"Tactical antennas"? Well...

 In the last year, the ham addressed market was flooded with a military style VHF/UHF antennas. 

The retailers are targeting the preppers which, we know, are avid buyers of "green" stuff  like camo Baofengs and other things like that.

I ordered a few of those antennas from different sellers on a big online store and some of them even arrived.

They are made from three different parts: a small rubber base, a gooseneck which can be put into the place or removed and a long radiator made from which seems to be steel band wrapped in a nice plastic cover.

I played a little with them and I was not impressed about the performance.

Then, I tested the black rubber base on my Sitemaster 331 to see how is it the SWR and something pretty strange happened.

The rubber base had dips around 150 MHz and 450 MHz. All of them. For me, a deep dip is an indication  that somewhere inside them is a tuned circuit. 

One of them had the rubber sleeve losen so i took it apart. Inside it was indeed a tuned circuit. A coil from ground to the radiator and from the hot center pin, two capacitors were going on different taps on the coil. A few turns was shortcircuited with solder-something-alloy. Some similar antennas are sold for CB portable radios so, probably, the short is not there on those versions.

The coil was made around a white plastic cilinder which turned out to melt around 220 Celsius.

What was really strange was the wire from which the coil was made! It was not copper but steel!

Another bad sign was the assembly between the central pin isolator and the coil support. Only a few mm is there to take all the mechanichal stress. 

They are made this way probably to change the connector for different "versions".

After that, I was eager to test my assumption about the long flat radiator. I stripped the thermo plastic sleeve with a cutter and exposed a yellow steel tape. Yellow on both sides. 

On the inside, the steel tape was marked in meters so my theory was right: those antennas are a new form of recycling the measurement tapes.

In my opinion, these antennas are just shit.

Software defined lab power supply

Sometimes in the lab there is need to monitor the power parameters during some period of time and put it on a nice graph.

Because I couldn't find something like this and because it is fun to make things, I start to wonder what if I put an Arduino on a power supply!

So, the lab supply must have:

-Variable voltage between 1- 14.4V

-Current monitor

-Start/Stop

-Overcurrent protection

-Serial output with time markers

Because I am lazy, I used some ready-made modules.

The main power supply is a modified 12V/5A SMPS; with a little tweak it now deliver 17V/4A.

The modification was made in the feedback circuit where the TL494 reference is compared with the output voltage.

The variable output voltage is made with a DC/DC Step down module able to handle constant voltage from 1.25 to Vsmps - 2V at around 5 A.

The output voltage and current are measured with the Arduino ADCs and I used two 2.5 LM4050 precision shunt reference in series to have Aref at 5V. 

The DC/DC Step down is controlled with a PCF optocoupler driven by a digital potentiometer MCP41010 on SPI.

The output relay is used for fast protection as a "crowbar" circuit and, in the future, will connect the output  to a controlled discharge circuit to characterise batteries.

By code, this power supply can be used to deliver regulated voltage and monitor the current or to charge various batteries.

The schematic:

The code is on Github.

Bandpass VHF and UHF filters

 For the next project (IRIS) I need two small filters, one for VHF and one for UHF. 

The goal is to get rid of the out of band signals.

On modern (especially portable) radios, the front end receiving circuit is not so selective and the received signal to noise ratio is pretty bad, sometime making receiving impossible.

Therefore, wherever is possible, some good, selective passband filters has to be put in place.

The next project has to do with small signals and I must make those filters for VHF and UHF hamradio bands.

Fast and dirty tests looked OK so I made these filters. 

No drawings, just experience :-)

The VHF filters is inspired by a picture found on VE3IUL site.

A nice web page about filters here.

I tested with my IC E92 portable and I could be heard with SLO which, is around 100 mW.

Xiegu G90 - backlight for Front panel keypad

There are not many features missing from the Xiegu G90... At least, when is about hardware, in the firmware, there is another story.

When I was replacing the STM32F103 in the front panel, I was asking myself if I can add backlight to the front panel keypad. At that moment I was focused on that repair job and I put the ideea on other shelf.

These days I will get involved into a big project and I will have to let down this kind of PMR (Pimp My Radio)  projects so I thought this is the right time to gave it a chance.

I have around some SMD LEDs and some ideea so, I get to the bench and opened, once more, the front panel assembly.

I did some tests about how the light is diffused in the rubber keypad and I investigated the places where I can put some LEDs.

The space between the PCB and the keypad is none so we need some alteration in the keypad rubber to accomodate the LEDs and the wires.

First try was with the tip of the soldering iron but, to my surprise, nothing had happened.

Then, I tried to use a 3.5mm drill to remove the rubber in an "organised" manner... nothing! The rubber act like rubber and get back into the hole.

Short story: I couldn't found the proper way to make 3mm holes with low risk of destruction.

The problem is that I must embedd not only LEDs but also the wires that goes to them. About the wiring, I had in plan to use 26 Gauge wrapping wire (around 0.5mm) so a proper way to make them too has to be found.

Here is the optimal position for a bunch of wide angle SMD LEDs to diffuse the light into the keypad.

NOTE 1: the botom line of keypad is already illuminated by the backlight from the LCD. Not very bright but enough to be seen into the dark.

NOTE 2: the colour of the LEDs has to be different than the two LEDs for Function and CW decoder because the light will be conducted in those too and will cause them to appear lit.

Custom ATMEGA328p board

 There is a time when an Arduino is too big and has useless features.

An ATMEGA328p on a breadboard, using internal clock at 8 MHz with a common Arduino Bootloader has to be made.

ATMEGA328 datasheet.

Some references here, notes to myself but also usefull (maybe) for others.

Pin map:

The Reset circuit should be a resistor from RST pin to Vcc and a 0.1uF capacitor from RST to whatever....