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
Category: Amateur Radio
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 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
Real time clock 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
APRS: how many digi hops to make it to APRS-IS
APRS is almost exclusively source routed, and depends greatly on sensible path configuration by each and every user.
This is one of those cases where individuals acting independently and rationally for their own personal behave contrary to the whole group’s long-term best interests by depleting some common resource (the tragedy of the commons).
Increasing the available WIDE path length does expose a station’s packets to more iGates, but the average effect of everyone following that strategy is to literally exponentially increase channel busy as the available hops is increased. Continue reading APRS: how many digi hops to make it to APRS-IS
APRS traffic study – VK2OMD-3 11/10/2014
A study of APRS traffic was conducted by analysing the log of VK2OMD-3, a VHF APRS ‘fill-in’ digi and iGate.
The capture period was during the busy hour(s) (BH) 0600-0900 local time on Saturday 11/10/2014. Continue reading APRS traffic study – VK2OMD-3 11/10/2014
Notes on my fork of aprx
aprx is APRS iGate / digipeater server software for the *nix environment by Matti Aarnio. In my case, I am developing and running on RPi / Rasbpian Wheezy.
This article comprises notes on the digipeater module as modified over recent weeks to address shortcomings in its operation. Continue reading Notes on my fork of aprx
APRS test drive – 20140930
A short test drive was conducted to evaluation APRS effectiveness in capturing a motor vehicle journey of about 30km.
The test area is between two digipeaters spaced almost 40m apart, so within the overlapping coverage area of VK2RHR-1 about 17km NW of the test area, and VK2AMW-1 about 17km SW of the test area.
Three position capture devices were used:
- APRS on 2m (blue track on the maps);
- APRSdroid (green track on the maps);
- Bushnell Backtrack Detour (stand alone GPS logger) (red track on the maps).
Synthetic fibre rope for antenna rigging
Fibre rope has applications in antenna rigging, typically for halyards and tails to support the ends of wire antennas such as dipoles. The use of fibre rope for guying applications has issues due to shrinkage when wet.
Much is made of the ‘best’ fibre rope for these applications, and the almost universal answer is black Dacron (Polyester) in small sizes from 2.5mmm to 6mm diameter. The smaller sizes are usually a braided construction, commonly known as venetian cord. Claims are that the Polyester rope is strong, UV proof and rot proof. Whilst Polyester rope is resistant to mild acids and alkalis, it is damaged by strong alkalis (such as might develop when an alkaline solution dries on the rope). Continue reading Synthetic fibre rope for antenna rigging
Headless aprx APRS server – RPi packages
In earlier articles I documented a trial of aprx v2.08r593:
Encouraged by Kenneth Finnegan who merged some fixes by WB4XO (which still didn’t work properly), I set about resolving some problems.
Further fixes and some enhancements have been pushed to the source fork at . This was forked from PhirePhly/aprx which in time may pull the changes.
You can browse for brief descriptions of the changes.
Recent Debian packages for RPi based on my fork have been uploaded to https://owenduffy.net/files/aprx/ .
End fed wires – another matching case study
A reader of my article End fed wires – new hams love ‘em asked about the performance of the matching transformer described at (Osborne 2014).
(Osborne 2014) gives the transformer design above using a FT82-43 ferrite toroid with three turns on the primary. The concept is to adjust the antenna length and C1 for a ‘perfect match’. Continue reading End fed wires – another matching case study