Ramsey QT1 User Manual

QUICK TONE CTCSS

SUB - AUDIBLE TONE

ENCODER DECODER

Ramsey Electronics Model No. QT1

Caught in the maze of low frequency tones?

Looking for an easy way to update your rig with sub-audible frequency tones? Let the Ramsey Quick Tone do the job for you with digital accuracy!

• Sharing a channel using (C)ontinuous (T)one (C)ontrolled (S)ub-

audible (S)quelch or PL ? This is the complete circuit solution for you!

• Mini size quality circuit board designed to fit inside many

transceivers.

• Add tone capability to access your favorite repeater with this easy

to assemble kit.

• Encodes / decodes any of the 39 standard CTCSS tones with quartz

accuracy - no “tweaking” required!

• Setup includes compete digital filtering of TX audio to eliminate

“talk off” interference from normal speech audio components.

• Operates with any 5-15 VDC source - even includes an on-board

voltage regulator for noise free operation.

• COMPLETE with hookup instructions and documentation to guide

you to a finished project that works first time - every time!

• Easily bypassed for no-tone operation.

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PARTIAL LIST OF AVAILABLE KITS:

RAMSEY TRANSMITTER KITS

• FM10A, FM25B FM Stereo Transmitters

• AM1, AM25 Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• SR2 Shortwave Receiver

• AA7 Active Antenna

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70A Speech Scrambler/Descrambler

• TT1 Telephone Recorder

• SP1 Speakerphone

• MD3 Microwave Motion Detector

• WEB1 Walking Electronic Bug

• ECG1 Heart Monitor

• PG13 Plasma Generator

• TFM3 Tri-Field Meter

RAMSEY AMATEUR RADIO KITS

• HR Series HF All Mode Receivers

• DDF1 Doppler Direction Finder Kit

• QRP Series HF CW Transmitters

• CW7 CW Keyer

• 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.

QUICK TONE CTCSS ENCODER / DECODER INSTRUCTION MANUAL

Ramsey Electronics publication No. QT1 Revision 1.0

First printing: 1994

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Ramsey Publication No. MQT1

Price $5.00

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

QUICK TONE CTCSS

SUB - AUDIBLE TONE

ENCODER DECODER

TABLE OF CONTENTS

Introduction to the QT1 ................. 4

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

Schematic Diagram ..................... 10

Parts list ........................................ 6

QT1 Assembly Instructions ........... 7

Parts Layout Diagram ................. 11

Hook-up Configurations ............... 12

Troubleshooting ........................... 16

Ramsey Kit Warranty ................... 19

RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive

Victor, New York 14564

Phone (585) 924-4560

Fax (585) 924-4555

www.ramseykits.com

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INTRODUCTION

With todays’ ever shrinking radio frequency spectrum, it has become common place to “share” radio frequencies using a tone squelch arrangement.

By transmitting a low frequency audio tone (sub-audible to the radio and most of us) we can enable our transmitter to connect with receivers specifically listening for the particular tone one happens to use. This will eliminate much of the background “chatter” that may also be taking place on a desired frequency.

This “tone squelch” arrangement is commonly used on many repeaters to make them exclusive to the repeater club members only. The problem is that many of the more reasonably priced rigs do not include tone capabilities and that older equipment had no provision for this “modern” squelching arrangement.

Their has been various ways to “update” older rigs for tone operations for years, but these solutions were primitive, usually encoding or decoding a single tone per unit and requiring extensive test equipment to align.

Enter MX-COM and one of their latest innovations in CTCSS technology.A single 24 pin Integrated Circuit capable of encoding or decoding any of the 39 standard tone frequences available. That’s the heart of the Quick Tone unit with some external setup and control parts.

QT1 THEORY OF OPERATION

You’ve probably already noticed that the QT1 kit doesn’t contain a whole lot of components. The majority of the circuitry is contained inside the integrated circuit with only a few external components that actually do the “brute force” control of your transceiver.

The MX-COM IC is itself a testament to todays ever evolving digital circuitry (including modern day compact disc players and the like) so without getting too involved let’s take a look at what is being accomplished inside the IC. Have a look at the schematic diagram (on page 10 of the instruction manual) and follow along.

In the received audio path the radio’s audio is routed to the tone decoder input of the chip. Depending on the sub-audible tone frequency selected (using the programming inputs), as well as if that particular tone frequency is present in the audio input, the RX decode output (pin 15) will go to a logic level one for a valid tone decode. This output is then re-routed to the IC, inverted, and used to drive an open collector muting circuit that “grounds” the

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received audio until the sub-audible tone is detected. When that occurs, transistor Q1 is turned off and the audio signal is free to drive a speaker or headset output.

Another receive audio path is directly through the MX-COM. IC. The received audio is routed through an internal high pass filter which digitally filters out any low frequency CTCSS component in the received audio. Another advantage to this internal audio route is that the tone squelch function can be easily overridden by simply switching the Push-To-Listen (abbreviated PTL) pin of the IC to a logic 1 condition. In this way it is easy to check the radio receivers frequency for traffic that is not using your tone squelch setup.

The tone generation function is straightforward. When the Push-To-Talk line (abbreviated PTT) is grounded, the IC generates the programmed sub-audible tone. This audio signal is fed out pin 16, where a level adjustment potentiometer is located. This low frequency audio component is available to be added to the modulation input to the transmitter.

The TX audio path through the IC also makes use of the high pass filter to remove any stray low frequency components of the audio to eliminate any intermodulation product which could cause a “talk off” condition when transmitting.

This previously mentioned “programming” is easily accomplished using jumper blocks and we’ll discuss them in more detail when we’re actually ready to select our tone frequencies. The same goes for the TX/RX audio inputs and outputs, so lets get the “feel” of the circuit by building it before we discuss actual hook ups and adding unnecessary confusion.

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QT1 PARTS LIST

Please check the boxes after the components have been identified, and it is also handy at this time to “sort” the like components into groups or bins (an egg carton does nicely) to avoid using the wrong component during assembly.

RESISTORS

 3 10K ohm resistors [brown-black-orange] (R1,5,6)  1 470K ohm resistor [yellow-violet-yellow] (R2)  1 820K ohm resistor [grey-red-yellow] (R3)  1 1Meg ohm resistor [brown-black-green] (R4)  1 5K ohm trimmer potentiometer [black color marked 502] (R7)

CAPACITORS

 1 33pF disc capacitor [marked 33] (C10)  1 68 pF disc capacitor {marked 68} (C8)  1 .01 uF disc capacitor [marked .01 or 103 or 10nF] (C11)  1 .1 uF disc capacitor [marked .1 or 104] (C9)  8 1 uF electrolytic capacitors (C1,2,3,4,5,6,7,12)

SEMICONDUCTORS AND INTEGRATED CIRCUITS

 1 1N4148 diode [glass case with black band] (D2)  1 1N4002 diode [epoxy case marked 1N4002] (D1)  1 NPN small signal transistor [marked 2N3904] (Q1)  1 78L05 voltage regulator [marked 78L05] (VR1)  1 MX-COM MX165CP 24 pin IC (U1)

MISCELLANEOUS PARTS

 1 Mini 1 MHz crystal [marked 1000J] (Y1)  1 12 pin jumper block  6 Pre formed jumper blocks (P0 - P5)  1 12” length of black, red, and white hookup wire  1 24 pin IC socket

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+ 14 hidden pages