I'm a member of the DCARA here in Denton,TX (North TX). We're setting up nodes around the county and I'm trying and still planning to link with our "Mesh Hub" node at 16km distant. Radio Mobile calculates a -76dBm RX level which seems marginal looking at the noise floor. So, I would like to understand the internal switching topology within the Rocket M2 of the chain ports. Do I understand correctly that the ports are power divided in diversity mode, therefore a -3.5dB loss? If so, appears I should use a separate 23dBi grid parabolic on each chain and configure one for RX and the other for TX, effectively dedicating 1 rocket for this long haul link instead of the 12dBi Omni on chain1 and the single 23dBi grid on chain1 aimed to the node target. Sounds like I could gain another 3+ dB. However, again without understanding the internal switching topology configuration within the Rocket, this is just an educated guess.

Any advice help here would be appreciated, as I can act as a long haul link to my closer neighbor K5WXR with which I have good link with by using another Rocket with sectionals.

Thanks in advance & 73,

Bob AF5RS

As far as we know, on all the dual chain devices the max power is split between the two ports when in diversity.  The units may not let you go above maxpower-3dbm as it derates max power for the fact that only one antenna is in use (at least this was what was seen during initial testing on some models)

When running a dual chain device (Linksys, Ubiquiti Rocket, etc)  you always want BOTH chains to share similar antennas and be pointed in the same direction.  You would want one to be horizontal polarity and one to be vertical polarity (or some other combination)

A dual polarity dish would be best, they are high gain, high front to back ratio, tight beamwidth (aiming can be hard and you have to have a secure mount for long paths to avoid wind movement.)  An advantage of the tight beamwidth is it may reduce the noise floor a bit as well since local nodes no longer are in the beam path of the node.

Mixing an Omni and a directional is generally going to be a less than optimum, the nodes will take the STRONGEST signal and decode that without making a calculation as to  being different nodes.

Dual Chain tends to run better so the Rocket M2 with a RocketDish or any other dual polarity dish (I like StreakWave for its antenna selection on wifi gear) would be good for a backhaul.

I don't know how 2 grid antennas will work, but if using one vertical and one horizontal you do gain the dual chain feature at that point and theoretically it should work. Or even if both anteannas are same polarity if they are at offset from each other they may catch signals different based on atmospherics.  If you already have the 2 grids i would say it would be worth a trial.

The NanoBridge may also work but its 5db less than your grids (18dbm) and its also 5dbm output lower (10dbm total difference) so if loss is already a concern this would likely not be ideal.

Understood, thanks for the additional input. The firmware asks for the antenna config for each chain, I assume your suggestions imply staying in diveristy mode on both chains. Seems logical better gain could be realized using RX on one chain and TX on the other, if in fact the internal split is truly switched around. I appreciate the same antennas fed in diversity mode on TX or RX should be equivilent, however, assuming imprefect phasing that may not be the case and separating TX and RX may in fact improve S/N. Just a theory, I'll do range testing in both diversity on both vs. separate RX & TX. Do you have any empirical data between the different chain config modes? And yes, I do have 2 identical grids to experiment with on both chains vs. the hybrid config I'm using now. I'll post the results.

Thanks again & 73,

Bob AF5RS

We have a solar powered linksys node on a hill. I am able to get in from 6 miles out with a Bullet M2 HP with 25 dbi grid and my friend is able to to get in from 9 miles out with M2 HP and 35 dbi grid. Hope that info helps.

Andre, on your benchmark test exactly what was the chain to grid configuration on the M2s on both ends of the path? Single chain 0 with a single 24dBi grid for TX & RX, not using chain1? Or, dual 24dBi grids using diveristy, or what? We seem to be getting unrepeatable results with different configs. Can't tell yet what's best so curious about you exact chain to antenna configs.

Bob AF5RS

Bob,

I'm having a hard time attaching the Radio Mobile path prediction to this post.  If you'll an email to my callsign at arrl dot net, I'll forward you the analysis.

Andre, K6AH