The KISS TNC – too simple, too stupid?

An important element of early AX.25 networks was the Terminal Node Controller (TNC). Essentially, a TNC was a packet assembler / disassembler (PAD) pretty much equivalent to the PAD of X.25 networks but adapted to AX.25, and commonly, an embedded modem.

The TNC-2 was a hardware configuration which became a de-facto standard, and various firmware packages became available each with their own advantages and disadvantages. and a range of protocols for the host connection.

One of the inventions was the KISS protocol (KISS for keep it simple stupid) from Mike Chepponis (K3MC) & Phil Karn (KA9Q), and an implementation for TNC-2. Continue reading The KISS TNC – too simple, too stupid?

RPi headless aprx server using soundmodem

I have posted several articles on headless APRS servers based on RPi. This article describes one based on RPi, AX25 soundmodem using a $2 USB sound card, and aprx v2.09.


Above is the server hardware. It uses the Sailer sound modem and kernel AX.25 support. This is currently configured as a RX only iGate for 30m, hence no tx audio path and no PTT (though on HF, PTT can be done simply using transceiver VOX). The small black USB module is a Belkin WLAN adapter. Continue reading RPi headless aprx server using soundmodem

Diamond X-50N #2 at VK2OMD

I have a bit of a soft spot for the Diamond X-50N. It is a fairly rugged vertical for 2m/70cm. Though I live in a rural setting, I resist the temptation of high gain antennas of this type as they tend to suffer fatigue problems resulting in noise in quick time, whereas the rigid one piece X-50 seems to last and last (I have another that must have had 25 years outdoor service).


The X-50N is mounted on a telescopic steel mast at 11m at its base, and fed with 10m of LDF4-50A to the antenna entrance panel, and 2m of LMR-400 to the radio. The XN50N has three short radials which are visible in the pic above, but somewhat obscured by a fan of four upwards pointing wires to discourage birds perching on the gibbert for the G5RV. Continue reading Diamond X-50N #2 at VK2OMD

VK3AQZ RF power meter (RFPM1) – filter response example

This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to plot the response of a 144MHz filter.


Above, the RFPM1 as used.

Screenshot - 24_11_2014 , 10_29_43

Above, the test setup. The filter (DUT) is connected between a standard signal generator (SSG), and the RFPM1 connected to the filter output. A DVM recorded the DC voltage on the ‘CAL’ terminals of the RFPM1. A series of measurements was made from 140 to 148MHz and the results calculated and plotted in Excel. Continue reading VK3AQZ RF power meter (RFPM1) – filter response example

APRS: does pre-emphasis make much difference

This morning I have been observing a weak APRS signal from a digipeater located on a prominent hill about 200km away, VK1RGI-1.

VK1RGI-1 is characterised by having a pre-emphasised transmission, but about 1.5KHz deviation, about 6dB low.

Nevertheless, VK1RGI-1 packets can be fairly reliably decoded at a strength that does not show any segments on the IC2200H S meter, less than -115dBm (by measurement). Continue reading APRS: does pre-emphasis make much difference

APRS: how popular are Kenwood trackers

APRS has evolved to be all things to all men.

It inventor, Bob Bruniga, generalised the original meaning Amateur Position Reporting System to Amateur Packet Reporting System as he extended APRS to include all manner of generalised broadcast and point to point messages.

Perhaps in doing that,it was recognition of the inability for many reasons of APRS to provide reliably good position reporting performance in practice.

Any thinking person understands that there is conflict between use for timely reporting of position and loading the radio channel up with generalised message traffic, or even extending the RF coverage of a position report by repeating it many times into adjacent precincts. But simple minds muttering “use it or lose it” ruin APRS for position reporting by sending repeating traffic without a demonstrated demand.

Attempts to emphasise position reporting performance tend to be opposed in my experience mostly by owners of Kenwood trackers (eg DM-710), and the weather propagators. Many Kenwood owners like to see position reports from a very wide area repeated into the local area so that they can be displayed on their radio. There are other features that generate traffic that appeal to Kenwood owners.

This article looks at how significant the Kenwood users are in terms of unique packets reaching APRS-IS, the basis of mapping for most users these days. Continue reading APRS: how popular are Kenwood trackers