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)

Review of APRSTRACKER v0.11firmware

I recently built a FoxDelta FOXTRAK APRS tracker.

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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 v0.11firmware

Spoiling balun action with ‘shielded twin’

In a QST column in 2008, a correspondent asked the question

… I have the ladder line terminated to double coaxes that run about 12′ (4m) inside the house to an antenna tuner. Should this pair of coaxes be grounded at one end or both ends?

ShieldedTwin

The Doctor gave a detailed diagram (above) and his advice was… Continue reading Spoiling balun action with ‘shielded twin’