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
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.
Above is the RPi sitting on a TNC-X KISS TNC connected to the TNC’s USB port. In this case, aprx uses the supplied KISS interface, it does not use Linux kernel support for AX.25. Continue reading Headless aprx APRS server
A lot of radios are made today to use an electret microphone which has a higher output than common dynamic capsules and may require a preamp to comfortably obtain sufficient audio.
This article describes a microphone + preamp intended as a drop in replacement for an electret capsule.
An electret capsule contains an integral FET preamplifier, and the common two terminal version of the capsule depends on an external load resistor (commonly around 4.7kΩ and source of supply current (commonly from 6-12V via the load resistor.
Above is the preamp schematic from an LTSpice model. A common emitter amplifier operating in this circuit has re of about 20Ω, and so voltage gain from collector to base is very high at 3000/20=150 (assuming total collector load of 3kΩ). Continue reading A simple preamp for dynamic capsules to suit radios using electret microphones
Hams impoverished for space to erect a ‘full size’ antenna for HF pursue a range of options and end fed wires figure highly.
New hams who heard the maxim that ‘any antenna is better than no antenna at all’ will try to use bed frames, window frames, balcony railings, anything metallic to get on air. This cry for mediocrity is to prevail over a quest for understanding, ham radio as it has evolved.
The ‘net abounds with conflicting advice:
- (Yates 2010) recommends a T50-2 powdered iron core;
- (VK2AVR 2014) states
do not use a powdered iron toroid.. they won’t work.
They cannot both be correct. Continue reading End fed wires – new hams love ’em
This article documents an open squelch data carrier detect (OSDCD) for a Flash Packet Radio Control Board (VK6) TNC-2. Continue reading Open squelch data carrier detect for Flash Packet Radio Control Board (VK6)
I have been doing some research on APRS recently, and Brian, VK2AH, kindly donated a MFJ-1270B.
Over the years I have heard so many reports that the MFJ-1270B does not accommodate twist (an amplitude / frequency slope usually the result of lack of pre-emphasis, usually the result of audio overdrive of the transmitter, and usual for hams). More detailed discussion is at The extent to which APRS works is often an accident.
There is no shortage of bad signals to test the tolerance of the TNC, with two local overdriven digis, and travellers through the area. Continue reading MFJ-1270B TNC review
This article describes a trial of javAPRSSrvr on a Raspberry Pi (RPi) as a headless system (ie without integrated screen and keyboard).
Above is the RPi sitting on a TNC-X KISS TNC connected to the TNC’s USB port. In this case, javAPRSSrvr uses the supplied KISS interface, it does not use Linux kernel support for AX.25. Continue reading Headless javAPRSSrvr
I was handed an Alinco DR-135 + T3-135 to troubleshoot. The reported symptoms were that it “never repeated the owner’s Foxtrak based mobile station”.
The T3-135 is an OT3 tracker/TNC built on a card to fit inside the Alinco DR-135 in the place provided for their own EJ-41U TNC. The rear DE9 port provides data access to the T3-135’s A and B serial data channels.
Continue reading Argent Data T3-135 review
This article documents an open squelch data carrier detect (OSDCD) for TNC-2.
The TNC commonly derives Data Carrier Detect (DCD) from its modem chip (often a broadband energy detector is used in modem chips). DCD is used to enable decoding of incoming Receive Data (RD), and to block transmission whilst the channel is busy. Continue reading Open squelch data carrier detect for TNC-2
A few weeks ago I built up a Foxtrak kit, see Foxtrak build.
During testing, I noted that VK2ZEN-5 occasionally corrupts Foxtrak packets, or more generally MIC-E encoded packets. It is a known problem with aprsd which has not been fixed in more than 10 years.
As a result of the fact that one local digi (OT3) never decoded the Foxtrak (DK7IN firmware), I tried aprstracker0.11 and original TinyTrak(1) firmware.
The aprstracker evaluation is described at Review of APRSTRACKER v0.11 firmware, it was unsuitable.
The TinyTrak(1) firmware didn’t work with the OT3 digi either.
The matter of Foxtrak / OT3 interoperatibility is discussed in more detail at:
A TinyTrak3+ was also evaluated, see TinyTrak3 v1.42 review.
Considering quality, price and performance, the Foxtrack works with most digis types but not OT3s, the DK7IN firmware has more feature than the original TinyTrak, but the combination is nowhere near as capable as the TinyTrack3+ which is less than double the price as landed in Australia.