Section 3
AMPLIFIER/STATION INTERCONNECTIONS
(See Fig. 5)
Coaxial Cable Types & Connectors
Connect the transceiver RF output to the ETO 91(3 RF INPUT with 50 ohm coaxial cable -
RG-58C/U or equivalent Use "UHF" type plugs, such as Amphenol 83-1SP, with reducing
adapter to fit RG-58.
Coaxial cable from the 91(3 RF OUTPUT to antenna should be RG-8A/U, RG-213/U, or
equivalent high quality type with a PL-259 UHF-type plug on the amplifier end. RG8X cable
is not recommended.
T/R Control Cable
The 91(3 has a full break-in vacuum relay QSK system requiring only the normal interconnec
tion when used with a modem QSK transceiver. The 91(3 requires a contact closure (short
circuit) on transmit from its RELAY jack center pin to chassis. This function is supplied by the
transceiver, usually from a dedicated relay that is normally open in receive and closed in
transmit. Shielded wire should be used for the T/R control cable. The 91(3 end must be fitted
with a common phono (RCA-type) plug and the other end with a plug suitable for the trans
ceiver (usually supplied with the transceiver).
The T/R relay contact must close before application of RF drive. 91(3 protection circuitry
prevents "hot switching" with RF drive applied. If a T/R timing problem is suspected,
contact ETO customer service for assistance.
ALC
The use of external ALC is not normally needed or recommended when the ETO 91(3 is used
with modem transceivers. However, the 91(3 does generate a negative-going ALC control
voltage that can be fed back to most transceivers if required, to minimize the possibility of
overdriving the amplifier. This external ALC voltage is available at the 91B's rear panel ALC
jack via a common phono connector. 91(3 grid current exceeding about 1mA will initiate ALC
and light the green GRID LED. About 5-10mA yields full ALC output - nominally -10 Vdc -
and the red GRID LED lights. If the exciter requires a lower ALC voltage the 91(3 ALC poten
tiometer may set accordingly. While driving the amplifier, adjust the ALC pot to limit maxi
mum transceiver output as desired. We recommend contacting ETO customer service before
attempting to use external ALC with the 91(3 .
7
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