Antenna #2

Antennas

Idiot's guide to antennas Preferred type of antenna is affected by several factors, but mostly by transmitting site. In the middle of the area you want to cover you'll need an omnidirectional antenna which transmits equally all ways, while outside your coverage area you can beam the signal in with a directional antenna. Before going on air get a low VSWR by adjusting the position of the antenna and any of it's adjustable pieces. Aim for 2:1 or less. Use low power into the antenna when tuning it up and making adjustments. If you were using 100's of watts and a bit of the antenna came off in your hand the VSWR could be so bad as to blow the final transistor. For the same reason check the DC continuity of the antenna with an ohmmeter before plugging it in, to be sure it's what it's meant to be, either a short circuit or an open one, depending on the antenna type. A dipole shown below should be an open circuit. A PIECE OF WIRE OR TV ANTENNA IS NOT SUITABLE FOR FM BROADCAST BAND TRANSMITTER! You have to realize that antenna was, is and will always be crucial part of the system. Special care has to be taken! It is usually good idea to place antenna away from your transmitter, power supply and audio system. If you cannot meet these requirements, you could experience feedback and other RF problems. Interestingly, RF energy can make CD players and other digital devices go bezerk. Try placing 30W-driven antenna next to yours. Dummy Load Dummy load is not actually an antenna, it dissipates all transmitted power in a form of heat. So what's the use of it? Well, it is presents an ideal match for an output of your transmitter (usually 50ohms). Since all power (virtually 100%) is transverted into heat there won't be any interference to your neighbors while you do tuning and testing. This is what dummy load is usually used for; testing and tuning transmitters. If you don’t have dummy load, you can build one easily from a BNC or other RF connector and the proper wattage/value of CARBON resistor(s). DO NOT USE WIREWOUND OR METAL FILM RESISTORS! A useful one can be constructed with 4 -220 Ohm 1/4 watt resistors in parallel (220/4 = 55 Ohms) with center conductor to outershell (ground) of an RF connector. That is pretty close to 50 Ohms and if you use 1/4 watt resistors you get a nifty 2 Watt Dummy Load for testing your equipment without an antenna. Commercial Dummy loads are available at our website, check under Transmitter accesories. The simplest possible antenna for VHF is known as the Half-wave Dipole: Dipole Both elements can be either aluminum/copper tubes or wire. The lengths of each dipole, L, is calculated from your transmitting frequency by this formula: L = 71/F (meters), where F is operating frequency in MHz A half-wave dipole used vertically is omnidirectional, but when used horizontally it has a figure of eight coverage like this (view from top): Note: A dipole needs a Balanced Feed as it is symmetrical, but a coaxial cable provides an Unbalanced Feed. What's needed is a Balun (BALance to UNbalance) transformer. These can be made out of bits of coaxial cable. If you don't do this power will be radiated from the feeder. You CAN use it without BALUN, but you might get lower-than-expected performance and unusual radiation pattern due to interactions with the feeder. We recommend this antenna to beginners, as your knowledge broadens go for one of the following babies: GP Antenna Click here for alternative image. Most designs on the web don't compensate for the fact that GP antennas are not wideband antennas. Here is a Freq./element length chart for this simple GP antenna, all elements are in millimeters: Frequency Radiator - B Radials - A 108MHZ 660 693 104MHz 684 720 100MHz 713 749 90MHz 792 819 If you have SWR meter (and you SHOULD have one) leave a few inches extra for the radiator and adjust it later by cutting to achieve minimum SWR. Slim Jim This is a vertically polarized omnidirectional antenna. Radiation efficiency 50% better than ground plane antenna, due to low angle radiation Unobtrusive No ground plane radials, so low wind resistance Fully weatherproof 50W input impedance Low VSWR - 1.5 to 1 or better Integrated balun Construction Details J- Pole We will publish a number of antenna designs here, these have all been submitted to our forum by our forum members, most notably NormB in his best days. A number of links is provided at the bottom, leading to design sources or other interesting resources regarding J-pole antenna construction. Some of the designs were made for 144MHz (2m ham band) and need to be scaled down for 100MHz operation. This usually means increasing element size for roughly 144/100 = 1.44 (44% increase).

FM Antenna Broadcast 88-108Mhz

Introduction

Antenna is final device for sending any information from your transmitter. In fm transmitter you need signal transmitted to any direction so you need antenna type that transmitted with polarized circularly. Gain Antenna -3.2 dB, bandwith 500 KHz with maximum power handling 500 Watts. In order to use antenna on 88-108 MHz, broadband antenna type must be designed with no tune involved.

How Your Signal Amplified
Amplification of signal to transmit based on antenna gain in Decible. Signal from transmitter be able to doubled, tripled or even become more power. The value is called ERP (Emmittion Radiating Power). For Doubled your transmitter power to be ERP Power need stacked 4 antennas (3.12 dB gain antenna), 6 antennas (5.12 dB), 8 antennas (6.4 dB).

ERP = Transmitter Power x Antenna gain

FM Amplfier 100 watt (88-108 Mhz)

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.



The Block schematic and datasheet

TV Amplifier 100 Watt / UHF

The TV amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from band IV - V in UHF.

Amplifier Circuit

The total description of the amplifier is given in Figs 6 and 7 and Table 8 (in datasheet). The amplifiers 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.

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.

(For Complete Datasheets klik here)

Antenna Power Devider

This Power Divider Combiner not only use for dividing or combining RF power on RF amplifier constructions, but also use in dividing RF power if you use more than one antenna for higher gain.

The Construction of simple power divider combiner with the equation below :
Z = 1.38 x log (1.08 x (D/d)) for square tube

Where,

• D = The Inner Width of the tube
• d = The Outer Diameter (OD) of the inner conductor
• Z = Impedance

The Equation of Impedance Approach :

Z = 1.38 x log (1.08 x (D/d))

Z = 35.88 Ohms

Pict : Example for 2.4 Ghz

• A = Chasis mount N Jacks
• B = Solder the N center connectors pins directly to the inner of the copper conductor
• C = 12.7 mm (1/2 inch) outer diameter (OD) copper conductor
• D = 25.4 mm (1 inch) square aluminium tube, with wall tickness of 2 mm For ¼ wave power divider, the impedance theoritical needs to be around 35, 35 ohms and impedance of the equation = 35.88 ohms with test result SWR Reading <1.3

Notes :

• If you construct it with circle tube, the equation Z = 1.38 x log (1.00 x (D/d)).
• (D/d) ratios for ¼ and ½ wave length with more ports ( 1-4, 1-6 , and 1-8) at next update
• Ring Circular FM Broadcast Antenna to support your power combiner with more than one antenna at the next update

Antenna UHF

ANTENNA UHF

ANTENNA UHF 2 DIPOLE

Out Put Connetor dapat diganti sesuai dengan kebutuhan.

Tune antenna dilakukan dengan mengatur kerapatan plat sirip yang menhubungkan plat radiasi







Antenna UHF dimensi yang lain







TABEL


ANTENNA 4 DIPOLE

Pre-Amplifer UHF 10 dB

UHF Preamplifier

This circuit is designed to work at UHF frequencies in the range 450-800MHz. It has a gain of around 10dB and is suitable for boosting weak TV signals. The circuit is shown below:-

The MPSH10 transistor used is available from Maplin Electronics order code CR01B. Alternatives that may be used instead are BF180 and BCY90. The tuned circuit comprising the 15nH inductor and 2.2pF capacitor resonate in the centre of the UHF band. The 2.2pF capacitor may be exchanged for a 4.7pF or a trimmer capacitor of 2-6pF to improve results. The approximate frequency response is shown below. N.B. This is a simulated response using the TINA program produced by using a swept 20uV input swept over the frequency range 400-800MHz. Output was measured into a 1k source and the frequency generator has a 75ohm impedance.

Construction The coil is half a turn of 18-20 SWG copper wire bent around a half inch drill bit. This ensures a low Q and therefore broad tuning. High frequency work requires special construction techniques to avoid instability (unwanted oscillations) caused by feedback from output to input. Veroboard is not suitable for this project as the capacitance between tracks is around 0.2pF. A better approach is to use tag-strip or a PCB. The circuitry should be enclosed in a metal case and a screen made between input and output. As the transistor is used in common base mode,its low input impedance is a good match for 50-75 ohm coax cable, whilst at the same time providing full voltage gain to the upper frequency limit of the device. The 15nH inductor load, having almost a short circuit impedance at DC, has an impedance of 56ohms at 600MHz. This inductance and 2.2pF capacitor form a tank circuit at the transistors collector, providing maximum gain at resonance. Note however that the voltage gain will be reduced under load, when the circuit is connected to the input of a TV set or a very long piece of coaxial cable for example. Hence the simulated Tina plot.