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If you were going to build a whole new system from scratch and set
some minimum requirements, 9600 baud would be a good idea.<br>
<br>
Several years ago I built a batch of magnetic mount trackers for
ambulances and support vehicles at Burning Man. We had two dozen
9600 baud trackers on a single channel with a network cycle time of
6 seconds, and each tracker transmitted every position packet twice
for a total of 8 packets per second. They were all received by a
single TM-D710. The transmitters were half-watt modules on the 70cm
band and I think they were maybe $20 each. They worked well and we
could track ambulances until they disappeared into the hills about
15 miles away on their way to Reno.<br>
<br>
Higher power radios tend to not have such a fast TXD though.<br>
<br>
Scott<br>
N1VG<br>
<br>
<div class="moz-cite-prefix">On 2/16/2022 2:04 PM, John Gorkos
wrote:<br>
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cite="mid:8ab3e5d7-f74c-de32-8f49-9032d93577ae@gmail.com">
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<p>The simple answer is "It doesn't really buy us anything, and it
decreases the range of the transmission."<br>
The majority of on-air time for a TNC/Radio combination is taken
up waiting for the radio to key up and reach full transmit
power. This is the "txdelay" setting on your TNC, and is
generally tuned to your radio. It defines the time between when
the hardware closes the PTT button and begins to actually send
modulated audio. Typical values range from 150-400
milliseconds. Regardless of the data rate, this txdelay is
constant. The actual data transmission is generally a fraction
of the time we spend just waiting for the radio to key up.</p>
<p>So, even though you;'re sending data ~4x faster, you're still
waiting for the radio to key up, and the channel is useless
while that's happening. If it takes 250ms to transmit at
1200bps, and you've got 250ms of txdelay, you're tying up the
channel for ~500ms. At 9600bps, you're on air for ~340ms.
Also, bandwidth and distance are roughly inverse: quadruple the
data rate, cut your transmission distance by 4x.<br>
<br>
In the end, it's generally not worth it.</p>
<p>John Gorkos<br>
AB0OO</p>
<div class="moz-cite-prefix">On 2/16/22 13:36, Jonathan Delaney
wrote:<br>
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<div dir="auto" style="font-family: "Open Sans",
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"Helvetica Neue", Arial, sans-serif,
"Apple Color Emoji", "Segoe UI
Emoji", "Segoe UI Symbol"; font-size:
14px;">The <wbr>discussion <wbr>this <wbr>past <wbr>week <wbr>has <wbr>made <wbr>me <wbr>wonder <wbr>on <wbr>why <wbr>APRS <wbr>9600 <wbr>is <wbr>not <wbr>used. <wbr>To <wbr>my <wbr>knowledge <wbr>most <wbr>if <wbr>not <wbr>all <wbr>APRS <wbr>mobile/<wbr>handheld
enabled <wbr>radios <wbr>have <wbr>a <wbr>TNC <wbr>capable <wbr>of <wbr>9600 <wbr>bps <wbr>however <wbr>we <wbr>still <wbr>set <wbr>them <wbr>to <wbr>1200. <wbr>Is <wbr>this <wbr>because <wbr>most <wbr>of <wbr>the <wbr>digis <wbr>and <wbr>igates <wbr>still <wbr>use <wbr>1200? <wbr>What <wbr>would <wbr>it <wbr>take <wbr>to <wbr>get <wbr>everyone <wbr>to <wbr>change <wbr>to <wbr>9600?<wbr></div>
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