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[aprssig] kenwood d7a and packet RX

Henk de Groot henk.de.groot at hetnet.nl
Thu Mar 3 22:26:31 UTC 2005

Wes Johnston schreef:
> The thread yesterday about battery life got me thinking about how you receive
> packets with a d7a with the battery saver on.  You don't... unless the
> frequency stays pretty busy and prevents the reciever from going to sleep.

You don't... Not when you use it as a tracker like is done here. The radio 
wakes up to do the transmission and hears others.

There is another way to save even more power.

When we assume that the TH-D7 will not hear 90% of the other stations 
anyway and the channel access is pure ALOHA, then you can just send when 
there is something to send (this is ALOHA, pure ALOHA has no carrier sense).

We can use this fact to save even more power, just switch the TH-D7 to 
duplex operation where you receive on a silent channel and transmit on the 
APRS channel. This way the radio does not have to receive and decode the 
other APRS packets which will save even more power. A refinement is not to 
loose all carrier detection. What I did once is to use a very small offset 
between RX and TX. RX was off frequency enough not to decode packets 
anymore but close enough to the APRS QRG to detect other carriers.

This kind of operation will make the TH-D7 even look more like a tracker, 
the simple trackes also so not have a receiver (although they do some 
crude DCD checking). Since packets are not received anymore you save power 
since there is no APRS decoding anymore.

Never run in battery save mode if you want to receive APRS packets... 
(Altough with the standard Kenwood TX delay of 500ms you could set the BAT 
saver to 0.4sec without loosing the packets transmitted by Kenwoods...)

Kind regards,


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