Category: Ham Radio
I recently put a node up for San Francisco Wireless Emergency Mesh. It’s something I’ve been intending to do for a while but just never made the time. One of the SFWEM members reached out when he saw me on APRS.fi and asked if I were interested in putting up a node. Since it was something I’ve been meaning to do for a while, I got to work.
The hardware I’m using is a Ubiquiti Rocket M5 with an AMO-5G13 omni directional antenna. The hardware runs a custom firmware from Amateur Radio Emergency Data Network. The setup and configuration is well documented and went smoothly. After mounting the Rocket M5 on a roof mount and running an ethernet to a POE, the node was online.
This node provides good coverage of the general area. It’s currently connected to the rest of the SFWEM mesh network by node KJ6WEG-OAK-Griz-SectorM5 up on Gizzley Peak.
Things got interesting when I started to add a second node. This one is based on a NanoBeam M5 and is intended to create a point-to-point connection to another node on the network, most likely KJ6DZB-USS-HORNET-SOUTH on the USS Hornet.
Putting two devices on a network with the Aredn firmware is supposed to allow them to set up a device-to-device (DtD) connection over the network instead over the RF network.
The Aredn DtD documention was a bit confusing to me. Specifically when I read about the use of VLANs, I assumed that putting the switch ports for both nodes on VLAN 2, they would find and communicate over the network. That’s not what was needed. I know, for whatever reason I suffered a VLAN mental slip.
My network configuration had three VLANs: 1 as the default, 2 for AMPRNET and 3 for Lorawan devices. Since I thought that Aredn wanted to be on VLAN 2, I reconfigured all the switches as: 1 as the default, 2 for Aredn, 3 for Lorawan and 4 for AMPRNET. But this configuration doesn’t work. The SFWEM nodes could get an IP address from the router on VLAN 1 for their WAN interface but they didn’t see each other.
After a few frustrating hours staring at configuration screens, reading and re-reading the Aredn docs, chatting with SFWEM members on slack and wading through my VLAN experience, I realized that I was misunderstanding the use of untagged, VLAN 1 and VLAN 2 by the Aredn firmware. What I realized is that the nodes want to be on their own VLAN and they’ll send WAN data tagged for VLAN 1 while tagging packets for VLAN 2 when doing any DtD communications.
I reconfigured my network switches again but this time as: 1 as the default, 2 for Aredn DtD, 3 for AMPRNET, 4 for Lorawan devices and 5 for SFWEM. The important part here is that the ports for SFWEM nodes are set to tag VLAN 1, tag VLAN 2 and untagged VLAN 5. This gives the Aredn their own default network on VLAN 5, makes VLAN 2 available for DtD communications and allow VLAN 1 traffic to leave the switch for the great beyond.
Both nodes are now online and connected via DtD.
I’m now a licensed Amateur Extra!
I previously posted about monitoring how long my vx8-dr would last on different types of batteries. One of the things that I noticed was that there is a relationship between battery voltage level and the output power but I had no way of watching what was happening. So I invested in a Diamond SX-600 SWR & power meter along with an MFJ-261 dummy load and re-ran parts of the battery test.
2,000 mAh lithium ion w/ power
This is pretty much what I would expect. As the power available from the battery goes down, the output power on the radio goes down.
AA alkaline w/ power
This, ladies and gentlemen, is utterly ridiculous! Starting with fresh AA alkaline batteries, the output is less than 1 watt and it quickly deteriorates from there.
I swapped out the AA alkaline for AA lithium ion and found a similar output power level. Since it started with less than 1 watt output power, I didn’t bother running through the whole test. This was not at all what I expected, The input power voltage level is critical for the vx8-dr to perform well.
My original intention was to use AA lithium ion and / or AA alkaline batteries as a backup power source for the vx8-dr in the event of an emergency. This now looks like a bad plan. Running on anything less than the lithium ion battery packs has a detrimental effect on output power. It might do as a backup to the backup power but I don’t think it’s a good idea to count on it.
Right now, I’m thinking multiple 2,000 mAh lithium ion battery packs, a charging dock and perhaps a solar panel to charge it all. Plus an automotive plug adapter. And a plug w/ anderson powerpole connectors.
This was an interesting experiment!
I was asked about the discrepancy between the maximum measured power out of 4.2 watts with the battery voltage of 8.2 and the published maximum of 5.0 watts. I have a couple thoughts on that though they’re not based in much more that aether.
- The published specs may be coming from theoretical maximums.
- The published specs may be coming from values measured in a lab under ideal conditions.
- Maybe the battery’s just not quite fully charged.
- The SX-600 power meter may be off calibration.
I did plug the radio into the wall wart that comes w/ the charger. The voltage showed at 10.8v and the output power at 4.3 watts. Using the automotive cigarette plug, the voltage shows at 12.8v and the output power was measured at 4.5 watts.
BTW, the manual for the vx8-dr has specs for the supply voltage maxing out at 12v.
From all this, I take the maximum output wattage as being 4.5 with a more typical of 4.0 to 4.2.
I had an experience a few weeks ago whereby I couldn’t join the ORCA net on my vx8-dr because of a low battery. From that, I thought I’d run a test to look at how long different types of batteries run in the vx8-dr. The basic protocol is to setup the vx8-dr to transmit APRS location messages on a regular basis and measure the battery voltage over time. The voltage measurement comes from the vx8-dr itself. Yes I’m trusting that it was accurate but with the test running the same way across all the types of batteries, I think it’ll be a valid test. Besides, the reading from the vx8-dr is what I’ll be using in the field.
The vx8-dr can use 4 different types of batteries: 2,000 mAh lithium ion, 1,100 mAh lithium ion, AA alkaline and AA lithium ion. I ran a set of tests over the course of 8 days.
2,000 mAh lithium ion
1,100 mAh lithium ion
AA lithium ion
I unintentionally left the vx8-dr running over night and the battery level only dropped 0.2 volts. That was very unexpected.
I came to a few conclusions from this test:
- Measuring the voltage will most likely be a good way to keep track of when to change batteries.
- Just measuring the voltage doesn’t provide any data on how well the transmitter is working with the available voltage / power.
- Judging by the AA lithium ion battery test, I need to re-run the 2,000 mhA and 1,100 mHa test. It looks like the voltage level of the lithium ion batteries may not be linear. That may put a kink in the use of the battery voltage to determine remaining power.
I’ll re-run the 2,000 mHa and 1,100 mHa tests over the next few days to see how long the batteries last. Perhaps lithium ion batteries don’t have a linear voltage level over regular usage.
More importantly, I need to expand the tests to determine the output power level as the batteries are used. I’m not yet sure how to do that. Maybe it’s time to invest in an RF power meter.
I had a thought yesterday, in the event of an emergency the internet connections will be down. Wouldn’t it be useful to have a localized APRS display to show the location of various people. Set up a radio to listen for APRS transmissions, send them to a small computer, run a webserver on the computer w/ OpenStreetMaps on it, have a wifi connection and power connections. Drop it all into a portable case of some sort and it can be made available to a local group of people who need access to the data.
There’s a bunch of unknowns here but it could be an interesting project. Would it be useful? Reliable? What else is needed?