Feed Line of 250 feet for HF/VHF
I bought into a new project - I will be on the 4th floor at 14 meters AGL and the top of the elevators is at 77.5 meters AGL. I can install a beam or two here and run the lines down the elevator shaft. I'm open to suggestions as to feedlines (I want 4) from the shack on the 4th floor to the roof. Also are there any considerations for running the lines down the elevator shaft like noise or RF?
1000' spool of either Times Microwave LMR-400 or LMR-600 (very low loss and high quality coax).
Quality only hurts once!
A single run of 7/8" Heliax or the Korean equivalent and a remote antenna switch is one option.
At 250' the smaller stuff has too much loss at VHF.
Ive run 450' of 1" 75 Ohm CATV hardline in the past for 6M where the loss was spec'd at .22dB/100'. It still worked well working DX with 1200W and didnt hurt reception either.
Quality only hurts once!
Wonderful quote! May I steal it?
"The more you know, the less you don't know."
I meant Columbia
You're fortunate to be able to get VHF antennas up 77m above the ground, they should work great.
Elevator motors are notorious for generating a lot of RF noise on HF. On VHF, probably not so much, but I guess you'll see.
A government which robs Peter to pay Paul can always depend on the support of Paul.
-- George Bernard Shaw
Why not buy a shed and have a shack up there, it'll be cheaper !
I agree at the least 7/8" Heliax or the LMR-600 I use both at that long of a run forget the LMR-400.
73 de Fred N0AZZ
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That is an awesome set up. To have the authorization to run antennas on the top of the building is fantastic! I wouldn't look at the long coax run as a drawback - it will take some $$ to do it right, but you have no room to complain being allowed to do it. We have enough of a problem at the club station - we did the same thing, run the lines through the elevator shaft. The hard part is getting access to the roof and working on the antennas....
In any event, I would recommend the 7/8" Heliax also. I run that for UHF transmitters for work and it does a nice job. Most runs are in excess of 200', upwards of 300' by the time we run it down the towers and in to the control/power rooms. For VHF it would work even better at those lengths. It won't be cheap to buy new, but it is worth it.
I would also suggest grounding at the top and a polyphaser at the bottom, grounded as well.
If you need jumpers LMR-400 works pretty well. What I do is make up my main run of the 7/8" and if I need a jumper to the antenna I put a female N connector at the top of the tower then run an LMR-400UF jumper with a male N connector on both ends. Our base install kits come with TWS-600 (TerraWave Solutions, basically the same stuff as Times Microwave LMR-600) in 17' runs but it is just about worthless for our installs. I have two runs at the home QTH for my HF line to my attic antenna
I would suggest separate runs for VHF+. For HF you can use a switch without much loss, but I would be hesitant to run a remote switch for anything from 6 meters on up.
Get you a tower section or two and throw up some beams. That sounds like a heck of a station!!!
My rule of thumb is, when loss is expected to equal or exceed 2dB, it's time to look at a better feedline. LMR400UF just has 2dB of loss at 30 MHz & 250 feet. For VHF, you're going to need significantly better feedline. For this setup, KM1H has the bestest idea... one really good feedline + remote antenna relay. Note that, for VHF, you'll need a good relay setup.