An upcoming project calls for a stand alone GPS logger.
The requirement is for a GPS stream that allows correction using RTKLIB, but this trial is of a lesser GPS as proof of concept.
Above, the equipment consists here of a Ublox NEO-6M based GPS module (~A$15 incl on eBay) at left, an Openlogger (~A$15 incl post on eBay) at right, and a 12V-5V converter (~A$7 from Hobbyking) at bottom. The latter is a 5A converter, way overkill, but it was on hand. The GPS module has a 3V regulator on board for the NEO-6M chip.
Continue reading Trial of prototype stand alone GPS logger
This article demonstrates an automated Return Loss scan of an antenna using:
- IC-7410 transceiver with CIV;
- 40dB power attenuator;
- Return Loss Bridge (RLB);
- RFPM1 with USB data logger (A prototype data logger for RFPM1); and
- a PC orchestrating the test.
- measurement of a large number of data points;
- improved accuracy by reducing the risk of recording errors; and
- reducing the tedium of a measurement task.
Continue reading Return Loss sweep using IC7410, RL bridge, and RFPM1
I had need of a portable serial data logger for proof of concept of a supplementary data logger for an APRS tracker.
The requirement is to capture RS232-TTL data at 4800bps, 8N1 to a data file for later extraction. The logger needs to restart automatically and append new records to the existing file.
A spare Raspberry Pi2 was applied to the job as a headless data logger.
Above is the RPi2 with an inexpensive FTDI USB/RS232-TTL adapter. Only the ground and RD wires attach to the modified TinyTrak. Continue reading A cheap and cheerful data logger
This project is a data logger accessory for Lou Destefano’s (VK3AQZ) RF Power Meter kit (RFPM1).
The RFPM1 develops an analog signal 0-2000mV corresponding to 0-100dB input power range, -85-16dBm. The module described here produces a digital output scaled -85.0 to 15.0 for 0-2000mV input.
The hardware is based on a clone of the Digispark ATTiny85 USB development board, about A$3 incl shipping on eBay. Differently to the original Digispark, the board above has a micro USB connector on board. The vero ‘mother board’ carries a resistor and 10t pot for calibration adjustment. Continue reading A prototype data logger for RFPM1
In designing a Guanella 1:1 balun, selecting a ferrite core that has been characterised by the manufacturer simplifies the design process greatly.
The manufacturer’s full characterisation includes curves for complex permeability vs frequency and from these the magnetising impedance of the core can be calculated. Note though that tolerances on magnetics are usually fairly wide and they can be quite temperature dependent.
The inductor will usually exhibit a self resonance that is not revealed by the above calculation, but can be reasonably well modelled by adding a small equivalent shunt capacitance, see (Knight 2008). This equivalent capacitance is usually very important and not so easy to estimate, and is often best estimated by careful measurement of the self resonant frequency of the inductor (taking care to back out fixture effects). With experience, one can make a fairly good first guess so that the process is not too iterative.
Some writers say that Cs increases as turns are increased, but (Knight 2008) shows quite the opposite.
Controlling inductor self resonance is a lot about controlling added stray capacitance, eg connecting wires, encapsulation in conductive boxes etc.
Above is a plot of common mode impedance of a FT240-43 ferrite toroid with 11t wound in Reisert cross over style and Cs=3pF. Different scenarios will give different results, but the form will tend to be similar to above. Continue reading Some tools for designing a Guanella 1:1 balun using ferrite toroids
At Characterising an unknown ferrite toroid an ‘unknown’ ferrite toroid was characterised. This article uses that information for design of a Guanella 1:1 current balun.
The proposed design uses 11t of small coax wound in the Reisert ‘cross-over’ style.
The impedance of a single turn vs freq was used to predict the impedance of an 11t choke. Such a choke exhibits a self resonance that can be represented as due to an equivalent shunt capacitance. This equivalent capacitance is not easily estimated, and can best be determined by calibrating an analytical model of the choke for the same self resonance as exhibited by a real choke.
Above is common mode impedance from an analytical model of the choke, assuming an equivalent self capacitance of 11pF.
Continue reading Designing a Guanella 1:1 balun using the ‘unknown’ ferrite toroid
The ‘unknown’ toroid is wound with a single turn and measured with a VNA, an AIMuhf in this case.
Of interest in the first instance is the apparent inductance of the single turn winding at low frequencies where typically permeability µ is fairly constant and core loss is fairly low. Continue reading Characterising an unknown ferrite toroid
There seems a never ending stream of low end antenna analysers appearing.
The Mini60 antenna analyser is one in that vein, and is sure to prove popular because of its low price. As is common, there does not appear to be an English language user manual and the specifications in eBay ads are not very reliable (eg weight: 200kg).
Above is a screenshot from an online demo of the Mini60 on a 7MHz antenna. Continue reading Mini60 antenna analyser
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
Yet another release of AIM software is available, 910A at the time of writing. I have downloaded and tested 8 versions this year, most have been wanting. Again, there is very little detail on what has changed and likely impact on historical measurments.
A quick set of measurements was made on my test inductor pictured above. Continue reading Accuracy of AIMuhf system – AIM910A vs several recent versions on a ferrite cored inductor