I’m going to be moving into a new building and the antennas will be on the roof (above 17th floor) and our apartment will be on the 4th floor. There are 3 channels – each 50 cm by 20 cm to bring the coax up from the 4th floor to the roof – once carries cable TV/cable internet, another telephone and intercom lines and the other contains gas. I’m planning on using LMA400 for HF and LMA500 for VHF. I’m using an AL80B but plan to upgrade to a AL82B once I move. Which channel would you select that I run the coax down (ie: causes less interference).
I'd pick the one that carries cable TV/internet. They should be using quad-shielded cable or hardline for that. LMR400 is also double-shielded.
I can run my coaxial transmission lines right up against my cable TV coaxial lines and there's no interference of any kind, even at legal-limit output power, on any band.
A government which robs Peter to pay Paul can always depend on the support of Paul.
-- George Bernard Shaw
Regardless of shielding, I see a common-mode mess in the making. RF can flow on the outside of the braids, despite the
number of shields and effectiveness. The antenna is hopefully balanced, and perpendicular to the feedlines.
I second WIK on that. You don't want to run your feedlines in the same soffit as gas line, and you don't want to run them next to telephone wire. AM and SSB transmissions will certainly cause problems with telephone wiring, and you don't want that.
Make sure to use good cable, and make sure to use proper grounding practices up on the roof, including using properly balanced antennas. This means using only proper dipole, verticals with counterpoise, or beam antennas. I would avoid long wires or verticals without radials (unless you have a lot of metal underneath you to act as a counterpoise.) You absolutely don't want RF coming down the feedline and causing problems with someone's TV reception: that will get you hated quicker than practically anything else you can do.
This is probably redundant, but I'd also put surge suppressors at the top and the bottom of your feedlines. I'd put one on each feedline where it exits the channel and crosses the roof to your antenna, and I'd install a suppressor (or switch with a built-in suppressor) as close as possible to where your feedlines enter the shack. Use a big, fat grounding strap and connect all your radios to that strap and that strap to ground. I would definitely take this opportunity to make your system as clean as possible, both to keep potential lightning strikes from being an issue and to ensure that you don't annoy the neighbors.
Certainly this and watch out you avoid any coupling to the building communications system , in this country the comms ground is violet (au) and you really need to decouple from that area , good luck it could be interesting
Originally Posted by K6ABZ