niedziela, 26 października 2014

Second launch with new payload

Our project has a new payload - redesigned APRS tracker and a VHF/UHF voice repeater.

APRS tracker is made of Arduino Nano, and G-Space Bluetooth GPS receiver - with RS232 data bus taken from the mainboard. Arduino Nano is powered using internal GPS receiver battery (3.7 V) upconverted to the 5V. We are using awesome QAPRS library ( to generate the modulated audio signal and pass it to the VHF transmitter.
APRS tracker internals

APRS tracker mounted to the back of a VHF radio

Another part of the payload if a VHF/UHF radio repeater. We started to build our own but a more effective  solution (resulting in lighter payload) was to use a repeater build into a Wouxun KG-UV8D dual-band, handheld radio.

Don't worry - this line only looks like it is loosely attached to the radio :)

Here is both tracker and repeater connected to the kite:

Due to a weak wind we were able to lift the payload only 73 meters above the ground. APRS direct radio path was 59 kilometers. Wouxun UV8D was set up to work as a two-way dual band repeater  on 145,500/438,500 MHz frequency pair. Kite operators were calling on a 438,500 MHz frequency. Launch site was about 80 km from Warsaw (Poland) and unfortunately our friends in Warsaw that were monitoring 145,500 MHz frequency weren't able to get a usable signal.

All transmitter were using 5W of power each. Unfortunately this time we were forced to use lower quality antennas (all-use uhf/vhf vendor supplied) which resulted in weaker coverage. We confirmed that all parts of a set-up: kite, line winder, APRS tracker and voice repeater work fine and their weight is low enough to be lift up during moderate wind conditions.

Next goal: to lift payload 250 meters above ground and establish reliable voice connection. We also plan to achieve direct path APRS data transmission of 150 km.

wtorek, 14 stycznia 2014

Elegant solution for carrier detect in Wouxun/Baofeng radios

Building small and light repeater, I came across a problem of getting carrier detect signal from a Baofeng BF-888 radio. I like this radio so I didn't want to drill any holes in it for additional wire.

Looking at a pinout of plug used for external speaker and programming I found one unused pin - tip of the 3,5mm jack. For unknown reason there is a 3V voltage on this pin and you can draw up to 50mA from it.
Probably some more expensive external microphones use it for their amplifiers.

This voltage is also present on a Wouxun KG-UVD1 radio I own (looking at the service manual you can see circuit providing it). This is probably some kind of standard for Kenwood  type connector used in most cheap Chinese radios. This is even referenced by some companies selling those:

Anyway -  when receiving a transmission, you don't need a microphone amplifier, right? :). So my idea was to ground this pin every time radio opens its squelch.

When it comes to BF-888, to get carrier detection status you need to use one of the IC pins from the back of a PCB. Unfortunately, connector socket pins are from the front side of a board. I didn't want to drill a hole in a PCB to lead a wire between its sides, so using a multimeter I found a solution :). One of the pins visible at the bottom of a board (the one with resistor soldered by me) is used to power an audio amplifier.
To conserve power, amplifier is powered up only when radio receives a transmission and opens its quelch (CTCSS and DCS settings are of course validated before).

My circuitry is trivial - using 5kOhm resistor, power from audio amplifier enables BC547 transistor and grounds tip of the radio connector - voltage on the connector drops from 3V to 0V. Squelch closes, radio disables audio amplifier and shuts down transistor. Voila :)

This technique has one drawback - radio enables audio amplifier also when generates sounds by itself - beeping when battery is low, etc. You need to be aware of it - if this is a problem for you, consider disabling internal sounds when programming your radio. Or drill a small hole in a PCB and get real carrier detect signal from the back side.

Have fun.

BF-888 radio carrier detect circuitry