Here I propose an affordable yet precise tool to align the wheel of the bike. It consists of a tiny laser mounted on a PCB which serves as a pivot point.

Put a 9 volts battery and proceed as described in the picture below. Put the tool against the rear sprocket and rotate the tool. During the rotation keep the tool perpendicular to the sprocket. The laser will follow the chain from the sprocket up to the gearbox sprocket. If the laser spot is situated at the same distance along the whole path then the rear wheel is aligned correctly. If not, align the rear wheel.

The installation itself is not difficult at takes around 1 hour with a coffee break.

All procedures can be split into these steps:

1. Before taking your screwdriver check the OLED. Connect it to +12V power supply (see image in one of the steps below). Welcome screen should appear.
2. Remove top, bottom and side parts of the FT-290 case.
3. Remove all front panel knobs by simply pulling them. Also unscrew rotary elements behind knobs.
4. Gently pull on front panel. Control board and keyboard are hold together by a couple of bolts and form a sandwich which we need to separate.
5. Once done, we gain the access to the display unit. Unplug it from the keyboard unit (9 pin connector).
6. Desolder red and black wires from the original (old and ugly) display. These two wires serves as a +12V source and power supply the backlight of the S meter. We need them to power up the OLED module.

1. Install the OLED module pcb in the place of the original pcb.
2. Solder +12V from the step 5 to the OLED module. Please no mistakes here, +12V is going to Gray wire and the ground is the Orange wire (see photo).

1. Reinstall everything back.
2. Last important thing, make sure the switch on the back side of the rig is in LAMP position.

Some pictures of the installation

1. Installation guide

Yaesu FT290 yet a very good ham radio rig suffers from a leaky screen which is a natural phenomenon touching soon or late every transceiver of this generation.

In this article, I propose a replacement alternative that is based on the latest OLED technology offering an average lifespan of 30000 hours.

The history started with my FT-290 which needed the screen to be replaced. Looking on the internet for brand new replacement parts I discovered that not match at all information exists on the subject. The only interesting source was found on the ZS1KE website where the author build its own version of the display based on the Arduino microcontroller and describes the communication protocol used by the transceiver to send the info to the original screen which was of great help for me. 

Unfortunately, no contact information of ZS1KE was found, nor any shop where his display can be purchased, I decided to develop my own variant.

The architecture was based on the ST microelectronics microcontroller (MCU) which was acting as a translator between FT-290 data protocol and the OLED screen base on the SSD1306 controller.

First of all, for development purposes, the FT-290 was replaced by an FPGA board which was more or less an emulator able to provide screen data in a good shape and format equal to those sent by the transceiver. As for the MCU, a Nucleo evaluation board was taken.

Using a couple of buttons on the FPGA board I was able to increase and decrease numbers shown on the OLED. This was a big validation step.

Once the Nucleo board can intercept the data from the pseudo rig and send the information to the OLED, I could replace the FPGA board with the FT-290 to see if it works!

After another couple of hours, the OLED was finally able to show the frequency of the transceiver which was 145.001.5 MHz. And of course, this was not static, the frequency was changing almost by miracle when the rotary encoder of the rig was actioned.

The only thing to do was the integration of the OLED into a small place inside of the FT-290. For this purpose, the Nucleo board was replaced with a custom PCB holding a small STM32F103 controller and a couple of resistors.

At this stage, the regulator was initially designed to be supplied with +5V from one of the wires of the ribbon JST connector. However, this voltage was not able to produce enough current to power the OLED and the MCU in my case. Maybe some further investigations should be done. In the meanwhile, the power was migrated to the +12V line also available in the rig. The closest one was directly connected to the old screen to supply the backlight lamp.

Since the power supply was migrated to the +12V line, the temperature of the +3.3V regulator U1 should be checked and the power consumption evaluated. Depending on the percentage of use of the OLED matrix, the current draw varies from 40 to 70 mA. The temperature of the regulator, in this case, is close to 40 °C which is good.

The dimensions of this PCB were carefully designed to be equal to those of the original screen and thus avoid any mounting problems. The position of the OLED screen was also adjusted to fit at its best the window in the plastic cover.

Once everything is assembled back the rig is alive again with a good and clear display showing the frequency but also all other functions like CLAR, Memory, etc.

This OLED module is available on ebay from f4hwk-fr (myself), where you can ask me for any questions.

For measuring the noise figure of amplifiers in a 50 ohm system, noise source which generate Gaussian RF white noise are often used. Here I present a simple prototype of such a source based on two transistors and a zener diode. At the heart of the assembly is therefore a zener diode 1N759 which is the source of noise. Then this noise is amplified by an amplifier based on two BFR93A transistors. The first stage of the amplifier provides the bulk of the voltage gain, while the second allows an adaptation of the output to 50 ohms.

The voltage gain simulated under the amp’s LTspice is 16 V / V (fig.1) and the output matching to 50 ohm (fig.2) are very good on the whole band.

The proto was made on a prototyping plate. The voltage of the + 5V supply of the transistors is supplied by 7805 to have a stable behavior. The voltage of the + 15V diode supply ideally should also be regulated, however I have noticed that the generated noise hardly varies between the range of +/- 1V from the nominal voltage.

We see that with the source switched off at 50 MHz we measure a noise voltage of 36nV / sqrt (Hz), i.e. -135.9 dBm / Hz, while after switching on the noise increases to 92nV / sqrt (Hz), or -127.7 dBm / Hz. The measurement shows that the noise generated is fairly constant over the entire band. The ENR obtained from the source with respect to the thermal floor of -174 dBm / Hz is then around 46 dB.

We also notice the presence of a peak around 56 MHz which I did not understand the nature, it is probably not an oscillation because there is no harmonic of this frequency. Apart from this peak, the spectrum is clean up to 3 GHz. The next step would be to put it in a shielded box and maybe replace the proto plate with a correct PCB.

Some modifications of the broadband noise source presented previously. This second version is based on a two-stage amplifier, with the same BFR93A transistors. The difference here is that the amplifier is supplied with + 12V in order to use a 7812 regulator both for the amplifier but also for the zener diode. The stable and fixed voltage of these two parts is large enough to have a constant noise level. The zener diode used is Panasonic DZ2409100L of 9.1 V in a SMD box.

It can be seen that the voltage amplification of this version is greater, of the order of 25 dB in a 50 ohm load.

The realization is made in the same way, on a plate with hole with a good ground plane (important for the RF) which is in contact with the regulator 7812.

Finally everything is put in an aluminum box. The anodization of the case has been removed from the connections to improve the shielding.

We see that the PSD of the spectrum analyzer (HP8594E) without the noise source is -135 dBm / Hz. With the source on, however, the noise floor rises and displays a PSD that goes from -105 dBm / Hz at 1 MHz to -130 dBm / Hz at 200 MHz, which represents an ENR of up to 69 dB compared to the floor thermal of -174 dBm / Hz.

Here I present a portable Yagi type antenna for the 2 m band, i.e. 144-146 MHz. This is very easy to do, deploys in less than 1 minute and costs only 5 euros.

The design of this antenna was made from an electromagnetic simulation of FEM type. The parameters have been optimized in order to obtain maximum gain starting from a design of a Yagi antenna with two elements, which are the excitation dipole and the reflector. The material necessary for the manufacture of the antenna is illustrated in FIG. 1, it is easily found on the market, but for this antenna everything was purchased from leroymerlin, the store references are given. The material is composed of 3 threaded rods with a diameter of 4 mm (ref. 65299675, 0.52 euro / piece), a square PVC tube with a 15 mm x 15 cm section and a length of 1 m (ref. 65289994, price 2.8 euros ) and some nuts and bolts. You will also need something to cut / saw the rods and a drill (fig. 2).

The dimensions are given in mm in figure 3. From bottom to top we have the strand of the reflector made up of two parts, the total length of which is 98 cm. Then the two identical strands of the dipole. And finally the support, which is the PVC tube with the drilled holes. To power the dipole you also need a piece of coaxial cable. For my part I used an RG316 type cable. The important dimension concerning the latter and the length of the hooks which must be within 40 mm.

The final antenna as well as some technical details on the assembly are given in figures 5,6 and 7. It is noted in figure 6 that an adjustment of the SWR is possible by unscrewing the locknut and varying the length of overtaking.

After assembly and adjustment of the SWR according to figure 6, it should look like what I measured in figures 8,9 and 10. Namely a very good match between 144 MHz and 146 MHz (SWR of 1.2 ). At SWR of 2 the bandwidth is relatively wide and ranges from 138 MHz to 151 MHz.

Finally in terms of gain, the 3D simulation of the antenna promises us a gain of around 6.2 dBi (fig. 11-13), which is pretty good for a 2-element Yagi antenna.

tags: Baofeng UV-5R, NA-771 Nagoya, comparison

Here I am comparing the SWR of the original antenna with that of the obviously counterfeit Nagoya NA-771 antenna.
As can be seen in fig.2 which concerns the original antenna, the latter has a good adaptation in the 2 meter band. In the 70 cm band it is out because its resonance arrives rather than expected, ie at 405 MHz. Around 450 MHz, the antenna is suitable for a ROS 3, which is not perfect, but usable. In fig.3, on the other hand, there is an antenna that cannot be used in the bands provided. In the band around 144 MHz, it has an S11 of -2 dB, and at 70 cm, it has an S11 of -1 dB. Despite the fact that the antenna costs only 3 euros on Amazon, it is still not good to sell antennas that do not work. In practice this manifests itself in permanent cuts with the UHF relay, things that do not happen with the original antenna in my case.

tags: balun, long wire antenna

Here I show my realization of a 1: 9 “BalUn” (actually a UnUn) for the 3-50 MHz band based on two FT114-61 toroids. The use of two toroids instead of one makes it possible to increase the power handling as well as to reduce the number of revolutions required due to the increase in the AL factor. AL measurement, made with a 5-turn winding, determined that the AL of the two tori is about 170 and the resulting inductance is 4 uH.

By putting its values ​​in LTSpice and by putting a load of 450 ohm (transformation 1: 9) at the end of the balun, we see that the latter allows a bandwidth between 3 MHz and 60 MHz for a SWR of 2: 1 (S11 < -10 dB) in the simulation.

The realization of this balun is made according to the wiring illustrated in the figure below. The winding is made with a copper wire of 1 mm in diameter. To ensure a certain seal, the balun is placed in a PVC tube.

To validate the operation of the balun in terms of impedance transformation, a measurement of S11 is made when the balun is loaded by a resistor of 470 ohm. The measurement confirms the result of the simulation and shows that the bandwidth of the balun is between 3 and 50 MHz.

Regarding power handling,
this balun has been tested several times with a transmission power of up to 50 W without any observed problems.

tags: yagi antenna, 70 cm, cheap, simple
This Yagi antenna that I present here was developed with the aim of capturing signals between 430 and 440 MHz from amateur radio satellites. The antenna has three elements and is relatively simple to make and very low impact.
The simulation of the digital model made it possible to fix the dimensions of the antenna and to obtain a prognosis on the bandwidth. In Figure 1 we note that the passband at -10 dB (SWR 2: 1) ranges from 427 to 458 MHz.

The antenna support is a square PVC profile with side 11.5 mm.
The gap between the reflector and the director is 300 mm. The director and the reflector are made with a threaded rod of diameter 4 mm.

The driver element is a folded dipole made from RG316 coaxial cable.
The total length of the dipole is 300 mm. In order to give rigidity to the cable, the latter is inserted into a PVC tube in which an opening is created in order to weld the attack line.

The antenna is almost finished,
just insert the threaded rods and glue the dipole with a glue gun. The ends of the PVC tube are also filled with glue.

The measurement of the SWR of the manufactured antenna (fig.
9) shows that the antenna has a bandwidth between 419.5 and 451.2 MHz for a SWR of 2: 1.

In terms of antenna gain, the simulator promises a gain of around 7.8 dBi.

In the 145 MHz band, this level corresponds to -30 dBuV or 0.03 uV
In the 435 MHz band, this level corresponds to -16.5 dBuV or 0.15 uV
In the VHF band the squelch level and the corresponding voltage (10 kHz FM channel) are shown in the figure below.