These are important tips for making a successfull CoCo.
1. Coax and Velocity Factor
1.1. You must know exact VF (Velocity Factor) of the coax your going to use to build a Coco.
1.2. You should only that coax for which you know the exact manufacturer and model number, and obtain datasheet from manufacturer or seller for that particular make & model number of coax.
1.3 Use VF only from manufacturer’s/seller’s datasheet/specifications. No guessing, or estimation of VF, or using VF figures given on various tutorials on web sites or youtube.
1.4. Off the shelf coax from Super Markets, Satellite TV Supply Stores, etc normally dont have any datasheet or specs available. Some large stoees do provide specifications on their web site, but these specifications do not have Velocity Factor specified. Do NOT use such coax for making a CoCo.
2. Type of Braid of Coax: Soldered vs Push-Pin Construction
Coax are available with braid made of either Copper or Aluminum or Steel. The copper braid is preferable as it allows soldeing, while aluminum or steel braid cannot be soldered, and only a push-pin type of element assembly can be used. The push-pin method of construction is mechanically weak, as movement of coco during installation or use can result in slightly pulling out the pins, resulting in substantial performance drop. The soldered construction is free from this shortcomming.
3. Calculating length of CoCo elements
The length of element should be calcuulated by following formulae
Length of element in mm = Velocity Factor x 275/2
Accuracy is the king, both in using accurate VF to calculate element length, AND in cutting & assembling the elements. An error of a millimeter or two can result in poor performance.