Welcome to my homebrew page...

The original diagram was taken from the data sheet of Mitsubishi 2SC1946A designed to operate at 175MHz. Both input and output tuning network was modified to work between 88 to 108MHz very well intended for our main purpose. Large heat sink is required since the 2SC1946A must operate at 100% duty cycle. Forced air cooling aids in dissipating the heat produced by the rf transistor. The use of high voltage trimmer capacitor is a must and the use of ground plane technique is best suited for this project. RF input of 1 to 2 watts coming out from the exciter is enough to drive this amplifier to produce 20 to 25 watts of rf output assuming that the DC supply is at 12 volts. Take note that this rf amplifier is operated in class C therefore, the need for low pass filter in the output must be installed to avoid interference caused by the harmonics generated by this amplifier. --- 73 de hevir

This collinear antenna works perfectly after the installation. The antenna is basically two dipoles excited in-phase and theoritically exhibits 3 dB of gain when compared to a dipole. 3/8" aluminum tubing was used here but i suggest 1/2" will do the job even better. The quarterwave stub is made of #12awg stranded wire and is grounded at the center(null). When properly tune, this antenna should have SWR value of 1:1.1  to 1:1.2.   73 de hevir

Feels good to have a new ticket. I would like to give thanks to my fellow hams (DX1CW) who have provided me the reviewers that made possible for me to pass the Class A amateur exam.   ---73 de DU1VSS

This fm rf amplifier uses 2SC1971 transistor to provide 5 watts of output. Output matching is adjusted via the two 40pF trimmer capacitors likewise also to the input. Note that the emitter of this transistor is directly grounded on the heat sink and should have a good thermal transfer. Driving power of 100 to 200mW can be applied in order to provide 5watts of output. Use a dummy load to tune this amplifier and remember that  the transistor is biased in Class C, sufficient filtering should be followed after the output to minimize all the harmonics. Use  ground plane construction technique in the PCB lay-out for best result, the more the grounding the better. If you have hard time finding the 10uH rf choke, try to wind 1/2 meter of 0.2mm enamel wire over a 33K 1/2 watt resistor  and solder the coil ends to the legs of the resistor ---73 de hevir

Here is a simple battery charger circuit intended for 12 Volt gell-type battery. Current is limited by the 7805 regulator IC and the limiting resistor (62 ohms) to approximately 250 milliamperes, anyway most small sized gell-type battery capacities ranges from 2.5AH to 7.5AH so charging time should take several hours. When the battery is full, the regulator adjust its voltage output from 15 volts down to 5 volts automatically terminate the charging process.  ---73 de hevir

Another evening project is this OPC-478 cloning cable for my Icom IC-2200H. Credit is given to Icom which the original circuit was taken and also to the cloning software (CS-2200H) used on this project. The prototype board supply was taken from the RS232 port of the computer while if this does not work, the 5 volts can be supplied externally. A quick check on the COM port setting of your PC before running the cloning program will prevent any conflict. If your PC does not have RS232, you can have an RS232-to-USB converter available in computer shops. ---73 de hevir

The circuit  uses the MOC3020 optocoupler that drives the triac to switch 220V of AC volt to a load. We have this project after one of our incubator heater failed due to a faulty mechanical relay. The triac on this circuit can be directly mounted on a suitable heatsink without a need for an insulator. The original circuit was taken from the MOC3020 Motorola datasheet.    ---73 de hevir 

The circuit is run by 555 timer IC for its PTT sequence that is 4 seconds "on" and 4 seconds "off". Transmission is about 50% duty cycle that minimize the transmitter heat. Tone IC is any thing that generates sound, I got mine from a magnetic door open sensor which I bought from Japanese Store in Festival Mall. The prototype when connected to a portable transceiver is ready to go on air.  ---73 de hevir

Here is a sample interface unit configured as a server. At the left of the interface is an IC-T2H portable transceiver where the interface is connected.  During installation, there are some points to consider. Avoid putting rubber ducky antenna on the radio since rf radiation can interfere the interface function, also never put too much strains on the shielded wires since these can be easily damaged. Adjust the unit for proper sensitivity for a continuous transmission when the audio is present at the input. After tune-up had been completed, the server is good to go on-air. If you wish to include a station identifier on the server, you can download Say The Time at www.4shared.com , and if you want a simplex repeater just download the program with this link http://www.4shared.com/file/251787798/7e70eb78/simplex.html . There are lot of things you can do with the interface, its for you to discover.  ---73 de hevir

Another weekend project is this microphone preamplifier which came from my new book Hints and Kinks for the Amateur Radio. The amplifier is a single transistor powered by the 8 volts from the radio transceiver. I can't find any vintage desk microphone casing so I ended up with this pink jewelry box which I obtained from a novelty store, anyway the output audio was very nice and a little treblish. All the needed parts are available at my favorite electronic store at very minimal cost. ---73 de hevir

Learning morse code is fun and exciting. At first, I don't see the importance of it thinking that this is just an obsolete form of communication. With the encouragement and help of my friends on the air, I was hooked with it and began to search different circuits about the morse code oscillator. I started with the 555 timer IC taken from my ARRL 1989 edition handbook but the audio quality of the oscillator was very irritating to my ear. This was due to the inherent square wave output of the 555 IC. Several search in the internet brought me the idea of constructing an audio oscillator that will generates a pure sine wave at 800Hz. In my project the circuit was the popular Bridge-T oscillator and then feeds to an audio amplifier to increase the output audio. The resulting output tone was nice and pleasant to hear as what the other station gives compliment to my oscillator.

The PCB board and the speaker were enclosed on an empty CPU power supply casing. On the side of the casing, my homemade straight key is mounted using a contact cement. The straight key was constructed using a hard disk motor. Kindly check the attachment for the oscillator circuit.  ---73 de hevir

I just brought my new Steady-Volt 24Amps, 13.8Volts power supply
that cost several thousand bucks at RadioCom somewhere there in
Pasay. I was excited and at the same time curious on what is inside
of the unit. When I came home, I did not bother to check
the output voltage if it was correct but I did open the
unit to check the inside. To my surprise, there was not even one IC
present in the regulator board of the supply. Further checks revealed
that regulation was accomplished using an ordinary zener diode,
resistors,capacitors and few transistors. To my contentment, I tried
to trace their original circuit to find out how it works and the
results are:

1. Zener diode was used to provide regulation. It is known that
zener diode is not capable of sustaining good regulation
specially on higher current.

2. The power transistors were wired in series
pass configuration and is installed after the regulator. This design
flaw is the main reason why the supply could not maintain
regulation when the load draws high current.

3. The OVP circuit (over voltage protect) is continuously on (relay)
while the power supply unit is idle. With this condition, the relay
coil might easily burned and will not sustain long hours of continuous
operation.

Several research on the internet leads me to the data sheet of LM317
from National Semiconductor which have the example applications of
their product. One example of LM317 circuit looks promising and can be easily
be replaced with a 7812 regulator to eliminate the use of biasing resistors.
The regulator circuit employs a PNP transistor that drive the bases of the
current hungry pass transistors. The 7812 regulator IC was wired as
wrap-around thus,it can able to maintain good regulation even if the load
draws more current. Prototype followed after I have secured all the
needed parts on the circuit. Final testing of the modified unit showed a
very stable output voltage at a varying load currents. My modified power
supply was able to power my IC-2200H at 65 watts and to the IC-720 HF
transceiver 100 watts on SSB.    ---73 de hevir

Working with distant stations can be more easy if we are using a directional antenna. A very common type of this is the Yagi-Uda whom every ham is familiar with. Yagi antenna able to achieve higher gain because if its ability to concentrate rf signal in only one direction, a similar comparison to this is the flashlight whose light energy can be focused to a certain direction and thus able to illuminate more distance as compared to an ordinary incandescent bulb.

 
On this project, with only few number of hand tools, I decided to construct the seven elements directional antenna designed by Cushcraft. The original design uses the conventional gamma-match method on its driven element and the solid aluminum rods on its parasitic elements. Deviating from the original design due to limited source of materials, this project uses anodized aluminum square tubing instead of a round tube for the antenna boom. The  driven element together with all the parasitic elements are all made from 3/8" anodized aluminum tubing. Securing these elements on the square boom is no sweat thanks to the help of the plastic element insulator which can be obtained from electronic stores. The parasitic elements were drilled on the center so that a stainless screw will secure its place on the side of the boom, this also provides DC ground for lightning protection of the antenna. The plastic element insulator help to secure each element straight and aligned on the square boom.

The main modification here is the driven element because it uses the center fed - open dipole design instead of the conventional gamma-match method. This approach eliminates the difficulty of tuning since the dipole is feed by a 1:1 coaxial balun. Once the dimensions are followed closely, there is no need to do further adjustments since antenna resonates  at 144Mhz with SWR reading near 1.0 .....      73 de hevir