R7800 X4S: Antenna specifics info wanted anyone know?

[davidm71]

Hi,

Was wondering if anyone know the details of the antenna's used on the R7800 X4S router? How many db are they rated for? Wanted to replace them with more powerful antennas but the fact it uses two different kinds confuses me as I think I have read that the rear antennas are 2.4/5 ghz and the side antennas are 2.4 ghz antennas and that the router prioritizes the ones on the left first for use..

Thanks

 

[Internet Man]

The FCC filings should have a lot of this info but it can be difficult to make sense of it all. I am far from an expert but will try to suggest some things to look at.

The Internal Photos might be a good starting point.

Since this device has four spatial streams for both the 2.4GHz and 5GHz radios and only four antennas, all antennas must be dual-band. Looking closely at the internal photos you can follow four lines from each radio chip through front-end modules to the four shared U.FL connectors with wires running to the RP-SMA connectors for the external antennas.

The "Test Report" documents list some information about the antennas and suggest that all of the antennas are identical.

There are two relevant test reports (Test Report (NII).pdf, Test Report (DTS)_rev.pdf) from the original filing on 11/4/2015. An updated test report covering 5GHz operation was submitted with a Class II Permissive Change filing on 1/21/2016 but the listed antenna gain values are unchanged. Another updated 5GHz test report was published with the filing on 10/21/2016. DFS test reports were included on 10/21/2016 which suggests that Netgear was working toward adding support for DFS channels at this time. Antenna gain values were added to the table for DFS frequencies.

RF Exposure reports seem to compute the effective directional gain from the four antennas for each frequency. I doubt that simply buying antennas with higher advertised numbers would actually help at all.

I think that you should heed Tim's advice from another thread recently:

Antennas are part of a router's RF chain design. You may think by swapping them you are improving performance. But you could just as easily be degrading it.

 

[davidm71]

I appreciate the advice and the in depth response. Going to run some tests and see if the rssi scores get better or not. My actual plan was to replace the antennas with Asus AC88U antennas if I see an improvement in scores otherwise I'll take my extra antennas and use them on back of my wireless usb/pci adapters. The Asus antennas are rated at 8 db according to the listing I found. Not sure about the Netgear ones but I guess I will find out and when I do report my findings. Thanks.

 

[thiggins]

In general, most routers/APs ship with "unity gain" omni-directional antennas. Since antenna gain varies over frequency, you may see higher gain, as shown in the table Internet Man included in his post.

The original intent of the "RP-SMA" connectors used by routers that used connectorized antennas was so that users could not change the antennas and violate FCC rules. We all see how that plan worked out....

 

[davidm71]

Well what is confusing about this particular router is the fact that it uses two different kinds of antennas. Will have to dig into those documents to find out more. Thanks.

Edit: Looking at those documents now. I swear you have to be an engineer to make sense of them!

All I can gather is that different operating modes have either high or lower db output but doesn't really mention specs regarding the actual antenna hardware.

 

[Leon Straathof]

In general, most routers/APs ship with "unity gain" omni-directional antennas. Since antenna gain varies over frequency, you may see higher gain, as shown in the table Internet Man included in his post.

The original intent of the "RP-SMA" connectors used by routers that used connectorized antennas was so that users could not change the antennas and violate FCC rules. We all see how that plan worked out....

I started my own thread on the antenna questions, but this one is really interesting because it tells that the design type of the R7800 antenna is a dipole which is the simplest design there is. Maybe i should try and build a dual band antenna for the R7800 if i build a dual band staggered coaxial antanna and put it on 1 of the 4 connectors i would have the same performance close and when out of reach of the stock antenna i would still be connected with 1 stream on a huge horizontal plane meaning ground floor. Hmm getting my electronics tinker stuff from the shed i think....

 

[davidm71]

Was able to increase my signal strength by 8 db by taking a copper sheet and after giving it a slight curve taping it to one antenna on each side backwards with the middle antennas at distance of a few inches away.

 

[heidarren]

I'm not sure the spec of R7800 antenna but I did try to put R7800 antenna on my AC86U, the signal and speed seems lower than the original AC86U antenna, few dBm lower and transfer speed from my PC to iPad Pro dropped from 68MB/s to 59MB/s, never try it vice versa

 

[Leon Straathof]

Was able to increase my signal strength by 8 db by taking a copper sheet and after giving it a slight curve taping it to one antenna on each side backwards with the middle antennas at distance of a few inches away.

Although i put this in the category ghetto hacks if it works for your, congratulations however to replicate the same result for everyone i recommend more precise work. Thanks for the reply anyway.

 

[cordezz]

Was able to increase my signal strength by 8 db by taking a copper sheet and after giving it a slight curve taping it to one antenna on each side backwards with the middle antennas at distance of a few inches away.

Perhaps you could upload a picture of that, please.

 

[davidm71]

Perhaps you could upload a picture of that, please.

Will do later tonight.

 

[davidm71]

Did some more testing using Merlin RSSI Bridge score and it did in fact improve by about 6 db.