This article documents a line-up procedure for the MFJ-1270B TNC. This is an advanced procedure, you should not tackle it without appropriate knowledge and experience. Continue reading MFJ-1270B TNC alignment
A nuisance with the device is the lack of a simple means of disabling PTT. This is particularly important if the system is being used for noise figure measurement with an expensive calibrated noise source which will not withstand transmitter output.
This note describes the fitting of a front panel PTT disable switch. Continue reading Signalink USB PTT disable
The Signalink USB turned out to be a disappointment for several reasons but the main one was that the noise floor was almost 20dB higher than an ordinary $10 Creative desktop sound card. Continue reading Signalink USB noise floor improvement
APRS has had problems since its inception, and it is not surprising… but the future of APRS has arrived. Continue reading The future of APRS is here…
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