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Username: Tech833

Post Number: 1814
Registered: 8-2002
Posted on Friday, February 05, 2010 - 8:16 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Truck Spec Oil Coil antenna review

‘Trucker’ style antennas are those having a 3/8 inch, 24 thread stud and typically fall into one of two categories- Helical fiberglass, like the Firestik, and base or center loaded metal. Fiberglass antennas offer flexibility and vibration resistance, as well as being inexpensive. They lack power handling capability and bandwidth (for those who want to travel outside the CB band).

The Truck Spec Oil Coil is unique because not only can you see the loading coil through a clear plastic cover, it is actually filled with oil. Yes, the liquid kind. The Truck Spec Oil Coil is a nearly exact copy of the now gone Van Ordt antenna company ‘Audio King’ that was released around 1980. The 1981 Audio King ad claims the antenna has a dB gain of ”4.5 and better signal to noise than other antennas”. I have to admit, the antenna looks really neat. Van Ordt made some of the most innovative and best performing antennas the CB market had ever seen to that point. It is nice to see that their unique designs have outlived the company itself.

High quality materials are used for the Oil Coil antenna construction including a solid stainless steel lower shaft with the 3/8 inch threads integral to the shaft material itself. The tapered, stainless steel whip held in place by two setscrews that provides a solid, secure grasp on it. You can tell this is a heavy duty antenna when you pick it up. It feels brick solid and, although not the biggest, is probably the heaviest of all the large coil mobile antennas I have reviewed so far.

The Truck Spec antenna’s oil submersed loading coil is 14 turns of enameled copper wire wound over a grooved plastic insulator. The inners are sandwiched between two heavy, chromed metal tapered ends, and fully enclosed in a clear plastic radome that is filled with clear mineral oil. You can move the antenna around and see the small air bubble move around inside so you can quickly tell that there is still oil in it. That also means this antenna will not be affected by weather, rain, or snow due to its sealed nature.

I installed the Oil Coil on a few different vehicles and a base ground plane to measure the bandwidth and experiment with power handling capability. The Oil Coil effortlessly tunes to the 10m amateur band so I was also able to legally use up to 1500 watts of power for some real-life on air testing.

In all of the installations, a low SWR was quick and easy to obtain. The Oil Coil is not picky about coax cable length like some other ‘trucker’ style ungrounded type antennas, probably due to all the RF capacitance on either side of the coil which somewhat balances the current through it. 1:1 SWR in the center of the CB band would give better than a 1.2:1 SWR on the outer edges in my installations. The Oil Coil has a somewhat low Q coil, which helps the overall bandwidth of the antenna. Although, the Oil Coil isn’t as broad-banded as some of the other large-coil types and the 9 foot whip, it still has much better bandwidth than a typical fiberglass helical wound antenna and just barely better than the Wilson 5000 Trucker. The under 2:1 SWR curve in one sweep was just over 2 MHz. wide, but the under 1.5:1 bandwidth was much better than the Wilson 5000 Trucker at .762 MHz. vs. .368 for the Wilson.

When at highway speeds, the lower half of the Oil Coil doesn’t bend at all, and the whip bends about 15 degrees from vertical at 65 MPH. Since the lower shaft is not flexible, nor is the coil form, if you do strike a solid object it probably will break. And, leave an oily mess. So, some care is required if you have a Truck Spec Oil Coil on your rig.

On-air testing showed better transmit and receive performance than a Firestick. The Oil Coil tuned for the CB band did not require retuning for receive into 10m, but the Firestik gets noticeably deaf outside the CB band and was almost useless on 10m, even for receiving only. In band, signals were typically 2 s-unit better on transmit and 2 s-units better on receive over the short Firestik. On the range, gain was measured at -2.9 dB compared to a ˝ wave dipole antenna.

The Truck Spec Oil Coil will handle 1,000 watts with ease. The small diameter coil wire would probably get very warm with that much RF current flowing through it if not for the cooling aspect of the oil around it. The Oil Coil takes a real long time before any mentionable heat buildup is detected, which is good, since excessive heat would cause the antenna to fail.

If you want to add a 4” heavy duty spring to the Oil Coil, you need to shorten the whip by only about 1 inch, in my tests. There is certainly plenty of travel in the whip mounting stud, so you can make this adjustment easily, and repeatedly.

The fit and finish of the Oil Coil is very good. It is clear that a great deal of attention is paid to the metal-to-plastic radome seal so that the oil does not leak out. Except for the plastic coil cover, the rest of the antenna could probably survive a firing squad. Rough handling won’t bother this antenna. In fact, vibration is actually ‘good’ for this antenna since it will help circulate the oil over the coil wire as you drive.

For a 5-foot tall antenna; the Truck Spec Oil Coil really does deliver. Besides, just how cool is it to have a ‘live’ liquid in your antenna! The wow factor is tops, the performance is good, and the price is right.

Your radio 'Mythbuster' since 1998