Frequency does matter

Recently we installed a PTP 550 link for a client.  This is a connectorized version with 2-foot dishes on it for a four-mile link.  Overkill you say, but the idea is the dishes make up the gain and not transmitter power.  A much cleaner signal can be achieved which falls within the FCC guidelines for total EIRP.

So let’s get to it.  Our first image is out path.  This link had clear line of sight from a 150-foot foot water tower to a 240-foot tower.

Google Earth Path

The 240 Foot tower

150 Foot water tower

After getting out of the cold we let things burn in for a few days. This is what an initial spectrum analysis looked like.

Radio Frequency set on 5820 mhz

Radio Frequency set on 5200mhz

As you can see the RSSI was within 2 DB, which isn’t terrible.  However, due to interference, the MCS rates are markedly different, which is what results in the big differences in speed.  Please note this is only with one radio enabled and on a 20mhz channel.  We fully expect bigger speeds once we up channel sizes and enable the second radio.

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MTIN Family of Sites
https://indycolo.net
https://j2sw.com
https://startawisp.info

Cambium PTP550 Data Rates

Some info on the cambium PTP 550 Data Rates

“Downlink Max Rate” specifies the maximum downlink MCS value that the Rate Adapt algorithm will choose.
MCS values range for data from MCS 9 to MCS 1 for one or two Spatial Streams (Single Stream and Dual Stream respectively). A higher MCS value (e.g. MCS 9) carries more data, but requires more link budget / stronger radio signal. Thus, MCS 9 provides the most data, but the least robust link (i.e. greatest chance data can be lost) and MCS 1 provides the least data, but the most robust link (i.e. least change data can be lost).
DS MCS provide two streams of independent data over the two transmit chains while SS MCS provide one stream of data over both transmit chains.
Setting “Uplink Max Rate” to a DS MCS 9 – DS MCS 1 value will allow this MCS and all lower dual stream MCS values to be used along with all similar or lower single stream MCS values. For example, choosing DS MCS 8 means that DS MCS 8 – DS MCS 1 and SS MCS 8 – SS MCS 1 will be used in the Rate Adapt algorithm. Setting “Uplink Max Rate” to an SS MCS 7 – SS MCS 1 value will allow this and all lower single stream MCS values.

Rates Highest to lowest
DS MCS9 – 256-QAM 5/6
DS MCS8 – 256-QAM 3/4
DS MCS7 – 64-QAM 5/6
DS MCS6 – 64-QAM 3/4
DS MCS5 – 64-QAM 2/3
DS MCS4 – 16-QAM 3/4
DS MCS3 – 16-QAM 3/4
DS MCS2 – QPSK 3/4
DS MCS1 – QPSK 1/2
SS MCS9 – 256-QAM 5/6
SS MCS8 – 256-QAM 3/4
SS MCS7 – 64-QAM 5/6
SS MCS6 – 64-QAM 3/4
SS MCS5 – 64 QAM 2/3
SS MCS4 – 16-QAM-3/4
SS MCS3 – 16-QAM 1/2
SS MCS2- QPSk3/4
SS MCS1 – QPSK 1/2

MCS\Rx Sensitivity  20 MHz       40 MHz       80 MHz
Lowest MCS          -90 dBm     -87 dBm       -83 dBm
Highest MCS .       -66 dBm     -62 dBm        -59 dBm

 

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MTIN Family of Sites
https://indycolo.net
https://j2sw.com
https://startawisp.info