Back in October, I acquired 250 feet (~75m) of LDF2-50 (3/8″) Heliax cable for approximately $150. The cable also came with 9 x 41PW connectors which sadly are of no use to me presently as they are for the more common 1/4″ Heliax. The price of the 41PW connectors alone is higher than what I paid for the lot, so perhaps I will try to recover some of my funds by selling some of the less useful (to me) items.
Connectors for the LDF2 cable which I acquired are not cheap, they cost $20/ea and are generally only of the “N” type (to maintain low-loss / constant impedance characteristics). I picked up four connectors to work with – saving two for future use.
The model number I purchased was: L2TNM-PL which is the so-called positive lock model. The connectors are large and heavy, hopefully their quality matches the aesthetic of the connectors.
Installation of these N-type connectors does not rely on soldering in any manner, instead, the connection is made via tight physical tolerances. There are some really nifty cable preparation tools available for the various sizes of Heliax, though as I am performing a limited amount of cable work, I opted to use a good sharp knife and some sand paper in lieu of fancy tools.
The instructions which come with the connectors indicate the lengths of the cable components required, including the number of “ridges” in the bond to expose. The first step is to cut the cable with a fine-tooth hack-saw, ensuring the end is as close to square as possible.
If you try to use a clamping cutter (i.e. linesman pliers) you may not be able to save the shield (bond) of the cable.
The first step is to remove a portion of the polyethylene sheathing from the cable. This is a simple operation which only requires you to cut a ring around the cable just deep enough to touch the copper shield.
Be sure to make this “ring cut” at the top of one of the shield’s ridges. This is explained in the instructions which come with the connector(s).
Next, make a longitudinal cut to begin peeling back the sheath, exposing the beautiful heavy copper shielding beneath.
Again, try not to cut too deep – I scored the length a few times, peeling the polyethylene sheath back as it became possible. The goal is to avoid scoring the copper shield if at all possible.
A good sharp knife is a must for this!
Once the copper shield is exposed, the copper shield can be cut back to the specified length. This portion of the work was too difficult to document well (read: I was too lazy to set up the camera with interval shots, etc) so it will not be shown.
What you are looking to achieve is the removal of a small portion of the copper shield from the end of the cable. I simply scored the copper shield with a sharp knife, then I used a pair of side-cutters to nip away the copper, peeling it like a tin can, using the scored line to prevent removal of too much shield.
If the center conductor is too long, you can simply file it down (or sand it in my case) to match the specified length.
The actual installation of the connector components is extremely simple. The only trick would be to torque the connector to the specified value. I opted to go with just a snug fit for now – perhaps I will get out the old torque wrench to check the installation.
I hooked up the Heliax cable (all 250′) to my spectrum analyzer and found that the cable loss over the length is well within specifications (I saw just over 10db at 1.5GHz). I look forward to being able to use this extremely low-loss coax in the (hopefully) near future. This cable will allow me to situate my ham shack nearly anywhere in my house and still make it out to a modest tower.