VU3SQM offers an interesting directional coupler based on a Sontheimer coupler, and using AD8307 power sensing for a nominally HF coupler. I must say that I am not a fan of Sontheimer couplers… but that is what the board uses.
This article lays out a preliminary design review to assist in selection of appropriate toroids, and ordering of the needed parts.
Above, the top side of a PCB. Continue reading VU3SQM directional wattmeter build – #1
Elecraft produces a directional coupler that may interest QRP aficionados. It comes with instructions for 20dB and 30dB coupling factors rated at 25 and 250W respectively from 1 to 30MHz.
This article reviews the magnetics design of the -20dB / 25W coupler.
The coupler uses a type of Sontheimer coupler (Sontheimer 1966) and these are commonly poorly designed. The first question is whether the magnetising impedance of T2 which appears in shunt with the load is sufficiently high to not give rise to poor insertion VSWR. Continue reading Elecraft CP-1 directional coupler – magnetics review
We have had wired broadband service delivered to these premises for almost ten years, supplied by five vendors: Telstra Bigpond, iiNet, Amaysim, Southern Phone and now Exetel.
At The first seven days of Exetel broadband Internet access I discussed the performance failure of the service observed over the first seven days.
Following that, a fault report was submitted to Exetel, and at their request, further observation of speed and ping test latency.
I have an expectation that “I want it to deliver most of the rated speed, most of the time during the hours that I want to use it”.
As a result of behaviour of the industry, the ACCC gives some guidance on terms used to advertise a service, and a service expectation.
Essentially they say:
Standard Plus Evening Speed—plans using this label will deliver a minimum speed of 30Mbps during the busy period. This plan would be suitable for a higher usage profile (e.g. streaming an ultra-high definition movie and streaming music on one or more other device during the busy period)
So on that measure, how well did they perform?
Above are the results of file transfer tests conducted automatically, the above are filtered for those in the ACCC’s defined “evening hours” on which they base their service level enforcement. All x symbols in the pink area break the 30Mb/s minimum. Continue reading The first 21 days of Exetel broadband Internet access
I have an inexpensive (~$10 inc post) digital temperature controller that was observed to have very high RF emissions and was unusable because it was incompatible with radio operations here.
There has been enhanced firmware for a STC1000 controller based on a PIC chip, but in my experience, most seem to be made with an STM8S003F3 chip. More recently, what appears to be a port of the PIC software to STM8 has been published at https://github.com/Emile666/stc1000_stm8.
The enhanced firmware is directed at home brewing for control of long running fermentation processes etc, incorporating storage for a number of multi-step programs (profiles). It is not really suited to more general applications like a fridge controller as for example it is more difficult for the common operation to set the set point.
I thought it might be entertaining to try it out.
Installation of the firmware was straight forward, I had the necessary programming adapter and software.
Interestingly, after updating the firmware, the device would not start on its original power supply. My suspicion is that the new firmware runs the LED display at higher duty cycle and the power supply could not withstand the load.
Since the power supply had RF emission problems, it was removed and the device converted to 12V DC.
Above, the large components of the switched mode power supply were removed, a Polyswitch protective device installed and input routed to the output terminals of the old 12V output switched mode power supply (white wire is -ve, brown wire is +ve). Continue reading STC1000 firmware change
On Thevenin’s theorem looked at a simple source network to demonstrate some key characteristics and limitations of Thevenin’s equivalent circuit.
The example network used was linear in V,I for all V,I combinations possible. Let’s now look at a network that is not linear for all V,I, but is sufficiently linear over a sub range to be usefully modelled using Thevenin’s equivalent circuit.
For the purpose of discussion, we have a Black Box with just two terminals and is a source of DC voltage and current, and the internal implementation is hidden from us.
A series of measurements is made with different load resistors attached and the voltage and current at the terminals is recorded and plotted uniformly stepped currents.
The V,I characteristic is clearly non-linear, but on closer examination there are two fairly linear regions, from 0.008 to 0.060A and 0.08A to 0.1A. It is a device that is usually used in the region below the knee, and for our application, let us concentrate on 0.008 to 0.030A. Continue reading On Thevenin’s theorem – #2
Seeing another long running discussion on QRZ about transmitters and antennas, and maximum power transfer and Thevenin equivalent circuits prompts some discussion.
Thevenin published his theorem in 1883, the following is an English translation: Continue reading On Thevenin’s theorem
I purchased a FT232R adapter which claimed to use an FTDI chipset, indeed the seller’s pics showed an FTDI label.
Above, the labelled chip in the seller’s pics. Continue reading Counterfeit FTDI – another form
We have had wired broadband service delivered to these premises for almost ten years, supplied by five vendors: Telstra Bigpond, iiNet, Amaysim, Southern Phone and now Exetel.
The change from Amaysim was at Amaysim’s choice, they decided to quit the wired broadband business stating that they could not make a profit, and they sold their customer base to Southern Phone.
Southern Phone was unable to deliver the VOIP service we have had for many years through all of those broadband suppliers, so we churned to an Exetel “Standard Plus” service.
The cutover was badly coordinated, there was a 12 hour outage, and I had to phone Exetel (yes, wait in the interminable queue to try to get the modem PPP credentials, it had DSL service and was routed to Exetel, just needed the authorisation details for Exetel).
Telecommunications providers are all about strong procedures for handling usual business, and this part of the business is known as provisioning. The events with Exetel hint that their provisioning processes are not sensitive to churning an existing NBN connected service which should be done to minimise disruption, including advising the logon credentials, doing it when their support desk is open, holding if the customer needs a new modem etc. This is the bread and butter of the business, but a FAIL to Exetel on this occasion.
First impressions are lasting ones… so how do they come back from that start?
I have an expectation that “I want it to deliver most of the rated speed, most of the time during the hours that I want to use it”.
As a result of behaviour of the industry, the ACCC gives some guidance on terms used to advertise a service, and a service expectation.
Essentially they say:
Standard Plus Evening Speed—plans using this label will deliver a minimum speed of 30Mbps during the busy period. This plan would be suitable for a higher usage profile (e.g. streaming an ultra-high definition movie and streaming music on one or more other device during the busy period)
So on that measure, how well did they perform?
Above are the results of file transfer tests conducted automatically, the above are filtered for those in the ACCC’s defined “evening hours” on which they base their service level enforcement. All + symbols in the pink area break the 30Mb/s minimum. Continue reading The first seven days of Exetel broadband Internet access
I have started using Arduino Pro Micros recently, and sourced inexpensive clones from China.
Experience is that all manner of inexpensive small microcontroller modules from China are likely to have issues with the bootloader: it isn’t there, it is back level, not suited to the actual clock speed.
I have come to routinely install a current / known / working bootloader to avoid wasting time down the track.
The Pro Micro does not have an ISP header, and the QFN package does not suit a chip adapter, so the next option is an adapter that can connect to the board with no pins, male or female headers, top or bottom.
Above is an adapter built on a small piece of Veroboard. If you are ging to copy it, make it one row of holes higher. I did initially, and in a miscount of rows, I incorrectly removed the top row. The black mark identifies the pin 1 of the Pro Micro, and the adapter connects to the side with the /RST pin.
The headers on the adapter engage JP6, preserving the pin ordering, pin 1 to the black mark on the veroboard.
Continue reading ISP adapter for Arduino Pro Mini / Pro Micro
We have had wired broadband service delivered to these premises for almost ten years, supplied by five vendors: Telstra Bigpond, iiNet, Amaysim, Southern Phone and now Exetel.
Download speed is an important performance characteristic, and fairly quantifying it is a challenge.
If I were to express my service expectation as “I want it to deliver most of the rated speed, most of the time during the hours that I want to use it” we can express that by better defining the three terms:
Let’s consider that most means 80%, so the critical value of speed is 80% of the rated speed, eg 80% of 12Mb/s is 9.6Mb/s.
Let’s consider that most means 80%, so the critical value is 80% of the time.
I sleep at nights, and use the Internet variously during the day, the most important times for service to be adequate are from 06:00 to 20:00.
Capturing the foregoing, I could write “Download speed must exceed 80% of the rated speed, 80% of the time between the hours of 06:00 and 20:00” each week.
This is known as a Service Level specification.
Statistically, this is stated as the 20 percentile speed measured between 06:00 and 22:00 over a week must be greater than 80% of the rated speed.
A realistic simple HTTP download is scheduled every half hour, and the effective download speed is recorded. This data has been gathered for many years.
Over the nearly 10 years of service, the rated speed has varied, 8, 12, and 50Mb/s at different times. To compare these, the speed in any one observation needs to be normalised to the applicable rated speed, so for this purpose speed is calculated as a percentage of the applicable rated speed.
Above is a plot of the measured speed over a period of many years. Continue reading Yet another change of Internet broadband access