Appropriate setup of audio drive of an AFSK APRS FM transmitter is important to ensuring that the signal can be copied by all receivers in range.
Excessive audio drive results in a signal that cannot be decoded by some receivers event though it may be very strong.
The TNC-X does not have any facilities for producing steady tones for adjusting the tx audio output for the desired deviation level, so alternate firmware was developed solely for this lineup function. The regular MCU chip is replaced by the adjustment chip for the lineup then the regular MCU chip is reinstalled. Note that this is not an augmented version of the regular firmware, it is for adjustment purposes only… do not overwrite the original chip. Continue reading Audio level setup on TNC-X (MFJ-1270X)
This article shows how to analyse 1200Bd AFSK FM signals off-air to identify defects in setup that will degrade system performance, and the shared channel generally. Continue reading Are you getting the best performance from your FM AFSK APRS transmitter
This article documents the build of a TNC-X, a basic KISS only TNC using modern components, including option of an on board USB interface.
Above, the PCB after assembly and cleaning. Continue reading TNC-X build
Foxtrack is an inexpensive kit form basic APRS tracker, taking a GPS NMEA feed and producing audio frequency shift keyed output to key an FM transmitter. It incorporates a limited TNC function and some intelligent position reporting algorithms
Above is the top view of the Foxtrack PCB. Continue reading Foxtrak build
I recently built a FoxDelta FOXTRAK APRS tracker.
FoxDelta supply the FOXTRAK with firmware by DK7IN, but also recommend APRSTRACKER by PE1RXQ and PE1ICQ.
APRSTRACKER v0.11 was trialled as it offered promise of a better SmartBeaconing implementation and support for altitude, course and speed reporting. Continue reading Review of APRSTRACKER v0.11 firmware
I attempted to decode APRS on 147.175MHz, most traffic being received from two fairly local digipeaters (VK2AMW and VK2RHR). Continue reading The extent to which APRS works is often an accident