400c PTP Link

Hi all, just looking for some advice/insight on a 400c ptp link that we just put up in place of mimosa backhaul. So we just swapped the radios and left the original 2ft dishes in place, 2ft dishes on either end. It is a 18km link and we are getting poor results for signal, -73/-76. The mimosa link was around -67/-70 but was better in previous months. Maybe I have a bad antenna but not sure. We tried firmware 5.4.2 and 5.4.1 but no difference in performance. Is it possible connections for chain 0 and 1 were switched on the antenna or will that not matter?

Lot of questions…

  1. what TX power and EIRP were you using with the Mimosa?
  2. What TX power are EIRP are you using with the F400c?
  3. When you use the F400’s alignment tool, take note of the combined signal, but also take note of each chain… the delta between chains should be very low, usually within a couple dB of each other. If there’s a large delta between chains it could mean that there are issues.
  4. Are you operating in a part of 5GHz that has a limited EIRP?
  5. Have you used LinkPlanner to model the link? The F400c’s are in there along with some generic 2’ dishes.
  6. With most modern radios systems that use MIMO, including the e4k series, you don’t need to make sure that your chains match up on each side.
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Thank you for your reply! As per link planner we should be at/around -52dbm… so real world I was expecting -56dbm. TX power is 25 so our EIRP is 53… Here are e-align for Master and Slave…



Both towers are rural sites, tried tuning on both ends and this was best we could get, similar link elsewhere has -55 signal, rural as well.


Something is seriously wrong with the link, most likely physically… you need to go through and double check everything.

Thank you, appreciate it… with the 400c replacing the mimosa radios we also used new cables so its either radio or antenna, if that makes sense.

Forgot to mention that this was a network we took over so we started upgrading it to Cambium products so I am suspicious of the antennas.

Digitalman, definetly with power output of 25db, 2ft antennas and clear LoS you shou; be getting -5x . there is a big issue there…

While defective antenna / cables are for sure a possibility that almost always presents with one chain way better / worse than the other chain (unless you have water/moisture in both pigtails possibly?) It really looks like you either have a buss parked directly in the middle of the link blocking LOS or you have somehow done an amazing job of aiming side lobes at each other (and even well aimed side lobes normally have a pretty pronounced chain imbalance because they have different side lobes).

I would say possibly a bad radio but that would also normally present as bad at one end and good on the other and/or huge chain imbalance.

Or as suggested your TX power isn’t what you think it is, on both ends. We no longer have a 400 link so I can’t look at one and I don’t remember what the status/home page showed on the 400’s but do they show “Transmitter Output Power” ? I’m not talking about what you think you have TX power set to but does the radio show you somewhere what the TX power actually is ?

EDIT: Just trying to come up with things that would result in the chains and both ends being so similar.
What model of dish are you using ? Is it possible you are using a frequency the dishes don’t really support ?

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Apreciate everyones response. It is a bit of a hard one… no concrete evidence to support bad radio or antenna.

The status is showing 25 for TX power

I am not exactly sure the model of dish… they look like aletix 2ft dishes no markings of brand… we took over an older wisp but I am using the same 5GHz frequency as the mimosa radio… with that said, before we swapped radios we had a storm roll by and we had to truck roll to do physical power cycle the mimosa radio. Upon logging in the mimosa radio would only negotiate at 100mbps not 1000mbps and all troubleshooting lead to radio was issue with 100mbps negotiation, so that just sped up the timeframe to replace radios with cambium 400c. Before swapping the mimosa link was at -67db with the same tx power. So I was surprised that we had -75 even after we tried to fine tune on each side. As I said previously we have 4 other 400c links working fantastic.

there’s really something very wrong with the physical installation. 2ft dishes should have 28 to 29dBi gain.
18km at 5.5GHz is 132dB free space loss. Thus, link calculation :lab_coat:

25dBm TX Power + 28dBi TX antenna - 132dBm free space loss + 28dBi RX Antenna == -53dBm receive signal

You should have around -53dBm signal level at this link, if it was running 5.5GHz frequency. It changes a decibel up or down when running 5.1 or 5.8GHz.

PS : 25dBm TX is not good, I would not use more than 20 or 21dBm for maximum modulation.

Because you had tremendously less signal with original Mimosa devices and you can’t have anything more with new Cambium gear, there’s nothing wrong with those radios. You have to fight your antennas, coax cables, connectors, line of sight, aiming and similar things.

Linking at 100Mbps is totally different topic which has nothing in common with radio signal strength.

I would start with making sure those dishes are 5GHz dishes. I have seen a case, where old antennas were used for new radios without anyone noticing that antennas are 2.4GHz :slight_smile:

Can you please provide a screenshot of your master’s Status page (the default 1st page that loads)?

ALSO, just to confirm, you’re using ePTP mode on both radios right?

Everyone has given great advice but i do ask have you turned down your TX power on both ends so that your RX signal is in the -85 region then tried realignment? Aligning at high power settings tends to make the radios a bit insensitive to small adjustments.

Thank you everyone for the tremendous support! We really appreciate it and I apologize for the late response.

@Lubomir_Zaciatocny we will be investigating the antennas frequency band and thank you for your insight!

@Eric_Ozrelic ePTP mode is enabled on both radios, thank you!

@Douglas_Generous we will definitely consider and try your suggestion! Thank you!