[islandlabs] Ground Tests Update

Joe toolfox at gmail.com
Sat Mar 26 20:35:21 UTC 2011

Last night, I took Fluffy (the high-output APRS unit that will fly on
the next launch) and started doing second-round ground testing.

The antenna was removed and replaced with a magmount unit. APRS was
switched on and placed in the freezer. The magmount antenna was plopped
on the top of the fridge.

I've now got an APRS-enabled refrigerator!

The chase computer was set up in the living room and packets were
monitored. 100% success in capture for the first 90 minutes, then I had
to swap out the battery for the tracker (I knew a NiMH rechargeable
9-volt wouldn't last long, but I was surprised that it ran for as long
as it did). I was able to see this through the reported battery voltage
and temperature in the packets.

At 2 hours and 45 minutes, I suddenly stopped receiving packets,
although the transmit LEDs were still going strong on Fluffy.
Unplugging the audio cable from the receiver to monitor the
transmissions showed audio packets weak and distorted.

I pulled out my HT and punched in the test frequency; the packets were
strong and crisp! Then I saw the problem: the scanner's display had a
little "B" in the upper corner...the batteries were dying on the
receiving end.

Replaced the batteries and the computer was picking up packets again.
Extended the test to about 4 hours; no further problems.

The tracker's internal temperature sensor was down at about 15 degrees
F (-9 C) and the radio kept on going.

With hand warmers and an insulated capsule, the radio's lithium-ion
battery should be good for the duration. During this test, I was
sending packets every 10 seconds to overstress the transmitter's
battery load.

I'll see about repeating the test with packets at 30-second intervals
(the rate I'm going to use on the launch so we don't overload the
national APRS network) to see what happens to the transmitter circuit
when it's got longer intervals to cool down between transmissions.

More ground test are scheduled for this weekend. I'll report on the
results as they come in.


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