Crystal controlled 147.460 MHz

Crystal controlled 147.460 MHz FM transmitter

The XFM1 transmitter is a crystal controlled tone modulated FM transmitter designed for model rockets but suitable for wildlife, balloons and many other applicaTIons requiring a small, frequency stable FM transmitter. Use this transmitter with a scanner or 2 meter amateur radio receiver. Transmitter ground range is approximately 400 yards (5 feet above ground). Field tests were done with a ICOM IC-W32A transceiver with 0.16 micro volts of receiver sensiTIvity through the standard 8 inch antenna. Air to ground transmissions can improve range significantly as will a direcTIonal high gain antenna or a more sensiTIve receiver.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: 3 days (two CR1632 batteries in series)
Receiver Type / requirements: FM, 144.455-147.460 MHz., 0.16microvolts sensitivity or better
Receiver Antenna: directional antenna recommended but not required.
Other: Knowledge of radio direction findingTRANSMITTER
The transmitter is a crystal controlled 147.460 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 ”49.39 Mhz (3rd over tone), However, custom crystals can be used if other frequencies are desired. If other frequencies are desired a 3rd overtone series crystal can be ordered from a crystal manufacture. Microprocessor
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 .Power Supply
The transmitter is powered by two (2) 3 volt lithium “button” batteries type BR1632 or CR1632. Average battery life is 3 days of continuous operation. AntennaThe transmitter antenna is 12 inches of 20 to 24 gauge common "hook-up" wire. The range of the transmitter can be doubled by attaching a wire (counterpoise) of the same length as the antenna from the positive supply extending in the opposite direction of the antenna. Both the counterpoise and the transmitter antenna can be coiled on a 1/2 to 3/4 inch diameter to shorten the length of the antenna and to allow storage inside a payload compartment. Coiling the antenna does shorten the range of the transmission. A method that works well in most cases is to suspend the module from the nose cone by the coiled counterpoise, and extend the transmitter antenna into the payload compartment or out the bottom of the payload compartment and along side the fuselage. The coiled counter poise provides a shock absorbing function during lift-off. Construction: Construction of the telemetry transmitter is straightforward. 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.

Note: There are 8 solider pads that are not drilled (have no holes). These pads are for use by anyone that would like to extend the design of the transmitter through their own experimentation and programming. These pads provide easy access to the other pins on the PIC chip and can be programmed for analog inputs or Digital I / O by the knowledgeable experimenter. If you are not interested in experimenting with the programming you can use the circuit as-is in the basic tracking mode.

Testing:

Coating the circuitIf the transmitter is to be exposed to the environment or hot ejection gases it needs to be coated with a protective coating of polyurethane. The circuit board and all the components with the exception of the battery and the battery terminal should be coated with 2 coats of polyurethane to protect the circuit from environmental factors. OperationHave 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. Ins tructions for building two good inexpensive RDF Yagi type antennas can be found at http: //Articles/uhf.htm and http://home.att.net/~jleggio/projects/rdf/tape_bm.htm. The first one was designed by Kent Britain, WA5VJB and the second one was designed by Joe Leggio, WB2HOL. You might also need an RF attenuator for when you get close to the transmitter (check Joe's attenuator plans at http://home.att.net/~jleggio /projects/rdf/p_atten.htm) Body Fade: If you use your body to shield the receiver's monopole antenna a cardioid sensitivity pattern (see picture) is achieved. The peak null position is approximately 180 degrees opposite the transmitter location. (Note that the patterns are not always as shown. They can vary depending on the antenna, the way it is being held and objects in the area that may reflect the signal). operator should take a reading by holding the receiver close to their stomach The antenna should extend vertically and be about 6 inches in front of the body. Turn slowly lis tening for the strongest signal (loudest beeping) or highest reading on the "S" meter. 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.





Directional Beam antenna: A “beam” or “Yagi” antenna is probably the simplest and best all around choice for a directional antenna. A simple 3 element antenna can be built for about $ 10.00 using common materials. The sensitivity pattern shown below is when both the transmitter and receiving antenna is polarized vertically (the elements are pointing up and down). If the antenna of the transmitter are not vertical then the pattern will be different unless the receiving antenna is orientated to match the transmitter antenna. Since the transmitter antenna's orientation is not always known some experimentation must be done with the receiving antenna. (Note that the patterns are not always as shown. They can vary depending on the antenna, the way it is being held and objects in the area that may reflect the signal) .Practice helps a lot!

To achieve adequate performance you will need a receiver with at least 0.16 micro volts of sensitivity. Most 2-meter Amateur (ham) radios are at least this sensitivity. Scanners may or may not be sensitivity enough.

Component Side View



reversed foil side

2 "x 0.65"

foil side

Transmitter parts

Via In Pad PCB
What is Via In Pad? In shortly,via in pad is the via holes are at the SMD pad.The vias are very small,usually under 0.3mm.Why and how? First is there is no enough space to layout,you have to put the vias and holes closer even together.Second it helps thermal management and for high frequency boards,it may help improve signals.
Because the SMD pads are for SMD components loading,so the solder can not flow to inner layer or the other side when assemble.That is the most important for via in pad board.
How PCB manufacturers like us to do via in pad board? We will fill all vias with non-conductive epoxy and plate copper over it ,so the vias are flat same as others. Many PCB factories are unable to do such capability.
The key technology is how we fill vias and guarantee there is no any solder (surface finishing) in the holes.
Filled via in pad is a way to achieve intermediate density with an intermediate cost compared to using blind/buried vias. Some of the key advantages associated with using the via in pad technology are:
.Fan out fine pitch (less than .75mm) BGAs
.Meets closely packed placement requirements
.Better thermal management
.Overcomes high speed design issues and constraints i.e. low inductance
.No via plugging is required at component locations
.Provides a flat, coplanar surface for component attachment
Via in big pads are not a big problem.but for BGA,that is technology.As BGA pads are very small,10mil or 12mil,and there is no enough space.Manufacturing is not easy as other boards.

Via In Pad PCB

Via In Pad PCB,6Layer Via In Pad PCB,Touch Pad PCB,Via In Pad

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