An experimental propagation beacon on 144.385MHz – part 2

An experimental propagation beacon on 144.385MHz laid out plans and some first test results.

This article explores a possible deployment scenario and likely paths over which it may be ‘heard’ using Spectrum Lab or the like to dig the signal out of the noise.

Path

Transmit end

Tx power is 10W with on-off keying (OOK or A1 CW).

Tx antenna system gain ~17dBi.

Receive end

Rx antenna gain is 9dBi.

Rx NF specification is 12dB (4236K).

Above are the results of an ambient noise test. In this case, the noise floor at the antenna is some 7000K, it is probably ~7dB higher than a modest weak signal station. Continue reading An experimental propagation beacon on 144.385MHz – part 2

An experimental propagation beacon on 144.385MHz

An experimental beacon on 144MHz has been deployed for evaluation. The beacon is designed to permit observation of aircraft enhancement propagation by way of a 200+s unmodulated carrier in each 300s cycle. Ident is by very slow Morse code. Necessary bandwidth (ITU-R SM.1138-3) is just under 5Hz, requiring 5Hz receiver bandwidth for ‘crisp’ decoding under weak signal conditions, but 1Hz receiver bandwidth is better for observing aircraft reflections.

There has been long running argument about whether such propagation paths are reflection from hot gasses behind the aircraft, or reflection from conducting skin on the aircraft. With increasing use of reinforced plastic skins, we may observe different response from similarly sized aircraft, depending on the skin, and these differences may be frequency dependent.

An interesting topic for study.

Details:

  • frequency: 144.385MHz, 144.384Hz USB dial freq, 144.385MHZ dial frequency in CW mode on modern transceivers (accuracy should be within 200Hz);
  • power: 20W EIRP (current details: https://vkspotter.com/?action=beacon-item&bid=355), ACT, horizontally polarised, antenna is 20m AGL;
  • modulation: ~5 minute cycle uses A1 Morse modulation (OOK) QRSS1 (1s dits) callsign (VK1OD) followed by key down for the rest of the cycle;
  • location is QF44op.

Continue reading An experimental propagation beacon on 144.385MHz

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 an inch 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