Ramsey Electronics AF1 manual Introduction

INTRODUCTION

Radio men know that the CW signal is the most reliable mode of transmission when operating on the amateur radio bands. There are, however, some inherent problems that exist in CW reception.

When listening to a carrier wave, or CW signal, our receiver is simply letting us hear the difference between the local oscillator inside the radio and the desired receive frequency. While this is the simplest form of reception (no demodulation of the signal is required) it is also prone to receiving multiple signals at one time making the desired carrier quite difficult to copy.

In an attempt to limit the number of carriers heard through the receiver one of the easiest solutions is to filter the received audio to only allow a single CW tone to be heard. That's where the Ramsey AF1 filter comes in to help.

AMPLITUDE

BANDPASS

FILTER

DESIRED SIGNAL

UNDESIRED

SIGNAL

	250	750	1250	1750
0	500	1000		1500

FREQUENCY (Hz)

The audio filter board creates an audio frequency bandpass filter to remove the undesired tones. It also has a selectable bandwidth (the width of the bandpass filter) of 100, 250, 500, or 750 Hz. The center frequency of this filter is also tunable from 400 - 1000 Hz, so you can tune the radio to frequency that you would like to hear, not to whatever frequency the filter wants to “listen to”.

When designing the new Ramsey SX series of HF frequency transceivers, our engineers developed a superior audio filter using the latest in switched capacitance filter technology integrated circuits. In fact, the filter performed so well that our AF1 kit is a "spin-off" from the HF radio project.

AF1 • 4