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
Garmin GPS35 is a GPS pod with serial connection carrying NMEA data.
They are supplied with a range of connectors, and for use with APRS systems, one may want to replace the connector with the common DE-9 wiring for trackers. Continue reading Garmin GPS35 DE-9 (F) wiring
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
New hams are often advised quite poorly, justified by the mantra that “any antenna is better than no antenna at all”. The more confident the advisor, the more jargon, the more unsupported, the more the advice is soaked up by eager newbies. Not just soaked up, but learned so the newbie can talk like the pro… even if they also do not understand the subject matter. Spruiking BS has always been a feature of ham radio.
Recent online discussion illustrated and recommended a 40m dipole strung on a timer fence at a height of about 1.5m to a new ham with a 10W power limit in search of good solutions from ‘experts’. Continue reading Effect of ground on HF horizontal dipole efficiency
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
Many years ago I bought a Tigertronics Signalink USB, principally for measurements using FSM and NFM.
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
Many years ago I bought a Tigertronics Signalink USB, principally for measurements using FSM and NFM.
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