MAST HEAD
GaAs-FET PREAMPLIFIERS
EVV 2000 HDX * EVV 700 HDX
INSTRUCTION MANUAL
INTRODUCTION
Receiver sensitivity and following the DX performance of 2m- and 70cms Transceivers can be
described with their noise figure, which normally is in the range of 6 ... 8 dB.
Remarkable improvement in sensitivity can be achieved by the use of a low noise preamplifier
such as the EVV Line of models in front of the receiver/transceiver.
The total noise figure then reduces to about 1 dB, which means an improvement of 5 ... 7 dB!
If the EVV preamplifier is located closed to the antenna system, receiver sensitivity also can be
improved by the cable losses, which results in a total improvement of 6 ... 10 dB!!
The input stage of both EVV models is equipped with a dual gate GaAs FET, which performs
with a noise figure of less than 1 dB and a good intermodulation performance.
These new EVV HDX models are employing a second stage amplifier, running in Class A push
pull for low noise figure and superior large signal handling.
Beside the PTT receive/transmit switching mode, a RF VOX circuit allows comfortable and
reliable Receive/Transmit ( R/T ) switching.
The output bandfilter efficiently selects unwanted signals away from the amateur radio
frequency band for lowest distortion.
POWER SUPPLY and TRANSMIT / RECEIVE SWITCHING
All EVV HDX preamplifiers require a DC supply of about 12,5 ... 15 V DC at 300 mA.
12,5 V should be regarded as a minimum for operation of the preamp closed to the power
supply.
For mast mounting please allow for additional voltage to compensate for the voltage losses
across the feeder cable.
A supply voltage of 13,8 V is fine for typical coaxial cable lengths of less than 20 m.
Cable lengths of up to 50 m require a higher supply with 14 - 16 V as recommended.
The supply can be fed to the preamplifier by two separate ways:
Via a separate DC cable
•
A dual wire line connecting the UHF PL-259 plug in the middle of both N-type connectors
allows operation and switching without any additional sets such as a remote controller.
The DC voltage has to be applied for the RECEIVE status, while TRANSMIT the supply
must
on side of the transceiver used.
If the supply isn't switched to ZERO while the station goes to transmit modes, the
preamplifier gets RF power spikes appearing to the output.
We hardly recommend to avoid this, but the internal RF VOX circuit even then will detect
the RF power and switch over to Transmit mode.
In this operation case the maximum RF power allowed is less than with an exactly PTT
operation - 200 W max. on 2m and 100 W max. on 70 cm.
be switched to OFF. This simply can be arranged by relays or solid state switches
Via the coaxial cable line
•
The most common way to feed and switch the mast head preamp became the use of a
remote controller unit, such as the dressler EVV-INTERFACE.
The INTERFACE will be located between the transceiver (or final linear amplifier) and the
antenna preamplifier in use.
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