VK2XSO posted a sweep of “Return Loss (SWR) (the lower plot) from 500 to 2500MHz of a 50Ω load through ~5m of RG59” apparently to demonstrate his knowledge of transmission line basics. As he says “here are also many other things we can deduce from looking at these two lines.”
For students of transmission lines, some deductions… Continue reading Exploring VK2XSO’s transmission line example
This article explores the way in which VSWR varies along a feed line.
The graph above shows R and X, and VSWR along a feed line with a 100+j0Ω load at 3.6MHz. The feed line is Belden 8262 50Ω coax, manufacturing tolerances are taken to be zero, and the displacement is relative to the feed point, ie -ve distance is distance before the feed point, the feed point then is at the right hand side of the graph.
Continue reading Feed line length affect on VSWR
A reader of Why the preference for Guanella 1:1 current baluns for HF wire antennas asked if a similar model can be built for a Ruthroff 4:1 balun.
Hams tend to insist that the Ruthroff 4:1 balun cannot be represented by transmission line elements, but they are quite wrong. Continue reading A SPICE model for a Ruthroff 4:1 balun.
I am often asked why I recommend a Guanella 1:1 balun with high choking impedance for most HF wire antennas over voltage baluns and 4:1 current baluns. This article explores the topic using SPICE models for a voltage balun, 1:1 current balun, and 4:1 current balun. Continue reading Why the preference for Guanella 1:1 current baluns for HF wire antennas
This post explains a technique to drive a KISS TNC with a specially constructed packet that contains an ISOCHRONOUS test packet, a packet that will produce equal high and low tone alternation in the transmitted AFSK signal.
Above is the waveform recovered from a receiver without de-emphasis (a Motorola R2009D communications analyser in this case).
Continue reading Adjusting KISS TNC AFSK tx level using an isochronous test packet
Readers of my article Galvanised steel wire OCF dipole have asked whether the analysis applies to an ordinary centre fed half wave dipole, and this answer is no, not exactly, but very close.
The current distribution on the OCF is very slightly different to a CF dipole, and this causes a very slight change in loss, 16.55W vs 16.68W.
Updated 24/10/14.
I purchased an Opentracker USB (OT-USB) after a review of documentation and some screen shots of the configuration tool OTWINCFG which suggested that the product ‘understood’ the challenges. Continue reading OpenTracker USB review
Viscous digi is a feature to reduce unnecessary digipeater transmissions. Upon receiving a packet, the viscous digi puts it in a hold queue for a configurable time pending hearing another digi repeat the same packet. If none are heard, then it is repeated as usual, otherwise it is discarded. Continue reading aprx: evalution of viscous digi
One of the shortcomings or RPi for (m)any serious applications is that it lacks a hardware clock so when it starts, the clock is not set correctly.
This deficiency can be overcome to some extent for some applications with the fake-hwclock module and SNTP where the RPi is always connected to a network.
The standard scheduling daemon cron does not run tasks that were missed because the system was not running at the time they were scheduled. It is a significant shortcoming that has been overcome by adding another element, anacron, which wraps the cron tasks and is scheduled by cron and at startup. All of this is very dependent on correct clock time, and for RPi systems that lack a hardware clock (the out of the box hardware), the system time can be quite wrong at the time anacron is scheduled as part of the startup procedure.
Continue reading Cron configuration improvements for Raspberry Pi
One of the shortcomings or RPi for (m)any serious applications is that it lacks a hardware clock so when it starts, the clock is not set correctly.
This deficiency can be overcome to some extent for some applications with the fake-hwclock module and SNTP, but this is not a solution if the RPi is not always connected to a network time reference.
One solution is a real time clock module such as the DS1307, or better still the DS3231. The latter has an internal crystal with 2ppm (5s/month) accuracy from 0-40° which is much better than typically achieved with a DS1307 (which is dependent on the external crystal). Continue reading Real time clock for Raspberry Pi