Ramsey Electronics PR100 User Manual

VHF LOW NOISE
PREAMP KIT

Ramsey Electronics Model No. PR100

Boost up those weak signals without adding in unwanted noises!
The PR100 has a three section tuned circuit and a double helical
filter to allow only the desired signal to be amplified, while
attenuating signals outside the band. A perfect match for any 2
meter receiver!

• Extensive filtering for low noise operation, 1dB
noise figure!

• Three section tuned circuit and double helical filter

• Centered on 145 MHz and is 2.8 MHz wide

• 16dB Gain

• Perfect match for any VHF Receiver

• Powered through antenna feed line, or separately

• Runs on 12VDC

• Designed to fit inside of 1 1/2” PVC for quick and

easy mounting

PR100 y 1

RAMSEY TRANSMITTER KITS

• FM100B Professional FM Stereo Transmitter

• FM25B Sythesized Stereo FM Transmitter

• MR6 Model Rocket Tracking Transmitter

• TV6 Television Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

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• SR2 Shortwave Receiver

• SC1 Shortwave Converter

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• SG7 Personal Speed Radar

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• AVS10 Automatic Sequential Video Switcher

• WCT20 Cable Wizard Cable Tracer

• LABC Lead Acid Battery Charger

• ECG1 Heart Monitor

RAMSEY AMATEUR RADIO KITS

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• CW700 Micro Memory CW Keyer

• CPO3 Code Practice Oscillator

• QRP Power Amplifiers

RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN. New

kits are always under development. Write or call for our free Ramsey catalog.

Ramsey Electronics publication No. MPR100 Revision 1.0

PR100 PREAMP KIT INSTRUCTION MANUAL

First printing: February, 1995

PR100 y 2

Ramsey Publication No. MPR100

Manual Price Only: $5.00

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

VHF LOW NOISE

PREAMP KIT

TABLE OF CONTENTS

Introduction to the PR100 ............................. 4

How it Works ................................................. 4

Schematic ..................................................... 5

Parts Layout .................................................. 6

Strategy ..................................... .................... 7

Assembly Steps ............................................ 8

Alignment ...................................................... 11

Installation .................................... ................. 12

Troubleshooting ............................................ 13

Warranty ........................................................ 14

PR100 y 3

RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive

Victor, New York 14564

Phone [phone]

Fax [phone]

INTRODUCTION TO THE PR100

This amplifier is a truly necessary piece of equipment for your 2 meter receive
applications. With 16dB of gain, you mount this up on your mast on the antenna
to boost those weak signals to a receivable level. This results in clear,
unbroken reception, and a more pleasant listening experience.

The filtering of the preamplifier is narrow enough only to allow the desired
frequency band through, while rejecting all others. This prevents many
problems associated with interference such as intermodulation and front end
overload. Having such a narrow bandwidth also reduces background noise that
would normally be present in wider band amplifiers.

Hookup is very simple in that the unit is powered through the same cable that
you receive your signals through. It is possible to ‘feed’ the 12VDC up the coax
cable to the preamplifier. No new wires to run and makes for less
weatherproofing.

The PC board was designed to fit within a 1 1/2” PVC pipe, so a simple
enclosure could be created out of one piece of pipe and two endcaps. Glued
together it can make for the perfect weatherproof enclosure.

HOW IT WORKS

There really isn’t much to the preamplifier if you look to the schematic at the
right. It mostly consists of filtering, and has only one active part, Q1. We will
start from the Antenna end of the preamp, and then on to the receiver end.

J1 and J2 is where the user can connect two different antennas. Some people
recommend that you use two turnstile antennas at right angles to each other for
good satellite imaging, if you’re using this with a weather satellite receiver. This
allows for good coverage of the horizons. Normally you will only use one of
these jacks.

From these jacks the unfiltered RF passes through C6, into the bandpass tank
circuit consisting of inductor L3 and capacitor C8. This tank circuit and the next
two are eventually tuned to be centered at 145 MHz. C4 allows some of the RF
from the first tank circuit to be allowed into the next, but is very small in
capacitance to offer a large reactance (resistance to AC). This high reactance
allows the tank circuits to perform their jobs better by giving them a higher Q
factor. This means that the spectrum of RF the tank circuits will allow through
becomes narrower due to the high Q.

PR100 y 4

The RF passes through two more tank circuits consisting of L4 and C9 in the
second, and C12 and L5 in the third. Every time the RF goes through an
additional tank circuit, the bandpass bandwidth of the RF is narrower. The
narrower the bandwidth is before the active component of Q1, the better.

The narrow bandpass allows Q1 to devote its amplification to just the desired
signals. This means that it doesn’t amplify nearly as much noise, and won’t
amplify signals outside of the bandpass area. Q1 amplifies the RF up to a
respectable level, where it is sent out to FL1, the dual helical filter.

With steep cutoff frequencies and low loss, FL1 has very good bandpass
characteristics for our preamp. This filter is essentially a series of tank circuits
that have very high Q, and is designed with a specific frequency band in mind.
It is tuned by the user to be centered at 145 MHz with the two coils inside.

L2, L1, and C1 allows the DC fed through the coax line to pass on to Q1 to
power it, while rejecting the RF so that the unit does not self oscillate. C3
blocks the DC from coming into the filters, but allows the RF down to the cable.

PR100 y 5