In spite of predictions that the overhead projector is yesterday's technology, these devices remain popular with presenters in the educational, corporate and government sectors. And why not? The beauty of the overhead projector (OHP), is that it is a simple, completely interactive way to present ideas, and continues to be a valuable partner for the presenter. Simple to set up and operate, you can concentrate on your message without having to fumble with high-tech equipment or technology you're not familiar with.

Here are some things to consider when purchasing an overhead projector. OHPs come in two basic styles - open head and closed head. The sturdier-built closed head OHPs have their lens array completely enclosed, most typically within a box, protecting the lens and mirror from dust and scratches. You can choose the focal length based on how far you wish to project from your screen. It's usually better to purchase a projector with more lumens, making it better equipped to project an image in a room with lots of ambient light. And while some OHPs are heavy and bulky, traveling presenters also can choose from an assortment of lightweight, compact overhead projectors.

Simple preparation is also a great reason to purchase an OHP. Preparing a presentation can be as easy as printing out existing documents onto transparancies, using a standard inkjet or laserjet printer. This requires much less time than assembling a complex computer-based presentation,which would also require extensive video and audio equipment.

Complete Mobility With Wireless Mics

Wireless mics offer the user freedom to move around, without being restrained by a cable. Selecting a wireless mic system can be confusing. One of the most important considerations is what type of transmission system will work best for your application. Use the definitions below to help you decide.

VHF (very high frequency)
The VHF band offers low equipment cost. However, VHF is prone to interference from many sources. Due to the limitation of available frequency bandwidth, it is only feasible to operate, at most, two or three units simultaneously on traveling frequencies.

UHF (ultra high frequency)
The primary physical characteristic of UHF radio waves is their much shorter wavelength so a shorter length of antennae is needed for UHF systems. The available radio spectrum for UHF use is almost eight times greater than for high-band VHF, so a greater number of systems can be operated simultaneously.

IR (infrared)
This signal is line-of-sight, so it does not transmit through solid objects. This is desirable when security is an issue, or when numerous systems are being used in the same building since the signal will not pass through walls.

In addition to selecting the transmission system, another feature to consider is the number of antennas. This does not necessarily affect the number of mics that can be used, but it does affect signal quality. Single-antenna receivers use one receiving antenna and one tuner, similar to a FM radio. These work well in many applications but can be subject to momentary losses of signal, or dropouts. Diversity receivers use two separate antennas and two separate tuners; a circuit in the receiver automatically selects the best signal, so the chances of dropout are greatly reduced.

Wireless mic systems are available in many configurations to accommodate various end-user requirements. Choose the mic and transmitter based on the source to be miked. For example: a handheld microphone with built-in transmitter, a lavalier or tie-clip microphone with body-pack transmitter, or a headworn mic with body-pack transmitter. The latter two are generally used when hands-free presenting is necessary. Handheld mic/transmitters are generally used when the mic is going to be passed from one presenter to another.

Wireless mic systems connect to the rest of your sound system the same way that a standard wired microphone does. Most wireless receivers put out a signal that is identical to wired mics, so the output jack on the receiver simply connects to the same input on your audio mixer, amplifier or PA system. In applications where the output of the wireless receiver is incompatible with the inputs of the sound system, an adapter cable may be required.

How To Select The Right Projection Screen Format

Screen format is measure of the ratio between the height and width of the screen and is usually determined by the projection source. For example, if you're using A/V equipment such as a slide or overhead projector, select a screen with an A/V format that has a 1:1 ratio. If you're projecting a standard television signal, select a screen with an NTSC format that has a 3:4 ratio.

The most common projection screen formats are:


A/V (1:1 Ratio)
Common to standard
AV equipment



NTSC (3:4 Ratio)
Common to standard
US broadcast TV









HDTV (9:16 Ratio)
Common to standard
US high-definition TV



Letterbox (1:1.85 Ratio)
Common to standard
wide-screen cinema








We carry a full selection of projection screens in a wide variety of formats, surfaces and sizes.

Selecting The Correct Projection Screen Surface

If you're using an incorrect surface (such as a wall or window shade) for projecting images on during a presentation, you're probably getting a lot less visual clarity than you would with a screen designed for your particular presentation application. Screen surfaces are designed with projector presentations in mind so that you get the brightest and cleanest image possible. The descriptions and diagrams below help determine which screen surface is right for you.

Matte White/Da-Mat
All purpose surface. Offers the
widest viewing angle, while
sacrificing brightness and contrast.

F1500
Offers the wide viewing angle of
Matte White & Da-Mat, yet provides
superior brightness. Ideal for use
with data/video projectors.

Cinema Vision
Provides brighter, more uniform
images than Matte White. Narrower
viewing angle reduces color shift.

Pearlescent
Ultra-smooth coating provides high
reflectivity and brilliance without
loss of image quality or resolution,
resulting in high color and contrast.

Video Spectra 1.5
Superb color and contrast. Designed
for graphics, data and video display.
Narrow viewing angle restricts audience
size, yet ensures optimum performance.

Using Distribution Amps For Multiple Monitors

A Distribution Amplifier, sometimes referred to as a splitter, is a device that allows you to connect a single video source to multiple displays or projectors. For example, if you have one computer and you want to display it on six monitors at the same time, you would use a distribution amplifier (DA) in between the computer and the monitors, using cables to interconnect the units. A distribution amplifier not only provides a solution for feeding a signal to multiple displays, it also buffers the video source from the loads (displays), ensuring that each display appears as if it were connected directly to the source.

In most cases, the outputs on distribution amplifiers are equalized evenly and are designed to handle a range of cable lengths. For example, one output might feed a monitor that is only 5' away from the distribution amplifier while another output might feed a monitor that is 40' away from it. The length of cable that can be used on an output varies depending on cable quality and signal resolution. If you simply need to amplify the signal over an extremely long run of cable (up to 100') a 1-in 1-out distribution amplifier, or line driver, can be used. A line driver will not "split" the signal the way a distribution amplifier does, but it will prevent signal loss from your data source over a distance of approximately 100'. To send a signal further than 100', you can continue adding a DA or line driver at 100' intervals.

Travel On A Budget With Teleconferencing

Teleconferencing systems offer a wide range of benefits depending on your needs and budget requirements. Depending on the number of people you wish to communicate with and the size of your conference room, you can find a variety of ways to make meetings easier and more efficient. Everyone in your office can use and benefit from this technology because all of Polycom's teleconferencing systems are easy to setup.

Some advantages to teleconferencing are:

. Attend a business meeting hundreds of miles away without leaving your office
. Reduce travel expenses
. Reduce travel time requirements
. Schedule meetings minutes ahead of time instead of days or weeks
. Keep in touch with other branches of your business

Simply stated, teleconferencing pays for itself many times over within the first months of use!

On a tight budget?
Choose an audio teleconferencing system for a fast and economical way to discuss important business matters. Or select the ViaVideo system which offers portability and ease-of-use. All you need is a computer with internet access and ViaVideo will send full-motion video and full-duplex audio as well as data. Known internationally as an innovative market leader in voice and video communications, Polycom's products have become trusted, familiar part of the landscape in conference rooms across the world.

Getting The Most From Your DVD Signal

Always verify system compatibility by checking the inputs and outputs on your TV and DVD, as well as your AV receiver, if you intend to use one. Below are the most commonly used connectors in video and audio equipment..

Composite Video: 390 Lines*. A composite connection utilizes a single RCA plug and is common to all DVD players. It produces a good picture with minor loss of detail.

S-video (separate video) Video: 400 Lines*. An S-video connection utilizes a single cable with a mini 4-pin connector, vastly improving picture quality. The video signal modulates with separate luminance (black-and-white) and color, producing more detail and fewer color defects.

Component Video: 500 Lines*. Component video utilizes 3 discrete RCA cables (not always available on less-expensive models), improving on S-video by splitting the color signal into red, green and blue. This produces a superior picture with the widest range of color.

Progressive Scan: 480 Lines redrawn 60 times per second* Only for HDTVs and digital-ready sets that support it. Progressive scan, also known as 480p, provides a sharper, more precise image by redrawing all 480 consecutive lines of the image 60 times per second. (As compared to every other line redrawn 60 times per second on an analog TV.) This offers the quality of film.

*Horizontal resolution

Analog Stereo Audio: Common to all DVD players, analog audio utilizes the standard left and right channel outs, providing Dolby Pro-Logic surround. These let you plug directly into your TV, regular stereo system or AV receiver connected to multiple speakers to achieve either 2-channel or surround sound.

Digital Stereo Audio: Digital audio utilizes one of two connectors: fiber optic or RCA/coaxial. Both support Dolby Digital and Digital Theater System (DTS 5.1) formats which send a 6-channel audio signal to the 5 stereo speakers + 1 subwoofer in a typical surround system. In order to translate the encoded signal, these audio outs must be routed through an outboard decoder, an AV receiver with digital decoding capabilities or a DVD with built-in decoder.

Using Lamination To Protect Your Documents

Laminating is an easy and cost-effective way to protect your important documents from water damage and regular wear and tear. We offer a variety of laminating machines, ranging from desktop models to large, commercial laminating machines. The two types of laminators are roll laminators and pouch laminators. Roll laminators offer variable film lengths to laminate posters, banners, and any odd-shaped documents. Pouch laminators have a lower operating cost and precut laminate pouches allow for quick lamination of commonly sized documents.

When choosing a laminator consider the following:

. What size documents will you be laminating? Pouch laminators are more cost effective for items 11" x 17" and smaller. Roll laminators handle larger sizes.

. What laminator film thickness will you use? If you don't intend to use thick films, then choose models that can laminate from 3-5 mil. If you want to be as versatile as possible, you will want one of the models that can laminate materials from the thinnest (1.7 mil) to the thickest (10 mil) films.

. How many items will you be laminating at one time? If you have occasional uses and don't expect to laminate more than a handful of items at any time - a pouch laminator may suit your needs. If you are going to be laminating 100's or 1000's at a time, a roll laminator would likely be a better choice. For small items less than 5", even with larger quantities, a pouch laminator is the better choice since it is difficult to feed smaller items into a roll laminator.

. How fast do you need to laminate? If you have many items to laminate and time is an issue, pick a model with a high motor speed or an adjustable speed control.

We are your source for roll and pouch laminators as well as laminating film, pouches and mounting boards.

Audio Cables - Balanced or Unbalanced

High quality audio cables and their connectors are integral to creating a successful audio chain in your installed or project-based sound applications. There are basically two kinds of cables used between any audio devices. These are balanced and unbalanced. A balanced connection will incorporate a cable with two wires (one for the active, outgoing signal and one for the return) that are separated and protected from outside electrical interference by their individually wrapped shields. Cables with flexible mesh shields lend themselves to more rigorous coiling and uncoiling.

An unbalanced cable has a single wire surrounded by a shield, but here the shield carries the returning signal as well as insulating the wire. These cables are more susceptible to signal loss or noise from nearby sources such as fluorescent lights and electrical cables. Balanced audio connections are generally used with low-impedance equipment, while unbalanced connections are used with high-impedance equipment. As a rule, balanced connections will offer much better performance.

When assessing whether an existing cable is balanced or unbalanced there are a few guidelines you can follow. Almost all cables with two XLR connectors are balanced. They offer the most professional solution for conducting audio signals. 1/4 inch connectors are found on cables used with many semi-pro and consumer types of audio equipment and are almost always of the unbalanced high-impedance type. Miniplugs come in two sizes, 3.5 and 2.5 millimeters. They are frequently used on consumer and semiprofessional video equipment. They almost always indicate an unbalanced audio connection.

When upgrading your audio equipment: look for heavy-duty and, when appropriate, "balanced" cables. We offer a full-line of audio and video cables, connectors and adapters as well as the components necessary to assemble and repair your own.

Photographic Lighting Made Simple

In addition to illuminating your subject for proper exposure, lights can shape, highlight, model and define your subjects to create eye-catching photos and videos. Whatever your video or still imaging project, auxiliary lighting can go a long way towards improving the outcome. Here are two simple light placements possible with a small selection of lights, stands and mounting accessories:

Figure A illustrates the basic 2-light set-up, which is the starting point for all lighting set-ups. The main light gives you general illumination. When a built-in flash is inadequate, this light is placed near the camera, generally slightly higher and angled down toward the subject. The fill light is placed at a 45 degree angle to the subject, softening and filling in some of the shadows created by the main light. It can also bounce off the ceiling for a softer effect. Varying the placement and intensity of your fill light will vary the contrast in your image and give you a great degree of control over the mood and texture of your image.

Additional lights enhance the sophistication of the lighting scheme and give you greater control over the final appearance of your image or video. In Figure B you will see a 3rd light used to light the background. This enhances the separation of the subject from the background, and creates greater definition. Adding a color gel to your background light is a simple way to get the effect of an entirely different background.

Whether you're a still photographer or a videographer, a professional or an amateur, we have the lighting accessories you need.

How to Choose the Right Data/Video Projector

Choosing a projector comes down to 5 basic points:

1. The brightness
2. The resolution
3. The size/weight
4. The contrast ratio
5. The cost

The brightness of any projector, be it an overhead or a data/video projector, is measured in ANSI lumens. With the constant advancement of the technology, most projectors now have at least 1000 lumens. The higher the lumens, the more light is projected, the brighter the image. If you have a room with windows that you cannot cover, or if you need to have the lights on during your presentation, it is important to have a high lumen output so the image can be seen. If the lumen output is not high enough and there is a large amount of ambient light (i.e.: sunlight) the image will look washed out, so it is important to know the lighting conditions when selecting a projector.

The resolution of a projector is related to how accurately the image is projected. The resolution is the number of pixels that can be displayed. Most projectors are either SVGA (800x600 pixels) or XGA (1024x768 pixels). An SVGA projector can take an XGA image, however the image will be compressed which may cause blurring and 'ghosting' of the image, particularly text. In this case, it is important to know what the projector will mostly be used for-video or presentations with text and graphics. If you are using it mostly for PowerPoint type presentations, you will want the projector to have the same resolution as your computer output to get the best image.

The size and weight of the projector is a very important feature. A traveling salesperson who takes his/her presentations on the road will probably want a portable unit that can pack into a travel case, next to a laptop, and hop on a plane. Weight may not be a factor when considering a projector that will be permanently installed, but dimensions may be an important consideration.

Projectors are either LCD, which means light has to go through glass with liquid crystals inside, or DLP, which is a mirrored chip that reflects light. An LCD projector that has only one glass that shows three colors is smaller than an LCD projector with 3 glasses that each show one color: red, green, or blue.

The contrast ratio is the difference between the darks and the lights, to put it simply. The higher the contrast ratio, the more dramatic the difference between black and white is. DLP projectors have a higher contrast ratio because light is reflected by the mirrors, not absorbed through layers of glass as in an LCD. A higher contrast may be more important in home theater applications.

Projector prices are primarily dictated by the technology. LCDs cost more to manufacture, so they are more expensive. DLPs are not as expensive to manufacture and consequently they are less expensive.

Keeping all of these factors in mind, selecting a projector can still be an overwhelming task. A toll-free call to National AV's product advisors gets you well qualified advice to help you choose a model appropriate for your application and budget.

Care and Feeding of Your Data/Video Projector

Data/video projectors are great tools for presentations and business meetings, but only if they are working properly. They are not difficult to use or take care of if you adhere to proper maintenance habits and if you have good trouble shooting tips to follow.

The following article outlines proper care techniques and good trouble shooting advice, equally valuable for the technically proficient and phobic. Plus, when all else fails, it's good to know that National AV Supply.com's technical support team is readily available to personally walk you through any other difficulties you might have with a projector purchased from National AV.

Suggestion: Print this out and keep with your projector.

Projector Care

Your data/video projector should last for many years and need very little maintenance if you take care of it properly and be sure to follow the simple care tips below:

• Always use the "Standby" button to cool the projector after each use. The projector should no longer be warm prior to packing.
• Take special care when packing the projector so that the lens won't get damaged. Always use the lens cap. Replacing a lens can be costly.
• Separate the projector from the cables when packing. This will avoid any unnecessary damage to the projector.
• Avoid the use of excessive force when operating and packing the projector.
• NEVER ship the projector in anything but an ATA shipping case, which is designed specifically to protect the projector during shipment.

General Information:

A projector is simply an extension of your monitor; it can only display what is being sent from your computer. If you have a VGA projector with a VGA laptop or a SVGA projector with an XGA laptop, you will not be able to enable simultaneous viewing.

Trouble Shooting

So, you're ready to give a presentation and the projector appears to be set up properly. Yet, you don't have a picture on the screen. Don't panic. Review the trouble shooting tips below. Likely, your problem is just a small issue that can be resolved simply and quickly. If not, please feel free to contact a technical support representative or it may be time to seek repairs.

Issue: The projector won't come on.

• Confirm that the power cord is plugged in properly
• Verify that the "Standby" button is on
• Check/replace the lamp assembly

Issue: "No Signal" is displayed from the projected image.

• Verify that your computer is running at a resolution equal to that of the projector.
• When using a laptop computer, verify that simultaneous viewing has been enabled. All laptops are different (look for the "Function" key that looks like a monitor or that reads LCD/CRT), and then press the "Function" key on bottom left side of keyboard. Then choose the key that toggles your display options.
  • Verify that the projector is in computer mode (press "Computer" or "Input" button) for computer presentations
  • Verify that the projector is in video mode (press "Video" button) for video presentations
  • Replace VGA cable
  • Try connecting to another computer

Issue: Image is not stable.

• Adjust image using sync button on projector
• Verify that both the computer and projector are running at the same resolution
  • If not, identify the native resolution of the projector (i.e. 800x600, 1024x768, 1280x124 pixels) and set the computer to the same resolution. If using a laptop, you may lose the ability to simultaneously view both images.
  • If yes, go to the "Display Properties" window within your operating system and select (click) "Advanced Properties". Locate "Refresh Rate" click and select "60 hz" as this is a known compatible frequency for both PC's and workstations. If you cannot access any selections under "Refresh Rate", select "Optional" for the current setting.

Issue: Image is still not stable.

• Under "Advanced Properties", select "Adapter Types" and show all devices. Select "Standard Monitor Types" and repeat steps for optimizing refresh frequency.

Issue: Image color is off (red or blue).

• If background has a green, red or blue tint, reset all settings to the factory standard.
• Replace the VGA cable.