53928702-vhf-tracker.docx

if you build this receiver from these plans, please let me know what your experience is, especially if you use it with the FM108 tracking transmitters. These plans are for individual use only... any commercial use of the design, plans, or other associated material will require payment of a licensing fee. E-Mail to:[email protected]

Copyright ©2002 Jerry Baumeister

VHF 1 Tracking Receiver (also receives FM broadcast and AM air bands) The plans that follow will lead you through the assembly of a superregenerative radio designed to be used with FM 108 MHz tracking transmitters. It can also be used to listen in on aircraft and control tower communications and the top of the FM broadcast band down to about 105 MHz. This receiver when used with the “Beeping tracking Transmitter (108 MHz)“ makes a good transmitter locating system suitable for model rockets, balloons and assorted other objects. The kit contains a Printed Circuit Board (PCB), all electronic components and an antenna. The builder will need to provide a 9 volt radio battery and a headset. The receiver is designed to be used with the common stereo headsets used on most portable radios, CD players and MVD players. It should have a 1/8 inch diameter plug. Construction is simple and reliable if reasonably good soldering practices are followed. Circuit Description: This circuit is a self-quenching regenerative RF receiver also known as a superregenerative receiver (fig 1). A superregenerative receiver performs two basic functions. First it feeds back a portion of the received signal from it’s output in phase to its input; and second a super audible quenching oscillator drives the amplifier through the point of oscillation and maximum sensitivity and then quenches the oscillation repeatedly. This keeps the feedback from driving the circuit into self-oscillation and allows the signal to be regenerated over and over again. In this version of the circuit, both functions are performed by the circuitry associated with Q1. The rest of the circuit, shown to the right of L3 in the schematic, comprise the audio amplification circuit and are centered on the LM386 Audio Amp IC. In this configuration the LM386 is set at a gain of 200 and feeds it’s output to a standard 1/8-inch diameter stereo phone jack. The audio can then be heard by plugging any standard stereo headset into the jack.

The controls consist of C1, C2, R3 and R6. C2 provides the frequency selection. C1 provides fine-tuning, R3 adjusts sensitivity and R6 is the volume control.

Construction: Construction is made simple and reliable by utilizing PCB construction and several fixed inductors. Only one coil needs to be hand wound. Please refer to Fig 2 "Component Placement:". NOTE: Take you time and use good soldering technique in order to prevent solder bridges and “cold“ solder connections. Use a 25 to 40 watt soldering iron with a pencil sharp point; trim all leads after soldering and check each solder joint with a magnifying glass for bridges and solid connection. Please refer to the "Component Placement" illustration when installing parts. All components are installed on the blank side of the board (not the foil side). When installing components bend the leads to match the hole spacing. Push the leads through the holes at the proper location being careful of polarity on the IC and transistor. Solder the leads on the foil side of the board being careful not to produce solder bridges between the foil tracings. Trim all excess leads immediately after each component installation. Assemble the circuit by starting on the bottom left side of the PCB and work your way to the right being careful to place the components in the correct positions. Common component markings are list in parentheses after each part. Abbreviations for color codes are: BK= black BR= brown RD= red OR= orange YL= yellow GN= green BU= blue VO=violet GY= gray WH=white SL= silver GD= gold Install L1 (SL/GN/BR/RD/SL) Clean ¼ inch of the lacquer from both ends of L2 (1 ½ turn air wound coil). Next install coil L2. If it is not already wound or if it has become malformed you can form it by winding 1 1/2 turns of #22 wire on a 5/16 inch form. You can wind the coil on the shaft of a 5/16 inch drill bit and

then remove. The coil does not have to be exact but needs to be close. Be sure to clean the ends of the coil wire before soldering to the PCB. The spacing between the loops will be approximately 1/16 inch. Install C1 (not marked ) Install C2 ( not marked ) Install C3 (22) Install Q1 (NTE108). Make sure that the flat side is facing towards the “top” of the PCB. Install C4 (6.8) Install C5 (202) Install C7 (105 or .1) Install L3 (SL/GN/BU/GY/SL) Install R1 (BU/GY/BR/GD) Install C6 (102) Install R3 ( 503 ) Check your work. All holes on the bottom left quarter of the PCB should have components in them Install L4 (SL/GN/GY/RD/SL) Install R2 (OR/OR/OR/GD) Install R4 (BR/BK/OR/GD) Install C11 (203) Install R5 (BU/GY/RD/GD) Install C12 (10uF) Install IC1 (386). Install with PIN #1 to the bottom left. See illustration for pin location. Install C10 (473) Install C13 (104) Install R6 (53 ) Install C14 (220uF) Install C15 (102)?? Install R7 (BR/BK/BK/GD) Install C8 (1000 uF) Install J1 the phono jack Install H1 the battery holder by inserting the copper brads through the holder and then through the PCB. Solder the brads to the PCB and cut off the ends flush with the PCB. Install the battery snap connector. The red wire goes into the hole next to the “+” sign and the black wire goes into the hole next to the “-” sign. Install T1 the antenna. Push the antenna screw through the PCB from the foil side and screw into the base of the antenna. Make this a tight connection. This completes the assembly of the radio. It can be used as is or mounted to a small block of wood using the 4 wood screws included with the kit (see diagram). It can also be mounted in a small project box .

A complete parts listing is included with Mouser Electronics (www.mouser.com) part numbers. Mouser is not the only source for the parts; in fact the parts are readily available from most electronic parts supply companies. Operation: Connect a 9-volt radio battery to the battery connector and a stereo headset to the speaker jack. You should hear a hissing noise if your receiver is working. Tune the receiver by adjusting C2 with a non-ferrous tool. C1 can be used to fine-tune the circuit or to shift the tuning range of C2 (increase the capacitance of C1 if you want to receive FM broadcast below 107 MHz). With C1 In its highest capacitance position C2 will tune the receiver through the lower portion of the aircraft band and the top portion of the FM broadcast band. With C1 in its lowest capacitance position C2 will tune the receiver through the aircraft band and a little higher. C2 is at its highest capacitance when the small dab of solder on the top of C2 is lined up with the middle pin. A good way to set the receiver to receive a signal from a 108 MHz transmitter like the FM108 tracking transmitter is to set C2 slightly to the right of its highest capacitance and then tune C1 until you hear the signal from the 108MHz transmitter. Listening to the aircraft band You may have to tune around a bit and listen for a while before hearing any aircraft transmissions. Pilot communications are generally short and to the point. Transmission is limited to a few seconds. Since VHF communications are “line-of-sight” you will be able to hear aircraft at 30,000 feet a100 miles away or more but may not be able to hear the control tower that is only 10 or 20 miles away if your view is obstructed by buildings or hilly terrain.. One thing to watch out for is strong local signals. The received signal may be garbled if the signal is too strong. This is usually the case when tuning FM broadcast band stations. To remedy this problem turn the sensitivity to its lowest point and put the antenna in the down position.

Radio Tracking the FM108 transmitter Hold the radio with the antenna fully extended against the front of your body shielding the antenna with your body. Slowly turn while listening to the “beeping” signal from the FM108 transmitter. The beeping will be the loudest when you are facing the transmitter. If the “beeping” is loud when facing all directions then lower the antenna to the point where you can barely hear the signal when facing in one direction. Continue to reduce the length of the antenna as you approach the transmitter. Why doesn't the VHF1 receiver use a directional beam or yagi antenna?? A directional beam antenna for this frequency would be to large for field work. Such an antenna would be over four feet wide and would present a considerable problem moving through brush and trees. The relative short telescoping antenna when shielded by the operator’s body works

very effectively for direction finding and is relative easy to work through heavy brush and trees. This technique is sometimes referred to as "Body Fade" and it produces a cardioid sensitivity pattern (see picture). The peak null position is exactly 180 degrees opposite the transmitter. As mentioned above, the operator should take a reading by holding the receiver against their stomach (the edge of the receiver opposite the antenna should be touching the stomach area). The antenna should extend vertically and be about 6 inches in front of the face. Turn slowly listening for the strongest signal (loudest beeping). Move in the direction of the strongest signal (opposite the direction of the weakest signal). Periodically stop and take another reading, adjust the course and continue to work towards the transmitter. Since the “null” point is much narrower than the maximum signal point it may be easier to use the “null” point to establish the most accurate direction to the transmitter. With a little practice a person can become quite efficient in locating the transmitter although the path taken will be somewhat zigzagged. Receiver pattern

schematic

parts Component

Mouser Part Number

Component

Inductors:

Mouser Part Number

Resistors:

L1

.12 uH coil

70-IM2-.12

R1

680 ohm

291-680

L2

.15uH

Air wound; 1.5 turns on 3/8 form #26 insulated wire

R2

33K

291-33K

L3

.68 uH coil

70-IM2-.68

R3

50K pot

323-409H-

50K

L4

.82 uH coil

70-IM2-.82

Capacitors:

R4

10K

291-10K

R5

6.8K

291- 6.8K

R6

5K pot

323-409H5K

R7

10 ohm

291-10

C1

2 - 5 pF trimmer

659GKG5R016

C2

2.5-12 pF trimmer

242-3810-12

C3

22pF

21RD722

Q1

NTE 108 Transistor

526-NTE108

C4

6.8pF

140-500N26R8D

IC1

LM386

513NJM#386BD

C5,C11

.002 uF

140-CD50V2202Z

C6

.001 uF

140-50Q5102Z

Additional:

C7

1uF

80T350A105K025

PCB

C8

1000 uF

140XAL10V1000

J1

stereo jack

161-3504

C10

..047 uF

581SA105E473M

H1

battery clip

534-071

C9

omit

not used

S1

battery snap

12BC005

Semiconductors:

C12

10 uF

80T350C106K010

C13, C15

0.1 uF

21RX310

C14

220 uF

140XAL16V220

component placement

mounting

T1

Antenna

43AR106

Screw for antenna

48SM026

Foil side pattern

Reversed foil pattern

return to jerry's home page E-Mail to: [email protected] Copyright ©2002 Jerry Baumeister Revised - 9-23-02