BA datasheet, BA circuit, BA data sheet: ROHM – Fm Stereo Transmitter,alldatasheet, datasheet, Datasheet search site for Electronic. Page 4. Page 5. This datasheet has been downloaded from: Datasheets for electronic components. Part, BA Category, Communication => Freq/Signal Converters/Generators. Description, FM Stereo Transmitter. Company, ROHM Electronics. Datasheet.
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This design is a 2 stage amplifier that has about 17db of gain, suitable for an input of 50 to MW. Its basically a Veronica 5 watt vco transmitter, without the vco. The transistors are a 2N and a MRF Output power is 2. The maximum dc voltage recommended is about volts. This RF FM Amplifier is always essential for the amateur that wants it strengthens some small transmitter. FM radio amplifier 25W A simple 25W fm radio amplifier used as a final stage for a 2. Use a very good headsink because this transistor get very hot: Solar charger Coils values: RF power amplifier 80W by C This is a pretty conventional design, using bipolar transistors in a tuned class C circuit.
Thanks to the use of two stages, the amplifier can be driven to full power with less than 1 watt driving power, so that a large gain margin results in this transmitter. Bipolar VHF power transistors have a severe affinity for low frequency self-oscillation. To obtain stability in this amplifier, I employed several techniques, such as placing the resonances of base and collector chokes far apart, damping the chokes with resistors, using RC combinations for absorption of unwanted frequencies, using feedtrough capacitors for bypassing on the board, etc.
It took some tweaking, but the amplifier ended up unconditionally stable. The impedance matching network between the two transistors calls for such a low inductance, that it would be impractical to make it with actual wire.
So I used a micro stripline etched on the PCB. Also, the power and SWR sensor at the output was made with micro striplines. Input should be at least mW to achieve 1W output. It is recommended to enclose the amplifier in a metal case.
See How to be a Community Radio Station for links to reviews of some of the more popular exciters. Who is this design for? These people run the following risks: Thermal and RF burns Electrocution Destruction of expensive RF components and test equipment Unwanted spurious RF radiation, resulting in interference to other users of the electromagnetic spectrum, thus risking a visit from the state, and consequent risk of equipment confiscation, fines, and possibly imprisonment.
A great deal of stress and frustration. Why this design is necessary I believe the quality of the vast majority of schematics datasgeet designs for FM broadcast equipment available on the internet to be far from satisfactorily. See my advice on building from plans on the web. In particular the information available on VHF RF power amplifiers is even more desperate, for example designs using dinosaurs of devices such as the TP This design is based on a new MOSFET device, with the attendant advantages of high gain high efficiency ease of tuning Seeing as most of the designs on the web are over 10 years old, using a recently introduced device should maximise the useful life of the design.
I also use this design as a vehicle to demonstrate the amount datashheet information required for a third party not ratasheet with mind-reading skills to successfully build this amplifier.
The point is this: Conversely, a person not at that skill and experience level will require detailed instructions to succeed. Do not confuse this with the older, now discontinued, MRF device. January – Motorola changes their RF power device product portfolio more oftern than some people change their underparts. Computer Simulation The initial feasibility was performed using a linear RF and microwave simulation package, specifically Supercompact.
The version used was 6.
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For this device, Motorola provide S parameters and large signal single ended impedances. The S parameters are measured at 0. Whilst this is satisfactory for small-signal devices, the use of S parameters measured at small drain currents is limited for power amplifier design. While the S parameter information measured at 0. These are measured by the device manufacturer by tuning the datasheett up for best performance at each test frequency in a generic test fixture.
The test device is then removed, and a vector network analyser is used to measure the complex impedance looking back into the matching network, whilst these are terminated with 50 R.
BA Datasheet Rohm pdf data sheet FREE from
This procedure is carried out for the input and output matching networks. The advantage of large signal impedance data is that it can be measured at the actual output power that the device is designed to generate, and as such are more representative in a power amplifier scenario. Note the large-single impedances only provide information to enable an input and output matching network to be synthesised, they provide no information about the likely gain, efficiency, noise performance if relevant or stability of the resulting amplifier.
This is the file used to synthesise the input network. This information comes from design experience. All optimisation values have been constrained with maxima and minima to keep the resulting network realisable. Initially, a 3 pole matching network was tried, this was not capable of providing a sufficiently broadband match across the 20 MHz.
Using a 5 pole circuit allowed the optimisation goal to be achieved. Note the 33R gate bias is included in the simulation, as this helps de-Q the input network, and improves the stability in the final amplifier. A similar procedure was performed for the output network. In this simulation, the drain feed was included in the simulation. Although on the face of it, the value of this choke is not critical, if it gets too large stability can be comprised, if it gets too small, it becomes part of the output matching network, which in this case was thought not be desirable.
Component choices As the input power is only half a watt, standard ceramic capacitors and trimmers were used in the input matching circuit.
L1 and L2 refer to schematic could have been made much smaller, but were kept big for consistency with the inductors used in the output network. On the output network, mica metal clad capacitors and mica compression trimmers were used to handle the power and keep component losses to a minimum. The wideband choke L3 provides some lossy reactance at lower RF frequencies, C8 takes care of AF audio frequency decoupling. The use of an enhancement mode N-channel MOSFET a positive voltage biases the device into conduction means the bias circuitry is simple.
A potential divider taps off the required voltage from a low voltage stabilised by a 5. Purists would temperature stabilise the bias current, but as the bias is not critical in this application, this was not bothered with. RF input 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.
The base of the power device sits through a cut-out in the floor of the diecast box and is bolted directly onto a small extruded aluminium heatsink. An alternative would have the base of the power device sitting on the floor of the diecast box. This is not recommended for two reasons, both concerned with providing an effective path to conduct heat from the FET. Firstly the floor of the diecast box is not particularly smooth, which results in a poor thermal path.
Secondly, having the floor of the diecast box in the thermal path introduces more mechanical interfaces and hence more thermal resistance. Another advantage of the chosen constructional technique is that it correctly aligns the device leads with the top face of the circuit board.
Using the specified heatsink will require the use of forced air cooling a fan. If you plan not to use a fan, a much bigger heatsink will be required, and the amplifier should be mounted with the heatsink fins vertical to maximise cooling by natural convection. The circuit board consists of a piece of fibre glass PCB printed circuit board material clad with 1oz Cu copper each side. I used Wainwright to form the circuit nodes – this is basically self-adhesive bits of tinned single sided PCB material, cut to size with a hefty pair of side-cutters.
An easy alternative is to use pieces of 1.
datasbeet These are glued onto the ground plane with a cyanoacrylate type adhesive e. This method of construction results in the top side of the PCB being an excellent ground plane. The only exception to this daatsheet the two pads for the gate and drain of the FET. These were created by carefully scoring the top layer of copper with a sharp scalpel, and then removing the slivers of copper with the assistance of a fine point soldering iron tip and the scalpel.
Running the iron tip along the isolated piece of copper loosens the glue sufficiently for the Cu to be peeled off with the scalpel. The gate pad thus created is clearly visible in the photograph of the prototype Having made the aperture in the PCB for the base of the power device to sit through, I wrapped copper tape through the slot to join the upper and lower ground planes.
This was done in two places, underneath the source tabs. The copper tape was then soldered top and bottom. See photograph for suggested component positions.
BA Datasheet(PDF) – Rohm
The vertical screen to the right of the enclosure is a piece of double sided PCB material, soldered to the top ground plane on both sides. This is an attempt to improve the final harmonic rejection, by reducing coupling between the inductors that form the output match and the inductors making up the LPF.
To do these kind of soldering jobs a 60W or greater soldering iron will be required – preferably a temperature controlled one. This iron will be dataeheet over the top for the smaller components so a smaller iron will be required as well.
As mentioned below, the LPF inductors are soldered directly to the tabs of the metal clad capacitors. Use the FET as a template, if required, but don’t blow it up with static. Make sure you’ll end up with the drain on the right side.
When you look into the top of the box you should now see a piece of heatsink revealed, the same size as the base of the FET. Rig yourself up some static protection if you’ve got an old blown-up device or a bipolar device in the same package you won’t have to bother with this and drop the device into the aperture in the board.
Use the FET to give you give the centre positions of its’ mounting holes Take everything to bits again. Use just enough solder to get a smooth finish but not too much to create raised areas of solder, especially on the bottom, as these will prevent the PCB sitting flat against the box floor. Create the two islands for the FET gate and drain, as detailed in the above paragraph Solder copper tape between top and bottom faces of the PCB underneath where the source tabs will be Create the PCB islands, tin them, stick them on the PCB using the photograph as a guide Create and fit the screen between the amplifier and the LPF areas Fit all the remaining PCB components, with the exception of the FET Fit the PCB to the box and the heatsink Fit the and connect and the RF connectors and the feed-through capacitor Taking anti-static precautions again, apply the thinnest continuous film possible of heat transfer paste to the base of the FET.
This can be conveniently done with a wooden cocktail stick Bend up the last 2mm of each of the FET’s leads. This will make it much easier to remove, should the need arise Screw the FET to the heatsink.