Range Testing with D-Star
I'm a networking nut. I get a kick out of pushing data around in oddball or unusual ways, and I suppose it also appeals since I can experiment with amateur radio and I don't have to talk to someone! ;)
Shifting bits is one reason I decided to get into D-Star. In fact, the very first on-air thing I did with D-Star was to connect two Linux boxes via PPP link using two ID-800s. Talk about abysmally slow! But hey it worked.
I recently added a couple ID-1s to the collection. Hideously overpriced, those things. But I wanted to experiment with data on 1.2GHz, so finally gave in. First thing I tried with those was to put one on my home network, the other in the car. I drove to the far side of the lake and was able to connect to my home network just fine. Sweet!
I then tried testing coverage at various locations around the lake, but had some trouble with the network connection - it turns out at some point the DHCP client quit working. It was also quite tedious to stop at a likely spot, fire up the laptop, try to get a connection, repeat... I needed a more automated way to see where I could and could not reach my house!
After much delay - it's just a hobby after all - I wrote a Python program that generates "pings" which include position data from a GPS, time, so forth and will respond to received pings with an "ack" packet. At this point the program just uses the slow-speed data of DV mode. It has proven interesting and instructive already.
I made two trips with the 1.2GHz radios, the first using a simple 1/4 wave antenna on the truck, the second using a high-gain (4 stacked 5/8 wave) mobile antenna. The antenna at the house is a Diamond F1230AII at about 25 feet. I had expected the gain antenna to perform a bit better than the 1/4 wave, but they were actually about the same. The gain antenna did have better received strength, but comparable data loss.
The track for the 1/4 wave:
And the track for the gain antenna:
The green dots are generated from the log of all packets sent from the truck. Red dots are from the log of packets properly received at the house. My house is about 2/3 up the vertical track just above the "Royal Oaks" label.
Then I hooked up the ID-800s and took a trip on UHF. As expected, there was a marked improvement. There was a slight advantage in antenna height and power too, the radios were at 25W (ID-1s are 10W max) and the UHF antenna at home is about 40 feet high. On the truck I use a VHF 1/4 wave, not ideal but functional.
One issue that became quite clear while conducting the 1.2GHz tests was that being in a moving vehicle was a major detriment. One of the two major "coverage gaps" is when I'm traveling at 50MPH down Route 66. I had very good signal strength from the house, but there was quite a bit of flutter and the packets almost always corrupted.
The other major gap to the south is due to terrain. I'm in a terrible spot for UHF/SHF! My house is at the base of a hill. Four houses to the south, the ground level is well above my roof! Even the tallest antenna - the 40 foot UHF - is still below the ground level at the top of the hill. Then there are the trees and houses! The hill isn't wide, and runs downhill toward the lake. The southernmost (and all green) portions of the tracks are when I have the hill between the car and house.
My clearest direction is to the west and northwest, but there is still a sea of leafy green trees the whole way to the lake.
Next step is to modify the program to generate TCP/IP packets and run the same track with the ID-1s in DD mode - I'd like to see how much coverage differs between DD and DV. Maybe more driving in other directions to see how coverage fares there.