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Monday, August 26, 2019

Cleaning a Power Bank

One common option to supply the small TTGO LoRa boards is to use a small power bank. For supply small devices like these boards I use one really cheap power bank, so cheap it can be obtained for 0.80 euros from China (with no 18650 li-ion cell included, of course).

The 0.80 euros power bank



It seemed to work just fine but powering a 433 MHz TTGO board I noticed the power bank itself radiates a lot of noise in this frequencies.  UHF noise from a switching mode power supply is a new record for me!

But... Can it be cleaned?

Saturday, August 17, 2019

Fuses in TTGO LoRa V1.6

Today, probably the most common ESP32 LoRa board is the TTGO V2-1.6. In a very small factor it offers OLED screen, WiFi, Bluetooth, micro SD slot, li-ion charger... and a lot of problems.

The problems seem to come from the polyfuses installed in the board. There are two of them, and each one offers a different set of problems.


Sunday, July 7, 2019

The Screaming TTGO T-Beam

If you are playing with LoRa devices it is pretty sure you have some ESP32 LoRa boards, and probably a ESP32 based TTGO T-Beam. This board is quite interesting because it includes a GPS, making very easy to compute distances of messages sent and received through LoRa chips.

TTGO T-Beam ESP32 based LoRa Board

Saturday, November 25, 2017

Icom IC-R7100 and its clicking noise

Some time ago an Icom IC-R7100 arrived to my shack. It's a nice receiver and works surprisingly well but almost the very first time I powered it up an annoying feature came up: every time the squelch opens or closes, It produces a clicking noise.


It is ok for the first five minutes but it can be irritating after that.

Sunday, September 24, 2017

Repairing an Anritsu MS2711A handheld spectrum analyzer

One night, I was searching eBay with no especial interest when I found something interesting, a cheap non working Anritsu MS2711A spectrum analyzer. The photos shown a turned on analyzer, and some signals (noise) appeared in the LCD. The LCD had some dead lines at the bottom, but nothing serious.

A small size spectrum analyzer is very tempting. I have another two full-size spectrum analyzers but they are so big and my space so limited I rarely use them. These small units are somewhat very limited compared to a real spectrum analyzer, but I was pretty sure I would use it much more often than the two units I already have.

After a few minutes, I decided to buy it.

Friday, September 8, 2017

Repairing the OM345 hybrid module

Recently I had to repair a Marconi 2022E signal generator. It's a nice unit, relatively small, and well suited for amateur use. Talking about repairing the old Marconi instrumentation is talking about the Phillips OM345 hybrid modules. Why? Because they has a really high failure rate and old Marconi equipment make extensive use of these modules.

Sunday, July 16, 2017

Considerations about the Hiland Adjustable DC Regulated Power Supply Kit‎

My "lab" power supply was a homemade one I made/upgrade some years ago. It was constructed around a LM350K TO-3 regulator and worked very well. But I really missed one function: adjustable current limit.

The LM350K regulator has a fixed current limit around 2-3 amps, but usually that is just too much current for a prototype. Many times, when something went wrong, one or more components went burnt.