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My wireless system doesn't have as much range as it should. How can I check it for proper operation? Are there any tests I can do to see if my transmitter is putting out full power?

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Here's a reply to a problem with range on RAMPS. The test described can be done with any of our UHF receivers.

Vin,
I didn't get into the thread before, because I wanted to make some distance versus RF display measurements before I started mouthing off. What we wanted to determine was a setup such that a user could make a simple, repeatable measurement to check our equipment for proper operation. This "test" should show the proper operation (or not) of a Lectro transmitter and a Venue receiver. Here's the setup:

  • Two vertical right angle whip antennas, type A500RA, are on the back of the Venue receiver.
  • The Venue receiver is about 1 meter above the ground with no large metal objects close to the antennas other than a metal or plastic cart surface under the Venue and the metal case of the Venue itself.
  • The UM or SM transmitter is held by the metal case at arm's length away from the body with the antenna vertical.
  • Line of sight between the transmitter and the Venue.
  • All done outdoors.

We are not trying to duplicate a real use case here but we are trying to eliminate all variables such as body and clothing absorption (15 dB), antenna gain factors (0 to 5 dB), defective antenna amplifiers (30 dB), bad cabling (60 dB), reinforcement from room walls (6 dB), etc. Under our simplified but repeatable conditions, whether you have RF interference or not, the Venue RF display for a good system will be full scale at a separation of 100 meters. You may get dips due to multipath but moving a foot or more in any direction should get you out of the multipath. Again, the maximum reading is the correct one for this test since multipath will rarely increase the signal more than 6 dB but can decrease the signal by 30 dB.

We did this test in our parking lot with a clear line of sight between a UM400 100 mW transmitter and a block 26 Venue receiver. To double check the real world against theory we did a path loss calculation. Here's the path loss formula:
The formula for path loss between two 0dBd antennas given a separation D and a wavelength y with y=0.461 meters at 650 MHz is Path Loss in dB = 22 + 20 Log (D/y).

For 650 MHz at 100 meters separation the Path Loss = 69 dB. Since a 100 mW transmitter power level is is 20 dBm then the signal at the Venue antenna is 20 dBm - 69 dB = -49 dBm. Full scale on the Venue is 1000 uV or -47 dBm. (Remember 0 dBm at 50 Ohms is 0.224 Volts not .775 Volts as in a 600 Ohm audio system.) In any case, the -47 dBm at full scale is scarily close to the theoretical path loss result of -49 dBm. Ground bounce reflections can add 6 dB to the numbers and diversity antenna addition can add 3 dB. In any case, with some hand waving, the actual measurements seem very valid.

As long you have line of sight between the transmitter and Venue, it doesn't make any difference what kind of ground surface you are on. Interference, even at high levels will only increase your RF readings on the Venue scale. The European 50 mW units will shorten the 100 meter readings to 70 meters. The LM would be about 70 to 90 meters depending on the particular LM. The SMq, UM250 and UM450 250 mW units will increase the full scale range to 160 meters.

This test only checks the power level of the transmitter and the RF operation of the receiver; it does not address any added factors such as interference in the area or the rest of your setup. It does give you a starting point for diagnosing problems but it is only valid under the 5 conditions above. If you perform the above test and the results are good, then you can start adding antennas and cabling to the system. The remote antennas, cables, amplifiers, etc., should give at least the same distance results as this right angle whip test or there is something wrong. Before I get buried in replies that say full scale at 100 meters is impossible, reread the 5 strict requirements above; this is a very special test setup.

If you get the correct readings for RF level, then the next most probable cause of short range is interference. Then the Venue scanning function should find the problem.

Posted 1 year agoby LectroAdmin
#133