KB0YH’s STLcalc v2.05

In the light of Small transmitting loop calculators – a comparison a reader asked my thoughts on yet another small transmitting loop calculator, KB0YH’s STLcalc v2.05.

There are lots of small loop calculators published, and yes, I have added to the number. Most are some form of elaboration of formulas published by (Hart 1986), and given ‘imprimatur’ by ARRL (Straw 2007). These formulas are deeply flawed, see Reconciling W5QJR’s loop formulas.

For that reason, my first step in reviewing any small loop calculator is to look for hints of Hart. Continue reading KB0YH’s STLcalc v2.05

Another small efficient matching transformer for an EFHW – 2643251002 – #4 – G8GYW build and measurement

The article
Another small efficient matching transformer for an EFHW – 2643251002 – #2 – prototype bench measurement continued the development of a transformer design.

This article analyses measurements at 7.1MHz reported by Mike, G8GYW of his build of a similar transformer.

Above is G8GYW’s build, that is a cm grid on the bench. Continue reading Another small efficient matching transformer for an EFHW – 2643251002 – #4 – G8GYW build and measurement

Digital directional wattmeter – based on G8GYW – part 2

Digital directional wattmeter – based on G8GYW – part 1 laid out the basis of a project. This article discusses some changed code and calibration.

Changed code

Most of the code was changed, importing work done on other projects.

The important thing is that the code provides for a third order polynomial curve fit to measured data.

Also included is a calibration mode which displays the calculated voltage at the forward and reverse detectors given the nominal 1% voltage dividers in the circuit and the measured ADC reference voltage on this chip. Continue reading Digital directional wattmeter – based on G8GYW – part 2

Garden environmental telemetry project – part 3

Garden environmental telemetry project – part 1 laid out plans for a simple maker / DIY IoT garden environmental telemetry system.

Earlier experiments highlighted the disadvantage of analogue sensor connections. This article reports tests on sensors connected using digital signals.

Above is the Dragino RS485-LN LoRaWAN end node, about $90 incl shipping. In this application it will be used to read two MODBUS sensors (each with two data channels) and forward the data to The Things Network via LoRaWAN, then after some processing, RESTFUL submission to Thingspeak. Continue reading Garden environmental telemetry project – part 3

Some wooly thinking on Antenna Factor online

Antenna Factor is often given / used as a parameter for an antenna (system).

An antenna with (nearly) constant AF can be quite convenient to simple field strength measurement where the AF value establishes a simple relationship between antenna terminal voltage and the external electric field strength.

Antenna Factor (AF) is the ratio of field strength to antenna terminal voltage for an antenna, dimensionally \({AF}=\frac{E}{V}=\frac{V/m}{V}=1/m\), AF units are 1/m or can be expressed in dB as \(AF_{dB}=20 \log_{10} AF \text{ dB/m}\).

It is lazy practice (though not uncommon) to simply express AF in dB, but wrong.  Continue reading Some wooly thinking on Antenna Factor online

Garden environmental telemetry project – part 2

Garden environmental telemetry project – part 1 laid out plans for a simple maker / DIY IoT garden environmental telemetry system.

This article reports tests on three sensor configurations, all using a Pt100 sensor with 4-20mA converter.

This article reports

  • Pt100 remote from a 4-20mA converter (ie long Pt100 3 wire wiring);
  • Pt100 with co-located 4-20mA converter (ie long 4-20mA loop wiring);

Pt100 remote from a 4-20mA converter (ie long Pt100 3 wire wiring)

The 4-20mA sensor is 8m of CAT5 cable from the Pt100 element. The Pt100 signal sensitivity is about 400µV/° @ 15° (25000°/V).

Above, some experiments in AC powering and earthing shows the analog sensor chain prone to noise. The first half of the display is powered from a small power bank (18650 cell with switched mode boost converter). The second half is with the 5V derived from a DIN rail mount Chinese 230VAC power supply (copy of Meanwell MDR-2–5), not the quietest of output. Continue reading Garden environmental telemetry project – part 2

LED plate driver failure – 24W round plate

This article documents failure of a 24W LED oyster. The luminaire was purchased complete on eBay for about $45.

After about two years use, the light became sensitive to switching transients on the mains, visibly blinking when other appliances were turn off or on. After some time, this progressed to oscillating on and off for a few seconds on a cold startup, but on hot startup it was stable. Continue reading LED plate driver failure – 24W round plate

Digital directional wattmeter – based on G8GYW – part 1

This article describes a low power digital directional wattmeter based on the design published by G8GYW at https://github.com/G8GYW/g8gyw.github.io .

The complete wattmeter was purchased on Aliexpress for around $70, principally for the hardware as it was intended to replace the firmware.

Above is the seller’s picture of the wattmeter, it has a different display to that used by G8GYW, different resolution but still an I2C OLED mono display. Continue reading Digital directional wattmeter – based on G8GYW – part 1

Diagnosis of a 9:1 transformer from NanoVNA plot – part 2

Diagnosis of a 9:1 transformer from NanoVNA plot discussed an example measurement of a 9:1 transformer on a binocular ferrite core. These are often recommended for use with Beverage antennas on 160 and 80m bands, and this was the maker’s application. In that article, I hinted that the core might not be #73 as the maker thought, or wished.

This article reports measurements of a 9:1 transformer wound on a Fair-rite 2873000202 (#73) binocular core. The pic above shows the test fixture. Continue reading Diagnosis of a 9:1 transformer from NanoVNA plot – part 2

Diagnosis of a 9:1 transformer from NanoVNA plot

A chap recently posted online a question:

I have added two 1:9 transformer (2T/6T) back to back (high side together) and measured with the nanovna – 2 port measurement, as the binocular core I am not confident BN73 or not.

Also I swiped with one port S11, with one transformer where the high side is terminated with a 470ohm resistor load.

Please advise if it can be used for beverage antenna for 160/80m.

Let’s focus on the second test, and assume that the measurements are valid (and that is often an issue), that the 470Ω resistor is close enough to 450+j0Ω and the connections are short.

Above is his s11 sweep from 1 .5-7MHz.

I suspect this is actually #43 material. Continue reading Diagnosis of a 9:1 transformer from NanoVNA plot