Furuno FAR-2107 Series Service Manual page 518

The pulse forming network PFN2 is a concentrated constant L/C circuit.
The modulation pulse that drives the magnetron develops when the energy
stored in the PFN2 is discharged, note that SCR1, SCR2 and SCR3 is controlled by
TX TRIG signal. The pulse length is determined by the delay circuit, coils and condensers.
The delay circuit is controlled by K1, K2 and K3.
Pulse length
S
M1
M2
L
CR1 and 2 prevents the energy stored in the pulse forming network from discharging to
the input line.
The pulse transformer T801 boosts up the pulse by the pulse forming network.
Since the impedance of the pulse forming network and the input impedance of T801 is
matched, a pulse with half of the network voltage is developed across T801 primary
winding. T801 boosts this pulse up (X-band: 770V x 18.3 times and S-band: 770V x 14.2
times) and applies the resultant output to the magnetron.
PFN
K1 K2 K3
OFF OFF OFF
ON OFF OFF
ON ON OFF
ON ON ON
Table 9.4.2 Pulse length
S-band Pulse
length
0.05 – 01.0 us
0.12 – 0.22 us
0.50 – 0.70 us
1.10 – 1.30 us
9-14
9.4 Block Description
X-band Pulse
length
0.04 – 0.10 us
0.12 – 0.25 us
0.50 – 0.70 us
1.10 – 1.30 us