Hi,
Just want to ask if there is a standard separation distance between two Force 200 radios in 1 pole?
Or is it okay if they are near each other?
Thank you.
Hi,
It is recommend to have a 1.5 meter separation ( Horizontally & vertically ) in ideal situation b/w two radios.
Hi,
This is noted. Very much appreciated with your reply.
Thank you.
It is recommend to have a 1.5 meter separation ( Horizontally & vertically ) in ideal situation b/w two radios.
Just curious, is that due to noise from the electronics of the radio itself causing interference ?
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Yes- this will reduce the effect of EMI
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So, dumb question, if the radios need to be 1.5m apart to prevent them from interfering with each other how does the radio not interfere with itself ?
The radios are TDD - time division duplex, meaning that they are in transmit mode or receive mode, but never can they be in both at the same time.
For everyone reading this, the 1.5m separation makes some assumptions. Since every device that we co-locate on towers has a directional antenna of some fashion, so anytime we mount antennas on towers, they have some kind of relationship to each other…there is free space loss between them, as well as the directivity of the antenna contributes to the isolation that 2 antennas have in relation to each other.
1.5m of separation provides about 50 dB of free space loss as a rule. Then side to side isolation of directional antennas can range from 10dB to 25 dB or more…you have to consult the antenna polar chart to see what the value might be in the direction that your antenna(s) are from your antennas you are calculating. For this example, lets assume we have 10 dB from each antenna. Add the losses up, and we have 70 dB of isolation that 1.5m separation gives us with the Force 180 antennas.
If our 2 Force 180’s were on the same channel, we don’t have enough isolation to prevent interference. The Force radios operating as PTP do not have any synchronization, so we can have one radio in TX mode, while the other radio is in RX mode. In this worst case situation, assuming 5.8GHz with EIRP 36 dBm, the RSSI that the co-located unit receives is +36 dBm TX - 70 dB isolation = -34 dBm. In this case when one is transmitting, the other receiving on the same channel, the receive is wiped out by the co-lo’d transmitter. So we use a different channel for each system. To summarize a lot of radio theory, each system’s receiver can provide up to 50 dB of off channel receive isolation (called adjacent channel rejection). Assuming that we are 2+ channels separated, we have 45 dB to 50 dB isolation. So now, our -34 dBm RSSI would be -84 dBm RSSI, which is a very common noise floor value on many sites. This combination now works.
Remember that the more unsynchronized radios we add to a tower, each one contributes to the noise floor rise on that site. Best practice is to use as much GPS synchronization as you can…using the same TDD split on each system so that all radios co-located are in TX mode at the same time, and RX mode at the same time. In this situation, you do not have to worry about co-located equipment contributing to noise rise. For example, if you have ePMP 3000 AP’s synchronized with GPS on a site, use a PTP550 or PTP670 for backhaul, both can be GPS synch’d, and TDD radio set similar to the ePMP3K.
Hope this helps with understanding what might be happening on your site…any questions, please ask, as there are many true RF experts in our community.
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I assumed OP was talking about subscriber radios since he was asking about F200’s on a pole. If so, then he could mount 100 of them on his pole and as long as they are all talking to the same TDD AP then side lobes nor front to back nor free space or TX power is relevant because not one of them will ever TX while another is trying to RX.
So I asked specifically if the problem due to “noise from the electronics of the radio itself causing interference”
Cambium Sreejith said yes “this will reduce the effect of EMI” so either I’m misunderstanding him or he misunderstood me or we both misunderstood or this is about EMI coming from the electronics not the antenna.
For example, we recently had to replace an old (our first, 14’ish years old) 900Mhz motorola Canopy radio when the local fire department started having problems with noise on one of their repeaters (our radio/antenna was about 2m from their antenna and the two had coexisted without problems for 14’ish years). Turned out something was wrong with that old 900Mhz radio, but it was electronics in the radio itself causing the problem and had nothing to do with the 900Mhz energy from the antenna. We didn’t touch the antenna we just replaced the radio and the noise on the fire department’s repeater went away. In fact we could shut off the TX on that radio and/or disconnect the antenna and it had no affect on the interference the fire dept was seeing.
Had that 900Mhz radio of ours been spewing out 900Mhz noise from whatever was malfunctioning then it would have been interfering with it’s own ability to see it’s own 900Mhz clients but instead it was spewing out 270Mhz noise and interfering with a the fire department’s repeater. SO if a 5Ghz F200 spews out noise that could cause problems for a near by 5Ghz F200 then how does it not cause problems for its own 5Ghz radio ?
I am genuinely curious however if the concern is EMI from the electronics of the radio itself then is it because it may interfere/cause RX noise for near by radios or is it actually causing problems with the circuits of the radio (like the EMI of a solar flare or a malfunctioning electric device can cause problems with electric circuits)? Actually causing problems with the circuits of a near by radio seems pretty unlikely (but hay maybe not as unlikely as I think, that’s why I’m asking) so that just leaves causing noise / interference affecting the RX … but if that is the case, if the electronics on the radio actually generate enough noise to cause interference for a near by 5Ghz receiver then how do they not interfere with their own 5Ghz receiver ?
I think it will decrease EMI effect
The local oscillator is the point source for unwanted EMI radiation off any device. If one of the suppressor capacitors that controls the harmonics becomes defective then the device can emmit harmonics that would be strong enough to lift the squelch of another radio system if it is a shared harmonic. The fact you were 2m from their high gain antenna makes the interference even more of a possibility due to how much gain is in that radio system. Any device can cause harmful EMI, including your 30yr old pocket calculator.
As for multiple f200’s on a pole, it would be application specific. Example of slave side of a pair of backhauls in ptp-tdd mode then you can place them as close as you physically can with out too much trouble save for being pointed in near the same direction where you may see some noise from the other radio. If it is two SMs connected to two towers for redundancy then at least 1m vertically or 2m horizontally should be given to provide isolation between the radios. If its two radios for two clients in a shared building (duplex) and they are connected to the same AP then you can place them so that they are touching if you wanted with minimal issues as they will only be transmitting when allowed and only when given a time-slot to do so. I am not saying that this is best practice but it is possible to do this and have it work just fine.