Wednesday, 16 April 2014

The Review of Fmuser 5W FM Transmitter

The Review of Fmuser 5W FM Transmitter
Hi Sky Blue !
Yesterday I received my Fmuser 5W FM Trasmitter package.
I quickly packed it up to test it.
Can only say that it really meets my needs, and this at a great price.
So many thanks for a very nice deal.

I will mostly use it in the car to get sound from my iphone into car stereo.
To update the car radio with original accessories would cost at least 450 U.S. Dollars,
so this was a very nice and cheap solution only cost me 120USD.

But I obviously had to try it at home too. So I connected the transmitter to
my GP antenna on the roof of the house (see attached picture) and started the transmitter.
I then went in the car for the simplest method of controlling coverage.

At full power, it was actually over 15 km coverage, which was well above my expectations.
At low power, I got a little more than 4 kilometers.
I enclose also two pictures which I have marked the approximate coverage.
If you wish to use this test including my pictures onto eg your homepage to promote this product, it's perfectly OK.

So once again thanks for a great deal!

Sincerely
 
/ Kenneth
 
 
 
 
 
You can participate in " Fmuser activities of the March to April 2013 ".
The  free gift is 2KM 5W FM Transmitter complete set value 120USD !
 Click here to check the details of the gift.

You should do :
1. Visit below link and Copy the Article in the link
    www.fmuser.org/news/Fm-transmitter/The-Review-of-Fmuser-5W-FM-Transmitter.html
2. Post this article in your country influential FM transmitter, ham enthusiasts, radio forum
3. Send the links which you have posted to our Email address sky@fmuser.org

Rules:
1. The person whom posted most links will win the gift,DHL free shipping to all over the world !!!
2. Deadline of this activities is China Time 23:00 19/4/2013 .
3. The winner name will be announced in China time 11:00 20/4/2013 on this page
We will have this kind activities every month, the gifts will be different from every month.
We hope no winners continue to participate in the next month.

Tuesday, 17 May 2011

Ham Radio BFO

 

Ham Radio (amateur radio) is a popular hobby amongst electronics enthusiasts all over the world. Basically the hobby involves a person in making his own gear consisting of a receiver and transmitter or a transceiver (a receiver and a transmitter in one unit) after procuring a licence from the Ministry of Communications. Home brewing or self construction, an integral part of the hobby, has been sadly neglected in our country, despite the fact that various institutions with governmental help have come into being recently.

Hams aboard can buy the latest transceiver off the shelf at a reasonable price and go on the air immediately. But in India, with a sixty per cent duty involved (now changed?), a commercial transceiver would cost a whopping Rs: 50,000. Hence, it is beyond the reach of an average Indian Ham.

The Indian ham is often handicapped for want of ham gear. To overcome this shortcoming a small receiver and a transmitter can be home brewed with indigenously available components. The total outlay may not exceed a few hundred rupees. Some of you may wonder if this is feasible with out fancy test equipment like oscilloscopes and LC bridges etc. Yes it is possible.

Two transistor AM radio Project

 

This two transistor AM radio circuit is also called “mini-radio”. It uses only 2 transistors and few passive components which makes is very easy to be constructed. Although the circuit is very simple, it functions very well without external antenna or ground connection. The transistor T1 works as a feedback regulated HF-amplifier and function as demodulator at the same time. The sensitivity of the receiver is dependent on the amount of feedback and can be adjusted by P1.

The demodulated signal comes out from the collector of T1. The signal is then filtered by C3 so that only the audio signal will be amplified by T2. The amplified signal is then delivered to a high impedance “earphone”. The coil is 65 turns AM antenna wire around a 10 cm long x 10 mm diameter ferrite rod. The tap is at the fifth turn of the coil counting from its ground end. The coil must be installed as close as possible to the PCB.

Transistor radio circuit diagram

The sensitivity of the radio receiver can be greatly improved by attaching an external antenna into it. The external antenna must be coupled to the hot end of the coil through a 4.7 picofarad capacitor. The radio receiver cand be powered by a 9 volt battery. It consumes only 1 mA.

2 transistor radio PCB layout


Source: http://electroschematics.com/

MOSFET-BASED PREAMPLIFIER FOR FM RADIO Project

 

FM transmissions can be received within a range of 40 km. If you are in fringe areas, you may get a very weak signal. FM DXing refers to hearing distant stations (1500 km or more) on the FM band (88-108 MHz). The term ‘DX’ is borrowed from amateur radio operators. It means ‘distance unknown’; ‘D’ stands for ‘distance’ and ‘X’ stands for ‘unknown.’ For an FM receiver lacking gain, or having a poor signal-to-noise ratio, using an external preamplifier improves the signal level.

The dual-gate MOSFET preamplifier circuit shown in Fig. 1 gives an excellent gain of about 18 dB. It costs less and is simple to design. Field-effect transistors (FETs) are superior to bipolar transistors in many applications as these have a much higher gain—approaching that of a vacuum tube. These are classified into junction FETs and MOSFETs. On comparing the FETs with a vacuum tube, the gate implies the grid, the source implies the cathode, and the drain implies the plate.In a transistor, the base implies the grid, the emitter implies the source, and the collector implies the drain. In dual-gate FETs, gate 1 is the signal gate and gate 2 is the control gate. The gates are effectively in series, making it easy to control the dynamic range of the device by varying the bias on gate 2. The MOSFET is more flexible because it can be controlled by a positive or negative voltage at gate 2. The resistance between the gate and rest of the device is extremely high because these are separated by a thin dielectric layer. Thus the MOSFET has an extremely high input impedance. Dual-gate MOSFETs (DG MOSFETs) are very popular among radio amateurs. These are being used in IF amplifiers, mixers, and preamplifiers in HF-VHF transceivers.

The isolation between the gates (G1 and G2) is relatively high in mixer applications. This reduces oscillator pulling and radiation. The oscillator pulling is troublesome particularly in shortwave communications. It is a characteristic in many unsophisticated frequency-changer stages, where the incoming signal, if large, pulls the oscillator frequency slightly off the frequency set by the tuning knob and towards a frequency favourable to the (large) incoming signal. A DG MOSFET can also be used for automatic gain control in RF amplifiers. DG MOSFET BF966S is an n-channel depletion-type MOSFET that is used for general-purpose FM and VHF applications.


In this configuration, it is used for FM radio band. The quadratic input characteristic of the FET input stage gives better results than the exponential characteristic of a bipolar transistor. Gate 1 is meant for input and gate 2 is for gain control. The input from the antenna is fed to gate G1 via C1 and L1. Trimmer VC1 is used to tune and select the input frequencies. Capacitor C4 (100 kpF) at the gain control electrode (gate 2) decouples any variation in G2 voltage at radio frequencies to maintain constant gain. Set preset VR (47k) to adjust the gain or connect a fixed resistor for fixed gain. The output of the circuit is obtained via capacitor C5 and fed to the FM receiver amplifier.

For indoor use, connect a ¼- wavelength whip antenna, ½-wavelength 1.5m wire antenna, or any other indoor antenna set-up with this circuit. You may use a 9V battery without the transformer and diode 1N4007, or any 6V-12V power supply to power the circuit (refer Fig. 1). The RF output can be taken directly through capacitor C5. For an improved input and output impedance, change C1 from 1 kpF to 22 pF and C5 from 1 kpF to 100 kpF. For outdoor use at top mast, like a TV booster, connect the C5 output to the power supply unit (PSU) line. Use RG58U/ RG11 or RG174 cable for feeding the power supply to the receiver amplifier. The PSU for the circuit is the same as that of a TV booster. For TV boosters, two types of mountings are employed: The fixed tuned booster is mounted on the mast of the antenna. The tunable booster consisting of the PSU is placed near the TV set for gain control of various TV channels. (For details, refer ‘High-Gain 4-Stage TV Booster’ on page 72 of Electronics Projects Vol. 8.) Mount the DG MOSFET BF966S at the solder side of the PCB to keep parasitic capacitance as small as possible. Use an epoxy PCB. After soldering, clean the PCB with isopropyl alcohol. Use a suitable


enclosure for the circuit. All component leads must be small. Avoid shambled wiring to prevent poor gain or self oscillations. Connecting a single-element cubical quad antenna to the circuit results in ‘Open Sesam’ for DXing.You can use a folded dipole or any other antenna. However, an excellent performance is obtained with a cubical quad antenna (refer Fig. 2) and Sangean ATS- 803 world-band receiver. In an amplifier, FET is immune to strong signal overloading. It produces less cross-modulation than a conventional transistor having negative temperature coefficient, doesn’t succumb to thermal runaway at high frequencies, and decreases noise. In VHF and UHF, the MOSFET produces less noise and is comparable with JFETs. DG FETs reduce the feedback capacitance as well as the noise power coupled to the gate from the channel, giving stable unneutralised power gain for wide-band applications. This circuit can be used for other frequency bands by changing the inputand the output LC networks. The table here gives details of the network components for DXing of stations at various frequency bands.

Tuesday, 22 March 2011

The VU-Transmitter for 20m

 

K.P.S.Kang, VU20WF of the recently formed VU QRP Club has designed several club projects based upon very small printed circuit boards. The first of these that I saw and built was a transmitter based on the W6BOY Pixie. My version is much bigger than the original - for ease of building.

The drawing shows the circuit of the VU Transmitter. T1 is a Colpitts oscillator with C1 and C2 forming the capacitive feedback divider. The oscillator is crystal controlled but VC provides some useful frequency shift. VC can be a small variable capacitor or a trimmer. The maximum capacitance should be in the 50 to 75pF range. Larger values offer more shift but attempting to move the frequency too much will produce instability and eventually the oscillation will cease. The addition of an inductor of about 16uH will offer several kHz of frequency shift. (see VXO Option)

C3 couples the signal to the power amplifier, T2. The biasing resistor R5 controls the output of T2. Usually a value in the range 33K to 100K is suitable. The higher the value - the higher the output of T2. 47K is a useful starting value for experimentation. I suggest that T2 is not run higher than 1 watt of RF output power. It will get warm and a small star heatsink ought to be fitted.

The collector load for T2, RFC1, is a home made RF Choke. Carefully wind 12 turns of 38 swg (about 34 awg) enamelled copper wire (any small enough gauge will do) through a ferrite bead. RFC2 is a small 100uH axial choke which is essential when using T2 as the receiver mixer. It also provides a useful RF load on the input of T2 and increases the drive to T2. The transmitter output is coupled from the collector of T2 via C4 to a low pass filter.

http://www.southgatearc.org/qrp/transmitter.htm

15 METER VXO-TUNED CW TRANSMITTER


An easy-to-build and affordable CW rig that puts out about 500 milliwatts on15 meters, this simple modification of W7ZOI's classic two-stage "Universal QRP Transmitter" (also known as the "Little Joe" ) features a VXO circuit that "warps" each crystal frequency by as much as 10kHz or more for increased flexibility. This transmitter's oscillator runs throughout the transmit period; voltage is keyed to the amplifier section while the oscillator is on. After construction,tuneup is a snap: connect a 12-15 VDC power source and 50-ohm dummy load or RF wattmeter and tune a monitoring receiver to the anticipated transmit frequency. Flip on the oscillator switch and adjust C3 until a tone is heard on the receiver. Play with C1and notice the shifting of frequency (the crystal frequency DECREASES asC1's capacitance INCREASES). Depress the key and adjust C3 for maximum output. Tuneup adjustment is now complete. Hook up an appropriate antenna (a 40-meter dipole works great on 15 meters without use of a transmatch or antenna tuner)and there you go - bring on the sunspots!

Unless otherwise noted, decimal capacitance values are in microfarads(uF);

whole-number values are in picofarads (pF or uuF).

s.m.=silver mica.

* = see below.

http://boni.narod.ru/15xmtr.html

10-M DSB QRP TRANSMITTER WITH VFO


 

NE602 circuit : 10-M DSB QRP TRANSMITTER WITH VFO
NE602
NE602 circuit : 10-M DSB QRP TRANSMITTER WITH VFO
NE602
The three schematics represent three building blocks for a 10-meter SSB transmitter. Or these blocks can be used separately as circuit modules for other transmitters. The VFO board uses an FET transmittal oscillator, the VFO signal is mixed in an NE602 mixer and is amplified by Q2 to a level suf-ficient to drive an SBL-1 mixer in the transmit mixer stage (+7 to +10 dBm). In the balance mixer/modulator board, an 11-MHz crystal oscillator drives a diode balanced mixer. Audio for mod-ulation purposes is also fed to this mixer. The DSB signal feeds a 28-MHz BPR The 1-W amplifier board consists of a 3-stage amplifier and transmit/receive switching circuitry.