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Standard Radio Data Port

The 6 way mini-DIN data port is a sort of standard on amateur radio equipment made by different manufacturers.  It isn't completely compatible between manufacturers, but in general, it is.  The pin numbering may be different, but the physical location of the pins is the same, even if they have different pin numbers.

The 6 way mini-DIN was intended for AX.25 packet data operation but it is useful for other data modes such as data file transfer using the DIGTRX or EasyPal programs.  The problem with using the loudspeaker and microphone connectors for data transmission is the radio's audio pre-emphasis and de-emphasis filters which were intended for speech.  It is possible to negate the effect of these filters, but the flat audio response offered by the data port is an easier way of doing things.

Some radios give a more level received audio response than others.  This can be observed using the audio spectrum analyser window which EasyPal provides.  As well as a received data signal having a sloping frequency response, the no-signal open squelch noise may also show a slope.  The standard data port has two receive audio pins.  One is for AX.25 1200 bps reception and the other is for 9600 bps reception.  If the 1200 bps receive audio pin gives a sloping response, the 9600 bps receive audio pin could well give a flat response.

The Kenwood TM-V7E gives a flat audio response graph on both of its receive audio pins.  Some Yaesu radios e.g. the FT-8900 and FT-8800 may not.  One difference between the two receive audio pins is that the 1200 bps pin is under squelch control, but the 9600 bps pin is never squelched.  The circuits below use the 1200 bps pin for the Kenwood TM-V7E radio.  The Yaesu FT-8900 probably only gives a flat response on its 9600 bps pin, so that should be used for EasyPal data transfer.  As that pin is not under squelch control, EasyPal thinks it is always receiving a signal and won't work in repeater mode.

The data interface circuit could be made using a change-over contact switch to select either the 1200 bps or 9600 bps receive audio pin.  The pin to use is the one which works without any data errors!

This picture shows the sloping received audio response of a Yaesu FT-8800 radio.  EasyPal uses a pass band of 350 Hz to 2450 Hz.

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Page updated on 09 January 2017

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