THE BROADCAST HARDWARE

i-mobile Wireless FM Transmitter with Remote Control

Mon, 09 Nov 2009 11:36:00 +0000

This handy MP3 FM Modulator turns any USB Memory Flash Drives / Memory Cards into an MP3 player. It also has the general line-in function for other portable audio devices (e.g. iPod). It is a perfect product to fully utilize and enhance your car audio equipments. You don't have to worry about the unstable playback from the traditional CD audio player, simply download the MP3 to the Memory Card / Flash Disk, plug this Modulator to your car cigarette lighter, tune your radio to match the frequency with this unit ... PLAY. i-Mobile Car Mp3 Player with FM Transmitter It plays all of your audio devices through your car stereo system for convenient listening anywhere.It also comes with a remote control for the easy control. Stop playing the music when you switch off the car engine, resume when you switch on. Features: Support USB host, SD/MMC Card and LINE-IN Function LCD display of frenquency / Track No. and Name of Song Car cigar socket power supply (12V or 24V DC power) Selectable Channels: 206 preset channels within 87.5 MHz - 108.0 MHz, 0.1 MHz interval. Package includes: Multi function MP3 FM Modulator (Black Color) 3.5mm audio Cable Remote Control Buy New: $14.89 i-Mobile Car Mp3 Player with FM Transmitter [...]

Two Way Radio-Microphone Connections

Sun, 11 Oct 2009 13:28:00 +0000

Are looking for internal cable connection of your rig microphone? Here is  the right place of your choice. This site collects any info about microphone connections and sockects. If you have any Microphone information You would like to add to help other radio amateurs or two way radios.

RF Power Amplifier 144 MHz 50W 2N6084

Fri, 09 Oct 2009 08:17:00 +0000

This RF Power Amplifier for 144-146 MHz. It uses a 2N6084 RF transistor with power output 50w max. It is a class C amplifier design, and therefore good for FM mode only.

RF Amplifier Broadband 88-108 MHz 100W

Sat, 19 Sep 2009 05:31:00 +0000

This RF amplifier for FM 88-108 MHz with no tune (broadband) needed to cover all the FM Band. This RF Power amplifier is equiped with a bipolar transistor, the famous MRF317.

RF Filter Design With AADE Version 4.4

Fri, 11 Sep 2009 19:59:00 +0000

Here's a free Filter Software you can download that it will design most classical passive ladder Low-pass Filter, High-pass Filter, Band-pass Filter, and Band-Reject filters and analyze them in both the frequency and time domains. You can also enter a schematic and parts list from a book or magazine for analysis.

Elliptical RF Low-Pass Filter 88-108 MHz

Fri, 11 Sep 2009 19:37:00 +0000

Here's a reference circuit for building Elliptical FM Low-pass Filter (from Cauer) for Power Amplifier 88-108 MHz. A ninth-order, elliptic, low-pass filter attenuates harmonics generated in the power amplifier. The capacitors for the filter are circuit board pads.

Harmonic Absorbing Filter for FM RF Amplifier

Wed, 29 Jul 2009 07:15:00 +0000

All RF amplifiers will "react" in some way when a low pass filter is attached. This reaction is mainly caused by reflected harmonics. All RF amplifers generate harmonics. When a low pass filter is attached to the amplifer most of the harmonic energy is reflected back to the transistor causing reduced efficency and output power. The transistor will also run hotter.

FM Transmitter for MP3 Player Powered from USB

Wed, 15 Jul 2009 11:18:00 +0000

This's a simple VHF FM transmitter for MP3 Player that could be used to play audio files on a standard VHF FM radio. The transmitter circuit use no coils that have to be wound. This FM transmitter can be used to listen to your own music throughout your home. When this FM transmitter used in the car, there is no need for a separate input to the car stereo to play back the music files from your MP3 player. This FM transmitter use a chip made by Maxim Integrated Products, the MAX2606 [1]. This IC from the MAX2605-MAX2609 series has been specifically designed for low-noise RF applications with a fixed frequency. The VCO (Voltage Controlled Oscillator) in this IC uses a Colpitts oscillator circuit. The variable-capacitance (varicap) diode and feedback capacitors for the tuning have also been integrated on this chip, so that you only need an external inductor to fix the central oscillator frequency. It is possible to fine-tune the frequency by varying the voltage to the varicap. Not much is demanded of the inductor, a type with a relatively low Q factor (35 to 40) is sufficient according to Maxim. The supply voltage to the IC should be between 2.7 and 5.5 V, the current consumption is between 2 and 4 mA. With values like these it seemed a good idea to supply the circuit with power from a USB port. A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply. There is not much else to the circuit. The stereo signal connected to K1 is combined via R1 and R2 and is then passed via volume control P1 to the Tune input of IC1, where it causes the carrier wave to be frequency modulated. Filter R6/C7 is used to restrict the bandwidth of the audio signal. The setting of the frequency (across the whole VHF FM broadcast band) is done with P2, which is connected to the 5 V supply voltage. The transmitter PCB designed uses resistors and capacitors with 0805 SMD packaging. The size of the board is only 41.2 x 17.9 mm, which is practically dongle-sized. For the aerial an almost straight copper track has been placed at the edge of the board. In practice we achieved a range of about 6 metres (18 feet) with this. There is also room for a 5-way SIL header on the board. Here we find the inputs to the 3.5 mm jack plug, the input to P1 and the supply voltage. The latter permits the circuit to be powered independently from the mains supply, via for example three AA batteries or a Lithium button cell. Inductor L1 in the prototype is a type made by Murata that has a fairly high Q factor: minimum 60 at 100 MHz. Take care when you solder filter choke L2, since the connections on both sides are very close together. The supply voltage is connected to this, so make sure that you don’t short out the USB supply! Use a resistance meter to check that there is no short between the two supply connectors before connecting the circuit to a USB port on a computer or to the batteries. P1 has the opposite effect to what you would expect (clockwise reduces the volume), because this made the board layout much easier. The deviation and audio bandwidth varies with the setting of P1. The maximum sensitivity of the audio input is fairly large. With P1 set to its maximum level, a stereo input of 10 mVrms is sufficient for the sound on the radio to remain clear. This also depends on the setting of the VCO. With a higher tuning voltage the input signal may be almost twice as large (see VCO tuning curve in the data sheet). Above that level some audible distortion becomes apparent. If the attenuation can’t be easily set by P1, you can increase the values of R1 and R2 without any problems. Measurements with an RF analyzer showed that the third harmonic had a strong presence in the transmitted spectrum (about 10 dB below the fundamental frequency). This should really have been much lower. With a low-impe[...]

Pre-emphasis for FM Transmitter

Tue, 14 Jul 2009 16:14:00 +0000

This Pre-emphasis circuit was specially designed to be used with the FM Audio Transmitter. The circuit uses a dual opamp. The first opamp (IC1A) functions as a mixer and a buffer for the following correction network. The input sensitivity can be adjusted with the help of R3 (a lower value reduces the sensitivity). The 50 μs correction for the pre-emphasis is carried out by C5 and R6. IC1B buffers the signal before it is fed to the transmitter via K1. Since the FM transmitter is a mono version, a 19 kHz filter has been included to prevent a stereo FM receiver from mistakenly switching to stereo mode due to the presence of 19 kHz components in the received signal. Any signals around 19 kHz are blocked with the help of a simple tuned circuit (L1/C4). R4 ensures that the Q isn’t too large. Due to tolerances you may find that the frequency can deviate from 19 kHz (in our prototype the resonance frequency was closer to 20 kHz). In view of thevalue of the inductor, a through-hole version has been used for this (see component list).Without the parallel circuit the crossover point of the correction network is about16.7 kHz. This is more than enough for audio via VHF FM. The addition of the parallel circuit causes the amplitude around 10 kHz to increase a little, and the –3 dB point is then reached at 13.5 kHz. In the prototype this cutoff point was about 1 kHz higher due to component tolerances. The board designed for this circuit has been kept as small as possible through the use of SMDs for most components. The dimensions of the FM transmitter board also played a part here. To make it easier to connect this circuit to the transmitter board, a connector was included on this board. The supply voltage and audio signals are carried via this connector. The board has been designed in such a way that it can either be mounted behind the FM transmitter or alongside it. When the pre-emphasis board is used R1 and R2 should be removed from the transmitter board. When the circuit is mounted behind the transmitter board it was found that the FM signal strength was clearly reduced, so it would be better if a length of wire was used as aerial and connected to the transmitter board (it just so happens there is a via next to C4). To measure the effect of the pre-emphasis circuit we first measured the frequency response of the output of a small radio. The result of this can be seen in the graph (1 = without pre-emphasis, 2 = with pre-emphasis). It can be clearly seen that the higher frequency components are attenuated by the de-emphasis filter in the radio. When the preemphasis circuit is connected to the transmitter the result is an almost flat response above 1 kHz. The ‘bump’ around 100 Hz is caused by a type of bass-boost in the radio to improve the quality of the sound. The low cut-off point has risen slightly due to the inclusion of two extra coupling capacitors in the preemphasis circuit, but in practice this will be hardly noticeable. The current consumption of the transmitter is increased by this circuit from 2 to just over 5 mA. The component values in the circuit diagram are for 50 μs pre-emphasis. For adaptations to 75 μs as used in the USA and other countries, please refer to the parts list. Author: Ton Giesberts, Elektor Magazine, 2009 FM Transmitter Pre-Emphasis Parts List Resistors (all SMD 0805) R1,R2 = 22kΩ R3 = 10kΩ R4 = 100Ω R5,R7 = 15kΩ (24kΩ for 75 μs) R6 = 3kΩ3 (3kΩ6 for 75 μs) R8, R9 = 100kΩ Capacitors C1,C7 = 4μF7 10V C2,C8 = 100nF C3,C6 = 47pF C4 = 2nF2 C5 = 2nF7 Inductors L1 = 33mH, e.g. 22R336C Murata Power Solutions (Farnell # 1077046) Semiconductors IC1 = TLC082CD SO8 (Farnell # 8453713) [...]

FM Power Amplifier 88-108 MHz 600W BLF574

Mon, 06 Jul 2009 04:27:00 +0000

BLF574, 50V, push-pull transistor using NXP’s High Voltage 6th generation of LDMOS technology was introduced recently and makes this FM amplifier possible with a single transistor. This eliminates the need for combiners and associated losses. The BLF574 is the latest high performance technology from NXP. These new 50 volt LDMOS transistors are ideal for that 1KW amplifier project. 600W BLF574 48V FM Pallet info. The two push-pull sections of the device are completely independent from each other inside the package. There is an internally integrated ESD diode protecting the gates of the device. The device is unmatched and is designed to be used for applications anywhere below 600 MHz where very high power and efficiency are required. Common applications would be FM and VHF broadcast, or in laser or ISM applications. Great care has been taken during the design of the high voltage process to ensure that the device achieves high ruggedness. This is a critical parameter for successful broadcast operations. The device can achieve greater than a 10:1 VSWR for all phase angles at full operating power. Another design goal was to minimize the size of the applications circuit. This is important in that it will allow amplifier designers to maximize the power in a given amplifier size. The design highlighted in this application note achieves 600W in the 88-108 MHz band. The FM amplifier circuits is only as wide as the transistor itself, so transistors can be arranged in the final amplifier as close as physically possible and still enable adequate room for the circuit implementation. This application note describes the design and the performance of the BLF574 for Class-B CW and FM type applications in the 88-108 MHz frequency band. FM Amplifier Bias Circuit A temperature compensated bias circuit is used. The bias circuit is supplied by an 8V voltage regulator (Q1). Q2 is the temperature sensor and must be mounted in good thermal contact with the device under test, Q3. R1 sets the quiescent current. The gate voltage correction is about –4.8 to – 5.0 mV/°C. R2 is used to reduce the Vgs range. Q2 generates the basic –2.2mV/°C at its base and this is multiplied up by the R14/R15 ratio for a temperature slope of about -15mV/°C. The multiplication ability of the transistor is the reason it is used rather than a diode. A portion of the – 15mV/°C is summed into the potentiometer R1. R4 sets the amount of temperature compensation. The ideal value proved to be 2kΩ. The value of R11 and R13 are not important to the temperature compensation. They are used only for base band stability and to improve IMD asymmetry at lower power levels. Taken from NXP BLF574 Amplifier Application Note [...]

Wireless FM Transmitter

Mon, 20 Apr 2009 05:11:00 +0000

The following transmitter circuit works on 88-108 MHz frequency range. The most important part of this 88-108 transmitter is the Colpitts oscillator. C3,C4,C5,C6,CD1-CD2 ans L1 determine the transmission frequency. The RF Oscillator circuit has the BF982 MOSFET transistor wich is the active part. The others 2 transistors separate the VCO from antenna.

FM Wireless Microphone Transmitter LMX4467

Mon, 20 Apr 2009 04:58:00 +0000

This simple FM wireless microphone transmitter can transmit speech over a short range. It can be used as a simple cordless microphone. The circuit uses two integrated circuits from Maxim. IC1 a MAX4467, is an amplifier raising the microphone signal to a level suitable for frequency modulation (FM). IC2 is a voltage-controlled oscillator (VCO) with integrated varactor (a.k.a. varicap diode). Its nominal frequency of oscillation is set by inductor L1. The inductor value 390 nH provides an oscillation frequency of about 100 MHz. For best performance, L1 should be a high-Q component. L1 may consist of 4 turns of silver-plated wire wound around a 10-mm drill bit, and stretched to a length of about 1.5 cm. The wire diameter can be anything between 26 SWG (0.5 mm) and 20 SWG (1 mm). No core is used. The MAX4467 is a micropower opamp for low voltage operation and providing 200-kHz gain bandwidth at a supply current of just 24 μA. When used with an electret microphone, some form of DC bias for the microphone capsule is necessary. The MAX4467 has the ability to turn off the bias to the microphone when the device is in shutdown mode. This can save several hundred microamps of supply current, which can be significant in low power applications particularly for battery powered applications like cordless microphones. The MIC Bias pin provides a switched version of Vcc to the bias components. Resistor R1 resistor limits the current to the microphone element. The output impedance of the MAX4467 is low and well suited to driving cables over distances up to 50 m. The MAX2606 intermediate-frequency (IF) voltage-controlled oscillators (VCO) has been designed specifically for portable wireless communication systems. The IC comes in a tiny 6-pin SOT23 package. The low-noise VCO features an on-chip varactor and feedback capacitors that eliminate the need for external tuning elements. Only an external inductor (here, L1) is required to set the oscillation frequency and produce a properly operating VCO. To minimize the effects of parasitic elements, which degrade circuit performance, place L1 and C5 close to their respective pins. Specifically, place C5 directly across pins 2 (GND) and 3 (TUNE). Potentiometer P2 then lets you select a free channel by tuning over the FM band of 88 MHz to 108 MHz. Output power is about –21dBm (approx. 10 μW) into 50 Ω. P1 serves as a volume control by modulating the RF frequency. Signals above 60 mV introduce distortion, so the pot attenuates from that level. To decrease stray capacitance, minimize trace lengths by placing external components close to IC1’s pins. Using a wire antenna of about 75 cm the transmitter should have a range of about 35 m. Try to keep all leads as short as possible to prevent stray capacitance. The FM wireless microphone transmitter operates on a single supply voltage in the range 4.5 V to 5.5 V from any standard battery source. The transmitter must be housed in a metal case, with shielding installed between the two stages (AF and RF). Try to keep all leads as short as possible to prevent stray capacitance. Source: FM Wireless Microphone [...]

Simple AM Transmitter with BC109

Sun, 08 Feb 2009 18:45:00 +0000

Here's a simple Amplitude Modulation (AM) transmitter. This circuit is deliberately limited in power output but will provide amplitude modulation (AM) of voice over the medium wave band. The circuit is in two halfs, an audio amplifier and an RF oscillator.

13.8V 20A Linear Power Supply With 2N3055

Tue, 03 Feb 2009 10:57:00 +0000

Linear power supplies for communication equipment are among the most commonly built electronic projects. Almost every technically inclined radio amateur has built at least one. But unfortunately most designs, even those published in well respected books, are unnecessarily complicated, or have some specific drawbacks. The design presented here is a little bit unusual in its arrangement, but offers some advantages over the usual designs that I will explain in the following paragraphs. A linear power supply has a transformer that steps down the line voltage to some voltage that is higher than what will be required at the regulated output. Then a rectifier and a filter capacitor transform the low voltage AC into a moderately filtered DC that still is unregulated and has some ripple. Finally, a regulating circuit "burns off" the excess voltage, leaving only the exact amount desired at the output, typically 13.8V for communication equipment. One typical mistake made by many amateur designers is using a transformer that has a voltage that's too low for the combination of rectifier, filter and regulator used. The situation is this: You need 13.8V at the output at all times. Your regulator eats up a certain minimum voltage, which depends on its design. Many regulators need at least 2V across them, so you need 15.8V minimum at the worst time across the filter capacitor. This is the voltage at the minimum point of the ripple waveform, but the capacitor needs to be charged to the maximum of this ripple voltage. So, the size of the capacitor defines how much additional voltage you need for this. A 60000uF capacitor, used at 20A, and discharging during almost a half cycle at 50Hz (10ms), will drop the voltage by almost 3.3V. So, you need to charge the capacitor to at least 19.2V under the worst conditions! If you are using a bridge rectifier made from silicon diodes, which loose about 1.2V each at peak current, then you end up having two diodes conducting at the time of charging the capacitor, dropping a total of 2.4V. So, the transformer needs to develop 21.6V peak voltage. This happens under heavy load, as most of the charging of the capacitor happens during a very short time, so there is a lot of voltage drop in the transformer, maybe 10 to 15%, depending on its size. So, you need to consider a transformer that develops about 24 or 25V peak voltage. Finally, you need to consider that the power line from which your design gets its power is not 100% stable! Allowing for 10% worst case sag in the power line, you end up needing a transformer that at nominal line voltage and small load provides about 27V peak! That would be 19V RMS. In the power supply presented here, several measures were taken to get rid of the problems mentioned above. The pass transistors are located in the negative rail and connected in common-emitter configuration rather than as emitter-followers. Thanks to this, the regulator's minimum voltage drop is extremely low, only about 0.1V for the transistors plus 0.5V for the equalizing resistors. The other advantage is that the collectors are directly connected to the negative pole of the power supply's output, which in most applications is grounded. That means that no insulation is required between the transistors and the grounded power supply cabinet! This eases the cooling very considerably. Thanks to the low regulator drop, a low cost 25V filter capacitor can be used. The voltage adjustment potentiometer is arranged in such a way that if the wiper contact fails, the voltage will go down, never up. This is an important safety issue, avoiding damage to connected equipment. This is a nice beginner's project, as all components are easily available all over the wo[...]

13.8V 20A Power Supply Using FET BUZ11-24

Tue, 03 Feb 2009 10:31:00 +0000

This is a regulated DC power supply, short circuit safe, and with current limiter. It has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. Let us see what we have got here. The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the lower power dissipation. The rectified current will be ironed by the C1, whose capacity should not be less than 40.000uF, (a golden rule of around 2000uF/A), but we recommend up to 50.000uF. This capacity can be built up by several smaller capacitors in parallel. The base of this design is a simple 12V regulator (7812). The output voltage can be brought to desired value (here 13.8V) by two external resistors (R5 and R6) using this formula: U= 12(1+R5/R6) The low currents (here 15mA) will keep the 7812 in its regular function. As soon as the current rises over 15ma, the voltage drop on R4 will open the Q3, actually handling the high output current. This is a PNP transistor (Ic>25) and current amplification factor of at least 20. The one that has been tested and proven here is the 2N5683. The current limiting resistance RL, for the maximum output of 20 Amps should be 0.03 Ohms, rated at least 15W. You can use the resistance wire or switch several resistors in parallel, totaling the resistance/power values. Values for other currents can be calculated by the rule: RL=0.7/Imax The RL and Q2 (3A PNP such as BD330) form a short circuit automatic fuse. As soon as the maximum current reaches 20Amps, the voltage drop over the resistor RL will open Q2, and thus limit the B-E Current of Q3. Parallel to Q2 is Q1, which lights the LED 1 whenever the current limiting circuit is active. When the fuse is active, the Q2 bridges the R3, so the full current would flow through the IC1, and damage it. Therefore the R4 is inserted, as to limit the IC1 current to 15mA. This makes it possible to run the IC1 without any cooling aid. The LED 2 will light up every time the PSU is switched on. There is an adjustable current limiter in parallel to the fixed output, thus providing adjustable current source for smaller currents. This circuit is very simple too. You will notice that there is no current sensing resistor. But it is really there, in a form of the Rds-on resistance of the N-channel FET, which actually handles the load cutoff from the source. The function of the FET is shown in the diagram 2. When the current Id is rising, the tension Uds over the resistance Rds rises very slowly in the beginning, but very fast after the knick. This means, that before the knick the FET behaves as a resistor but after it, works as constant current source. The D2, R3 and B-E connection of the Q4 will sense the Uds voltage of the FET1. When the voltage rises enough, the Q4 will shortcut the FET1 gate to mass, and cut the current flow through the FET 1 off. However, to enable the FET1 to open, there is certain gate voltage necessary, which in this case is brought up by the voltage divider consisting of R8, Z1, P1 and R9. So the maximum Gate voltage will be the one of the Z1, and the minimal will be around 3V6. The Z1 voltage (Uz1) will thus determine the max current flowing through the FET 1. The diagram 2 will show that for 5 Amps the Uz1 should be 5V6, and for 20Amps around 9V6. The Capacitor C4 will determine the velocity or the reaction time of the limiter. 100 uF will make the reaction time to be around 100ms, and 1n will make it 1us. Within the designed limits, the P1 will limit the current output in the range of 15mA to 2[...]

How To Design RF Filter Faster

Mon, 02 Feb 2009 11:59:00 +0000

How to design RF Filter Fast? A Windows® electrical filter design and analysis program designed to expedite the design of lowpass and highpass filters using Standard Value Components (nearest-5% values). You can view your spectrum analysis filter design. SVCfilter™ is a program designed to expedite the design and analysis of lowpass (and highpass) filters with nearest 5% component values. Here are some pertinent features: SVCfilter is 32-bit Windows® electrical filter design software nicely written to help the radio amateur, technician or engineer design and analyze lumped-element lowpass and highpass filters. Order, topology and family are all entered by clicking on buttons. If the Chebycheff or Cauer family is chosen then three options for passband ripple (.01, .044 and .200) are available. If the Cauer family is chosen then four options for stopband depth (30, 40, 50 and 60 dB) are available. Cutoff frequency is entered in the usual text box and can be from audio through UHF. Cutoff frequency can be as low as 0.1 Hz, allowing the value of .159155 [ i.e., 1/(2*PI) ] to be used. This, in conjunction with a termination value of one ohm, yields parts values for the textbook classic "normalized" design. System impedance by default is 50 ohms but a textbox allows entry of any value of your choice, for example 600 ohms for audio. Inductor Q values are set by default to a value of one million. A textbox allows entry of any value of your choice in the range of 10 minimum to one million maximum. The graphic output draws the schematic of the filter you have designed, and also plots the responses of that filter (both transmission and reflection). It selects the nearest 5% values for the capacitors and shows those values as well as the exact values and overlays the response plots for the nearest values on top of the original exact-value plot. Tuning buttons allow stepping the cutoff frequency up or down in 1% steps and immediately seeing the new performance of the redesigned filter on the plot. Place the cursor anywhere on the plot and see the transmission, reflection, VSWR and envelope delay values for that frequency. Inductors are retuned as necessary to maintain the response of Cauer filters after nearest capacitors are chosen. To maintain the high level of quality of the graphic output, the outputs to the printer are not "screen dumps" but instead are from a set of dedicated routines which write directly to the printer. The quality of the graphics as delivered by the printer will be limited only by that printer, commonly several hundred pixels per inch. The printer output on one sheet contains the schematic with parts values along with the set of responses. Click on the "Write Elsie File" button to write a file to drive Elsie the filter design and analysis program for followup filter examination in even greater detail. Click on the "Write Spice schematic" button to write a file to drive the LTspice simulator. (Tonne Software has no connection with Linear Technology Corporation.) This program was written to simplify the sometimes difficult task of lumped-element lowpass (and highpass) filter design by automating or setting as default some of the more frequently-encountered options. But it also includes analysis, uncommon for such an application. Download SVCFilter - How To Design RF Filter Faster in detail [...]

Directional RF Power Meter

Sun, 04 Jan 2009 15:59:00 +0000

Here's a powerful bench-top power meter that is based around two AD8307 log detectors which have a 90dB dynamic range for signal strength measurements. Tie that to a good directional coupler and you have yourself a very easy to build and calibrate power meter! Since the AD8307s respond very quickly to changes in signal level they are also perfect for deriving percent of modulation, peak power, average power and more.

FM RF Amplifier 88-108 MHz 100mW-8W

Mon, 29 Dec 2008 00:10:00 +0000

Here's FM RF amplifier 100mW-8W for 88-108 MHz. This amplifier circuit using the transistor BFR96 and 2SC1971 and equipped with a low pass filter

Where Go for Test Equipment Rental

Sat, 22 Nov 2008 01:24:00 +0000

Here is the best place to rent equipment when you do not want to buy it. At TestEquity, they not only strive to provide the best in new and used test equipment, but also the widest variety of purchasing options available. Whether your needs include buying, renting, or leasing equipment, TestEquity has a plan that will meet those needs. Below is a brief summary of our Test Equipment Rental and Leasing options.

Small AM Transmitter

Thu, 20 Nov 2008 18:14:00 +0000

Here's a small AM Transmitter you may needed. It/s built into a plastic project box, and uses a piece of perfboard rather than a printed circuit board. Of course, a PCB would have been much more elegant, but designing and making one would have increased construction time by at least five times! The RF transformer of the transmitter is actually a 455kHz IF transformer taken from a junked transistor radio from the 1970s. I removed its internal 470pF capacitor. With the external 100pF capacitor it can be easily tuned to 1MHz. It must have roughly 250 microhenry in the higher impedance winding, and the turns ratio of the low impedance one is about 1:10. The antenna of this AM Transmitter is a resonant multiturn loop. It has 19 turns of common household stranded wire, wound on a piece of strong cardboard that has 11 slits cut into its periphery. Why 11? Well, 10 or 12 sounds nicer, but we need an odd number, so that we can make the low parasitic capacitance winding! The wire changes sides of the cardboard through every slit, and to avoid having all turns touching each their neighboring ones, the number of slits must be odd.   Do you need an small AM Transmitter? [...]

4 Channel Video Mixer Edirol LVS-400

Sun, 16 Nov 2008 12:06:00 +0000

Here's a video mixer LVS-400 from Edirol , It  compact, simply-operated 4 channel video switcher is so easy to use, that even without any previous video experience, you can create very professional video transition and key effects for a professional video performance.

Circular Dipole Broadcast Antenna 88-108 MHz

Sat, 15 Nov 2008 20:34:00 +0000

Here's a Circular Dipole Antenna construction for FM broadcast 88-108 MHz. This antenna is made of copper pipes with a diameter of 15 mm. This is a dual antenna type circular polarization Vertical / Horizontal, one of its features is the main penetration, that is to cover urban areas.

Directional Coupler with RF Filter for 88-108 MHz

Tue, 28 Oct 2008 22:52:00 +0000

Here's Directional Coupler equipped RF filter with bandwidth is wide enough to pass any VHF 87.5 to 108 Mhz, cutoff frequency of 115 MHz being something similar. The harmonic 2 is located at 65 dB and harmonic 3 at 70 dB, to ensure optimum purity of the carrier. The low-pass filter is made in cells L / C type Butterworth, mounting parallel to 9 poles. Impedance input and output is 50 ohms. The low-pass filter is followed by the party meter reflectometer composed of a main line and two adjacent lines. Each of these lines are loaded by 50 ohm resistors R2 and R3-47ohms. These lines are direct and thoughtful fitted on each of them an attenuator, but in practice, I realized that these were not necessary attenuators, you need to remove R1, R6, R4 and R9 - 100Ohm strap and R5 and R8-82ohms.    HF detection is provided by two circuits at-Linear Technology, LTC5505 this circuit is expected of origin for higher frequency but retains excellent at 100Mhz, or for that choice. Related post: Simple VHF SWR Protection Circuit - 100w LCD PIC16F88 SWR Meter for VHF- UHF More detail Directional Coupler with RF Filter for 88-108 MHz [...]

20 dB/150 Watt RF Attenuator

Fri, 17 Oct 2008 20:44:00 +0000

Here is an attenuator schematic for your spectrum analyzer. It's simple, easy and cheap way to make fairly high power RF attenuators. These are useful for directly connecting the output of a high power RF amplifier into a spectrum analyzer, frequency counter or other piece of test equipment (additional attenuation maybe required).

Stereo Tool 3.30 for Winamp Plugin

Thu, 09 Oct 2008 16:30:00 +0000

This Stereo Tool application software is a Winamp plugin that delivers professional quality audio processing - for free. Stereo Tool is available in a free and a registered version. The registered version is intended for commercial users of Stereo Tool, especially aimed at FM radio stations.

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