noise source; this source can be
DC offset. The output of the mixer can then be selected as the output of the A7 board. The
output of the mixer can also be fed to the power combiner and summed with the 90 degree
shifted 10MHz. In this case, the output of the power combiner is the output of the A7
board.
If a PM spectrum is desired using a 10MHz source, the following happens. The 10MHz ini­
tially goes through the 90 degree power splitter. One of the 10MHz signals goes through the
doubly balanced mixer and is mixed with the -hp- 3582 noise source. The suppressed carrier
output of the mixer is summed with a 90 degrees phase shifted carrier, is in the power com­
biner and phase modulation is generated. AM is generated by mixing the 10MHz signal with
the DC offset Noise Source of the -hp- 3582. The output of the mixer is then AM modulated
10MHz.
The result from this is a flat AM or PM noise spectrum about a 10MHz carrier. If this AM
or PM modulated 10MHz is fed into the -hp- 3047 system, the output would be a flat AM or
PM noise plot.
REMOVING THE A7 BOARD FOR SERVICING
When servicing is required, the A7 board may be accessed by removing the cover of the
shielding box labeled "ARMSTRONG MODULATOR".
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