Most of the installations I have seen locate the antenna and radio next to each other. Usually, the mast is short and the radio can be accessed for repairs quite easily.
But what if one wanted to place the equipment on a tall tower that required a trained climber to repair or replace the radio. It seems that a better configuration would be to place the antenna on the tower and the radio/router at ground level, the two interconnected by heliax or similiar.
That leads to my question: Would this cause a problem? What would be the the maximum cable length beyond which frequency roll-off or unacceptable power loss begins? I realize the type of cable makes a difference, but I’m just looking for general knowledge. I have searched the forums but couldn’t locate the answer.
the best is a radio directly connecxted to antenna.
you can have at maximum 1 meter (or 2) of lmr400 cable. with good quality pigtail and N connectors you lost “only” 3db (the half of the power!).
you can place radio at the bottom of the tower using waveguide but it is very expensive.
“only” 3db loss ? I would rather a cable insertion loss of much less as most AP’s sectors have a gain between 14 to 17dbi for 90-120° horiz and losing 3db is turning a 14 to 11db and 17 to 14db, is a massive loss and is just one reason why I only use integrated antenna’s, no LMR cable & no N-connectors to seal as regards radio card or board replacement we use custom made mounting brackets to minimize the time involved in this.
If you really need the convenience of the radio equipment on the ground, get some good coax and go.
The school systems here were connected by 2.4GHz point to point shots for years with 100+ ft of coax. They had a good enough margin that it didn’t matter whether it had short coax or not.
As a matter of fact my backhaul pulls around a -50 with everything turned up. I could run 100ft coax to keep my equipment more easily accessible.
The other catch is coax costs more than ethernet. I think my climber would go up the tower 4-6 times before I broke even on the price difference.
edit: for the record I have a couple of backup AP’s with around 20-30ft LMR400. I can’t tell the difference between them and the 3ft LMR400. You will lose more signal due to connector loss than you will an additional 15ft of LMR400.
Yah, my problem is that the tower would need to be shut down and the station taken off the air for the climber. Almost impossible to do. That is why I wanted to put the equipment at ground level.
Thanks all. Yes, it would be mounted to a tower with FM antennas or, if possible, to a huge mast next to it. Even so, the climber won’t enter the area unless the FM is taken off. As you can imagine, it would be difficult to do or manage.
Yes, it is point-to-point only. I was thinking that I could install a higher gain dish to compensate for any cable loss. Am I thinking this through correctly? Of course, if everything needs to go on the tower, so be it. I’ll do that and just plan for redundancy and perhaps an extended outage. Also, this set-up will probably be at 3.65ghz or even 5.8ghz, so I’m thinking the cable loss could be quite large. Ah, tradeoffs
Thanks everyone for your advice and comments. I truly appreciate them.
29 dBi PacWireless grids, LMR400 and a RB711 5HND. As long as the path is clear, no fresnel zone problems, you should be fine. LMR400 should be about 11dB loss at 5.8GHz, my experience is that the connectors are worse than theoretical, the cable is better. My 7 mile link with 29dBi grids show about -53dBm, occasionally high -40s if the power is turned up and the weather is just right, 3ft LMR400.
Higher quality cable would always be an improvement, but you should have a little wiggle room.
If at all possible, I would have the other side of that link run a short cable.
Apart from signal loss by having the board + Radio card at ground level and low loss lead to antenna, If a radio card goes faulty I simply would not replace it until a visual inspection of antenna + lead + connectors was done because you could quickly find another goes faulty and you will have to send a climber up the mast , I have found radio cards to be are very reliable, at your location I assume bring a commercial radio mast it has lighting de-ionizer build it, another approach is to have two independent PTP links with two antenna’s combined into one enclosure, two radio cards, two boards and two separate sets of power supply, below is link for example, this way if one goes down second keeps going until a scheduled maintenance is performed. http://www.technologic.pl/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=65&category_id=56&option=com_virtuemart&Itemid=29
