We have an operational mesh network among several 911 towers at 2.4 GHz. We are considering installing a 5 GHz backbone.
I would like to estimate the 5 GHz s/n based on the known 2.4 GHz s/n, which ranges from 20 to 30 db on various links.
I would like to estimate the 5 GHz s/n based on the known 2.4 GHz s/n, which ranges from 20 to 30 db on various links.
At 5 GHz, we have an additional 6 dB free space loss, since the frequency is twice as high.
The gain of all the current tower antennas is 13 dBi.
If we put 31 dBi dishes at the towers at 5 GHz, we gain 31-13 = 19 dBi.
If we put 3 sector 19 dBi antennas at a central node at 5 GHz, we gain 19-13 = 6 dBi.
Taking this all together, we gain a total of 19 + 6 - 6 = 19 dB for each link.
Since the 5 GHz antennas have higher gain, their Fresnel zone is narrower, so that should help even more.
Is this a reasonable estimate?
Bob W8ERD
Is this a reasonable estimate?
Bob W8ERD
The free space loss is ony slightly more at 5 GHz than at 2.4 GHz. The 6 dB is a common misconception from a formula whose derivation assumes that the antennas are a constant size in terms of wavelength (the antenna gets smaller at higher frequencies).
On the other hand, if you have trees in your Fresnel zone, the effect of these will tend to be greater at higher frequencies. But as you point out, the Fresnel zone is smaller.
You did not say what antenna you are looking at, but the Ubiquiti 5G30 has 30 dB directivity only at about 6 GHz. It will be 29 or 28 dBi where you will likely use it.
The 5 GHz radios tend to transmit 1 dB less power than the 2 GHz ones - you need to see what the spec sheets say for yours. This is a function of data rate (MCS).
For SNR, you need to know about interfering signals. If you are up around 5.9 GHz you should be in the clear. Down around 5.8 there is a LOT of QRM is most populated areas (especially when seen from high elevations).
Ken
KE2N
This is the 5 Ghz dish I am looking at:
http://www.titanwirelessonline.com/Poynting-5-8GHz-31dBi-Grid-p/at-30gr-...
It sounds like you are saying I am close to being on the right track here, except for a few small changes. Is that right?
Bob W8ERD
OK - that is a pretty big reflector and it could have 31 dBi at the top of the band. A lot depends on the efficiency of the feed.
F/B and front to side rejection probably will not be as good as with a solid/parabolic unit. The price is right.
What radio are you planning to use? This antenna is not MIMO, so you would not use it with an M5 (for example) but only with something like a Bullet.
(With a MIMO setup you effectively get 3 dB more signal at the same data rate).
To answer your question - since the factors I know about sort of cancel each other out, your estimated looks good.
A couple weeks ago, I was diving into the FCC allocations and learned something new. Part 15 U-NII-3 only goes up to 5825 with last channel at 165. I had been thinking that the noise and this unlicensed space was all the way up to channel 175. That's true, the ISM device allocation goes up higher, but these devices are explicitly not permitted for "telecommunications " purposes. Thus, it is clear sailing above 5825 at tower sites. I'm seeing this all across the Los Angles, Riverside, Orange County--no WISPs are licensed above ch 165 and using this space.
We should all establish very strong beach heads from 5825 (ch166) to 5925 (ch 184) to hang in there when the future U-NII-4 big waves begin to cover this entire part 97 allocation on 5Ghz.
Joe AE6XE
I have been holding the fort over the Norther Virginia suburbs on 5900 MHz for nearly a year now. But I feel like I am standing in front of a speeding bus.
The FCC would like to open up this area for part 15 users at some point in the future. It is already used by radiolocation and satellite services so there is a lot of discussion https://apps.fcc.gov/edocs_public/attachmatch/FCC-13-22A1.pdf
Amatuer use is secondary and it already sounds a bit like part 15. (But note the last comment - emphasis mine):
" 94. Amateur Radio. Amateur service stations are permitted to transmit in the 5.85-5.925 GHz frequency segment on a secondary basis. Operation of these stations in this frequency segment must not cause harmful interference to, and must accept interference from, authorized stations in the fixedsatellite (earth to space) and mobile services (DSRC) and also stations authorized by other nations in the fixed service. 115 The FCC does not have detailed information on use of this band by amateur service stations."
Maybe we should send them some detailed information .....
Joe AE6XE
Thanks!
Bob W8ERD
yes an M5 would give you more computing horsepower/memory.
But to use the MIMO feature you need a different antenna than the one you showed a link to.