E - Z CW AUDIO FILTER Ramsey Electronics Model No. AF1 Here’s a quick and easy way to eliminate interfering CW signals! This filter uses a digital bandpass filter to knock out those unwanted signals. The adjustable center frequency and switchable bandwidth add some versatility to this hard working kit! • Utilizes “state of the art” switched capacitor bandpass filter IC’s ! • Four selectable bandwidths - 750 Hz, 500 Hz, 250 Hz, and 100 Hz all with digital accuracy.
RAMSEY TRANSMITTER KITS • FM100B Professional FM Stereo Transmitter • FM25B Synthesized Stereo FM Transmitter • MR6 Model Rocket Tracking Transmitter • TV6 Television Transmitter RAMSEY RECEIVER KITS • FR1 FM Broadcast Receiver • AR1 Aircraft Band Receiver • SR2 Shortwave Receiver • SC1 Shortwave Converter RAMSEY HOBBY KITS • SG7 Personal Speed Radar • SS70A Speech Scrambler • BS1 “Bullshooter” Digital Voice Storage Unit • AVS10 Automatic Sequential Video Switcher • WCT20 Cable Wizard Cable Tracer • LABC1 L
Ramsey Publication No. MAF1 Price $5.00 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR AF1 CW AUDIO FILTER TABLE OF CONTENTS Introduction to the AF1.................. 4 How it works.................................. 5 Parts list ........................................ 6 AF1 Assembly instructions............ 8 Schematic diagram ..................... 10 Parts Layout diagram .................. 11 Hook-up configurations ................ 13 Troubleshooting ........................... 14 Ramsey kit warranty .........
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.
THEORY OF OPERATION Let’s have a look at what makes our audio filter so special. Have a look at the schematic diagram and follow along. First, having a look at the power supply section of the AF1 notice that diodes D3, 6, 7,and 8 form a full wave bridge rectifier. We used this configuration so that an AC or DC power source may be used for the unit (and the polarity connection for a DC supply can be either way).
AF1 PARTS LIST Please check the boxes after the components have been identified, and now is a good time to “sort” the like components into groups or bins (an egg carton does nicely) to avoid using the wrong component during assembly. RESISTORS AND POTENTIOMETERS Please note that the kit contains some “special” 1 % tolerance resistors. They can be easily identified by the fact that they contain an extra color band, due to their more specific values.
MISCELLANEOUS PARTS 1 2 3 1 1 2.5mm power jack (J4) PC mount RCA jacks (J1, 3) DPDT pushbutton switch (S1, 2, 3) 1/4” stereo headphone jack (J2) AF1 printed circuit board RAMSEY Learn-As-You-Build KIT ASSEMBLY There are numerous solder connections on the AF1 printed circuit board. Therefore, PLEASE take us seriously when we say that good soldering is essential to the proper operation of your transmitter! • • • • Use a 25-watt soldering pencil with a clean, sharp tip.
Now, let's get building! Since you may appreciate some “warm-up” soldering practice as well as a chance to put some “landmarks” on the PC board, we’ll first install some “hardware” components. This will also help us to get acquainted with the up down, left - right orientation of the circuit board. Remember that the components will be mounted on the “component” side of the circuit board and soldered on the “solder” side of the circuit board. 1. Identify and install DPDT switch S3.
polarity. See the parts diagram for proper placement. The capacitor should fit snugly down to the PC board. When installing the components be sure to save some of the longer clipped leads to use later as “jumper” wires. 12. Install C11, another 1000 uF electrolytic capacitor. Be sure to observe the proper polarity. 13. Install C19, 10 uF electrolytic. Again, remember that polarity! 14. Identify VR1, the 7808 voltage regulator [marked 7808].
23. Install R22 and R21, both 100 ohm [brown-black-brown]. They are also mounted standing up. 24. Install stand up resistor R20, 1K ohm [brown-black-red]. 25. Form and install diode D1, a 1N4148 type small signal diode [small glass case with black band]. Be sure to orient the part as shown in the parts placement diagram. 26. In the same manner, install diode D2, another 1N4148. Note that the polarity of this diode is reversed. 27. Install C4, .1 uF disc capacitor [marked .1 or 104]. 28.
AF1 PARTS LAYOUT DIAGRAM AF1 • 11
31. Using a scrap component lead, form and install JMP11. 32. Install C13, .1 uF disc [marked .1 or 104]. 33. Install C2, .001 uF disc capacitor [marked 102 or .001]. 34. Install R1, 47K ohm [yellow-violet-orange]. I’ll bet you didn’t forget to stand it up. 35. Install C10, .01 uF disc capacitor [marked .01 or 103 or 10nF]. 36. Install C12, .01 uF disc cap (that's snazzy electronics lingo for capacitor). Again, its marked .01 or 103 or 10nF.
51. Install R3, 47K ohm [yellow-violet-orange]. 52. Install R2, 750K ohm [violet-green-yellow]. 53. Install R5, 100K ohm [brown-black-yellow]. 54. Install R7, 49.9K ohm [yellow-white-white-red]. 55. Install C14, .01 uF disc capacitor [marked .01 or 103 or 10nF]. 56. Now we’ll install the two MF8 switched capacitance bandpass filter IC’s. If you prefer to use an IC socket, you may install one if you wish.
Connect an audio output device such as a speaker or headset to the appropriate jack (J1 or J2, respectively). With switch S1 in the off position you should be able to hear the tone under test. Set switches S2 and S3 in the “out” position for maximum bandwidth. Push in switch S1 to energize the circuit. Bandwidth S2 S3 Adjust R14 for the proper volume level.
The Ramsey Kit Warranty Please read carefully BEFORE calling or writing in about your kit. Most problems can be solved without contacting the factory. Notice that this is not a "fine print" warranty. We want you to understand your rights and ours too! All Ramsey kits will work if assembled properly. The very fact that your kit includes this new manual is your assurance that a team of knowledgeable people have field-tested several "copies" of this kit straight from the Ramsey Inventory.
AF1 CW AUDIO FILTER Quick Reference Page Guide Introduction to the AF1 .................. 4 How it works .................................. 5 Parts list ......................................... 6 AF1 Assembly instructions ............ 8 Schematic diagram ...................... 10 Parts Layout diagram................... 11 Hook-up configurations .................13 Troubleshooting ............................14 Ramsey kit warranty .....................