RMonline Linking: RX Vs. TX Antenna Gain

9 posts / 0 new

Tue, 11/14/2017 - 13:04

w8awt

I am learning how to use RMOnline and I have a question regarding creating link studys. When the system asks for RX and TX Antenna gain how am I supposed to answer this? By RX and TX do they mean site one and site two? Or are thy literally asking for the gain of the (separate?) RX and TX antennas? If the answer is the latter, Wont both RX and TX antennas be the same since Ubiquiti does both on all antennas? As an example, if we have say a 11 dBi NSM2 on both sides of a 2.4 GHz link would the appropriate value for both RX and TX be 11 dBi? How would we answer this for a link with say a 11 dBi NSM2 on one end and a 25 dBi RM2 on the other side.

Thanks in advance for the help!
73,
Augustine
W8AWT
Twitter: @w8awt

Tue, 11/14/2017 - 14:30

ke6bxt

Are you coming or going?

When computing the theoretical path performance of a (duplex) microwave shot you need to compute each shot independently. In other words, a microwave shot between point A and point B is really a shot from A to B and another shot from B TO A. In the shot from A to B, A has the TX antenna and B has the RX antenna. Why is this important? Because the TX antenna amplifies the signal from the radio, thereby effectively raising the signal to noise ratio (SNR) along the entire microwave shot. The RX antenna amplifies both the signal and the noise at the receive station. If the signal level is below the noise level at the receive site, or more correctly, below the sensitivity of the receiver, having a higher gain RX antenna is not going to help the path performance, but having a higher gain TX antenna could potentially improve the SNR and make the shot work (in that direction).

See also: https://sites.google.com/site/orangecountymeshorganization/lqnlqandetx

Wed, 11/15/2017 - 07:38

(Reply to #2) #3

w8awt

Doesn't RMOnline compute the

Doesn't RMOnline compute the runs in both directions at once? Or do you have to compute both runs separately, reversing the RX and TX values on the second run to simulate the link in the other direction? I have never seen anyone do more than one prediction to try a path out but maybe I wasn't looking heard enough.

Thanks for your help!
Augustine
W8AWT
Twitter: @w8awt

Wed, 11/15/2017 - 11:35

(Reply to #3) #4

ke6bxt

"Most" people only use the

"Most" people only use the tool to see if there is line-of-sight. That is only one third of the question, Signal strength and path loss are the other two.

Sat, 11/18/2017 - 08:49

(Reply to #4) #5

K6AH

RMOnline is a one-way analysis

No. RMOnline only performs the analysis in one direction. Don does a great job of explaining the issue, but from a practical standpoint, you can assume the analysis is the same in both directions. That's because you will have no idea what the noise level will be at the RX end and must assume -95dB or 4uV. Even after installation, most of us don't have the equipment to measure the noise level... even the Ubiquiti radios don't have an absolute sense of what the noise level is (they only sense the relative noise and assume it to be -95dB for the charts). If you encounter the issue Don discusses, then treat it as interference and work to eliminate that problem after installation.

Andre, K6AH

Sun, 11/19/2017 - 22:48

(Reply to #5) #6

w8awt

Thanks So Much for the Explination!!

Thank you so much for the easily understandable explanation Andre! Thanks also to Don for elaborating on Andres comments, your detailed explanation was really helpful after what Andre said. Sometimes I just need things explained simply before getting into any detail! Just to clarify, I can think of RX and TX as exactly that: site one and site two? As a simple analogy: A transmitting station going to a single receiver?

Thanks again!!,
Augustine, W8AWT

Tue, 11/21/2017 - 13:07

kd0wmp

site 1 site 2

Yes, I don't use RM (I use Pathanal) but I normally think of Site 1 as TX antenna gain and site 2 for RX gain.

Marlon, kd0wmp

Wed, 11/22/2017 - 16:41

(Reply to #7) #8

w8awt

Thanks!

Thanks Marlon!!!

Tue, 12/19/2017 - 17:35

wa2ise

I had thought that a

I had thought that a directional receive antenna aimed at the remote site would increase the signal strength, and the noise would stay the same (assuming the noise is the same in all directions).

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