by Craig Henderson, N8DJB
C.E.O. of C.A.T.S.

The general line of "bell rotors" was developed by engineers at Cornell Dubilier Electronics about 1950 starting with the TR-2 and TR-4 series of rotators designed for directional TV antennas which were just then becoming popular. These models were meant to compliment their existing line of smaller rotators and in many cases, turned out to be the `big brothers" as some of the control units would work on both series.

As "Ham Radio" antennas became larger and larger during the 50's, the need for larger rotators became evident, so sometime about 1956, work started on a heavier design with a separate brake feature to keep the antennas from "windmilling." This eventually ended up as the HAM IV that we know today.

But first, the Ham-M

This was the result of beefing up considerably the older style TV rotators with stronger, heavier gears, a "pointed" wedge brake, and an improved indication system for direct readout to a meter with a scale for NESWN and degrees from 0 to 360. This model, (Ham-M) first debuted in November 1957.

The first Ham-M's, series 1 and 2, used a wiring format that was different and not compatible with later units. While these earlier units can be rewired, it is not generally considered economically feasible nor worth the time to convert.

Ham-M series 3 showed up late in 1959 after numerous complaints about the wiring and the meter "flutter" and the "backwards" scale. SERIES 3 addressed these problems with revised wiring that DOES MATCH the current models, an improved grounding system for the meter feedback circuit, and a more popular scale -SWNES -since most people in the U.S. wanted North in the center of the scale.

No major changes occurred in 1963 and 1967 when the later Ham-M SERIES 4 and 5 were brought out, but minor improvements continued to be made in reliability. Ham-M's continued until December 1973.


This model showed up in January 1974; and a number of rumors exist as to why this new control was developed. The most logical explanation is simply that a separate control was needed for the brake because as large antennas continued to grow in popularity, the instant stopping feature of the older style was causing more and more breakdowns. The HAM-II rotator was identical to the HAM-M at that time. The improved control was larger and more roomy inside, therefore lending itself nicely to the options which appeared later. Early versions of the Ham-II control unit had metal covers which were two shades of brown; later controls had covers which were black and white. Both had a gold faceplate and three plastic levers for direction control, along with a front-mounted calibration switch and on/off switch.


This model came out in the spring of 1977 to fulfill the needs of contesters and other "big-guns" whose antennas continued to get larger as the 70's and technology progressed. The wedge brake style which had served so well for almost 20 years was being overloaded more and more often by antennas with boom lengths that exceeded that of the average tri-bander. Monoband yagis with "looooong' booms were becoming more common to the point of being normal , and that "pointed" steel brake wedge just wouldn't hold. Consequentially, a new wedge was developed that was squared off on the end, and a new brake housing design was built to match. This was an incredible improvement, and is still being used. Also at that time, the control was modernized internally with a printed circuit board to replace the old "point to point" wiring style. A disc pre-brake was also added to the motor to stop "coasting".


This model came soon after the Ham-3, about January 1979, because all these new large antennas tended to break the cast, (pot-metal) type of ring gear used in the "bell-rotors" since the beginning. The improvement consisted of making the ring gear out of steel, actually cast out of a low-grade stainless steel and then machined for a precision fit to the other gears and the main casting. (This was copied from the T2X, but we'll get to that shortly). The other most noticeable change was the switch to black plastic covers on the control unit, probably to save money, and changing the color of the faceplate also to black.

Other changes within the next few years included changing the old rotary on/off switch to a toggle switch and redesigning the indication potentiometer in the rotator as another stab at improving the grounding for more reliable meter indication.

In l981,TELEX~HY-GAIN bought the rotator portion of CDE and continued to build the world's most popular rotators, the Ham-4, T2X, and several smaller models. However, as the years progressed, the material in the brake wedge somehow changed, and problems started to develop (like broken wedges) in 1985. Late in 1987, C.A.T.S. produced some hardened steel wedges and Hy-Gain followed suit in November of 1988. This was the last major change to date on this series and its popularity continues.

HAM-5 or HAM-V

This model came out in 1994 when Hy-Gain decided to "spruce up" their product line a bit. The rotator is the same as the Ham-4, only the controls are new. A new plasma display with digital readout was used for the new control; as well as auto-positioning pre-sets, slow-stop, and reverse-delay features. It also has the modern RS-232 connection for computer on the back via a standard DB-9 connector. Other amenities included 6 memory positions, auto-calibrate, and a delay for the brake.  


Starting in September 1977, CDE produced a different looking design commonly called the T2X. This model had much heavier upper and lower housings, and was painted a flat black color. It also had an extra row of ball bearings located at the bottom of the brake casting, which was made thicker to accommodate them. This means the T2X rotator will support heavier antennas than its smaller brothers, and is much more tolerant of side thrust such as when pipe mounted with a lower adaptor. Originally, the T2X had a specially made wedge that was much different than the smaller models, but this proved to be a problem. After several different designs the whole brake assembly was changed in 1983 to a similar, but not identical system like the Ham-4. One point worth mentioning is that all internal components such as the motor and all gears are the same as the HAM-4... this is not widely known. The only other change from the Ham-4 is the use of LED indicators in the control for showing activation of the brake and direction levers.

Note: Hy-Gain was sold to the MFJ corporation in May 1999 and they continue to build most of the rotator line; although in somewhat different fashion. As expected, quality suffered a bit initially but has now improved.

Back to main page