APRS Mark II

After constructing my Mark I APRS mobile digipeater, I quickly found that 5W was simply not enough power to get out.

I spent some time looking around seeing what others are using for APRS, but unfortunately all I really found were units with built in APRS. However, APRS is really just packet radio and after doing some research on what people are using to interface with packet radios I found some options.

I initially attempted to pickup some super inexpensive Motorola MaxTrac radios on ebay. They come deprogrammed, so I would have to build an interface cable, setup dosbox and the software to program them, and many of them would need to be fixed, and since I do not possess an oscilloscope I decided against it and started looking for something else.

Most modern radios CAN use the MIC jack combined with ext speaker for an interface. However, it is far better to use unamplified line level inputs/outputs. Far better is to use dedicated packet radio inputs. After searching around, I found that anything with dedicated packet interfaces was very expensive – even used. Without a dedicated packet radio interface anything close to 9600 baud FSK is unatainable. Fortunately for me I only care about 1200/2200 AFSK APRS, so I widened my search and found a few candidates.

I found a previously owned, but like new Yeasu FT-2900R listing on ebay for $123 + free shipping. The 2900R is 75W and it’s trivial to wire up a mic jack + ext speaker jack. However after reading reviews, the 2900R gets HOT at 75W even during normal usage, and the next lower power setting is 30W. This was more than I wanted to spend for a 30W radio.

I also found an open box TYT TH-9000D for $60 + free shipping that looked promising. The TYT-TH-9000D has a connector on the main board specifically for external interfacing. It also has a knockout for a 9pin D-SUB connector on the back with a plastic cap over it. Googling found me some digikey part numbers (A100196-ND and AE11063-ND). All of the amazon reviews for the radios complained about how cheap the mic was, and how poor the user interface was. The good reviews focused on the strength and clarity of the radio, the things i care about. The TH-9000D is a mono band radio that comes in 1 of 3 bands. After ensuring the one I was looking at was for 2m VHF I placed my orders. The 2m version is 65W 144-148Mhz transmit and 136-174MHz receive.

One of the things that made me very happy to see what that the connector on the motherboard provides PTT and COR.

More after the radio arrives…


ADEVICE plughw:1,0

ACHANNELS 1

MYCALL KG7VOR-1

#MODEM 1200

#DTMF
#ARATE 48000

AGWPORT 8000
KISSPORT 8001

PTT GPIO -17

FIX_BITS 1

GPSD

TBEACON delay=:30 every=10 symbol=/k via=WIDE1-1,WIDE2-1 power=60 gain=4 height=6 comment="Truck"
SMARTBEACON 60 2:00 5 15:00 0:15 30 255

DIGIPEAT 0 0 ^WIDE[3-7]-[1-7]$|^TEST$ ^WIDE[12]-[12]$ TRACE
#FILTER 0 0 t/wn

IGSERVER noam.aprs2.net
IGLOGIN KG7VOR 16545