Author Topic: LMR400 (solid center) for a beam?  (Read 5244 times)

0 Members and 1 Guest are viewing this topic.

0Land

  • New Site Member
  • *
  • Posts: 10
  • Karma: 0
  • Gender: Male
LMR400 (solid center) for a beam?
« on: March 31, 2012, 02:16:22 PM »
So I have a new Hexbeam waiting to be assembled.  I ordered some LMR400 for it but I didn't really know just how INFLEXABLE LMR400 really is.  It's kind of like rebar, you can bend it and it just stays that way.  :)

So my question is:  Is this going to work long term being bent (albeit slowly) back and forth as the beam turns?

I have some LMR400UF.  The UF (UltraFlex) is stranded center and is a lot more flexible.  I don't think I have enough of it for this run though.

Would it be a good idea to take a six foot piece of UF from the top of the center post down to below the rotor and then run the solid stuff back to the shack?  This involves a barrel connector, which is going to be a little lossy, right?

What say you all?

spacecase0

  • Hero Member
  • *****
  • Posts: 790
  • Karma: 34
    • my spiritual forum
Re: LMR400 (solid center) for a beam?
« Reply #1 on: March 31, 2012, 03:35:09 PM »
a flexible bit on the end sounds good
LMR 400 does not bend back and forth very well.

0Land

  • New Site Member
  • *
  • Posts: 10
  • Karma: 0
  • Gender: Male
Re: LMR400 (solid center) for a beam?
« Reply #2 on: March 31, 2012, 04:59:04 PM »
That's kinda what I'm leaning towards.

I'm hoping that the barrel connector, it's slight impedance bump and then the slightly different characteristics of LMR400UF don't look like an impedance transformer at the radio end.  From what I've read, most people don't really tune the wire radials on a hexbeam (by changing length), they are usually good to go.  I just don't want the extra section to screw up my match. 

I wouldn't THINK it would, it's still 50 ohm coax...

Thanks for the reply.

BTPost

  • Old Fart Ham
  • Prepper
  • Full Member
  • *
  • Posts: 361
  • Karma: 29
  • Gender: Male
    • Bruce's Trading Post
Re: LMR400 (solid center) for a beam?
« Reply #3 on: March 31, 2012, 05:38:43 PM »
The typical approach to solve this issue, Is to run your Heavy LMR400 to just below the rotator, and then Transition to a short piece (less than 10 Ft) of a  excellent Grade of RG-8 Foam Coax to span across the Rotation Area of the Tower. The addition of just 10 Ft of  Higher loss coax, will not introduce much of a actual Resistance Loss, to the Total Antenna System. Also make the Transition cable using the least Lossy Connectors for that Frequency Spectrum used on the Antenna. Type N, if your using more than 100 Watts, and BNC/TNC if your below 100 Watts. When I had a BIG Tower with Multiple Antennas, All the main runs from the shack were done with Beldon 9913 (Poor Man's Heliax) for HF Antennas, and 1/2" Heliax for VHF Antennas, and 7/8" Heliax for UHF Antennas. They all terminated on a galvanized Steel Plate, that was drilled and taped to accept Chassis Mount type N Female Connectors. Then all the coax runs, across the rotator section, were made with 6 Feet of RB-8/U Foam Coax to a second galvanized Steel Plate that terminated with duplicate, short runs, of the same Cable Types, that were used with each Main Run, from this second Plate and Chassis Mount Connectors, up to the individual Antennas. The six foot sections of RG-8/U Foam were just used to bridge the Rotator area on the tower. Just Say'en... YMMV...
Bruce in alaska AL7AQ

0Land

  • New Site Member
  • *
  • Posts: 10
  • Karma: 0
  • Gender: Male
Re: LMR400 (solid center) for a beam?
« Reply #4 on: March 31, 2012, 07:11:53 PM »
The typical approach to solve this issue, Is to run your Heavy LMR400 to just below the rotator, and then Transition to a short piece (less than 10 Ft) of a  excellent Grade of RG-8 Foam Coax to span across the Rotation Area of the Tower. The addition of just 10 Ft of  Higher loss coax, will not introduce much of a actual Resistance Loss, to the Total Antenna System. Also make the Transition cable using the least Lossy Connectors for that Frequency Spectrum used on the Antenna. Type N, if your using more than 100 Watts, and BNC/TNC if your below 100 Watts. When I had a BIG Tower with Multiple Antennas, All the main runs from the shack were done with Beldon 9913 (Poor Man's Heliax) for HF Antennas, and 1/2" Heliax for VHF Antennas, and 7/8" Heliax for UHF Antennas. They all terminated on a galvanized Steel Plate, that was drilled and taped to accept Chassis Mount type N Female Connectors. Then all the coax runs, across the rotator section, were made with 6 Feet of RB-8/U Foam Coax to a second galvanized Steel Plate that terminated with duplicate, short runs, of the same Cable Types, that were used with each Main Run, from this second Plate and Chassis Mount Connectors, up to the individual Antennas. The six foot sections of RG-8/U Foam were just used to bridge the Rotator area on the tower. Just Say'en... YMMV...

I had forgotten about Type N connectors.  I have two males and a barrel, both for half inch coax.

I think I'll use the UF instead of RG8 foam.  I already have about 30' of the UF, it IS pretty flexible and according to the Times Microwave coax loss calculator it's actually lower loss than the 8.

Either way, ya, don't run solid core all the way and expect it to last... and use low loss connectors at the junction.

Thanks for the help guys.