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Pocket Tracker FAQ
Q: What is the RF Power output of the Pocket Tracker? Q: Can the Pocket Tracker be powered directly from the typical, nominally "12 volt", vehicle electrical system? Q: Where are the LEDs in the Pocket Tracker. They do not appear on the Kit Contents drawing nor are the LEDs in the parts list on the first page of the illustrated Assembly Instructions. Does the Pocket Tracker kit include LEDs? Q:What's a fillet? Q: I don't own any suitable RF power measuring equipment. How can I tell if my Pocket Tracker is transmitting with the expected amount of RF output power? Q: What is the RF Power output of the Pocket Tracker? A: Unless you've got some special frame of reference, asking the power output rating of a Pocket Tracker is not a fair question. Please allow me to explain. I'll bet every packet or APRS station you've ever seen was using a transmitter that was originally designed to transmit a voice-grade signal, then loosely adapted for packet / APRS use. Voice signals have an audio frequency range from about 300 Hz to 5 kHz. Packet uses two frequencies: 1200 Hz and 2200 Hz. The transmitter in the Pocket Tracker was designed from the ground-plane up to be an APRS transmitter. The Pocket Tracker transmitter has a specially designed pre-emphasis stage that boosts the signal and reduces the noise. We also have a special way of setting the deviation to spread the modulation energy across the entire bandwidth of a standard FM channel, even though packet data only uses two tones that are just a kHz apart. Pocket Trackers sing real modem tones. You can clearly hear the difference. Everything else sounds ragged by comparison. APRS / Packet receiving stations love to lock onto and decode these pure, fully-modulated tones. If I attach a 5/8ths wave antenna to the BNC connector on the side of a Pocket Tracker I routinely get directly into a digi-peater that's 45 air miles away from me. The reporting rate (position reports making it to findu versus number of position reports sent) is the same as with high-powered mobile stations and pretty much independent of distance. I was out on a Search And Rescue mission last Fall. I was wearing a prototype Pocket Tracker in my vest pocket with a 4" stubby duck on it. That's two inches shorter than the antenna shown on the web page. A thin, flexible two-conductor cable connected the Pocket Tracker to the GPS receiver hanging in a pouch on my belt. I was 23 air miles from the nearest digi-peater. I really didn't expect anyone to see my signal. Imagine my surprise when I returned to base camp at the end of the day to see one of my friends standing there. He'd seen my signal on the web and decided to take a drive - 50 miles each way - to see what I was doing way out in the middle of nowhere. When I got home I downloaded my log from findu. My Pocket Tracker had been hitting the network all day long. It was getting directly into a digi-peater that was 23 air miles away. Last summer I tracked a balloon-borne "digital" transmitter that was putting out a signal with less than half the RF power of a Pocket Tracker. It was also transmitting with a stubby antenna, about 4" long. I tracked this transmitter from the launch point until it was 56 miles away from me. The signal was still strong, and the only reason I lost it was because it went behind a mountain. Luckily some of the recovery crews were already on the other side of the range so they were able to maintain contact with the transmitter. As verified by an independent third party calibration lab, Pocket Trackers transmit 220 mW. Those were third generation Pocket Trackers. Last week when we put our first fifth generation Pocket Tracker on the bench, we were getting 235 mW. Think of it as the QRP approach to APRS. We emphasize signal quality over signal quantity. Sorry about the long-winded answer. The question is not as simple as one might think. Keep on trackin'! TM Tony - N7MTZ Q:Can the Pocket Tracker be powered directly from the typical, nominally "12 volt", vehicle electrical system? A: Yes, the Pocket Tracker is designed to allow it to be powered directly from a 12 volt automotive battery. We support operation with a regulator input voltage up to 16.5 volts DC with ambient temperatures as high as 150 degrees Fahrenheit, provided that no additional load is attached to the Pocket Tracker regulator. The regulator in the Pocket Tracker is rated for an input voltage as high as 45 volts DC while delivering up to half an amp of regulated 5 volt output current - IF - it has an adequate heat sink. The Pocket Tracker only draws about 110 mA while transmitting, and only about 8 mA on a long term average (with the green GPS LED on full time), so in the interest of smaller size, less weight, and lower cost, we did not feel the need to include an additional heat-sink beyond that provided by the ground planes and hardware on the PC Board. If your automotive electrical system puts out more than 16 volts you've got bigger problems to worry about than your Pocket Tracker. We figured that even on a hot summer day the temperature in an enclosed vehicle would not exceed 150 degrees Fahrenheit. Given the typically low APRS transmit duty cycle we feel that supporting operation to 16.5 volts DC at 150 degrees F is fairly conservative. The regulator input and output capacitors, and the various bypass capacitors in the Pocket Tracker also provide pretty good transient suppression, so operation from an automotive electrical system should not present any problems. I've operated Pocket Trackers from the electrical system in my vehicles for many months with no problems of any kind. Keep on trackin'! TM Tony - N7MTZ 
Q: Where are the LEDs in the Pocket Tracker. They do not appear on the
Kit Contents drawing nor are the LEDs in the parts list on the first
page of the illustrated Assembly Instructions. Does the Pocket Tracker
kit include LEDs?
A: Yes, the Pocket Tracker uses surface-mount LEDs that are lined up along the end of U1 between pins 1 and 18. Since these LEDs are already soldered to the PC board they do not appear on the Kit Contents diagram or on the Parts List. You will need to place a jumper shut on J4 to enable the LEDs. Keep on trackin'! TM Tony - N7MTZ 
Q:What's a fillet?
A: The photo shows the fillets on one side of the shield. See where the solder has filled in the corner where the shield plate meets the two pads on the PC board? The solder filled corners are fillets. Another pair of similar fillets are on the opposite side of the shield in corresponding positions. The fillets should run the full length of the contact area between the shield and the pads on the PC board. Keep on trackin'! TM Tony - N7MTZ Q: I don't own any suitable RF power measuring equipment. How can I tell if my Pocket Tracker is transmitting with the expected amount of RF output power? A: The RF power output of a Pocket Tracker is closely related to the DC input current. If you can measure the DC current from the power source (usually a 9 volt battery or vehicle electrical system) you can get a good idea of the RF output power. Many DMMs (digital multi-meters), even the inexpensive ones, have the capability of measuring DC current if the proper connections are used and the meter is wired in series with the power source. Installing a jumper-shunt on J13 (the pair of pins near the shield) will put the Pocket Tracker in continuous transmit mode. It might be best to do this on the secondary frequency by installing the Frequency Select jumper-shunt (near the flat side of the board that normally contacts the battery) so that the jumper-shunt connects the center pin with the pin closest to the corner of the board labeled "J2". Use the LED enable jumper on J13 and power up the Pocket Tracker. Expect a current reading of around 100 mA. If the LEDs are on, add 3 mA for each LED that's illuminated. After completing the test, remember to remove the jumper-shunt from the J13 test pins and place the Frequency Select jumper in the desired position. Keep on trackin'! TM Tony - N7MTZ HiValue Radio - Simplifying APRS TM For more information, please eMail Return to the Pocket Tracker page. |