Model PRE-1
Remote-Powered Preamplifier With 1.8-4.5 MHz Filter
The PRE-1 preamplifier is intended for outdoor locations where the DC power will be provided via the coaxial cable. The unit has a nominal 12 dB gain, and includes a highpass/lowpass filter combination that rejects signals below 1.8 MHz and above 4.5 MHz. The passband includes the 160 and 80/75 Meter amateur bands, and all frequencies in between. When power is removed, a relay bypasses the unit, allowing the antenna to be used on other frequencies. The preamp circuit is a classic negative feedback type with emitter degeneration, biased to approximately 60 mA for good dynamic range performance. Similar circuits have been described by several authors in both amateur radio and professional literature. The filter provides good rejection of the AM broadcast band below 1600 kHz, as well as the 40 Meter ham band and the 49 and 41 Meter shortwave broadcasts bands.
Specifications
Amplifier type: NPN transistor with negative feedback and emitter
degeneration
Highpass filter: Elliptic function, typical 45 dB or more rejection
at frequencies below 1450 kHz
Lowpass filter: Chebyshev/elliptic hybrid with >45 dB rejection
at 7 MHz
Gain: 12 dB ±1.5 dB (within filter passband of 1.8 to 4.5
MHz)
Input/ouput impedances: 50 ohms nominal
In/out switching: Preamp is bypassed when power is removed
Power requirements: +12 to 13.8 VDC @ 125 mA, switched (provided
by customer)
DCB-1 DC Block: Injects DC power to coax, isolates the DC from
the receiver
Power indication: LED adjacent to the powered connector
Connectors (outdoor unit): (2) SO-239
Connectors (DC Block): (2) phono ("RCA") connectors for
coax; 2.1 mm DC power jack
Measured Filter Performance
The filter in the PRE-1 has a typical bandpass as shown in the measurement below:
Installation Notes
The preamp mounting bracket should be grounded, and the antenna used with the
preamp should include lightning/surge protection. Surge protection is not included
with the preamp because that type of protection should be installed at the antenna.
Although the preamp has a weather-resistant enclosure, additional weather protection
is advised, including weatherproofing connectors of the coaxial cables.
AY Technologies * antennas
by K9AY * www.aytechnologies.com