By Peter Yanczer

This is the first of a series of articles developed to guide you in the construction of a pair of instruments, when connected together will comprise a mechanical television system able to provide very recognizable images.Build a TVThe unit to be considered for construction will be the receiver/monitor or display and to be followed possibly later, a direct view camera. More about this later. This unit will be equipped with Nipkow disc. The display unit will look something like the photo the right. The skills necessary to build this mechanical television system will include working with wood, plastics, metals, optics and electronics. If you don't have these skills now, this project will give you the opportunity acquire them. In some cases, "special tools" may be required or when necessary, you can set up what are known as "work arounds". Depending on your skill level, you may find it necessary to have someone, possibly a friend or school instructor to help you out of the "tight spots". This shouldn't occur very often.

Whenever possible, I recommend that you use your ingenuity and try to do the task at hand yourself. Get information anywhere you can, but do the actual work yourself. Don't hesitate to do things over again (and again) and get them right. This can be an important learning experience for you and the more you manage to do yourself, the better off you will be.

A point of interest is that while John Logie Baird of Scotland did most of his work with a 30 line, vertically scanned system, some of his earlier work was done using 32 lines, the same as the system being considered here.

The display unit to be described here is based on a physical design by Grant Dixon, a member of the Narrow Band Television Association, (NBTVA). Peter Smith designed the electronic circuits for the monitor. Peter is also a member of the NBTVA. Check out the NBTVA web site. I am a NBTVA member and suggest you become one too.

This design will be based on successful past work of a similar nature by the author. Here on the right is a rear view of the receiver/monitorETS-TV #2.

Individual technical support where necessary will be limited to NBTV members. Non-members can request support by Email or the USPO. If you are not yet a member of the NBTV, I again invite you to join us in this fascinating hobby now. We would be very pleased to have you with us.
This web site will include sufficient information to guide you in the construction of this unit. The plan is to provide additional information on a monthly basis. As you progress in the construction, I too will be will be constructing a unit for myself. Progress on my unit will be documented on my web site, enabling you to make comparisons with your construction.

Since there will be no kit of parts available for this construction, for some parts, a range of specifications will be called out for you to consider. For instance, the requirements for the motors to drive the scanning disks will described in that manner. Other elements of the construction may simply leave most of the "design" up to you. There will be many opportunities for to use your ingenuity and give your project that personal touch.
Let's start out by defining what the system will be. This will be a "new" system for you and for me both.
So the specifications at this point will be for the most part, just goals. So don't be surprised if changes occur as we go along. You or I both can change them as needed, to suit our situation at the moment. This might be because you have a certain part that you want to use or because we don't have a certain part and want to incorporate something else that we do have. This might also occur if we lack certain tools or skills, but know of a way around the problem, if we can change an appropriate specification.

Here are the specifications we will start with. It is purposely brief so we can add to or change it as we go along.

Display unit: 12 inch diameter Nipkow disc. Scanning format: 32 lines, scanned vertically.
Aspect ratio: 2 vertical to 1 horizontal (2:1)
Scanning starts at the lower right edge of the image, progresses to the upper left , then repeats.
Image Frame rate: 12.5 hertz
Composite video signal input: 1 volt p-p, with sync pulses most negative, white most positive.
Sync level: 0 to 25%
Video level: 25% to 100%
This is what we will start with. With this much, we can define the scanning disc, some of the particulars of the light source and say a few things about the cabinet or case of the display unit. We can also begin making a list of parts we will soon need to progress beyond this point.

Materials you will need for this installment.

* 12" Aluminum square or circle. Alternate materials are listed below.

As good a place as any to start, would be for you to build your scanning disc. You might as well make two at the same time because the camera, to be built later will need one also. There is a place on this site that shows a way to build a scanning disc. Refer to that as one way to do do it. You might also look in some older books or magazines from the early 1930s, or late 1920s for this information.

Now you need to select the material for the disks. My preference is aluminum, from .015 to .030 inches thick. And you want it to lay flat. I also have used .060 engraving stock. It works very well. You can even use cardboard if you like. Many of J. L. Baird's first discs were cardboard and his larger discs were plywood. One of C. F. Jenkins kits included a cardboard disc, that wasn't even round. It was eight sided, like a stop sign. Some experimenters have used semi ridged vinyl or even a 12 inch LP record will do the job. Take your choice, but if you do use something like cardboard, you need to be more careful with it as you progress with the building. Also, if you don't have one, this might be a good time to purchase (or at least borrow) a dial type vernier caliper . For this project, a 6 inch caliper is adequate. This will offer you the means to accurately measure dimensions in thousandths of inches, at a cost of less than 20 dollars. I've seen them at prices as low as 15 dollars. Properly cared for, it will last you a lifetime.

When you have your material selected, locate a center point and scribe a 12 inch circle. Cut or saw the disc(s) out of the sheet of material. At some point you will need some sort of hub for the center of the discs, to mount them on the drive shaft. If you have nothing in mind for this yet, for now just put a .375 inch hole in the center position. Put the disc on a round shaft and spin it to see if the outer edge runs reasonably true. It ought to be within a 1/32 of an inch. If it is only a little worse than that, go with it, it will probably do. If it bothers you, you can always make another one later.

Probably the easiest way to locate the angular position of the holes is to first scribe the 12 inch circle then divide it in half, and each half, divide it again. Divide each of the quarters again, giving eighths and twice more until you have thirty-seconds. The scribe lines are the angular locations of the thirty two holes.

The first scanning hole in the is located .250 inches from the disc edge. Pick a line and mark the location of the first hole. Lightly, center punch it. Measure the distance from the center hole to this first hole and note its dimension. Reduce this dimension by .015 inches and mark and lightly center punch the second line (going counter-clockwise) at this new dimension, measuring again from the center hole. Reduce the dimension by another .015 and mark the third hole location. Repeat this process for the remaining 29 holes.

The holes are drilled with a #72 drill bit, (.025"). Purchase a few of the drill bits in a "high speed" grade. A hand drill should do nicely. Better yet if you have or can borrow a drill press. If necessary after drilling, de-bur the holes. This disc will provide an image size about .52 inches wide and 1.1 inches high.

Now you can add a row of synchronizing holes, all on the same radius about 1.50 inch from the edge. Mark and center punch each of the 32 scribed lines at the same radius and in line with the image holes. Drill these holes using a .062 drill bit. De-bur if necessary.

Paint both sides of the disc (unless it's already black in color) using a can of flat black spray paint. Not to much paint around the scan holes please.

Except for the hubs, these discs are complete. In the meantime, you might think of ways to mount your scanning disk to a shaft mounted in bearings of some sort.

If you would rather buy the scanning disc, I have them available for $85 postpaid in the USA. These are high quality precisely made laser cut metal discs, with spokes that improve performance. These discs have a 3/4" center hole.

Peter Yanczer

On to the 2nd installment