The Transmitter Palace

Wireless FM Transmitter

Mon, 20 Apr 2009 05:19:00 +0000

This wireless FM transmitter is designed to use an input from another sound source and transmits on the commercial FM band. This low power fm radio transmitter it is actually quite powerful. The first stage is the oscillator, and is tuned with the variable capacitor. Select an unused frequency, and carefully adjust C3 until the background noise stops (you have to disable the FM receiver’s mute circuit to hear this).

Power Supply with Over Voltage Protection 10A 13.8V

Wed, 07 Jan 2009 11:36:00 +0000

This power supply circuit will give 10 amps (12 amps surge) with performance that equals or exceeds any commercial unit. The circuit even has a current limiting feature which is a more reliable system than most commercial units have. Just like other commercial units, this circuit uses the LM723 IC which gives us excellent voltage regulation. The circuit uses 3 pass transistors which must be heat sinked. Resistor R9 allows the fine tuning of the voltage to exactly 13.8 volts and the resistor network formed by resistors R4 through R7 controls the current limiting. The LM723 limits the current when the voltage drop across R5 approaches .7 volts. To reduce costs, most commercial units rely on the HFE of the pass transistors to determine the current limiting. The fault in that system is that the HFE of the pass transistors actually increases when the transistors heat up and risks a thermal runaway condition causing a possible failure of the pass transistors. Because this circuit samples the collector current of the pass transistors, thermal runaway is not a problem in this circuit making it a much more reliable power supply. The only adjustment required is setting R9 to the desired output voltage of anywhere between 10 and 14 volts. You may use a front panel mounted 1K potentiometer for this purpose if desired. Resistor R1 only enhances temperature stability and can be eliminated if desired by connecting pins 5 and 6 of IC-1 together. Although it really isn't needed due to the type of current limiting circuit used, over voltage protection can be added to the circuit by connecting the circuit of Figure 2 to Vout. The only way over voltage could occur is if transistors Q2 or Q3 were to fail with a collector to emitter short. Although collector to emitter shorts do happen, it is more much more likely that the transistors will open up when they fail. I actually tested this and purposely destroyed several 2N3055's by shorting the emitters to ground. In all cases the transistors opened up and no collector to emitter short occurred in any transistor. In any event, the optional circuit in Figure 2 will give you that extra peace of mind when a very expensive radio is used with the power supply. The circuit in Figure 2 senses when the voltage exceeds 15 volts and causes the zener diode to conduct. When the zener diode conducts, the gate of the SCR is turned on and causes the SCR to short which blows the 15 amp fuse and shuts off the output voltage. A 2N6399 was used for the SCR in the prototype but any suitable SCR can be used. While over voltage protection is a good idea, it should not be considered a substitute for large heat sinks. I personally feel the best protection from over voltage is the use of large heat sinks and a reliable current limiting circuit. Be sure to use large heat sinks along with heat sink grease for the 2N3055 transistors. You will used this power supply on all kinds of transceivers from HF, VHF to UHF with excellent results and absolutely no hum. This power supply will be a welcome addition to your shack and will greatly enhance your knowledge of power supplies. Check out 2 Transistors Voice Transmitter Check this out Build A 10 Amp 13.8 Volt Power Supply [...]

900 MHz Directional Antenna

Wed, 12 Nov 2008 19:01:00 +0000

This is the Japanese Yagi antenna that said Yagi antenna. It is a simple system of high-gain directional antenna, Yagi antenna classical structure, the following chart.

Simple VHF SWR Protection Circuit

Tue, 11 Nov 2008 06:35:00 +0000

Here is a simple SWR protection circuit you can easily build. The directional coupler and detector components are from an old VHF SWR meter.You may want to replace the meter's existing RF bypass Capacitors with higher quality (mica) ones. You may also want to replace the line coupler's termination Resistors which higher wattage ones. Be sure to use the exact same value, or the SWR meter will be inaccurate. Also, be sure to use non-inductive Resistors (carbon-film or metal-oxide will work). This then feeds to all LM3914 bargraph display to light the LEDs, indicating the current SWR ratio. SWR When the ratio reaches approximately 3, it will engage the relay, cutting off the RF input to the power amplifier . You could also just a LED light or sound an alarm if you want to. You should compare the circuit schematic above to this one below : Visit this links for more, 4W FM Transmitter Directional Coupler with RF Filter for 88-108 MHz - 100w LCD PIC16F88 SWR Meter for VHF- UHF and click this link for building: The Windows ® program for drawing analog meter scales. [...]

Making 1 to 4 Balun for Matching Impedance

Wed, 24 Sep 2008 09:16:00 +0000

Here's the way to match 75 Ohm to 300 Ohm impedance. In case of making balun for 200-300 Ohm folded dipole antenna to 75 Ohm transmission cable.

40W Broadband FM RF Power Amplifier

Tue, 23 Sep 2008 08:57:00 +0000

Here's broadband RF power amplifier for FM amplifier design is based on Motorola MRF171A MOSFET. The amplifier was constructed in a small aluminium diecast box. RF input from transmitter and output connections are made by coaxial sockets. The power supply is routed through a ceramic feedthrough capacitor bolted in the wall of the box. This constructional techniques results in excellent shielding, preventing RF radiation escaping from the amplifier. Without it, significant amounts of RF radiation could be radiated, interfering with other sensitive circuits such as VCOs and audio stages, also significant amounts of harmonic radiation could occur. Any RF power amplifier must be followed by a low pass filter (LPF) to reduce the harmonics to an acceptable level. What this level is in a unlicensed application is a moot point, but as the output power is increased, more attention must be be paid to the harmonic suppression. In this RF power amplifier design used a 7 pole Chebyshev low pass filter. A Chebyshev was chosen as the phase and amplitude ripple within the passband was not critical, and the Chebyshev gives a better stop band attenuation than compared to say, a Butterworth. The design stopband was chosen to 113MHz, giving a 5MHz implementation margin from the highest desired passband frequency at 108MHz and the start of the stopband at 113MHz. The next critical design parameter was the passband ripple. For a single frequency design it is normal practice to choose a large passband ripple, for example 1dB, and tune the peak of the last passband maxima to the desired output frequency. This gives the best stopband attenuation because greater passband ripple results in more rapid stopband attenuation. A seven pole filter has 7 reactive elements, in this design four capacitors and three inductors. The more poles, the better the stopband attenuation, at the expense of increased complexity and more passband insertion loss. An odd number of poles is required as both the input and output impedance was designed to be 50R. 40W Broadband FM RF Power Amplifier [...]

250W Power Amplifier with the BLF548 for 100 - 450 MHz

Fri, 29 Aug 2008 19:10:00 +0000

The BLF548 is a balanced N-channel enhancement mode vertical D-MOS transistor in a SOT262 package, especially designed for use in wideband amplifiers up to 500 MHz. The transistor is capable to deliver 150 W nominal output power at a supply voltage of 28 Volts. Due to the low output capacitance the attainable bandwidth will exceed 300 MHz.

25-200 MHz Wireless Frequency counter

Wed, 23 Jul 2008 11:54:00 +0000

This frequency counter has 6 digits and will work from 25MHz up to 200MHz that you don't need to connect it with any wires to your equipment. Wires-interference and drift in the oscillation frequency. This counter use a small pick up coil to probe the oscillation. Just hold the pickup coil a few cm from the main oscillator coil and read the LED. The LED has 6 digits and the resolution is set to 1kHz. Schematic of Wireless Frequency Counter The hart of this project is the PIC processor. To this processor is 6 LED display connected. The info on the LED is scanned so only one LED is lightning at a time, but your eyes will see it as all LED are lightning at the same time. I use a sensitive prescaler which divide the signal with 64. The output of the prescaler is then connected to a counter input of the PIC processor. Prescaler You can use almost any prescaler on the market in this construction. I have found a prescaler called SP4633. It is a quit good one. High sensitivity and no self-oscillation. The prescaler use a small pickup coil to probe the RF signal. The pickup coil is made of a wire with two turns. A small portion of the oscillator signal will be picked up by this coil and amplified in the prescaler. The prescaler will also divide the input frequency with 64 and output the signal to pin 6. A NPN transistor is buffering the signal and amplify it to square wave shape and then the signal enter the PIC-processor. PIC-processor So how does it all work? Imagin you have a 200MHz oscillator. The prescaler picks up the signal and divide it to 200*106 / 64 = 3.125MHz output signal. Inside the PIC at RC0 is a 16 bit counter. This counter is first reset and then it counts during 64mS. If the frequency was 3.125000MHz during 64mS, the counter will reach 200.000 which will be presented to the display. The resolution will be 1kHz which is good enough for a handheld wireless frequency counter. Of course one can make the counting time longer and thereby get more digits, but I seldom need more than 1kHz resolution. Building and Testing  It is not a difficult project to build, but before you add the prescaler you should test the counter function. I used a external oscillator for this. See picture at right. The pic show you a crystal controlled oscillator. I use a 3.579545MHz crystal. Then I connected the output of the oscillator (pin 9) to the RC0 of the PIC (pin 11). If I use a 3.579545MHz and it simulate a division by 64 it means that the LED display should show 3.579.545 * 64 = 229.091MHz. If you don't have a 3.579545MHz crystal you can use any one from 1-to 15MHz, you will have to calculate so the output frequency is about 1 to 4MHz of the oscillator. Just multiply the frequency with 64 and read the display. Simple way to test the construction. The 64mS counting time in the processor is set by the software and is based on the crystal frequency at 18.432MHz. If you don't have this crystal you can use any crystal from 10 to 20MHz, but a small change of software must be done. I can help you with this, just mail me. Download PIC16F870 program (INHX8M format) fcount.zip 18.432 MHz Crystal - PIC program frequency counter. fcount2.zip 20.000 MHz Crystal - PIC program frequency counter. Source [...]

4 Watt PLL FM Transmitter

Sat, 12 Jul 2008 11:21:00 +0000

Here's a Phase Locked Loop (PLL) FM transmitter circuit with high gain amplifier on the final stage. If the unit is to be used with a stereo encoder, the pre-emphasis must be disabled. The audio input network has a potentiometer to set the audio level and jumper selectable pre-emphasis. The PLL FM transmitter uses the standard PLL architecture. The PLL error voltage is summed at the input of the audio buffer, which is implemented by a BC558 transistor. The PLL error voltage enables the RF output frequency to be locked to the frequency of a stable crystal reference oscillator. The summed PLL error voltage and audio modulation voltage is applied to the VCO by means of a dual varicap diode. The voltage controlled oscillator (VCO) of the PLL FM Transmitter is based on a novel double-ended architecture operating at half the output frequency. The variable trimmer VC1 sets the centre frequency of the VCO - more of this later. An RF sample is taken from the VCO (still at f/2) to the PLL. The VCO receives its power from a separate zener-stabilised supply rail. The PLL programmable divide chain is implemented by a handful of 74LS logic (74ALS for the first divide), rather than using a synthesiser chip. Download PLL FM Transmitter User Manual in pdf format : 1 2 3 4 5 6 7 8 9 10 11 [...]

Broadband RF Amplifier For TV Transmitter 5W

Sun, 15 Jun 2008 05:10:00 +0000

This Broadband RF amplifier is for driving small UHF TV transmitters, with gain is 7dB and can amplify a signal between 470-860 MHz. Drive input the circuit with 1 to 1,5 Watts signal. Better use double layer PCB with the second layer connected to earth.

RF Power Amplifer for UHF TV Transmitter #2

Sun, 15 Jun 2008 04:58:00 +0000

from RF Power Amplifer for UHF TV Transmitter #1 MECHANICAL MACHINING OF THE HEATSINK The raised edges at the top side of the heatsink have been removed because the printed circuit board has a width of 113 mm (see Fig.3). To fit the heatsink to the printed-circuit board the following machinings have been carried out: Rectangular holes of 2.8 mm deep have been mould in the heatsink because the transistor leads have to be soldered on the printed-circuit board. Also it was necessary to make avings of 4 mm wide and 0.6 mm deep at the positions of the straps on the printed-circuit board. The transistors have been fastened with M 2.5 screws in the heatsink (see Fig.4). To achieve that the printed-circuit board lays tight to the heatsink also savings have been made in the heatsink on the spots of the 8 rivets through the printed-circuit board. For fastening the printed-circuit board on the heatsink on 7 places, holes with M 3 screwthread have been made in the top side of the heatsink, corresponding with indicated holes in the printed-circuit board. The two hybrid couplers also have been fastened in the heatsink with screws through the printed-circuit board. Therefore 8 holes have been made with M 2.5 screwthread, corresponding with the printed-circuit board. The input and output connectors have been fastened to the heatsink with M 3 screws. The mid contact of each connector makes contact with the printed-circuit board. CONCLUSIONS With the construction of the BLV57 amplifiers a good thermal resistance (0.2 °C/W) has been achieved by means of a forced air-cooling. Attention has been payed to a good mechanical contact between heatsink and printed circuit board and a good ground contact on the printed circuit board by means of rivets and straps at the edges and under the emitter leads. (datasheet) [...]

RF Power Amplifer for UHF TV Transmitter #1

Sun, 15 Jun 2008 04:55:00 +0000

INTRODUCTION The construction taken from the application report NCO8101 two amplifiers for band 4/5 with BLV57 transistors have been described. Reactions on this report proved the necessity to give more information about the construction of these amplifiers. This construction has been based on a heatsink with a printed-circuit board at the upper side and the bias circuits and a forced air-cooling at the lower side. PRINTED CIRCUIT BOARD In the printed-circuit board rectangular holes have been made to mount the BLV57 transistors on the heatsink. For fastening of the printed-circuit board on the heatsink by means of screws, 7 holes of 3.1 mm Æ and for fastening of the hybrid couplers 8 holes of 2.6 mm Æ have been made on the indicated places (see Figs 1 and 2). Hereby has been taken into account the use of Anaren hybrid couplers, type 10264 - 3, suited for the frequency range of 500 - 1000 MHz. Because the 2 bias units have been situated at the lower side of the heatsink, the connections from these units to the circuit take place through the printed-circuit board and the heatsink. For this purpose 9 holes of 2 mm Æ are necessary (4 collectors, 4 bases and 1 ground). To make a good ground contact between the upper and the lower side of the printed-circuit board the following measures have been taken: On 8 spots rivets have been used and soldered at both sides to the metallization of the printed-circuit board. The holes of 2 mm Æ , needed for these rivets, have been situated as indicated in Figs1 and 2. Copper straps with a thickness of 0.2 mm have been soldered at all edges of the printed-circuit board. A good emitter to ground contact has been achieved by soldering 8 copper straps from the upper to the lower side of the printed-circuit board on the spots of each emitter lead. The input connector and the output connector have been screwed to the heatsink but the ground also has been soldered to the printed-circuit board. HEATSINK For the BLV57 amplifiers, described in report NCO8101, a blackened heatsink of Seifert Electronic, type KL-117 with a length of 191 mm has been used (see Fig.3). At the lower side forced air-cooling has been applied with a fan trade mark Etri, type 99 XU 01 - 81 with an air displacement of 16 litres per second). By applying this air-cooling the thermal resistance decreased from 0.5 °C/W to 0.2 °C/W. (datasheet) Continue : RF Power Amplifer for UHF TV Transmitter #2 [...]

Broadband RF Amplifier For TV Transmitter 14W #2

Sun, 15 Jun 2008 04:46:00 +0000

BIAS CIRCUIT
From Broadband RF Amplifier For TV Transmitter 14W #1
Below is the RF power amplifier's components part list and bias circuit for supply feeding.

Broadband RF Amplifier For TV Transmitter 14W #1

Sun, 15 Jun 2008 04:39:00 +0000

This RF power amplifier works in frequency 470 - 860 MHz UHF Band IV and V with power out 14 Watts with input power 1.5 Watts. The power amplifier is suitable for amplifying rf signal your tv transmitter with 0.5 - 2 watts power output.

Broadband UHF Power Amplifier For TV Transposers 3W

Sun, 15 Jun 2008 04:33:00 +0000

A Broadband RF Amplifier design is presented, suitable for application in TV transposers, operating in UHF band IV and V(470 - 860) MHz, with simple printed circuit board.

Broadband RF Amplifier For TV Transmitter with BLV859

Sun, 15 Jun 2008 04:26:00 +0000

A broadband rf amplifier design is presented, suitable for application in TV transposers operating in band IV and V (470 to 860 MHz). The design is based on two BLV859 bipolar transistors combined with quadrature hybrids. Typical results at the recommended class-A bias point (25.5 V/9.1 A) for the total module include 40 W peak sync output power at -54 dB three tone IMD level (fvision = -8 dB, fsound = -10 dB, fsideband = -16 dB) and an average gain of 10.5 dB in the (470 to 860) MHz range.

Broadband RF Amplifier 100W for TV Transmitter

Sun, 15 Jun 2008 04:16:00 +0000

The TV rf power amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from band IV - V in UHF. The amplifiers circuit of the input and output matching networks contain mixed microstrip-lumped elements networks to transform the terminal impedance levels to approx. 25 W balanced. The remaining transformation to 50 W unbalanced is obtained by 1 : 2 balun transformers. The baluns B1 and B2 are 25 W semi-rigid coax cables with an electrical length of 45° at midband and a diameter of 1.8 mm, soldered over the whole length on top of microstrip lines. To keep the circuit in balance two stubs L1 and L8 with the same length have been added. For low frequency stability enhancement the input balun stubs are connected to the bias point by means of 1 W series resistors. Large capacitors (C4 and C11) are added at the biasing points to improve the amplifiers video response.(in datasheet) Printed Circuit Board (PCB) The printed-circuit board laminate utilised is PTFE-glass with an er = 2.55 and a thickness of 0.51 mm (20 mills). A complete TV transmitter amplifier has been designed and characterised based on the BLV861, capable of operating in full band IV and V with flat gain and high output power in class-AB. BLV861 is able to generate 100 W CW power and a power gain compression below 1 dB in band IV and V. Overall gain of the amplifier is >8.5 dB and an efficiency of ± 55%. TV-measurements have been carried out showing a 1 dB compression point above 120 W PO, SYNC at VCE = 28 Vand 150 W at VCE = 32 V. Amplifier shows an agreed linearity performance in class AB operation both under two tone and three tone conditions. Biasing the amplifier at a VCE = 32 V results in a higher output peak sync power and a better linearity response. [...]

Broadband RF Amplifier 470-860 MHz with BLW32-33

Sun, 15 Jun 2008 03:55:00 +0000

This Broadband RF Amplifier for 470-860 MHz taken from Philips Aplication Note (AN_BLW32_33). Please download file in PDF format.The broadband rf amplifier for TV Transposer band IV/V designed with transistor BLW32 and BLW33. In this case, my RF Amplifier design replaced them with 2 pieces BLW34 have good result.

FM RF Power Amplifier For FM Broadcast 40W

Mon, 09 Jun 2008 11:22:00 +0000

This amplifier was built based on Marconi's website, A Design for a 40W broadband VHF RF Power Amplifier for FM broadcast. A few minor tweaks were made to the schematic and a few parts were changed to what I had available (mostly surface mount components). The heatsink is from an old Motorola Mostar 800 MHz radio, and has the perfect heatsink island to match the MRF171A. Also used is a Progressive Concepts external LPF7002 low pass filter because it was also on hand. Since the MOSFET uses 28 VDC, I had to homebrew a 28 Volt / 5 Amp power supply using the schematic found in the ARRL handbook.

FM Power Amplifier 1.2W

Mon, 09 Jun 2008 11:03:00 +0000

The following is a very easy to build amplifier that was designed to follow a Ramsey FM-10 and FM-25 transmitter. It is built on top of a simple PCB board surface style (all parts tacked on top, no holes in PCB.) The performance is excellent with power levels of up to 1.5 watts acheivable and harmonic suppression greater than 50db. Using this amp in conjunction with an Ramsey FM-10/25 can provide you with the ideal micro power radio station with usable range of up to 2 miles or more. If you use this unit to amplify a Ramsey FM-25, build the FM-25 in the low power output configuration. I feel this is a much better alternative than the Ramsey LPA-1 because it provides much lower harmonic output and it is relitivly bullet proof to antenna mismatches which has been known to destroy LPA-1s without the slightest warning. The PCB board is a single sided copper board etched or grinded out to the shown layout. The board size is 3 3/8" x 1 3/8" but anything close that can accomidate the parts without any lengthing of the lead lengths is fine. I recommend that if you don't have a good way to make the PCB that you buy the Radio Shack PCB Etching Kit, this kit works very well for this type of application. We've used laser printer iron ons for this board, but we've found that electrical tape or the resist pens work fine. Design and Schematic: Old Schematic New Schematic The amplifier is a 2 stage design. The first stage uses a high gain microwave transistor amplifier running class-A to boost a 10mw signal to about 150mw. In the first stage the resistor R1 (1.5K) gives Q1 (mpf-901 or mrf-901) and the Ramsey transmitter a nice stable input/output load to look at that should smooth out missmatches between the transmitter and the amp (note that this type of matching is only workable at flea power levels. Printed Circuit Board (PCB): 3 3/8" x 1 3/8" Construction Tips: Solder all the small low lying parts first; resistors, L3, L4, L5, L6. Then mount all the small capacitors; C5-C10, and C12. Next Q1, C1,C2,C3,C4, followed by L1, L2 and Q2. Finally add C11 and attache the input and output with coax to the connectors and/or transmitter. Part's Layout: For tune up you should simply tune C1, C2, C3, C4 and L1 for maximum output. This amplifier doesn't like to ocsillate, but this is always a possiblility. You can check for oscillation by tuning a FM radio up and down the FM radio band, if you hear multiple images of your broadcast your amplifier is in oscillation (not good). Updates and Modifications I would change the design slightly if I were to build more of these amplifiers. The input is not DC isolated. I would add a .001uh cap between the input and Q1. This is a must do mod if the amp is to be used as a stand alone device (ie not hardwared ont a FM-10). I would get rid of C12, it is not necessary since C2 blocks the DC between stages. I would move C1 to the other side of C3, this allows C2 to be adjusted without effecting the C1/L1 low pass filter. I would add another 5-50pf cap from the input side of L2 to ground, thus adding an extra element and more flexibility to the output/matching filter (I would and have done this addition on every amp that I have built with an output power of under ~3 watts, cannot get -50db down on harmonics without it.) The modifications listed above can easly be made to the existing circuit board if done during the assembly stage. Basically you would shift Q1 and its associated parts one pad to the right on the circuit board (since C12 is no longer necessary), and add a .001uf cap be[...]

MRF317 FM Amplifier Circuit for 88-108 MHz

Mon, 09 Jun 2008 10:52:00 +0000

FM amplifier is used for amplify signal from exciter in broadcast radio station. In this page, RF FM Amplifier uses solid state material with minimum gain 9dB. Input FM Amplifier needs 5-10 watt with power output about 100 watt.

WLAN High Linearity Power Amplifier

Mon, 09 Jun 2008 10:46:00 +0000

The SST11LP12 is a high-power, high-gain power amplifier based on the highly-reliable InGaP/ GaAs HBT technology. The SST11LP12 can be easily configured for high-power, high-efficiency applications with superb power-added efficiency while operating over the entire 802.11a frequency band for U.S., European, and Japanese markets (4.9-5.8GHz). It typically provides 35 dB gain with 16% power added efficiency @ POUT = 23 dBm.

Low Power RF Amplifier for 88-108 MHz

Mon, 09 Jun 2008 10:39:00 +0000

This application use a common NPN RF transistor called 2SC1970. You can also use other transistors like 2N4427 and some others. Check datasheets to se how much power the transistor can handle. 2SC1970 will handle 1.3W and 2SC1971 up to 6W. Most transistor has a power gain of 10dB meaning 10 times power amplification. This is the reason why you must use several stages to achieve a strong transmitter. In this construction we are getting higher power then ever and you must be careful with the transistor. A 50 ohm dummy load MUST be used while testing, else the final transistor will break. An antenna can be used but the antenna must be properly made else the transistor will break. Hardware and Schematic In all RF system and specially in RF amplifiers, it is very important to have a stable power supply and making sure you won't get any RF out on the power line. The Capacitor C12 and C13 will stabilise the DC power supply. L1, C10, C11 and L3 with C8, C9 will also prevent RF from leaking out to the powerline and cause oscillation or disturbances. L1 and L3 should be ferrite chokes or inductance's about 1 to 10 uH. Transistor Q1 will act as a buffer amplifier, because I don't want to load the previous stage to much. The input RF signal is passin C1 and F1 which is a small ferrite pearl where the wire just passing through. F1 with C2 will act as an impedance matching for Q1. F1 can be substituted with a coil as L4, but in my test I found that the ferrite pearls gave best performances. L2 is nit a critical component and any coil from 2-10uH will do the job. Q1 will amplify the input signal from 50mW to about 200mW. Q1 can amplify much more, but It doesn't need to do that because 200mW is good for the final transistor. If you want higher power you can decrease the resistor R2. If you look at Q2 you will also find a ferrite pearl F2 at the base to emitter. This ferrite pearls is to set the DC voltage to zero and be a high impedance for RF signals. I wounded the wire 4 times around this small ferrite pearl. You can substitute it with a coil of 1uH or more. C4, C5 and L4 forms an input matching unit for the transistor. Not much we can do about that… At the output of the final transistor Q2 you will find 2 coils L5 and L6. Together with C6 and C7, they form an impedance unit for the antenna and also for the transistor. Printed Circuit Board (PCB) - Download Above you can download a (pdf) filer which is the black PCB. The PCB is mirrored because the printed side side should be faced down the board during UV exposure. To the right you will find a pic showing the assembly of all components on the same board. This is how the real board should look when you are going to solder the components. It is a board made for surface mounted components, so the cuppar is on the top layer. I am sure you can still use hole mounted components as well. Grey area is cuppar and each component is draw in different colours all to make it easy to identify for you. The scale of the pdf is 1:1 and the picture at right is magnified with 4 times. Click on the pic to enlarge it. RF power This amplifier is based on the transistor 2SC1970 and 2N4427. The output power is about 1.3W and the input driving power is 30-50mW. You can use other transistor as 2SC1971 and get much more output power. 1.3W will still get your RF signal quit far and I advice you to use a good 50 ohm resistor as dummy load. Make sure it can take up to 5-10W, else it will be a hot resistor. You [...]

Telemetry Transmitter for Small Animal

Sun, 25 May 2008 10:30:00 +0000

The goal of this project was to build a small, cheap, light-weight telemetry transmitter to attach to a small animal. This version uses a commercial, low-power transmitter, the Radiotronix RCT-433-AS. The design worked well, but has a relatively high current draw of about 500 microamps. A CR1620 lithium coin cell runs the circuit for about a week. The current version uses a pair of CMOS oscillators to produce a chirp once per second. The circuit shown above has two standard CMOS multivibrators. The second is gated by the first. The duty cycle of the first oscillator is about 1%, or 10 mSec every second. A logic-high at the telemetry transmitter control turns it on. The circuit board was layed out using ExpressPCB software. You will need to download a copy to view the design file. The components are all surface mount. The dots shown below are on a 0.1 inch grid. Note the antenna lead at the lower left. At 433 MHz (70 cm wavelength) a quaterwave antenna should be 17 cm long. The battery is partly shown at the right. It is a CR1620 lithium cell, but any 3 volt source may be used. The transmitter module sticks out to the left. Visit page [...]

Wireless Telemetry for Animal Tracking

Sun, 25 May 2008 10:23:00 +0000

This project explored the feasibility of creating a cost-effective transmitter receiver pair to replace commercially available 150 MHz devices used in animal telemetry. Distance measurements of test circuits transmitting at 418 MHz were taken over clear ground and in forested areas. These measurements show a range of 300-400 feet in forest underbrush and acceptable dropoff over distance, demonstrating that 70 cm radiation can be used in this application. For testing, a 418 MHz Yagi antenna was constructed and shown to exhibit strong directionality and approximately 20 dB gain in the forward direction. Once it was determined that 400 MHz radiation is capable of forest penetration to the range specified, the telemetry transmitter design was optimized for greater battery life. After exploring several potential oscillator designs for transmitter input, an op-amp circuit was designed with appropriate PCB layout. A 433 MHz transmitter/receiver pair was constructed and tested to show signal range at the same level as earlier measurements at significantly lower power consumption rate. The final transmitter has a total current draw of 70 uA. This translates to roughly one and a half months of continuous operation using freely available 70 mAh lithium-ion coin batteries. Components for the transmitter receiver pair are available at considerably less cost than commercial devices, with component cost for each transmitter at roughly ten dollars and for the receiver at less than twenty dollars. Original document Wireless Telemetry: Christopher Yeou - Hwa Chau [...]

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