PMP 450 - Poor SNR. What can be done?


I have 2 SM's  (1x High Gain Intergrated PMP 450i and the other a  PMP 450 w/ reflector dish) connected to a single base station (450i) operating at 5885. Both links are about 5.4km from the AP. I've done an analysis in LinkPlanner and i should be achieving 6X MIMO-B in both UL and DL directions for both types of equipment. Instead, im getting 8X/1X MIMO-A for the reflector dish and 8X/4X MIMO-B for the High Gain Intergrated.

I've noticed that the SNR for the reflector dish is very low - sitting at about 12db MIMO-A. Ive done spectrum analysis at all sites at the same time (so AP's transmitter doesnt show in the analysis) and can't see any interference. Wondering what can be done to improve both links? Need them both to be 6X/6X MIMO-B to achieve the  40/40Mbps throughout rate. Configuration and stats of devices and links below - 

SM w/ reflector dish - 

Recieve power -74dBm


Air Delay  3.383 Miles

Channel Bandwidth  30Mhz

Region Code - Other/Other

Transmit Power  22dBm (target power 48dBm)

Modulation - 8X/1X MIMO-A

Frame Period - 5ms

Software version - 15.1.1

Link Capacity Test - 30 Down, 5 up.

High Gain  450i -

Recieve power -62dBm

SNR  22 V / 12 H dB

Air Delay  3.380 Miles

Channel Bandwidth  30Mhz

Region Code - Other/Other

Transmit Power  27dBm (target power 32 dBm)

Modulation - 8X/4X MIMO-B

Frame Period - 5ms

Software version - 15.1.1

Link Capacity Test - 100 Down, 25 up.

Both of the installations are on warehouse style roofs with the High Gain 450i about 1.8m high on a mount and the Reflector dish at about 500mm.

Any assistance would be appreciated. 

This may not be the entire problem, but it looks like your reflector is not aimed very well.

All things being equal if both SMs are the same distance from the tower then you would expect the reflector to have a 2dB better RSL than the PMP450i. The reflector has a gain of 25dBi while the 450i has a gain of 23dBi. So unless you are shooting through a tree on the reflector then you should be able to get pretty close to a -62dBm for receive level (if not better).

Let me know if you still have problems if this doesn't help. I have some other ideas.

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Hi Seth,

Thanks for the response.

On the 450i link we still need to achieve a little bit better SNR to hit the 6X modulation rate and get the 40Mbps upload bit rate . That was the initial thought (hence putting in the reflector compared to another 450i at the 2nd site), but we have since found that because the max transmit power on the 450 is 22dBm, it wont give a better UL rate (compared to the 450i's max TX power of 27dBm.

I've just had a picture sent through which indicates that there is a metal shed that could be blocking a bit of the signal.

I guess the question is at the site of the 450i - is there any equipment that we can use to get a higher TX power and more gain? Is there any equipment/antennas that you could reccommend to perhaps put onto a 450i connectorized radio and get the desired throughput?

I don't really know of any true cost effective solutions for higher gain. You could always go with a dish that you would typically see for a backhaul, but to get above 25dBi I think you are going to pay a pretty penny.

If the installer can see the tower (even with some obstruction) you should not be 12 dB off on RSL.

The PMP450i does have 27dBm transmit power, but it only uses it at QPSK. For 6X modulation the max is 25dBm. So your PMP450i  has 3dB of better Tx Power but a 2dB weaker antenna than the reflector. You should be within 1dB for RSL if they are both perfectly aimed.

I'm probably not much help here.