We are currently looking at using a connectorized Canopy 900 AP on a 50 foot tower; mounting the antenna at the top of the tower and keeping the AP at the bottom with a 50 foot LMR400 run in between.
I know there is going to be a certain amount of line-loss with doing that (about 3.5 dBm, according to LMR400 specs), which according to the path loss spreadsheet equates to an effective loss of about 4 miles of coverage.
Are there any ways to compensate for that? What kind of thoughts does anyone have on this idea? Could this work, or am I just shooting myself in the foot?
Thanks,
What a good idea.
I would use an LMR900 cable. Loss is only 1.6dB per 100’
Loss calulator:
http://www.timesmicrowave.com/cgi-bin/calculate.pl
Jerry
One more thing…
The Docs are very clear about setting the gain value in the AP lower then the gain of the antenna: DO NOT DO IT.
The purpose of not doing that is to prevent the output power from exceeding the FCC reg, right?
But what about using that to compensate for line loss? Say there is 1.1 dBm lost in the cable from AP to antenna. Would setting the gain 1 dB (still under the max power output) lower then the gain of the antenna incur the wraith of Motorola?
That would only increase transmit power - you still have the loss on the receive. Using the very low loss LMR900 or even LMR1400 would be the only real option.
Jerry
we are using 7/8 heliax on runs around 100 ft and 1-5/8 on longer ones up to 220 ft the 1-5/8 is 0.7db/100ft
Thanks for the info Jerry, md. It looks like using the LMR 900 or 1400 is what we are going to do.
I guess I’m curious why you wouldn’t mount the AP on the top of the 50-ft tower? Why run LMR at all? Can’t you just mount the whole thing on the top of the tower?
Also: concerning the loss on the receive end, wouldn’t this also expose you to more interference on that end if you start increasing gain to compensate for line loss? I don’t know…maybe I’m off here.
the radio is the most likely point of failure. Locating it at the bottom of the tower where it can be easily accessed is brilliant. Seems that it will be well worth the cost of the LMR1400 run at a total loss of about .5dB to NOT have to climb the tower in the rain.
Jerry Richardson wrote: the radio is the most likely point of failure. Seems that it will be well worth the cost of the LMR1400 run at a total loss of about .5dB to NOT have to climb the tower in the rain.
That was our thought exactly. I'd not be too keen on climbing a tower in the dead of a northern Michigan winter to replace the transmitter. We can lcoate the transmitter inside our box at the base of the tower, keeping it reletively protected from nature. The other thought we had was designing some kind of lift system on the tower. That way we could raise the lower the canopy system like a flag on a flagpole.
We decided on the former mostly because it will be quicker to get up and running. For our seccond tower, we'll probally use the lift system and see what one works out better.
As far as the interference issue, with such low loss we won't have to get high gain antennas. So it shouldn't be an issue.
“A lift system”?? :shock:
Wow. I guess we’re doing things a lot differently here in ND (winters here aren’t all that fun, either 
) We just mount our AP/SMs up on the tower and leave them. We haven’t had one fail yet, so our confidence is pretty high that we won’t have to do any climbing. I’d prefer not to make this any more complicated than it has to be, you know?
But if it works for you, that’s great! 
NO failures in ND? That’s amazing.
How many winters have you gone through?
Jerry
Jerry Richardson wrote: NO failures in ND? That's amazing.
How many winters have you gone through?
Jerry
No failures yet, at least not after they've been mounted. This will be our first winter, so knock wood. :P
ahull wrote: The other thought we had was designing some kind of lift system on the tower. That way we could raise the lower the canopy system like a flag on a flagpole.
We decided on the former mostly because it will be quicker to get up and running. For our seccond tower, we'll probally use the lift system and see what one works out better.
As far as the interference issue, with such low loss we won't have to get high gain antennas. So it shouldn't be an issue.
no need to design, check out www.glenmartin.com between their fold overs, the hazer tram, and http://www.alumatower.com/new/telescoping.html crank up you should be able to find something.
Invariably winter time is the right time to do ham radio antenna work in ohio, the only real problem I've seen with these types of towers are right on Lake Erie after an ice storm, coated with 2" of ice.
thanks
With the crank-up towers, keep in mind those were intended to be lowered before storms. They cannot be lowered when coated with ice. They are really for ham operators, not service providers.
Same ice problem with the other lift systems such as hazer trams.
These devices will not keep you off the tower during an ice storm failure.
i like the idea of antennas at the top and APs at the bottom, but honestly, i don’t think this is necessary. over three years of using canopy on our 500 ft tower we have only lost 2 APs… due to lightning. i think a big point of failure could be the connectors, so introducing ANOTHER connector (one at the top of the tower on the antenna and one at the bottom on the AP) would give a place of corrosion and possible problems. i see the additional cable between the AP and the antenna as another “piece of equipment” and my belief is to use as few pieces as you need so you cut down the number of points of failure.
climbing 500 ft is not cool. i’d be open to any ideas that would cut down the number of times that would have to happen. i like the thought about a “flagpole” type of invention, let me know how your tests go.