I’ve been considering changing my towers from WRAP / RB at the top to installing amps at the top, and running LMR400 down the tower. Most of my antennas are 16db sectors, and I was thinking about running some 23db amps (3db between cable and connector loss to make 36db EIRP).
I have 3 towers I would be doing this on:
2 80 ft towers
1 160 ft tower
The main issue is the 160ft tower is also broadcasting AM radio, and I’m concerned the LMR400 down the tower would pick up the AM and burn out the radios and/or amps. We have AC going up the tower now, using chokes, and fiber for network connectivity, but I need to find out whether I’ll have a problem.
My other concern is OFDM, because I would like to deploy 5/10/20 mhz channels in A or G, and most amps don’t support OFDM at the rated output, so as an example, a 1W G amp is only 23db in OFDM - but I don’t want 1W in non-OFDM, just 23db.
The final concern is noise and cable loss. I’m worried that 160 ft of LMR400 even with 10 or 15db of RX ampliflication might be too much loss. I really want to run a 2 or 3ghz MT base station at all my sites, at ground level, so I can work on it whenever I need to. We don’t have a high tower climber on staff (70 ft at max) so when I need work done on the AM tower it takes months (it’s been down since May, had to repoint the customers).
I’d run Heliax or bigger LMR, but it’s cost prohibitive, weight prohibitive (the 80’s at only Rohn 25G towers), and there’s still loss on the transmit and the recieve side, almost more than I would want to have.
I would recommend a lower loss cable. There is some smaller 1/2" heliax that is nice and is lighter than LMR400, but actually better than LMR600. If cost is a major fact, probably LMR600 would be the best.
As for amplifiers, I don’t like using them. But RFLinx seems to have the best ones. Some of their’s are adjustable and have band-pass filters built into them. They also will go ahead and pass RF even if they get fried (at least that is what they say).
That sounds good. I’m all for bigger cable except the fact that I don’t like the idea of any loss - I actually prefer the IDU / ODU style wireless stuff where a ultra-smart base station is at the bottom, and using commodity cable, you run it up the tower.
Of course, our 802.11 stuff doesn’t do that because it’s based on standard cards. But I feel that a proper powered amplifier at the top could work the same way, and like you said, some of them even passthru on failure. I just don’t want to have to climb for 90% of the maintenance and upgrade tasks.
I haven’t found any good prices on 1/2" Heliax, and having 21-26db at the bottom, 16dbi antennas, means I can have no more than 6db of loss to keep EIRP at 36db - at 160 feet, that’s 5.6db of loss, which is OK but still, what about my 5.8 backhauls and broadcasts, loss is much higher at 1/2" Heliax for 5800mhz.
Yeah, I hear you. Your right, 2.4 loss can be fairly tolerable on a longer run. I still hate the worry of bad crimping or moisture seepage. And at 5.8 the loss can get very problematic.
And heliax gets expensive. I love the connectors though, they just seem extremely rock solid. Even with bad weatherproofing, there probably won’t be in moisture getting inside it.