Tracking Transmitter XFM1
Crystal controlled 147.455 MHz FM transmitter
updated 3-5-2015

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• General Specifications:
  Frequency: 147.455 to 147.460
  Mode: FM  
  Size: 2 .75 "x 0.5"
  Weight: 8 grams (.3 oz) including battery
  Range (ground): 400 yards with counterpoise
  Frequency control: Crystal
  Battery life:4 days (two CR1632 batteries in series)
  Receiver Type/requirements: FM, 144.455 - 147.460 MHz., 0.16 microvolts sensitivity or better
  Receiver Antenna: directional antenna recommended but not required.
  Other: Knowledge of radio direction finding

TRANSMITTER
The transmitter is a crystal controlled 147.455 MHz FM transmitter.  The transmitter is tone modulated by a 12F675 microprocessor approximately every two seconds. A Morse code call sign ID is transmitted approximately every 30 seconds. If a call sign has not been specified it will transmit “XFM1”.  The transmitter is turned off between tone bursts which greatly extends the battery life. The circuit is designed to use a low cost “computer crystal” 49.152  Mhz (3rd over tone), However, custom crystals can be used if other frequencies are desired. If other frequencies are desired a 3^rd overtone series crystal can be ordered from a crystal manufacture.

Microcontroller
The transmitter is controlled by a program running on a PIC12F675 micro-controller.  It generates the "beep" tones approximately every 1 to 2 seconds an a station ID every 16 "beeps".  If no call sign is designated it transmits "XFM1".
The source code is available at www.jbgizmo.com .  The programmed  PIC 12F675 microcontroller is included with the kit or can be ordered separately (X!-PIC) .

Power Supp
The transmitter is powered by two (2) 3 volt lithium “button” batteries type BR1632 or CR1632. Average battery life is 4 days of continuous operation.

NOTE: Be aware that the small size of the circuit requires that GREAT CARE be taken to prevent solder bridges when soldering. Use a 20 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 Side View" 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. Trim all excess leads immediately after each component installation

1. If the crystal is not already installed on the printed circuit board (PCB), solider the crystal in place. If the crystal is not installed then carefully straighten the leads to match the holes in the PCB. The leads should be perpendicular to the base when properly bent. Bending the leads more than twice will cause the leads to break and the crystal will need to be replaced.
2. Solider the 8 pin DIP socket in the location marked as “IC1”. Position the notch end of the socket towards the battery end of the PCB.
3. Solder R1, 10K ohm resistor (brown/black/orange) resistor in the place shown.
4. Solder R2, 100K ohm (brown/black/yellow) resistor in the place shown.

   If you want to trade battery life for power output, substitute a 10Kohm resister for R2 (included with kit).  If you do this you will need to also add the extra 15pf capacitor as shown on the parts placement diagram (below).

   If you are unsure which you will prefer just install the 100K ohm resistor as described on step #4 and then install the 10K ohm resistor on the foil side of the board in parallel with the 100K ohm resistor.  You can easily remove the 10K resistor should you decide you need a little less power and a little more battery life after you make your tests.  You will still need to install the extra 15pf capacitor.

    

5. Solder C1, .001 microfarad capacitor in place (may be marked as 102)
6. Solder C2, the 22 picofarad capacitor in place (may be marked as 22)
7. Solder C3, 15 picofarad capacitor in place (may be marked as 150 or 15)
8. Using one of the trimmed off leads from the previous component installations solder a jumper at location marked J1.
9. Solder L1, 0.63 microhenry coil in place
10. Measure 3.25” of 22 gage magnet wire. Using a knife carefully scrape the lacquer from the ends of the coil for about 1/2 inch. Next construct the coil (L2) by close winding 4 turns of the magnet wire on the shaft of a 1/8" drill bit shaft (or similar size form) and then slide the coil off of the drill bit shaft or form. The coils should be tightly wound. Solder this coil in place at location L2 making sure that the solder adheres to the bare portion of the magnet wire..
11. Remove the emitter from the NTE108 transistor (if not already done)
12. Solder Q2, NTE108 transistor, in the place indicated. Note the orientation of the case on the diagram.
13. Solder Q1, NTE107 transistor, in the place indicated. Note the orientation of the case on the diagram.
14. The battery holder consist of two jumpers, made from the trimmed off resistor leads, soldered flat against the component side of the circuit board. These two jumpers form the negative battery terminal. The positive battery terminal is made from a small metal paper clip and arches over the top of the batteries. The depth of the arch should just be high enough to allow two 3-volt lithium coin batteries to fit under it. After the “hold down wire” is soldered in place the top portion can be crimped as shown in the “Component Side View” to increase the tightness of the holder.
    Solder the two negative battery contact jumpers as shown (using leads from the previous component installations ).
    Before Soldering  the “hold down wire” remove 1/4 inch of insulation from one end of the antenna wire and the counterpoise wire and slide them over the vertical portion of the hold down wire (see diagram). This will form an insulating sleeve and keep the bottom battery positive terminal from touching the metal.  Then solder the hold down wire in place as shown.
15. Install the antenna. Remove 1/2 inch of the insulation from one end of a 12.5” wire and feed through the hole in the circuit board as indicated. Wrap the circuit board end of the antenna around the edge of the circuit board and twist it around itself on top of the circuit board. Solder the antenna to the circuit board and where it is twisted together.
16. Install the counterpoise in the same manner as the antenna wire from the location indicated (opposite end of PCB from antenna).
17. Install the IC1 (PIC12F675) into the 8 pin DIP socket. Insure that the notched end of the IC is facing the battery end of the board.
18. Install the batteries by stacking two BR1632 or CR1632 batteries under the battery “hold down wire” with the positive side facing up. When you are operating the transmitter on a mission you will need to secure the batteries with several wraps of tape to insure that the batteries do not jar lose during launch or recovery.

NOTE:  In some circuits the transmitter will not turn off after "beeps" or after completing the call ID.  This condition can be corrected by adding a 15 pF capacitor at the location marked on the parts placement diagram( parallel to L1 and C2).  Holes are provided for this installation.  This condition can also be caused if the bottom battery touches the battery hold down wire.  Make sure the battery hold down wire's vertical length is insulated as instructed.

1. Install the batteries. Two 1632 batteries stacked with positive (+) side up. Confirm operation of transmitter. Note that due to variations in crystal frequency the actual frequency of the transmitter will be in the range of 147.455 and 147.560 Mhz.
2. Further secure the battery by securing it to the PCB with several wraps of electrician’s tape.
3. Verify operation.
4. Stand in the middle of an open short grassy area. Swing the transmitter by the antenna and throw it in the air (straight up).
5. Verify that the transmitter functions throughout the flight and after bouncing on the ground.
6. If transmitter still functions it is ready for use in model rocket tracking.
7. The two most common problems encountered in the test are.
   *Poor battery connections. Make sure the battery clip is slightly bowed and firmly against the
     battery terminal. 
   *Antenna wire not soldered to the circuit board adequately (cold solder joint).

Have someone hide the transmitter and practice finding it before you use it on a mission. Note: there are several good references for radio direction finding (RDF) that you may want to read. The ARRL Handbook has a chapter on RDF and can be found in most public libraries. Transmitter Hunting, by Joseph Moell, K0OV and Thomas Curlee, WB6UZZ is also a good book on the subject. Both books can be bought from Amazon.com.

Radio direction finding is best accomplished by using a receiver with a directional antenna like a “beam” or “Yagi“antenna, however a monopole antenna can be used by employing the “Body-Fade” method. Instructions for building an inexpensive RDF Yagi type antenna can be found at  Joe Leggio's (WB2HOL) web site.  You might also need an RF attenuator for when you get close to the transmitter (check Joe’s attenuator plans).

Practice helps a lot!

Receivers

Component Side View

                                reversed foil side                                                     foil side 

       2" x 0.65"