Connecting Antenna To Atu - Furuno FS-1575 Service Manual

Reference)
ATU output power in the MF band
Calculate power by the equation: Pa = Ia
Ia: Antenna current flowing through the dummy load
Ra: Dummy load resistance = 10 ohms
The efficiency of the ATU comes to 70 to 80% with 10-ohm + 250 pF dummy load.
For example, if the FS-2575T outputs 250 W, power outputted from the ATU will
reduce to 175 to 200 watts. As a result, Ia comes to 4.1 to 4.5A.
Ia = √Pa/Ra
ATU output power in the HF band: Power meter reading
The efficiency of the ATU comes to 80 to 95% although it depends on frequency
bands. As the frequency becomes higher, the power dissipation increases.
For example, if the FS-2575T outputs 250 W in the 4 MHz band, power outputted
from the ATU will reduce to 200 to 240 W.

5.3.2 Connecting Antenna to ATU

Connect a power meter or SWR meter between the FS-xx75T and ATU to make
measurement of Pf and Pr.
If Pr is high even though tuning is OK, for example if the Pr is 20% or more, check for
the antenna, the axial cable connectors, grounding of ATU, and antenna connection as
well as for burnout of and leakage in the ATU. Furthermore, ensure that the antenna
does not come into contact with structure.
If the Pr is high in a specific frequency band, it is supposed that antenna impedance is
extremely high or low. In this case, if the situation is changed by changing the length of
lead-in wire of the antenna, this problem is related to the antenna impedance. If it is
physically difficult to change the length of the lead-in wire of the antenna, it will be
wise to reduce the TX output power within a specified range.
FS-2575C
Fig. 5.3.2 Output Power Measurement circuit-2
CONFIDENTIAL (internal use only)
This confidential document is used only by FURUNO authorized persons.
It is strictly prohibited to reproduce the document in whole or in part without prior written permission of FURUNO.
× Ra.
2
50 ohm
power meter: Pf/Pr
T/R ANT
FS-xx75T
COUPLER
5-24
5.3 ATU Output Power
ANT
GND
ATU