shack4b.art

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SUBJECT: Shack Designs - part 4B

RF distribution


    OOPS. Make that 14 coaxial lines. I noticed I typed in the wrong
amount. We can drop the UHF TV line as discussed earlier. Now we have 
13 coaxial lines to look at. Of these there are four receive only 
coaxial lines; 500-1300 MHz LPA, Discone, 49 MHz dipole, and the FM 
band dipole. Generally, I run these to their respective receivers and 
let it go at that. Only if I know there is going to be a serious 
lightning storm will I disconnect them. Three are under the big 
LPDA. The 500-1300 LPA is near the top of the tower and usually this
coaxial line is disconnected when not in use.  I will explain 
how these lines are electrically secured.

    That leaves us with 9 coaxial lines used for transceive. Each of 
these enters the shack and goes to the RF closet. This closet can be
an RF panel, a gagle of coaxial lines hanging be the wall, a tangled 
mess, but it doesn't really matter except that these lines come in at 
a common point. At this point we will also have the groundwire 
terminate in the shack. Why? Because the not-in-use coaxial lines
will be attached to the groundwire. This creates at two-fold safety 
system. First, it protects the shack and operator from lightning 
using the safety cap I'll explain later. Second, the antennas and 
coaxial cable are 'safed' to ground and RFI is contained via open 
coaxial lines.

    The safety cap: If you use PL-259s or N connectors you will need
a bullet (F-F) and a Male connector to match your connector use.
Using this male connector, solder a shorting wire from the center pin 
to the sleeve. Attach this connector to the bullet. Now you have a 
safety cap for a coaxial cable. When this safety cap is clipped to
the groundwire, the centerpin and shield are grounded directly to the
groundwire. There is no electrical path to your rigs via the coax.
  
LABELS:

    Labels are a must in a multi-cable input station. Ever try to 
work 20m with a VHF discone and not discover it until you are ready 
to close shop?  Or have your HF vertical attached to your VHF Packet?
Funny as it sounds, you probably say it was a bad connector instead 
of the wrong antenna, I sure would. 

    I use a simple labeling system. For the LPDA, I label it 'LPDA'. 
For the Discone it's 'Discone'. For the 2m SSB Yagi it's '2M SSB'.
I use two inch wrap-around, covered labels. I replace them every
three years or as changes are made. (I've never reached the three 
year mark yet. Typical Amateur. <grin>)

BUNDLING:

    As the cables leave the antennas, run them at right angles as 
much as possible. At rotors be sure to leave twist loops and at feeds 
to the antennas use drip loops. Run your cables on one leg of the 
tower and be sure not to run them across areas that you normally step 
on when climbing the tower. At about 6 to 8 feet, right angle the 
cable bundle to the shack. Use a drip loop before entering the shack
and keep the bundle high as possible. This keeps the dog, kids and
curious pokers out of touch with the cables. I usually slap a 'HIGH 
VOLTAGE' label on the input to the shack. It's amazing how it works.

    Enter your bundle; leave about four feet of the bundle intact 
before breaking it out into it's separate cable runs. Secure the 
bundle to the wall at the point of break out.


    NOTE: ALWAYS run the Ground Wire separate with a separate entry 
point and run it as LOW and as DIRECT to the central ground point 
as possible. NEVER run the ground at hard right angles vertically.


DISTRIBUTION:


    This area is mostly dependent on your shack design. Keep away 
from RF cable over AC lines. Keep RF from Data Lines as much as 
possible. Distribution should be clean and right angled as much as 
possible to eliminate RFI. Take care with connectors. Make them 
clean, correct and strong. NEVER coat the threads or center pin with 
silicone grease. It is NON-conductive. 


-WS