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Verifying Radio Communications and Path Signal Strength – PING a Radio

Whenever 2 or more data radios are installed to communicate wirelessly, a vital design point is to establish that the radios are in communication with one another. Another design point to verify is that the effective radio signal path is sufficiently robust to provide reliable and consistent communications. Both of these objectives can be realized by becoming familiar with, and utilizing the PING feature in any Raveon data radio modem.

The PING of a remote radio is very similar to the PING of a remote IP address. In each case, the PING command is issued from a local device, the address of the remote device is specified, and if successful, the remote device automatically responds to the PING with the local device displaying the results. For a PING to be successful, communications in both directions between the local and remote device must take place. If a PING fails, one or both directions of communications may be assumed to have failed.

To PING a remote Raveon radio modem, several conditions must be met. First, both devices must be set to operate on the same frequency (ATFR, ATFT, ATFX parameters) the same bandwidth (ATBW parameter) and the same over-the-air baud rate (ATR2 parameter). Next, both radio modems must be operating in packet mode (ATMT parameter set to 0) and have unique valid addresses (MYID or ATMY, TOID or ATDT, and ATMK parameters). Finally, both radio modems should have remote access enabled (ATRV parameter set to 0).

To PING a radio modem, enter into command mode on the local modem and issue the following command:

PING XXXX

where XXXX is the 4 digit address of the remote device (e.g. PING 1002).

Alternatively, you may utilize Raveon’s free-to-download Windows GUI radio configuration utility Radio Manager. The PING execution is found on the interaction tab.

When the remote radio modem responds to a PING, and the response is received, the local radio modem will display a brief result without indication of error and include the RSSI (Relative Signal Strength Indicator) signal level of the responding (reply) transmission. To capture the RSSI of the outgoing (request) transmission, you must initiate the PING from the opposing radio, and capture the RSSI from this response.

Here is an example of a successful PING. In this case the PING is from modem 1001 querying the remote modem 1002:

Ping 1002

<RPR>

FROM=1002

-90</RPR

In the successful PING please note that an RSSI value of -90 is returned. This RSSI information can prove quite valuable.

Whenever installation trouble is encountered, and two radios do not appear to be communicating, it is a good idea to try and execute a PING. If the PING succeeds, you have verified that the two radios are in fact communicating, and you may consider other aspects of the system as potential failure points. A PING can also be a valuable tool in aligning directional antennas, which should accurately point towards the opposing target. While RSSI numbers are relative, generally an RSSI with a value closer to zero than -100dB (i.e. -97, -85db) will be strong enough to support good radio communications.   Note that this is not strictly the case, especially in environments where there is a lot of noise on the frequency in question. You should always look for a 20dB difference or more between your signal strength and background noise. For instance, if your background noise level is on average in the vicinity of -115db, you want an RSSI value of at least -95db, with -90, or -85dB being preferred, and providing some buffer against occasional noise spikes.

To acquire an instantaneous reading of the background noise level, ensure no device in the system is transmitting, and then type the command ATRQ. The background noise level will be displayed.

To strengthen the signal of a transmission you can consider several actions. First, if the output power on the radio modem is not already set at 100% (ATPO parameter), you can increase the output up to 100%. Second, consider slightly re-positioning our antennas, use higher gain antennas, or lower loss or shorter antenna cable. Third, install a power amplifier.   Raveon can recommend and source several amplifiers. In any case, ensure none of these remedial actions violate your radio license limits.

Author: Larry Topp

Filed under: Testing | Posted on July 5th, 2017 by am

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