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Laptop upgrade: Dell Latitude E7440 → E7270

by kkonrad26-12-201919-11-20204

I have been using my Dell Latitude E7440 laptop (i7-4600U / 16 GB RAM / 480 GB SSD) literally every single day for almost 6 years. I still say this is one of the best laptops ever built. I’ve been looking for a upgrade for quite a long time though. However, I could not wait any longer, because my current laptop would require some expensive investments, including new:

High-capacity battery – that would be the third one (original $100).
Keyboard – that would be also the third one (original $50).
LTE Cat 6 miniPCIe module – to replace the Cat 4 modem ($100).
Some case elements – e.g. bottom cover with rubber feet, but also palmrest w/ touchpad in the near future…

In fact, no wonder that I could not find anything suitable for a very long time, because my requirements for a new laptop were very detailed and specific.

MikroTik RouterBOARD hardware disappointment

by kkonrad25-12-201913-01-20200

I’ve been lately looking for a small 10/100M Ethernet switch with a USB and both PoE input and output port (Power over Ethernet). The MikroTik RouterBOARD hAP (RB951Ui-2nD) looked pretty good, so I ordered one. The 2.4 GHz Wi-Fi interface was unnecessary, but the price was acceptable anyway, as I found a used device in excellent condition at just $25 including shipping.

As usually, the first thing I did after receiving the package was the teardown. The PoE ports are usually dedicated for some remote devices connected with long Ethernet cables and located outdoors. Therefore, a special protection should be included in the front of the controller (QCA9531 SoC in hAP). Unfortunately, this is not the case of RB951Ui-2nD. Although the engineers designed the PCB of this device with TVS diodes on both PoE input and output ports, the final product does not contain them. Protection for other ports was not planned at all.

Arduino Uno R3 failure

by kkonrad18-12-201913-01-20200

Recently I’ve got a genuine Arduino Uno R3 from my friend to repair. The problem with his board was actually very generic – it has just stopped working. Personally, I don’t buy such boards, because they are extremely overpriced. I have been using several Chinese clones around for years and I have not encountered any problems so far.

At first sight, the USB interface was working fine and the board was detected by the system without any problems.

Warflying (Wi-Fi scanning) in an airplane up to 450 km

by kkonrad12-07-201921-03-20234

Recently I was traveling by plane over Europe. Of course, I could not resist to check what could be received on 5 GHz there, at an altitude of over ten kilometers…

I took the following equipment for Wi-Fi scanning onboard:

Mikrotik Routerboard SXT 5HPnD (AR9280),
Raspberry PI 3B with GNSS receiver, RTC and 10 V PoE output – see more: Wardriving @ 5 GHz,
USB power bank (5V/2.1A),
Nexus 7 tablet.

I was scanning using MikroTik SXT antenna with a built-in radio module. This device is as small as 14×14 cm. The dual-polarization antenna rated at 16 dBi is even smaller, at just 11×11 cm. It was connected to Raspberry PI single board computer.

June 2019: London, Manchester and Cardiff via tropo in Poland

by FMDX.pl04-07-201926-01-20200

Ten wpis jest dostępny także w języku polskim: Tropo: Londyn, Manchester i Cardiff w Polsce

The early morning of June, 27th 2019 brought one of the biggest tropospheric propagation from Western Europe we have ever observed from Poland. Looking at the results, it can be stated that it was the strongest tropo on the VHF FM band 87.5-108 MHz from the territories of England, the Netherlands and Belgium for at least 15 years (probably since ever), with many transmitters and areas received for the first time. The received signals reached the stereo and even RDS quality on many frequencies, and the maximum distances exceeded 1500 km.

Review: Airspy HF+

by kkonrad28-01-201903-08-202212

Airspy HF+ is a software defined radio receiver (SDR), which has been widely available since 2017. Unlike most of other devices, it has some cutting edge features like very high dynamic range sigma-delta ADCs and a polyphase harmonic rejection mixer. This receiver supports multiple frequency ranges: 9 kHz – 31 MHz, 60 – 260 MHz and 1.2 – 1.67 GHz (undocumented).

HF+ uses STA709 front-end tuner IC with two Σ∆ ADCs at 36 Msps, which are an equivalent to direct sampling at 72 Msps. The digital signal is decimated, scaled down and streamed via USB. The output I/Q stream provides 16-bit samples at 768 Ksps rate, but the usable bandwidth is a bit narrower though, up to 660 kHz. Actually, this is not much, but seems to be enough for HF, and some purposes at VHF band. More information about this receiver, including a detailed block diagram, is available on Airspy website. This review concerns VHF reception only (i.e. 87.5 – 108 MHz FM broadcast band).