This article continues on from Implementation of G5RV inverted V using high strength aluminium MIG wire documenting review after 5 years operation under a wide range of temperature, humidity and wind conditions.
Above is a view of the steel mast with the Inverted V G5RV rigged from the top of the 11m mast using a halyard though a purchase on a small gibbet to offset the antenna and feed line from the mast. There are lateral guys at 7m height, and the left hand one is non-conductive synthetic fibre rope. Atop the mast is a 2m/70cm vertical. Continue reading Implementation of G5RV inverted V using high strength aluminium MIG wire – 5 year review
Digital display for half wave detector with cubic spline interpolation – part 1 laid out the design concepts of a power meter display.
Whilst the preferred target was an Arduino Zero (SAMD21G) for its 32bit architecture, speed, and 12bit ADC, the code was developed to run on a Zero or a Arduino Nano (ATmega328P). Initially, my preferred approach of storing device calibration parameters in EEPROM was shelved because the SAMD21G does not have EEPROM, and it’s NVM alternative is not nearly as convenient.
Notwithstanding that, EEPROM support has been plumbed in and tested. For devices supporting Arduino EEPROM library, calibration coefficients can be supplied in EEPROM, or inline in source code.
The interpolation table is calculated separately in Excel (using a custom VBA function library), but could be done in any suitable tool.
Above is a screen shot extract of the spreadsheet, the column on the right is C array initialisation code for pasting into the project source code. The same values are loaded into the EEPROM data structure if used. Continue reading Digital display for half wave detector with cubic spline interpolation – part 2
Digital display for QRP labs 20W dummy load – part 1 and the following articles discussed an approach to compensating the non-linear response of the half wave detector by finding a polynomial curve fit over a desired range. Unfortunately, the range for a good fit can be smaller than one desires.
This article discussed an alternative using cubic spline interpolation and might be applicable to extend the range or for responses that aren’t well approximated by a simple curve fit.
Essentially, this technique applies a piecewise polynomial to fit the data points, and a relatively small number of data points may provide a very good approximation.
The graph above shows: Continue reading Digital display for half wave detector with cubic spline interpolation – part 1
Digital display for QRP labs 20W dummy load – part 1 laid out a initial study into the feasibility of an approach to the project.
A prototype has been built based on an Ardunio Nano (ATmega328P 5V 16MHz). The ‘328P is loaded with a custom build of Optiboot 8 supporting reading and writing EEPROM.
Above, another prototype using a 0.96″ 128×64 OLED display, an end to end test of a BAT46 prototype for function testing using an Arduino Nano and OLED display. This prototype is well within 5% accurate based solely on the LTSPICE model, assuming no error in the voltage divider, tracking well from 1W to 20W. When calibrated for the voltage divider and ADC Vref error, power displayed was within 2% of a proven power meter at several spots from 0.8W to 25W, on a spot check it is within 10% (0.4dB) at 1mW. Continue reading Digital display for QRP labs 20W dummy load – part 2
Later NanoVNA-H* hardware allows the device to start in bootloader mode by holding the jog switch in whilst powering on. It is a very convenient facility for firmware update, much more convenient than taking the case apart to jumper BOOT0 to VDD. (Some later firmwares provide a menu option to start the bootloader… but of course that is only useful if the firmware is running properly and may not be useful in the event of a failed firmware update.)
This was a mod I devised prior to the v3.4 hardware change, it is not identical to that change as it preceded it, but it works fine on v3.3 hardware and may work on earlier versions.
The mod calls for replacing R5 with a 1k (1402) and running a short jumper from the T terminal of the jog switch to the un-grounded end of R6.
To use it, hold the jog switch in and turn the nanoVNA on.
Above a pic of the mod. It is a simple mod, but very fine soldering so it might not be within everyone’s capability.
One of the many solutions for updating firmware on the NanoVNA-H* is using ST’s STM32CubeProgrammer.
It would seem that STM32CubeProgrammer deprecates the older DfuSe Demo utility… which remains available for download. Some online experts have inferred that the word Demo in the latter implies it is not the full quid… but they misunderstand the context.
The two are kind of incompatible in that they use difference device drivers. If you set your machine up for one, it breaks the other until you switch the correct driver in.
STM32CubeProgrammer uses libusbk (or the like) whereas DfuSe Demo uses the STub30 driver.
Above is a dump of the driver properties in my working instance. Continue reading NanoVNA-H* – a howto do firmware update using STM32CubeProgrammer
The QRP labs 50-ohm 20W QRP HF Dummy Load is an inexpensive kit for a low power dummy load.
The load comprises 20 x 1W resistors, time will tell what its continuous power rating is actually.
This article explores a possible design for a digital display of power using the provided pads for a half wave detector.
Above, the supplied connector fails a gauge test (the female part sticks out 0.4mm+ (0.015+”) too much… I should have gauged it before assembling the thing.
Above is a ReturnLoss plot from 1-100MHz, ReturnLoss is good below 60MHz, very good below 30MHz. Continue reading Digital display for QRP labs 20W dummy load – part 1
The VK-AMPS 2kW directional coupler is available at modest cost.
The coupler was purchased as an assembled module as pictured above.
It is a Sontheimer coupler and uses AD8307 logarithmic detectors in the FWD and REF channels. Continue reading Digital display for VK-AMPS 2kW directional coupler – part 1
The Revex W560 is a dual range VSWR meter that was also sold under other brand names.
The low frequency range is specified as 1.8-160MHz.
This project is for an external digital display to suit the low frequency band of the W560. Whilst this project is for a specific meter, the techniques are applicable more widely. Continue reading Digital display for Revex W560 directional wattmeter – part 1
How important is coupler Directivity?
Let’s discuss what the term means, and the uncertainty of measurement of DUT VSWR or ReturnLoss due to coupler Directivity.
Coupler performance parameters
Consider the above diagram, when terminated in a matched load, the key performance characteristics are: Continue reading How important is directional coupler Directivity?