This transmitter can be used for transmitter hunts, for remote key finding, or for radio telemetry in model rockets. It can be tuned to the two meter band or other VHF bands by charging Cl and Ll. 11 is four turns of #20 enameled wire airwound, 0.25 inch in diameter (use a drill bit), 0.2 inch long, centertapped. The antenna can be 18 inches of any type of wire. IC2 functions as an audio oscillator that is turned on and off by IC1 about once per second. ..
The AA-7 active antenna contains only two active elements: Ql (an MFE201 N-chanriel dual-gate FET) and Q2 (a 2SC2570 ripri VHF silicon transistor), which provide the basis of two independent,..
A 30- to 50-cm whip antenna provides reception from 10 kHz to over 220 MHz. Tl, a dual-gate MOSFET, provides low noise, high-input impedance, and high gain,..
Diagram shows a 100MHz oscillator operating on the fifth harmonic. Again to maintain the transistor"s gain, note the increase in the collector"s load resistance Rl because of the increase in the quartz crystal"s internal series resistance R5. C3 is needed at frequencies above 50 MHz to tune out the shunting effect of LLon Rl, to maintain a high load resistance for the transistor and get enough gain for oscillation. ..
This wideband antenna preamplifier has a gain of around 20 dB from 40 to 860 MHz, covering the entire VHF, FM, commercial, and UHF bands...
This circuit is useful in amateur radio VHF and UHF work where a mast-mounted antenna preamp is used for receiving. The kit controls T-R switching and change-over relay sequencing so that high RF levels are prevented ..
This VHF VCO circuit is suitable for 30 to 200 MHz. Q1 can be replaced by a 2N3563 for operation above 100 MHz..
Two IC rf modulators convert a suitable baseband video and audio signal up to a low VHF modulated carrier-Channel2 through 6 in the U.S., and 1 through 3 in japan-the LM1889 and the LM2889. Both !Cs are identical regarding the rf modulation function, including pin outs, and can provide either of two rf carriers with de switch selection of the desired carrier frequency. The LM1889 includes a crystal-controlled chroma subcarrier oscillator and balanced modulator for.....
Diagram shows a 50MHz oscillator operating on a third harmonic. The collector"s load resistor R1 has been increased because the quartz crystal"s internal series resistance Rs increases with frequency in the VHF range. The crystal"s internal series resistance Rs is 30ohm, and the transistor"s minimum current gain HFI, is 100. ..
The range of this transmitter is about 50 feet with a short whip antenna. The tone generator, is made up of a unijunction transistor, Q1, and R1, R2, R3, and C2. Transistor Q1 pulses on and off at a rate determined by the time constant of R1 and R2, together with the capacitance of C2 and the B1-emitter junction of QL Trimmer potentiometer R2 determines the frequency of the tone generated and allows a range of approximately 100 Hz to over 5 kHz. ..
This circuit uses low-cost IN4148 diodes and exhibits about 1.5 dB insertion loss from 10 to 1000 MHz w..
This transmitter can be tuned to the FM broadcast band, 2 meters,-or other VHF bands by changing C5 and Ll. The values given for C5 and Ll will place the frequency somewhere in the FM broadcast band. Ll is 4 turns of #20 enameled wire airwound, % inch in diameter, 5mm long and center-tapped. The microphone is an electret type and the antenna is 18 inches of any type of wire..
Amateur VHF relay stations are normally actuated by a 1750-Hz call tone. This might give problems if the relevant sendi..
This simple circuit gives 15 dB gain and can be mounted on 1 in 2PCB. Coil data is given for 85 to 95 MHz..
The amplifier uses a grounded grid circuit with either the Eimac 3CX1000A7 or 8877, ceramic/metal triodes intended for linear service in the HF and VHF ranges. The amp provides the legal power output of 1500 watts PEP and CW service with no effort and requires a driver delivering between 50 and 80 watts at 50 MHz. With a plate voltage of 3000 volts at 0.8 amps the amplifier performs at 60 percent efficiency. The grid is grounded by means of the grid ring of the 3CX1000A7.....
The amplifier uses a single MRF245 and provides 80 W with 9.4 dB gain..
This circuit uses an oscillator (2N2222) and a diode Dl as a nonlinear mixer. The frequency is set by a slug in Ll. ..
The low-cost Mini-Circuits MAR-X series of chips offer the RF builder a real advantage, with their inherent 50- input and output impedances (needed for RF systems). An MAR-1-based receiver/scanner preamplifier is shown. Ci and C2 are chip capacitors. Use 0.01 for HF, 0.001 for VHF, and 100 pF for above 100 MHz, depending on the low-frequency limit that you desire. ..
This RF converter converts amateur TV signals in the 420- to 450-MHz region to VHF channel 3 or 4, allowing reception of those signals on a standard TV receiver. RF amplifier Ql feeds mixer Ml, and Q3 acts as an IF amplifier. ..
A typical circuit at 20 MHz is shown. The crystal, which has an internal series resistance Rs of 14ohm, oscillates at its third harmonic. The diode clamp Dl and D2 provides a constant amplitude control. ..
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