Peterbilt 2005-Present SWR Tip

[murdoc]

Hi there, this post is aimed at helping those running a 2005-Present Peterbilt WITH COWL MOUNTED MIRRORS get your SWR down a little lower... I have a 2009 Pete 386 daycab running a single predator 10K mounted via a Predator stud mount to the factory mirror gear antenna location. I just upgraded to a 'terminal' style coax termination at the antenna and upon tuning antenna for low as possible SWR I found that I was not getting as low as I would like or have been in the past with SO-239/PL-259 connection at antenna... With PL-259 I was always able to achieve 1.0-1 across the band, now with terminal end, I was only getting 1.2-1 until.... Remove the aluminum lower tube-to-cowl mounting cover, 4 socket head cap screws (allen heads) and remove, notice where the cover 'saddles' the lower tube (aluminum saddle clamps against stainless mirror gear tube) using a stainless steel wire brush, thoroughly clean and remove any and all oxidation from both aluminum saddle and stainless tube that it clamps against, then apply a coating of Ox-Gard to both pieces where they will make contact as well as the 4 mounting bolts prior to instalation... This connection apparently is critical to ground of the mirror gear as a unit... Also remove one at a time the 'small tube' (the one that the actual mirror itself is mounted to) bolts where they attach to the 'big' tube, same thing, clean all areas of contact and apply Ox-Gard or similar anti-oxidant compound to all... I would not recommend using dielectric grease as it is not conductive, Ox-Gard is conductive and can only improve the connection electrically... I now am seeing SWR down around 1.05-1 as a result of all this and that I can live with... Verified using both MFJ 259-B as well as my LP-100a digital vector wattmeter... Hope this helps...
Murdoc

[626]

Great tip.

Also a great lesson in galvanic/ or dissimilar metal corrosion. Metals with a widely differing Anodic index can prematurely corrode when an electric current is passed through them or when they are immersed in an electrolyte.

Thats the fancy 50 cent word version.

The practical application for us radio guys is that aluminum is dissimilar to stainless steel. In addition, brass, copper and stainless steels tend to be compatible. A good match with aluminum is a galvanized or zinc coated steel. Many will argue that they have used aluminum and stainless together for years with out any problems. This post is merely to back up what murdoc has discovered.

Good post.

[murdoc]

GUNNY, thank you for the add-on, also, I would like switch up to a 'puck' mount, I'll shoot you a PM.

Murdoc