This article expands on Effect of ground on HF horizontal dipole efficiency with some more model detail for the technically minded. See the original article for model details and discussion.
Above is the efficiency curve expanded to 80m height, about 2λ. The graph assumes no matching loss (mismatch loss, changed line loss). efficiency may be significantly poorer if not matched efficiently. Continue reading Effect of ground on HF horizontal dipole efficiency – more detail
The Fox flasher MkII is designed to run directly from a 1S LiPo battery at 3.8-4.3V. The battery can be charged by a simple voltage limited charger to 4.1V with a small loss in capacity. This article describes a simple solar charger for such a battery.
The regulator uses a TL431 precision programmable reference in a simple shunt regulator.
Above, the 6V 1W PV array. Continue reading Solar power supply for foxflasher2
This tutorial shows how to explore an inexpensive HMC5883 3 axis magnetometer module with Arduino.
The magnetometer module can be purchased on eBay at very low cost (<$3), and is an ideal educational project for the budding Arduino practitioner.
It is an ideal low cost project for a first exploration of explore I2C, and the basis for a digital compass. This particular module breaks out DRDY which is useful for interrupt driven applications.
Fig 1 shows the test setup:
This tutorial shows how to explore an inexpensive stepper motor and driver board using an Arduino and included stepper library.
The stepper motor and driver board can be purchased on eBay at very low cost, and is an ideal educational project for the budding Arduino practitioner.
Fig 1 shows the test setup:
This project was designed ad-hoc as a learning exercise for a friend who ‘needed’ to acquaint himself with Arduino.
What better than a practical exercise that demonstrates some key advantages and disadvantages of the Arduino environment.
The project was a simple digital thermometer to display normal environment air temperature, say from -20° to 50° using common and inexpensive Arduino hardware with firmware developed on the free Arduino IDE, all using hardware that was on hand. Continue reading Arduino thermistor thermometer – a tutorial
A range of inexpensive serial to Hitachi style LCD interfaces are becoming available.
This article describes the settings for one sold by eshoppingcity1 (and others) on eBay (about A$6 for 5 inc post at the time of writing but they are getting cheaper). It uses the Philips PCF8574T I2C expander chip which is supported by the user developed Arduino LCD Library V1.2.
The Slot.it CA20Z is Ford GT40 supplied as a ‘white’ kit which requires assembly and painting work.
Above is the part assembled bodies for a CA20Z and CS23B after painting with Vallejo 73.601 grey primer surfacer and two full coats of Tamiya X-6 acrylic gloss. The inexpensive Chinese airbrush pictured has been used for a few bodies, and worked very well.
The bright colour should be easy to see in dark parts of tracks. Continue reading Slot.it orange CA20Z build
Transmit performance of 2m hand held transceivers reported relative field strength measurements for some transceiver / antenna combinations.
This article documents a more careful measurement of the absolute field strength of one combination, and application of that knowledge to the other results.
Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) and a small loop antenna.
Above, the RFPM1 RF power meter.
Above is the small loop used for field strength measurement. It is 2mm hard drawn round copper wire formed into a circle 185mm in circumference, and a common mode choke is used to connect the loop to the RFPM1 power sensor. The common mode choke is 0.6m of RG58C/U with 0.5m of ferrite sleeves over it and its loss is accounted for in the “Other Loss” item.
Continue reading Transmit performance of 2m hand held transceivers – absolute gain estimates
A poster sought advice of the forum experts about in service evaluation of the loss of some coax feed lines…
Has anyone tested old coax cable to see if the loss increased over time? I just tested two different coax cables at 146 Mhz with the use of a Bird Model 43 Wattmeter. Power measurements were taken at the input of each cable followed by the output. The load in both cases was a 146 Mhz Ground Plane.
The test results seem to show losses similar to new coax although Berk-Tek foam coax may have had a lower loss when new.
1. Berk-Tek 6211 RG-8X Ultra Flex Foam Coax – 68 feet
Measured 25 watts in and 11.7 watts out which represents a 3.3 db loss. …
Assuming that the stated measured power is in fact the indicated forward power on the Bird 43 directional wattmeter and given that the actual Zo of the line should be very close to the calibration impedance of the Bird (50+j0Ω), then the Matched Line Loss (MLL) is very close to 10*log(PfIn/PfOut)=10*log(25/11.7)=3.3db which is significantly above the expected 2.6dB for ‘ordinary’ RG-8/X and warrants re-measurement as it suggests that the cable might have degraded a little. In fact, the OP later reports 10.7W out for 25W in which is MLL of 3.7dB against spec of 2.6dB… a more convincing case for replacement! Continue reading An interesting case study – in service evaluation of coax loss
I have a little RC-4 temperature logger which has been a really handy device for ensuring that our freezers are cold enough, but no colder.
The RC4 has an internal sensor and is supplied with an external sensor that plugs into a 2.5mm TS jack on the side.
This article explores an alternative sensor that could be embedded in equipment of interest. The sensor is a NTC thermistor.
Firstly, I found that none of the 2.5mm TS plugs I had connected to the RC4 properly, but the T-R of a TRS plug worked reliably.
The display was observed with two 0.1% precision resistors and the thermistor characterised.
Above, it looks like nominally a 110k/B=4200 thermistor… which is a little unusual. 100k thermistors with B=3950 and 4200 are fairly easy to obtain though.
Above is a chart of the error in using the two commonly available thermistors. At low temperatures the 100k/4200 isn’t too bad, around 60° the 100k/3950 is better.
It is a simple matter in Excel to correct readings made with a different thermistor. Here is a VBA function to perform the conversion.
Function temp2temp(ft, ft0, fr0, fb, tt0, tr0, tb) 'function to correct temperature reading to a different thermistor r = Exp((1 / (ft + 273.15) - 1 / (ft0 + 273.15)) * fb) * fr0 temp2temp = 1 / (1 / (tt0 + 273.15) + Log(r / tr0) / tb) - 273.15 End Function
You could squeeze all this into a cell formula if you wished to avoid using a VBA function.
Above is an example measurement run made with a 100k/3950 sensor (Indicated) and the corrected data in brown.
