For example, say you've got a radio that is transmitting at 5 Watts and it has a reverse power of .2 Watts. That's actually pretty normal, since achieving a 1:1 ratio is quite hard to do. In that scenario, everything's okay. But, if you see that reverse power start to climb, to say .6 or higher, something is not right. You've got a bad radio, a loose connector, a squirrel's been gnawing on your feedline, something. Verify that it isn't the radio itself by putting on a different antenna, and see if it goes back down. After that, inspect the feedline, connectors and antenna for damage or water.
Thursday, August 30, 2007
VSWR
Troubleshooting RF systems can be difficult and having good diagnostics, both locally and over-the-air to remote sites, is critical in making an accurate determination of your system. One of the most important is VSWR or 'voltage standing wave ratio.' It is basically the
For example, say you've got a radio that is transmitting at 5 Watts and it has a reverse power of .2 Watts. That's actually pretty normal, since achieving a 1:1 ratio is quite hard to do. In that scenario, everything's okay. But, if you see that reverse power start to climb, to say .6 or higher, something is not right. You've got a bad radio, a loose connector, a squirrel's been gnawing on your feedline, something. Verify that it isn't the radio itself by putting on a different antenna, and see if it goes back down. After that, inspect the feedline, connectors and antenna for damage or water.
For example, say you've got a radio that is transmitting at 5 Watts and it has a reverse power of .2 Watts. That's actually pretty normal, since achieving a 1:1 ratio is quite hard to do. In that scenario, everything's okay. But, if you see that reverse power start to climb, to say .6 or higher, something is not right. You've got a bad radio, a loose connector, a squirrel's been gnawing on your feedline, something. Verify that it isn't the radio itself by putting on a different antenna, and see if it goes back down. After that, inspect the feedline, connectors and antenna for damage or water.
Wednesday, August 1, 2007
"How Far Do Your Radios Talk?"
One of my favorite questions! I get this one at every trade show I attend, without fail. And, it makes sense. My response is always, "Well, how far do you NEED them to talk?"
Radios can talk a very long way, given extremes. One of my pet peeves is when radio manufacturers put on their spread spectrum datasheets: "Range = up to 60 miles point-to-point *" Note the asterisk. Sure, they CAN talk 60 miles, with 1000 feet high gain antenna on either end! In fact, the longest spread spectrum shot I ever managed was 38.7 miles, but that was mountain peak to mountain peak.
In a real world SCADA application, however, ranges shouldn't have asterisks. Here are general range limits by frequency, with realistic gain antenna and realistic antenna heights (say 50-75 feet at the master and 20 feet at the remotes):
VHF, 5 watts = 20 miles
UHF, 5 watts = 15 miles
900 MHz, 1 watt = 8 miles
Radios can talk a very long way, given extremes. One of my pet peeves is when radio manufacturers put on their spread spectrum datasheets: "Range = up to 60 miles point-to-point *" Note the asterisk. Sure, they CAN talk 60 miles, with 1000 feet high gain antenna on either end! In fact, the longest spread spectrum shot I ever managed was 38.7 miles, but that was mountain peak to mountain peak.
In a real world SCADA application, however, ranges shouldn't have asterisks. Here are general range limits by frequency, with realistic gain antenna and realistic antenna heights (say 50-75 feet at the master and 20 feet at the remotes):
VHF, 5 watts = 20 miles
UHF, 5 watts = 15 miles
900 MHz, 1 watt = 8 miles
Subscribe to:
Posts (Atom)