Earth continuity testing of amateur equipment

Electrical safety testing of equipment is covered by AS/NZS 3760:2010 In-service safety inspection and testing of electrical equipment.

This article describes how to test earthing continuity of amateur equipment. It is only one of several tests described in (AS/NZS 3760:2010), but it is most relevant to ham equipment, especially so-called ‘boat-anchor’ equipment. Continue reading Earth continuity testing of amateur equipment

Revision of FoxDelta null modem adapter

FoxDelta supplies a null modem adapter with their FoxTrak tracker. The null modem is used only during configuration.

The adapter is supplied with hex pillars (jack screws) on both DE9 connectors, which prevents the adapter being plugged directly onto the FoxTrak, or onto a PC USB-RS232 adapter with pillars. Continue reading Revision of FoxDelta null modem adapter

Adjusting Foxtrak tx audio using an SSB/FM receiver exploiting Bessel zeros to calibrate the modulator

This article explains a method of setting the tx audio level of a Foxtrak using an SSB/FM receiver exploiting  Bessel zeros to calibrate the modulator. Whilst the Foxtrak is used in this example, the method can be used with any tracker or TNC that allows single modem test tones to be transmitted. Continue reading Adjusting Foxtrak tx audio using an SSB/FM receiver exploiting Bessel zeros to calibrate the modulator

AX.25 1200Bd AFSK FM – to pre-emphasise or not

Hams have used 1200Bd AFSK FM as the physical layer of AX.25 for decades, though with variable implementation quality.

Whilst the AX.25 packet networks of yore have all but died, the protocol is currently used with APRS, and so the related issues remain relevant… well as relevant as APRS remains. Continue reading AX.25 1200Bd AFSK FM – to pre-emphasise or not

Diagnosis of APRS reception problem

I spent some hours today trying to receive a balloon travelling nearby on 2m 1200Bd AFSK.

At the end of the day, I note that the balloon was decoded by only two receivers located in or near Sydney and that resulted in a record to APRS-IS. One was my own station which decoded three packets, and VK2RHR-1 which relayed 16 packets.

Given the balloon’s flight, it is notable that it was not relayed by VK2AWM-1 (which was 40km closer), VK2RAG-1 and VK2RTZ-1 at Gosford and Newcastle, and at least four igates in Wollongong, Sydney and Newcastle. Continue reading Diagnosis of APRS reception problem

Audio level setup on TNC-X (MFJ-1270X)

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)