Electrolitically oxidated aluminium for CB antenna. - Page 1
Forum section: electronics / general

author: Alana
author_rank: Frequent Contributor
timestamp: June 19, 2013, 06:50:25 pm
content: Is it any good for half wave unidirectional CB antenna? Would aluminum oxide coating interfere with RF operation?

author: Unknown
author_rank: Unknown
timestamp: June 19, 2013, 07:05:40 pm
content: Not as far I am aware !... electrons within the element will be displaced regardless of any coating or anodizing.

author: jamesb
author_rank: Regular Contributor
timestamp: June 19, 2013, 07:09:40 pm
content: Hmm, unidirectional antenna huh? Are you sure that is the term you intended?Is it transmit only or receive only?The oxidation should have very little effect for the antenna. CB is way below the GHz range and experiences relatively little "skin effect" which would have been a possible source of unwanted rectification (ie. spurious transmissions). Just be sure that your transmission line connection to the antenna is clean and secure - this is another source of headaches with older antenna systems.I would hardly worry about the aluminum oxide layer - it is actually a protective coating, preventing complete oxidation of the antenna. Hell, most antennas are untreated aluminum these days (of varying quality mind you).

author: Alana
author_rank: Frequent Contributor
timestamp: June 19, 2013, 07:28:59 pm
content: My mistake...Your answer leads to another question - how to ensure good electrical conductivity between antenna feeder wire and antenna and between peaces of antenna. I suspect that this may be a problem there. This antenna is home made by my neighbor out of 5 peaces of aluminum pipe connected together to form 5.5m mast. I may ask him for pics of his assembly if this helps.

author: jamesb
author_rank: Regular Contributor
timestamp: June 19, 2013, 07:53:47 pm
content: You really need not worry too much about conductivity of the antenna - even a rather poor connection between pipes will be okay. In a worst case, they will be capacitively coupled. Having said that however, you should ideally have a decent union between pipe sections.What you might try is lightly buffing the points at which the sections interconnect, ensuring a secure mechanical connection once you are finished. Some have had success cutting notches in the end of the "female" portion and adding a hose clamp for mechanical clamping (looking at down the end of the female pipe section, picture an O with + inside of it). The relief cuts allow the pipe section to be slightly crushed onto the mating section.

author: F4CPY
author_rank: Contributor
timestamp: June 19, 2013, 08:41:19 pm
content: HelloAntennas alloy is generally 6060, that mean Aluminium- Magnesium - Sillicium. This material has good properties toward corrosion. But, as antenna uses differents tube diameters, there will have a problem called "fretting corrosion". corrosion can locate between the adjustment and then the property of the antenna wil be affected (capacitive as previously mentionned)The solution is GREASE. Here I use grease with fine metallic particles (I used copper grease, aluminium grease...), even black grease (graphite, like "molykote" sorry for the trademark), will be perfect (even if there is electrical potential between graphite and aluminium). M² (antenna seller) provide their antenna with "penetrox" (curious name but that is not a joke!)I restored many antennas like this way, and I never had a problem. I live in the west part of France about 1 mile from the Atlantic ocean.If your antenna is an old rusty type, a little clean with fine sand paper, washing with light sodium chloride solution (soda), rinse with clear water, aplly grease and fit the elements.You can clamp the element with stainless steel screw or rivets or clamps used for garden hose (stainles steel too) marked A4 (316L) is better than A2 (304L).Didier