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
Some years ago I purchased a used MFJ-1263 microphone / rig switch with a view to using it as an ongoing test bed for my Roger Beep module.
The Roger Beep module was assembled with 6 way 90° single row header pins for easy connection and disconnection.
The module was built, tested and adjusted for audio output level and encapsulated in clear heat shrink. The cable was made from parts from ready made 3 way RC servo jumpers with the wires removed and inserted into more suited back shells. Continue reading Roger Beep fitted to MFJ-1263 microphone / rig switch
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
Towards a reliable APRS iGate discussed efforts to implement a robust and reliable APRS iGate / digi. The article ended by mentioning further work on initialisation scripts. Continue reading Towards a reliable APRS iGate – #2
There is little doubt that overall, hams have dumbed down as technology has raced ahead.
An interesting result of this is the appearance of new antenna analysers aimed at the dumb ham.
What is the dumb ham in this context? Continue reading The sign of reactance
I have been investigating ‘lost APRS packets’, a result of many root causes.
One is a perception that when I drive in the local area, I often do not hear my own digi ‘echo’ yet I find that it did receive a packet and submit it to APRS-IS. This problem is much more apparent using a TNC-X that with any other KISS TNC in its place. Continue reading TNC-X – channel access behaviour
During recent evaluation of a range of APRS servers and TNCs, I have inspected APRS-IS records and my own server logs to identify possible anomalies caused by the equipment under test.
In that time I have found defective records caused by digi / iGates: VK2JMA-5, Vk2YGV-5, VKWUWP-2, VK2UWP-1, VK2MPJ-1,VK2ZEN-5, VK2AMW-1, VK2RHR-1, VK2LKH-1, VK2MB-1, VK2BEN-1. Continue reading Does anyone assess to their digi / iGate performance?
An APRS iGate necessitates some form of computer in the centre of the configuration.
Over recent weeks, I have evaluated a number of configurations for VHF based on Windows and Linux (RPi) to assess their reliability, though it is doubtful that a configuration to rival UIDIGI reliability and availability is likely. Continue reading Towards a reliable APRS iGate
On 01/09/14 I commenced upgrade of Ubuntu 12.04 LTS “precise” to Ubuntu 14.04 LTS “trusty”. (LTS is for “Long TIme Support” and it is supposed to be the reliable stream rather than experimental.) Continue reading Ubuntu LTS upgrades get better – v14.04
APRS is characterised by a lack of standards or guidance, but mostly by a lack of compliance with those standards and a lack of understanding and common sense.
VK2UWP is travelling around the countryside and from the look of it, setting up a WIDE2 digipeater in the local caravan parks without regard to its dysfunction. Continue reading The mobile APRS W2 digi left town this morning