[OZAPRS] TNC

[James Cameron]

On Tue, Jan 12, 2010 at 07:26:23PM +1030, Terry Neumann wrote:
> There were rumours that some of the newer ultra cheap HH's apparently
> will go into sleep mode in some APRS situations  - check this out
> before you commit to buying one for this purpose.

For what it may be worth, I've tested a few Quansheng TG-25AT units in
various ways a few weeks ago, and the standby mode can affect APRS on
receive because the radio can take a while to notice the transmission
... because it only periodically powers the receiver.  The following
measurements were made:

- time after mute close before radio enters standby is 7 to 8 seconds
  (limit of reading one second),

- time between receiver activation events during standby is 0.70 seconds
  (limit of reading 0.02s),

- times are independent of supply voltage.

If you are operating a private APRS link the delay between PTT and data
should be 800ms more than normal, if there has been no activity for more
than 7 seconds.  This isn't too difficult to code if you are in full
control of your TNC firmware.

To allow the unit to work with the rest of the APRS traffic (not that I
have any here), you can hold down the Monitor key or short it
internally.

There's also a minor series capacitor effect on audio output that
corrupts the curve ... it happens when the mute opens and the audio amp
engages ... measured using Linux arecord and audacity on two units,
settling time is 25ms before the curve has lost the DC component.

No effect on transmit.

-- 
James Cameron
http://quozl.linux.org.au/