Heliax cable building R3 082625.pdf

August 26,2025 R3 Billerbeck, Brent D (FAA)

Heliax cable building/applying connectors.

This document was drafted as an effort to help vendors in building a quality Heliax cable for FAA procurements. The normal application is for cabling used in Localizer Antenna arrays. But most of these rules/advice can apply to other cable builds.

1. Cable Selection

a. All cables shall be free of any damage, abrasions, cuts, etc. over the entire cable surface. No kinks, sharp bends, flat spots or other similar damage shall be present.

b. All cables made from Heliax cable should be cut from the same manufacturers cable reel for each set of cables made. This is important to keep expansion and contraction of said cables in a Localizer Array similar to each other. Cable from different spools, or different manufacturer production runs could result in unequal expansion/contraction and therefore result in changes of phase or other parameters within the antenna array.

c. Preferred cabling for Localizer antenna arrays is phase stabilized cabling.

d. There are two known vendors that produce Heliax style cable. The outer diameter for the cabling is different between the two vendors. The primary cable used in the FAA is from CommScope.

2. Cable cutting/measuring.

a. Cable for similar runs can be laid out to view the physical length. Cable length should be approximately 6 inches longer than specified drawing lengths. This allows for the cable trimmed up to the same electrical/phase length of the reference cable during the production.

3. Applying Connectors.

a. Trimming Cable Ends

i. When trimming the Heliax outer sheath and the insulation around the center conductor, a thermal stripper is recommended. The outer shielding and the center conductor shall have no knicks or cuts in the surface. Using a knife or similar cutting tool can have such results.

When a connection is built and has a cut to a conductor or shield, over time vibration can cause this cut to the metal to increase and eventually break. This has been proven during vibration testing. Any cuts to either will be cause for rejection. This could mean rejection of the whole set if cable from the same reel is not available.

ii. There are alternate cutting means available for performing connector cuts. TED Mfg. & CommScope have developed such tools. If used, one needs to be sure the settings are accurate and regular checks should be made to inspect for any nicks to the shield or center conductor.

b. Cable Preparation

All residue from the cable sheath and the center conductor insulation needs to be thoroughly cleaned away. Leaving residue on the center conductor can result in poor or no solder adhesion during the soldering process. With the use of a Dremel tool or similar item, and a small wire brush inserted in the tool, the center conductor should be cleaned removing all residue. This will be done on each cable end whether residue is seen or not. DO NOT skip this step.

August 26,2025 R3 Billerbeck, Brent D (FAA)

c. Center Conductor Length within Pin

Prior to soldering (initial assembly) one should be able to see the center conductor of the cable easily within the hole in the pin assembly. If done correctly, the cable conductor is of sufficient length when it just goes just past the hole toward the tip of the pin. Not too long. The center conductor will be visible for at least 7/8 of the hole (minimum) to just past the top edge of the hole. Having a center conductor that is too short produces inadequate soldering of the cable inner conductor. Having a center conductor that is too long can have the conductor bottom out within the pin before it is fully seated in the proper position on the rest of the cable.

d. Connector Soldering

i. Add the cable nut to the connection prior to performing the soldering.

ii. The solder should be visible in the hole of the pin of the connector, filling the cavity within the pin assembly itself. If the hole is slightly filled with a small dimple in the solder near the top which indicates the solder pulled down into and around the cable conductor this is acceptable. A minimal solder quantity would be if one can see the cable center conductor still, but the pin cavity is filled. Solder should not flow outside of the pin hole. If it does flow outside, it must be cleaned off.

iii. Avoid cold solder joints. Apply proper heat to the connection when performing the soldering task. Resistive type soldering tools work well for this type of soldering.

iv. Avoid heating the cable too much to cause the melting of the insulation within the cable. If done, one will notice the insulation shrinking back between the outer shield and center conductor. A connection should be reworked if this occurs.

v. After performing the soldering, gently twist the pin to try and remove it. This is done to verify the solder adhered to the center conductor. This must be done with every connection built.

e. Connector Assembly

(For TED 7-10-41 connectors) When assembling the connector, push the connector nut up onto the end of the connector pin assembly mounted to the cable. Of course, you’ve slipped the cable nut onto the cable prior to soldering the pin assembly to the cable. Then push the connector body onto the pin assembly.

When tightening the connector assembly, DO NOT turn the cable nut. Turn the connector body only. Turning the cable nut can damage the connector or the soldering within.

4. Cable Assembly Testing

a. In addition to the testing called out within the drawings for cable length, etc. the vendor will perform both resistance testing of the center pin to outer shield, and a “meg” check. Resistance as noted shall be zero (0) ohms (+ 2 ohm, - 0 ohm). When performing the “Megger” test, equipment shall be set at a minimum 1000V scale or better. The Megger test will show an infinity reading.

5. Soldering & heat shrink

a. In building of Heliax cable sets for the FAA, not all connectors are soldered, or all the heat shrink reduced or shrunk within the various cables. Please confirm with the FAA Reps as to which are done or not done, even those spelled out in the drawings.