Gang,
I want to create a point-to-point link from my home in Glendale, CA to Mt. Wilson for my Amateur Radio repeater. The distance is 14.2 miles and optical between the proposed ends. I would like to use 4' dishes at both ends, not so much for gain, but for a narrow beam width (view) from Mt. Wilson, and extra gain at my home to hopefully be able to override interference from other users - as you well know, Mt. Wilson is a high profile site. This would be used only as a point-to-point control link and not linked to any other system.
I'm thinking of Ubiquiti equipment. How much through-put do I want?... As much as I can get. :>
I would like your recommendations and hopefully, specific model numbers and links to specific equipment suggestions would be appreciated.
Thanks in advance,
Burt, K6OQK
Glendale, CA
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5.8 GHz Point to Point Link info wanted...
Mon, 01/13/2020 - 14:09
#1
K6OQK
5.8 GHz Point to Point Link info wanted...
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A dish in the 4' ballpark would be significantly higher $$$$, and would certainly cut though a lot more noise. These may be harder to source as they would exceed part 15 power emissions and not commonly used.
There are AREDN nodes at Mt Wilson already. Reach out to Orv W6BI to compare notes, if not already. People are connecting in to 120deg sector panels on Mt Wilson on 3Ghz today at 15+ mi. I don't recall what is covering your area, but maybe there is a way to test from your QTH today?
Joe AE6XE
Joe, Im curious if your 65 Mbps is true measured thru-put speed or is the what OLSR is indicating, ie LQ (100%) NLQ (100%) TxMpbs (65).
The reason Im asking is Im using two MikroTik RBLHG-5HPNd-XL for a 20 mile back haul and OLSR reports a 103.5 TxMbps with (100%) LQ & NLQ
using 5.825 @ 20mhz. Im feeding it from my home ISP with 20 Mbps and only get a thru-put speed at the other node end of 10-12 Mbps.
Am I missing something or is the equipment your using that much better?
Eric
2 common ways to describe the link in terms of bps:
A) the raw protocol rate at layer 2 of the communication stack
B) the application data throughput at layer 3 of the communication stack
For 'A', the protocol rates are in the 802.11n specification and called MCS0 to MCS15. In commonly found tables of these speeds, be sure to use the Long Guard Interval (LGI) timing of symbols. Although on short distance links it might be able to select and use the Short Guard Interval (SGI) and have slightly higher link rates. Note, what is shown in mesh status is adjusted: (MCS rate) * (actual packet success rate). Thus in mesh status it might show, say ~98% of the MCS rate. It's an attempt to account for known packet loss. This rate is to a specific neighbor and the packet success is only the unicast or traffic addressed directly to that neighbor at the optimal MCS rate.
For 'B', this is generally measured using iperf. It will be considerably lower than 'A'. But put into perspective, a stand HD video stream from NetFlix will be 1mbps or less. If you have achieved 10mbps iperf measurement, this is 10! HD video streams. That's a functional link that will meet a lot of demand. Most home internet users with 100mbps premium service, rarely go over 10mbps use.
LQ% and NLQ% or not very good indicators. This is based on broadcast packets (addressed to everyone on the channel) at the lowest MCS0 rate, the common rate all neighbors can best receive. There is no use of RTS/CTS for these transmissions and packets are easily lost. When an iperf test is done, the protocol will use RTS/CTS and can reserve time slots on the channel, which includes hidden nodes, to minimize loss of data.
Back to the question...
In my case, the 65mbps is the top MCS15 protocol rate @ 10MHz channel. It's been a while since I did an iperf test on this link, it was over 10mbps. 3 or 4 hams have connect in to this P2P backbone link, so iperf rates may not be as high in recent times :) .
Joe AE6XE
Netflix recommends a 3 Mbps connection for one standard-quality stream and 5 Mbps for a high-definition stream. Two simultaneous HD quality streams would need around 10 Mbps, and so on.
So a 10 Mbps mesh network stream could maybe support two HD streams. Of course, running 720p resolution at 10-15 frames/second vastly reduces the required bandwidth.
But props for the great explanation - I learned something!
Orv W6BI
Netflix uses adaptive bitrate streaming to ensure the video can be enjoyed verses dropping out. At times we might see the image getting a bit blurry, but can still enjoy the movie. Netflix might go down to 256kbps ('B') or lower if the internet connection is saturated or degraded for any reason, not sure how low it will go.
ipCams will have (we need one that has) a config setting for this 'B' video stream rate. I set all the ipCams for events to ~750kbs, 15 fps, and 720p, which is still a great picture. Too often I've been bit because I forgot to change a default setting and the camera is at 4Mbps, 30 fps, and 1080p -- floods the network with an ipCam on this setting.
Joe AE6XE
If looking up the MCS rate, these are always in context to the 20MHz channel width 802.11n specification. If using a 10MHz channel width, then the table rates need to be cut in half. If on a 5MHz channel width, the rates are divided by 4 from the table.
Joe AE6XE
On a 10MHz channel width a symbol will be transmitted in 2x the time it is transmitted on a 20MHz channel width. Thus the receiver in 10MHz channel has more time receiving each symbol so a delayed reflected signal of the prior symbol doesn't corrupt the next symbol. The 802.11n 20MHz specification is primarily designed for short distances, 10s to 100s of feet. More time is needed proportionally as the link gets longer to mitigate reflected signals or fading and avoid inter-symbol interference (ISI).
Joe AE6XE