Accessibility Evaluation of the ProSisTel 2051D rotator.
By Kelvin Marsh M0AID
My first HF beam was a fairly lightweight 3 element Cushcraft A3S. I was fortunate to be given an old Kenpro KR600 rotator, and my friend G4JZL adapted the control box with a tactile pointer to show the heading. When I changed the A3S for the heavier 3 element SteppIR, it was time to beef up the rotator too.
At that time, back in 2009, I did not know any other blind amateurs with rotators. I was intrigued when I discovered that there were rotators available with computer control via RS-232 serial connection, and as I use a PC for logging and amplifier control, this seemed an intriguing possibility. I then had to satisfy myself the software could be used by a screen reader user. There was little point in investing significant sums in a new rotator that was controlled by clicking on a picture of a compass comprising of a large and inaccessible graphic!
I became aware of the ProSisTel range of rotators, as they were recommended by the UK supplier of SteppIR antennas. The PST 2051D was the recommended model for the 3 element SteppIR. The PST rotators use worm drives instead of the more traditional planetary gear wheel system, And have the advantage of being extremely sturdy and self braking. The PST 2051D is at the lower end of the model range, and PST has several much heavier offerings for very large antenna arrays. The PST 2051D is classed as a heavy duty rotator, capable of turning a full size 3 element HF beam. The rotation torque inch / lbs is 1720, and the braking torque inch / lbs is 10800 (figures taken from the Vine Communication rotator comparison table).
In a way, this evaluation is more of an accessibility review of the D type control box. Whilst I suggest this should be carefully checked before purchase, the control box should be capable of running any of the modern range of PST rotators.
The D type control box is the unit that sits in the shack, and is the hardware you would normally interact with. The box is very chunky, with an approximate height of 120mm, and a width and depth of 210mm plus front and rear panel protrusions. I only ever touch the controller when I switch it on. Whilst the control box is extremely simple to use with sight, it is not directly accessible by a blind amateur.
The current compass bearing is shown on a large digital display, and the new direction is selected by turning a rotary knob. The physical revolution of the knob bears no direct relationship to the ultimate direction. The sighted operator rotates the knob until the desired bearing is shown on the display. The knob could be rotated a few clicks, or could be turned completely several times, as there is no end stop.
Whilst I have noticed there can sometimes be a relationship between the clicks of the rotary knob and the heading for small movements, there is no reliable control possible.
Usefully, the rotator has the ability to automatically decide on the direction to turn. Just a small alteration in direction can cause the rotator to turn clockwise or counter-clockwise, to reach the desired heading with the minimum of movement. This probably sounds counter intuitive, until you understand the rotator has the potential to overlap by up to 70 degrees on either side of the selected stop position.
This probably needs a note of explanation. The rotator can be setup with a North or South stop position, and with a choice of turning ranges. Firstly, the rotor can be set to only turn by one complete revolution or 360 degrees. Secondly, to have up to a 70 degree over-lap either side of the stop position, giving a potential 520 degrees of movement. I use a 20 degree over-lap on either side of the stop position myself, so as not to overly strain the coax.
Here in the UK it is much more usual to be pointing the beam towards the South, so I decided to have a 0 degrees North stop. This means the rotator can be turning in a clockwise direction from 290 degrees West, through 0 degrees North, 90 East, 180 South, 270 West, 0 degrees North, and then keep on turning clockwise passed the North position, to a maximum of 70 degrees East. All this sounds complicated, but in reality it means you don’t have to turn the beam by almost one complete revolution, if you are wanting to point the antenna a few degrees either side of North.
So, back to the sighted operator directly using the control box. They just turn the knob to the desired heading on the digital display, there is a pause for a few seconds to allow for changes, and then the antenna turns. The control box automatically decides which way to turn to get there in the shortest time possible.
The 2051D control box also has the traditional Clockwise and Counter-Clockwise paddle switches. Again, these are of no real use to a blind operator as the display cannot be read. There is mention in the manual of the paddles being used to halt the rotator if it has been preset with the rotary knob or computer software, and there is also a warning that turning the rotator using the paddles does not invoke the slow start and stop facility.
When I first bought the rotator we set it up on the ground, without the antenna being attached, and I experimented with it. It soon became apparent that the slow start and stop feature only worked if the heading was changed using the inaccessible rotary knob, or by using computer software. If you are turning a large heavy antenna, it is highly recommended that you always use the slow start and stop. This causes the rotator to gradually reach the maximum turning speed over a few seconds, and minimises the shock to the antenna and tower of an instant start and stop.
Therefore, the only practical method of a blind operator controlling the PST rotator, is via the PC and the serial interface. If you don’t use a computer with your amateur activities or want to directly move the antenna using the control box, it will be worth reading the Yaesu G1000DXC rotator evaluation elsewhere on the Active Elements site.
As mentioned previously, I initially had concerns regarding the accessibility of any interface software. Any blind computer user will be familiar with the perils of buying and installing that vital program, the one used by all of your sighted friends, only to find that what can be done so easily with a few mouse clicks, is impossible with a screen reader. It was at this point I contacted Don G0MDO. Don has written a very accessible logging program for blind operators, and fully understands what screen reader software needs to work successfully. Studying the PST documentation, it seemed that third party software could be used to control the rotator, and when approached, Don G0MDO, the creator of White Stick Log, began work on White Stick Rotor.
I know Don had to jump through all sorts of programming hoops to write White Stick Rotor, and had to write simulation software to mimic the PST D type control box itself. At that time, neither Don or myself owned any PST hardware! We were fortunate to have the help of Ron at Vine Communication, who was happy to conduct some tests On a real control box.
Without doubt, White Stick Rotor was the last piece of the jigsaw, and gave me the confidence to buy the PST 2051D. Over the years, Don has continued to refine WSRotor, and perhaps there is still some improvement to be made. The software is beautifully simple to operate, and Don has even made itself voicing. There is an audio demonstration of White Stick Rotor on the Evaluations page in the Software section. Suffice to say, you type in the desired bearing, press Enter, and the antenna turns.
Subsequently, I have also used the N1MM contest software to control the PST 2051D. The program can be used stand alone, but is also able to automatically turn the rotator to the bearing of the callsign just entered. I cover the N1MM rotor setup and use on the Evaluations page.
Finally, the rotator is designed to be fixed inside a rotator cage. The manual warns against sitting it on a surface that is likely to collect water, as this can be drawn up through the drainage holes in the casing. There is a sturdy circular revolving table on the top of the rotator with fixing holes, and there are a variety of mast clamps available to mount the stub mast.
The best solution for me was to have a mounting plate with a solid shaft custom machined by G0WSC, to bolt to the table and to fit up inside the stub mast. The stub mast is then secured to the shaft and plate with a pin. This solution means that as the table revolves, the stub mast is perfectly centred and there will never be any slippage due to loosened clamps.