Thanks to information learned here in the forums, we are working on trying to balance our installations into a 10dB range. We were not aware of this as we deployed originally, so we have radios ranging from -35dB through -77dB. I have found that varying the power on the config page can help reduce jitter in a number of our cases, but we still (even with one of our radios’ transmitter output power set to 1!) can’t seem to get the power reduced significantly. Is anyone out there using really low gain antennas to get power down on close installs? If so, what do you recommend? Any other tricks for reducing power to work toward the magic 10dB spread on the clients?
Thanks for your time, everyone!
cvs wrote: Thanks to information learned here in the forums, we are working on trying to balance our installations into a 10dB range. We were not aware of this as we deployed originally, so we have radios ranging from -35dB through -77dB. I have found that varying the power on the config page can help reduce jitter in a number of our cases, but we still (even with one of our radios' transmitter output power set to 1!) can't seem to get the power reduced significantly. Is anyone out there using really low gain antennas to get power down on close installs? If so, what do you recommend? Any other tricks for reducing power to work toward the magic 10dB spread on the clients?
Thanks for your time, everyone!
I don't think that's the case.
I have configured the SM in the office at distance of about 10ft. and I don't get singnals in -35db. I assume the units signal mix should work down to 0 db. ( Accoording to IEEE specs )
BUT if you must
use Mini-Circuits,Agilents, Weinschel or any Atenuators in the market.
Remember you will atenuate the TX and the RX because the Canopy has one RF conector.
John
it was -39. Anyway, you recommend adding attenuators rather than going to a smaller antenna? Our lowest powered antenna currently are the Maxrad 9dBi antennas that came with the trial kit 20 pack. Without going to a mobile antenna, we haven’t really seen anything smaller than that. We wondered if some of you out there in canopyland were facing panels in the opposite direction or anything crazy like that to get power reduced.
Curtis,
You are correct, but you must have the power levels set to 28db in the AP
Else, in theory, it would be impossible to get that signal -31db using 915 MHz LOS, 9dbi antenna at a distance of 500 ft.
If you point the antenna to the back (180° away from the TX antenna ) that will get less power, but we are talking about 500’ away. At this distance I don’t know, it’s just to close.
Heck you can use a connector with bare wire on the center 3.23 inches long( a 1/4 wave dipole) and it should give you -38db.
That’s assuming the AP has full power of 28db.
Remember that I assumed AP TX= 1db and SM TX=1db.
Is this indoor or outdoor?
John
Yes, we have the ap set to 28, and this is outdoor. Do you just accept the wide range of power in your system then? Or do you use attenuation or some other way of limiting the APs received power? I am assuming that we don’t care what power level the SM sees from the AP (as long as it is adequate, of course), what we want to affect is the received power level at the AP. Otherwise we are desensing the AP which will negatively affect the weaker SMs, correct?
You could put an attenuator between the antenna and the radio. They cost about $30.00 dollars, see if you can get one on ebay 10 or 15db.
If it’s ok with you I think the 1/4 dipole is ok, but if have to purchase an antenna then buy a Cushcraft 6dbi vertical antenna and use some 50 ft of Time Microwaves LMR100A cable, total lost is about 11.5db.
The SM TX power should be about 19db.
I would use the 1/4 dipole.
John
I have been told that it will make no difference to a Canopy network getting all the units within 10 dBm. This is because it is a polled system and the SM’s talk one at a time. Also, what you are doing is getting the SM’s to see the AP at a set level which as the SM’s are lone units is not really important. The 10 dBm rule was for the AP so one SM would not swamp others, but as it polled this does not matter either.
This is only what I have seen discussed on another forum.
I have been told that it will make no difference to a Canopy network getting all the units within 10 dBm.
I have experimented with it and I can tell you that is absolutely matters, even with as few as 20 users. I had difficulty with several 15 mile customers not staying registered. I adjusted the output power on the hotter SM's (-60 and hgher) so that they all fell between -75 and -65 and the distant SM's registered and stayed registered.
As far as the -39 in the SM Status page, that's the power level of the AP at the SM. This is not important as the SM only needs to see the AP and no other source. What is important is the power of the SM's at the AP. This can be seen in the sessions page in the AP.
SM Radio Power Level = Power from the AP at the SM
AP Sessions Power Level = Power from the SM at the AP
If you are using a 13dBi Yagi and you are still too hot, then a 0 or 3dBi mobile antenna should do the trick.
As a rule, I attempt to keep all SM to AP links balanced on an AP. I do not attempt this across the entire network, but reduce my TX power to yield balance AP to SM links.
If you adopt low gain antennas, however, verify that you are not introducing potential interference issues via a broader primary beam. I wish somebody could suspend the laws of physics to give me a 3 degree 900 MHz antenna that I could mount on a customer’s roof as local 900 MHz noise gives me more grief than anything else in our network.
More info:
The SM 900MHz carrier is always on. The data is sent over the carrier when the SM is polled.
If the SM transmitter was turned off when it was not sending then you you would not need to balance the Rx power level at the AP.
Who says you need to use a 900 mhz antenna, get something tuned for another frequency say 2.4. I’m willing to bet your signal will still be quite satisfactory. That should net you a loss of about 20dbm. I’ve used a 2.4 antenna in the past with our WR gear on a short shot, did not see any negative side effects from it, with the exception of a much weaker signal. If there is a negative side-affect let me know, as I still have one close 900 link on a 2.4 panel.
BM
With the impedance mis-match the VSWR increases. As long as the net result is only signal loss you are OK, however if the jitter goes way up then its a problem.
My past experience with a 2.4 antenna on a 900 radio is/was with Waverider gear. The only loss was signal strength. There was no change in SQ. Does that hold with canopy? Someone with canopy will have to try.
We will be rolling out 2-3 new POP’s with canopy gear in 1-2 months, that is why I joined this forum. Have learned nearly everything I wanted to know between this and the BBR forum about canopy. So thanks for the rants/raves and all the good topics. I figure the real learning will come when the leases are signed and the gear arrives.
BM
milbrath wrote: Who says you need to use a 900 mhz antenna, get something tuned for another frequency say 2.4.
With a tremoundously mismatched antenna your SWR (http://en.wikipedia.org/wiki/Standing_wave_ratio) is going to be outrageous.
A high SWR basically means that the antenna is not efficiently converting the RF energy in the transmission line into radio waves. Instead of being transmited, the energy stays in the transmission line and feeds back into the transciever.
At best this causes the radio to heat up. If the energy feedback is high enough, it could cause physical damage to the transciever!
I don't like being this blunt, but this is a BAD idea.
Blunt is fine with me, I was always concerned their might be an issue with it but have yet to see one. I do have a WaveRider EUM thats been set up like that for over 2 years, we started with 2.4 and then moved to 900 so I just left the customers antenna that way. Never had a problem with the connection or needed to replace the radio. I’ll leave it running and if a problem happens I’ll post here about it.
BM
Since the output is only 680mW you are less likely to cause damage.
If the output was many watts, then then it would certainly cause heat and damage.
Jerry Richardson wrote: Since the output is only 680mW you are less likely to cause damage.
If the output was many watts, then then it would certainly cause heat and damage.
Very true. I guess its just the Ham in me comming through. This Part 15 stuff is nothing compared to a 500W HF rig. The underlying concept is the same though.
True, mismatching antennas should not be considered a “solution” by any means 
I would agree with “ahull” 100%
but
Jerry Richardson wrote
"Since the output is only 680mW you are less likely to cause damage.
If the output was many watts, then it would certainly cause heat and damage"
The amplifier on the 900 MHz unit is also very sensitive, plus the unit has almost no RF filters, only a silicon solid RF switch.
In the long run, Yes the 2.4 GHz antenna will hurt the silicon transmitter chip and at worst case it will degrade it.
Not to pick nits, but I did say “less likely”.
However, with that said, you are correct, the right answer is to not do it.