Monday, 21 February 2011



Interested in ultra low cost 2 meter antennas that are easy to build using cheap parts; that require no tedious matching and adjusting; that are almost invisible; that are portable, compact, quickly assembled; and that can be converted into a beam? These antennas are somewhat based on the "V" designs in other projects on this site.

They include the Ultra-simple wire version in figure 1
The Table Top version in figure 2
The 2 element beam version in figure 3

Fig. 1 Ultra-simple "wire" version above made on an SO-239 connector.Designed for hanging from any handy support and can be hung from trees, used inside motel rooms or as a "stealth" antenna.

Fig 2. Table top "wire" version above using a dowel or other simple base.Upper and lower elements must be self supporting. Use aluminum or copper tubing. Disregard the reference to the upper insulator in figure 2

Fig 3. Yagi or Beam version above

This is a variation of the designs above.By adding the extra reflector element about 16 inches behind the driven element and increasing it's length to 20 inches each side (5%), some gain can be realized! According to the article, this version had not been tested but should work with a bit of experimentation. It's no more than a standard dipole with a reflector added to come up with a 2 element yagi with all elements bent forward at a 90 degree angle.


In all of these designs, please note that the center conductor from the coax connection is connected to the element in the "down position". According to the article from which these designs were taken, this helps in adjusting swr!

Simply change the angle and or trim each half a very small amount for best swr. Remember on these antennas that the driven elements have to be insulated from each other and also their support.

The beam version can be made in a "T" shape with an insulated boom between the driven element and reflector and the "T" portion for the support mast. Small diameter PVC would be a good choice.You will have to use your ingenuity for the mounting of the elements to the support so the antenna will maintain the approximately 90 degree configuration. Experiment.

An alternate version of each antenna can be built with all elements either vertical or horizontal instead of in the form of a sideways “V”.These designs can be used from HF up thru 440 or above with a little experimentation.Just dig out that old formula you should have learned for a starting point for the lengths......468/freq = half wave dipole (driven element) and add 5 percent to the length for the reflector.

The spacing should be a little less than .25 wave lengths from driven to reflector.(According to the article, using a director and driven element arrangement would cause problems with a poor match and the spacing would be a lot closer.)Using an MFJ 259b or equal would help with tuning the antenna for your particular choice of frequency, but if you're not that lucky, then just use the old swr meter and very low power while testing. As always, start with longer elements and trim down. It is very difficult to add length!

250mW FM transmitter


A very simple FM transmitter electronic project can be designed using this circuit diagram . This FM transmitter electronic project works in FM band and it has a transmission power around 250mW ( thing that make it to work at above hundred meters ) . This FM transmitter electronic circuit is very simple and is based on some common transistors and electronic parts .
T1 transistor can be a BC107, BC171 or equivalent , and is used as an small audio preamplifier that amplify the audio signal from the microphone . Adjusting the R2 variable resistor, audio signal level from the input ( microphone ) can be adjusted until will be delivered to the T1 preamplifier (an over amplified signal applied to T1 can produce an overmodulation) . From T1 , signal is delivered to T2 which form an Hartley oscillator (frequency of this oscillator depends of C8,C9 and L1) .

The transmitter frequency oscillator works in FM band 87.5-108 MHz and can be set , adjusting C8 capacitor and L1 coil . L1 coil must have four turnings on a 0.8-1 mm cylinder support with a 6 mm diameter (space between each wire must be around 1 mm ) .Antenna used for this project can be a simple telescopic antenna or a 60-70 mm Cu wire .
This electronic project can be powered from a wide range input voltage from 9 to 12 volts Dc ( but can be used even a 18 volts DC .

simple FM transmitter electronic project circuit using transistors

HF VHF UHF active antenna electronic project


A very simple and efficiency active antenna electronic project can be designed using this electronic schematic circuit that is based on transistors. This active antenna electronic project is useful for a wide range of RF frequencies covering three RF bands HF , VHF and UHF . This simple active antenna is designed to amplify signals from 3 to 3000 MegaHertz, including three recognized ranges: 3-30Mhz high-frequency (HF) signals; 3-300Mhz veryhigh frequency (VHF) signals; 300-3000MHz ultra-high (UHF) frequency signals.

This HF VHF UHF active antenna contains only two active elements : Q1 (which is an
MFE201 N-Channel dual-gate MOSFET) and Q2 (which is an 2SC2570 NPN VHF silicon transistor). Those transistors provide the basis of two independent, switchable RF pre-amplifiers. Two DPDT switches play a major role in this circuit , switch S1 used to select one of the two pre-amplifier circuits (either HF or VHF/UHF) and switch 2 is used to turn off the power to the circuit, while coupling the incoming RF directly to the input of the receiver.

S2 is useful to give to receiver nonamplified signal access to the auxiliary antenna jack, at J1, as well as the on-board telescoping whip antenna.This circuit must be powered from a simple 9 volt DC power circuit ( or a 9 volts battery) and is very useful for use as an indoor antenna .

HF VHF UHF signal booster active antenna electronic project