Ohm's Law

Revisiting Ohm's Law

At least twice per week someone walks in to our store and asks to by a switch or a power supply. First words out our mouths are, "how many Amps?" The typical response is, "12 Volts". So we ask, "How many Amps" Always followed by a blank stare a pause and, "I don't know, its only 12 Volts"

Ohm's law applies to electrical circuits; it states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.


The mathematical equation that describes this relationship is:


I = V / R

A basic electronic circuit has three main properties; Voltage, Resistance and Current. These three properties lead to a great deal on confusion with folks who don't often have to think about them or deal with them.

Consider This simple circuit, a 10Volt battery and a light bulb. If we connect the bulb to the battery via some wire, current will flow through the wire and through the bulb making it light.

The battery provides voltage (V), electric pressure; also know as EMF, Electro Motive Force or Potential Difference.

For the beginner it is best to think of Voltage as electric pressure. ( Note, Sometimes V is represented with E for EMF so, I=E/R is the same as I=V/R )

The bulb and the wire provide Resistance, (R). Resistance impedes current, ( I ) flow.

Resistance is measure in Ohms. Current is measured in Amps.

If the bulb has a resistance of 10 Ohms the current in the circuit will be, 1 amp…

10/10 = 1

If the bulb has a resistance of 20 Ohms the current will be ½ or .5 Amps.

10/20 = .5

If we double the Voltage to 20V and the bulb remains 20 Ohms we get back to 1 Amp.

20/20 = 1


So, EMF in Volts divided by Resistance in Ohms equals current in Amps.

We can solve for any of the three variables as long as we Know the other two.

R=I x V, V = I x R

One way to think about this is to make a comparison to plumbing. Voltage is sort of like Water pressure in PSI. Current is similar to the amount of water flowing in a system and resistance is similar to the size of the pipe.

If the water pressure remains the same and the size of the pipe grows smaller, Less water will flow in the system, It the same or at least a very similar relationship.

What about Watts?

When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Devices convert electrical energy into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker) or chemical changes.


By the definitions of electric potential (volt) and current (ampere), work is done at a rate of one watt when one ampere flows through a potential difference of one volt.


1W=1V×1A

Electric power, like mechanical power, is represented by the letter P in electrical equations. The term wattage is used colloquially to mean "electric power in watts."


In direct current resistive circuits, instantaneous electrical power is calculated using Joule's Law, which is named after the British physicist James Joule, who first showed that heat and mechanical energy were interchangeable. Joule's Law is


P = V x I


where P is the electric power, V the potential difference, and I the electric current.
Joule's law can be combined with Ohm's law (V = RI) to produce two more equations:


P = I^2 x R


and


P = V^2/R


This is by no means a complete explanation and we are only talking about DC, (Direct Current) circuits AC, (Alternating Current) can get thing a lot more complicated. If interested, there are plenty of books and on-line resources that explain in more detail.

Start Here

Wholesale Electronics Inc.

123 W 1st Ave.

Mitchell, SD 57301

How to Watch Digital TV

( Get your money's worth out of your new TV )

Our transition to Digital TV has brought with it a lot of baggage. What used to be simple has become quite complicated.

I would guess that at least half of the flat screen 16:9 digital TV's in operation are not set up correctly. Some folks are not watching High Definition but believe that they are.

If you have cable TV you should be subscribing to your cable services digital package. Many “basic” cable services do not deliver HDTV to your home. If you are going to invest in a new, “Wide-Screen” TV you might as well give it the signal it needs to produce the best picture it can.

Most Cable TV companies will supply you with a box. From this box to your TV you should be using a HDMI cable. That is the best way to feed your TV digital video and sound.

If you have a DVD player, you should at minimum have one with HDMI output. Or even better, a Blue Ray DVD player will provide the best video.

If your set has only one HDMI input and you have more than one HDMI source, you will need an HDMI switch box to switch between the two sources.

There is a lot of programming out there that is not HD.

The old TV Standard known as NTSC produced video in an aspect ratio of 4:3. Many TV programs are still delivered to your set in the 4:3 package. For instance, most local news is still produced in NTSC and only up converted to digital as a last step before being transmitted to the public. And is transmitted in a 4:3 package.

Smaller market stations have been investing all the capital in getting their new DTV Transmitters on line to satisfy the FCC's transition requirements. At the studio, things are pretty much same as always. Slowly, these stations will eventually convert to DTV at the studio level.

All of the programs produced over the years were produced in NTSC and still are running in syndication. Smaller cable channels are not required to switch to DTV under the FCC's transition so many of them still operate NTSC.

Do not let your TV stretch the picture to fill the screen.

Most newer TV's will have a button on the remote that lets the user change the way the TV deals with programming that does not fit the 16:9 aspect ration. You want to set this so a 4:3 program is displayed as a 4:3 box on your screen and a 16:9 program is displayed full screen.

Otherwise, your TV is stretching the 4:3 image to fill the screen and degrading the quality of the image. It is the first instinct of most to have everything displayed at full screen. However, doing this is sort of like covering 10sq feet of wall with 7sq feet of paint, something has to give.

Many folks look at these stretched images and believe they are watching HD. Nope. Technically, they are watching video that is degraded from what they saw on there old 4:3 set because the new HDTV is distorting the image. It is a case of bigger is not always better.

If you understand this and still insist on filling your screen no matter what you are watching, that is your choice. It is your TV and do with it what you want. We just want to educate you as to what is going on.

Case in point, my siblings and I, for Christmas two years ago, bought a new TV for Dad. The Cable Company he subscribes to sends him many stations in both standard definition and HD. His favorite channel is 11 and can be viewed by tuning the cable box to 11. They send the DTV feed on cable channel 611. He still watches 11 and his TV stretches the video to fit the screen…

He just doesn't care. Been watching 11 for too many years… And of course, If I adjust the TV so that 11 has black side bars he complains…

I suppose eventually cable companies will do away with the standard definition feeds but for now they remain so that you can still use your 4:3 TV in the bedroom or kitchen.

A friend of mine purchased a new 40inch LCD the other day and asked me to show him how to run it. He had the HDMI and a coax going from the cable box to the TV and was watching ESPN with the TV tuned to channel 3 and the cable box tuned to ESPN's Standard Definition channel… He was adamant that he was watching the US Open in High Def… I disconnected the coax, used the “input” button on his TV remote to find the HDMI input he was plugged into; found ESPDHD on the cable box; his jaw hit the floor when he saw the difference.

How many are watching substandard images and believing they are watching the best their TV can do..?

I am a member of our local VFW, they spent $1K on a new plasma and will not upgrade the cable service to the HD package. It's $10 more per month. When I told them that they could have got an LCD of the same size for $650 and used the savings to pay for the HD package for the next 35 months they argued, “Well, sure but we got a plasma, that' better right?”. Arghhh….

June has passed and with the migration to DTV is over right? Not hardly. I'm guessing it will be at least a decade before things become simple again.

Terms:

DTV, Digital Television : A standard for broadcasting television signals through the air, Analogous to FM or AM. Is not the same as HD or HDTV.

HDTV, aka HD . High Definition Television: A video format for display on wide screen 16:9 televisions.

HDMI: High Definition Multimedia Interface . An interface for interconnection between digital media components, i.e. Cable TV converter box, Computer graphics, DVD, Blue Ray, Xbox etc… Carries both digital video and audio in standard or High Definition.

Aspect Ratio . The ratio of horizontal to vertical size; for example, 16:9. A 32” 16:9 TV would have a screen 16” tall. (32/16) X 9 = 16

NTSC: National Television System Committee , established in 1940. NTSC is an analog television transition system.

SDTV or Standard Definition Television : Television systems that have a resolution that meets standards but not considered either enhanced definition or high definition. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as analog, (NTSC) systems.

Many people are unaware that the icons that are used in the default configuration for Windows are not fixed but can be changed to suit a PC user's preference. Why should your desktop look like everybody else's? Put your own picture on the folder My Computer. Give all those folder icons some character. In this article we will learn some of the ways to spruce up the computer's appearance.

Where to Find New Icons

Before discussing how to change your icons, we need to know how to find a supply of possible new icons. Every Windows computer already has many files containing a wide range of icons. Many of the program DLL files have icons embedded in them. Also there are some special DLL files that are icon collections. These embedded icons are not immediately visible and viewing them requires either some special software (see list of references in the sidebar) or one of the Windows procedures given below. Depending on your version of Windows, files with icon collections may include cool.dll, moricons.dll, and shell32.dll. Many other DLL files will have one or two icons embedded. The DLLs are usually in the folders Windows , Windows\System , or in XP in the folder Windows\System32.

If the supply of icons that comes with Windows is too limited for your tastes, collections of icons can be downloaded from many places, some free, some not. There is also software for creating your own icons. Some references are given in the sidebar.

Shortcut Icons

The icons for shortcuts are easy to change in all versions of Windows 9X/Me/XP. Right-click on a shortcut to open the context menu and choose "Properties". The properties sheet contains a button "Change Icon." (Figure 1) Click this button to obtain the box shown in Figure 2.

Figure 1. Properties for a shortcut

Figure 2. Change icon

The entry for "Look for icons in this file:" will show the source of the present icon and the "Browse." button will allow for the selection of a different source file. The various icons contained within a source file will be displayed and the one that you wish can be selected. The source file in Figure 2 is a type known as an icon library. These files have the extension ICL. A file can also consist of just a single icon and nothing else and these files have the extension ICO. Unless you download icon collections from one of the many Internet sources, however, your icons are likely to be in a DLL file. Use the browse function (Figure 3) to search for icon-containing files on your computer. Browsing through files while in the "Change Icon" window will display whatever icons are embedded. Note that the entry for "Files of type:" has several choices. When first looking for icons, it is best to choose "All files".

Figure 3. Browse window for changing icons

Folder Icons

The default setting for icons for folders is the same rather boring generic manila folder. If, like me, you have some folders that you would like to individualize, Windows XP makes it easy to change. Right-click on a folder and open "Properties". Click the "Customize" tab on the properties sheet (Figure 4).

Figure 4. Customize tab on folder properties sheet (Windows XP)

Click "Change icon" and proceed as for shortcuts. The procedure for changing folder icons in Windows 98/Me is more complicated and involves a file called "desktop.ini". See the Microsoft reference in the sidebar.

Making Your Own Icons

The references in the sidebar list some software designed for creating icons but if you feel artistic you can draw your own, using most graphics programs. Or if you have digital photos or other graphics that you like, you can convert them into icon files. The only trick is to remember that icon files have a format of their own and must have the extension ICO. They are typically small files sized either 32x32 or 48x48 pixels. Other sizes are possible but these two are the most common. Color depth is frequently set at 256 colors.

An easy way to make new icons without a lot of special software is to use the Windows accessory Paint that comes with all computers. Use Paint to draw whatever graphic is desired and then save the file as a 32x32 bitmap (extension BMP) with 256 colors. There is one more step and that involves changing the format to ICO. There is a very nice free graphics program called IrfanView , which makes this quite easy. Use IrfanView to open any bitmap file that you created with Paint and then save as a file of type ICO. Presto, you have an icon file. IrfanView is also good for editing, cropping, altering, and enhancing digital photo files and other graphics so it can be used to create icons from your own photos or other graphics. Use IrfanView to open a photo of your dog, crop it or edit it to your taste and then save it as an icon file with extension ICO. The file can then be utilized as an icon as described in the sections above

Courtesy: vlaurie.com

Trouble Shooting Audio Hum, Ground Loops and Isolation

Patrick Ziegler Wholesale Electronics Inc.

Today's entertainment centers have changed quite a lot from those of several years ago. Today we have MP3's on our computers, phones and Ipods. Satellite and Cable TV can deliver digital music streams as well as theater quality sound to our great rooms and entertainment centers. As well as DVD's, DVR's etc…

The more sources we add to our audio systems the more likely we are to end up with an audible hum. If you have a sub woofer this can become even more annoying.

Electrical hum is generated for the most part by ground loops. For many, ground loops are mysterious and difficult to comprehend and/or fix.

All electrical grounds are not created equal. For instance, from the cable TV pedestal behind your house to the electrical ground at your AC outlet, there is some resistance. The wiring in your house from one outlet to another has some resistance in the wire and connections.

These resistances will create a difference in voltage between the two points, ( Ideally all grounds would be zero volts ) and a small current will flow between the two points.

Typically, these resistances are small and do not create problems. However, it doesn't take much to introduce a hum into your system.

Lets say your computer is in the den and you stereo is in the living room. So, you wire in a patch cord from the computer to your receiver and now you have a hum. There is nothing wrong with the receiver or computer or the patch cord. The trouble is, the ground in the den and in the living room outlets are not electrically the same resulting in a small AC current flowing between your computer's chassis and your stereo receiver's chassis through your audio patch cord's ground conductor.

If you had an AC volt meter with very long test leads you would be able to measure a small AC voltage between the two grounds terminals at the AC outlets. This same voltage difference is now carried to the chassis of your computer and the chassis of you stereo receiver.

This may be as small as 1/10 th of a Volt. However, the line level audio signal you are sending from the den to the living room is only 1 Volt peak to peak. 1/10 th or 10 mV is enough to cause a hum issue.

As of late, the most common cause of ground loop hum in audio systems is cable TV.

It is the same situation. The shield or outer conductor on the cable is not electrically the same as the AC ground that your cable box or TV is grounded to. And you are connecting audio from your TV or Cable box to your stereo receiver and viola, HUM…

The TV or Cable box doesn't even need to be turned on. As a matter of fact you can turn everything off except the receiver and you still have hum.

So, now you have an idea of what causes the problem so, how do we fix it?

What you don't do is start cutting of the third prong on you power cords. You might lose the hum doing this but you have created potentially dangerous situation.

That third prong ties the chassis of most all electronics to earth ground. If an internal component fails and shorts to ground you could now end up with dangerous voltages on the chassis of your electronics. With the third prong intact, this would trip a breaker or blow a fuse.

Also, most surge protection is useless without being tied to earth ground.

Troubleshooting is a process of elimination…

If you have cable or satellite TV connected to your system, disconnect the coax and see if the hum goes away. If it does, check that you have a grounding block where the cable enters the house and that it is in good repair and properly grounded. If this doesn't solve it you can call your cable guy and have him take a look. There are also ways of isolating your cable feed using RF Isolation transformers.

One easy cheap way of making an RF Isolation transformer is to take two TV Matching transformers or baluns and connect them back-to-back. They have to be isolation type baluns. You can check this with an ohmmeter. There should be no continuity from any point on the 300-ohm side to any point on the 75-ohm (coaxial) side. If there is, it is not an isolating transformer.

This cheap and easy fix can cause issues if you have digital cable. You could lose some or all of your channels. It is a cheap an easy fix and worth a try. There are devices specifically designed to isolate digital cable feed. With digital cable and HDTV a broadband isolation transformer is needed.

If you cable TV is not the issue, are there any two prong electrical cords in your system? If yes, unplug it and see if the hum goes away. If it does, try rotating the plug 180 degrees and re plugging it in, if you can't do this because of polarized outlets and plugs. Have an electrician check that the outlet is properly wired.

Do you have any gear plugged in to different electrical outlets or circuits? If yes, unplug them and see if the hum stops. If it does, have an electrician check the wiring for loose or otherwise bad connections from the outlets to the breaker panel on both outlets and /or circuits.

If you cannot fix the ground loop on the electrical side you can isolate your components from one and other on the audio side using one of these type devices. These almost always contain a transformer. Most folks won't care if there is a transformer between your source and your receiver however there is some loss of both level and frequency response with most transformers.

However, hiring an electrician can be expensive and he or she may not be able to find the problem. Remember, it only takes a small resistance to create trouble.

If you find the trouble is generated by your sub woofer here are some possible remedies…

• Try plugging the subwoofer into a different AC outlet in the room, one that isn't supplying power to your components (A/V receiver, TV, cable box, etc.). That might fix it.


• Try reversing the AC plug for your A/V receiver or the powered subwoofer. If it's a 3-wire plug or a polarized plug, which has one prong wider than the other, you won't be able to reverse the plug. For safety, do not use a "cheater plug" to bypass the 3-wire plug.


• With the power OFF, reverse the AC plugs one by one of any other components that have a standard 2-prong AC plug that isn't polarized. Each time you reverse a plug, turn on the system with the attached component and your subwoofer and see if the hum disappears. In some cases, reversing one or more plugs will eliminate the hum.
  

If none of the above steps get rid of the trouble, it is possible that your electronics is at fault. A bad connection or failed component within your receiver or other audio equipment can cause hum in your system.

Understanding Image Resolution

Understanding Resolution and DPI

I don't know how many times I have had this conversation only to see eyes glaze over with that deer-in-the-headlights look.

It really is not that complicated.

There are three things to consider.

1. Cameras


2. Monitors


3. Printers
   

Cameras are marketed by the number of pixels on their sensors . A pixel is the smallest element of an image.

Digital cameras range from 1 or 2 Mega Pixels up to 40 Mega Pixels or even larger.

A typical digital camera would be 8 or 10 Mega Pixels. For this discussion we will use the Canon EOS Rebel Xti 10 Mega Pixel Camera.

The Rebel Xti produces an image file that is 3888 pixels x 2592 pixels for a rough total of 10 million pixels.

For comparison we will use the Canon Powershot A590 8 Mega Pixel Camera that produces an image file 3264 pixels x 2,448 pixels. Multiply these two number and you get roughly 7.9 Million Pixels.

So why is having 2 million more pixels better?

Well, It's sort of like painting a wall. The more paint you have, (pixels) the more wall you can cover. Or, trying to cover a large wall with little paint will result in a splotchy paint job…

How does this apply to digital photography you ask…

Well, first we need to talk about DPI, (We should be talking about PPI or pixels per inch but for the sake of conversation and the fact that DPI is more commonly used we will stick to DPI or dots per inch even though technically we are talking about pixels). So, understand that a “pixel” is a “dot”. If you are a tech-head don't bust me out on this, trying to keep it at a tenth grade level here.

The human eye has its limits. Even the most near sighted person with his or her nose held directly up to a printed photo cannot resolve any more than 300 DPI. For this reason 300 is used as sort of a benchmark in photography.

Simply put, a human being can see the difference between 200 dots per inch and 300 dots per inch but cannot see the difference between 300 and 400… (Again, don't bust me out tech-heads… I know this is largely dependant on the content and detail of the image. We are working with generalities here today.)

So 300 DPI is our benchmark . Using the two cameras mentioned above we can now calculate the size of the image we can print using these cameras and maintaining our benchmark.

With the Rebel Xti 10 Megal Pixel camera we can print,

(3888 / 300) x (2592 / 300) or 12.9 inches x 8.6 inches

With the Powershot A590 we can print,

(3264 / 300) x (2,448 / 300) or 10.8 inches x 8.1 inches

So you see, The Rebel Xti puts more paint in your bucket…

As the printed image size increases, the 10MP camera will hold up longer.

Now, keeping things at a 10th Grade Math level you should be able to deduce that if we print duplicate photos from both of these cameras at 5”x7” we will se no difference as far as resolution is concerned. Both of these cameras have enough pixels to make decent 8X10 and smaller printed photographs.

A note about our Benchmark.

The 300dpi Benchmark is based on a person viewing a photograph at some standard distance, something in the neighborhood of 18 inches. So, for images in books and magazines 300 is a good number to shoot for.

For portraits and art that will hang on a wall or otherwise be viewed from several feet, a much smaller dpi can be used. In other words, you can print much larger for these images and still get away with it.

As mentioned above, the amount of detail in an image also plays into mix. A photo of a smooth surface takes little information to reproduce whereas a macro image of a bee or other insect will take allot of information or resolution to reproduce those details on the printed page.

But you said Monitors too…

Yes I did. You ever get an email from a friend with this image attached that is several times larger than your monitor?

Computer monitors generally display images at 72 DPI (Back off tech-heads!) You can do the above math using 72 instead of 300 to find out why that image is so big on your screen…

So, be nice to your friends and re-size or downsize that photo before you send it in an email.

Here are the top-ten screen resolutions used by visitors to weisd.com over the last year,

• 1024 X 768 (75% of the total)

1. 1280 X 1024


2. 1280 X 800


3. 1440 X 900


4. 800 X 600


5. 1680 X 1050


6. 1152 X 864


7. 1920 X 1200


8. 1300 X 2300


9. 1280 X 768

So you can now see that if you take the Rebel XTi image file and email it to you friend with a 1024x768 screen resolution without resizing it first, the image will be near 3 times larger than his or her screen.

My preference is to send images that are 800 pixels wide for horizontal or 600 pixels tall for vertical compositions.

Some programs like Microsoft's PictureViewer or Windows Explorer and others will automatically resize images so that they fit on your computer screen. This is convenient but these programs use simple and fast algorithms to do this and many times will result in an image that is degraded and just looks bad.

For best results, resize images for use in computing.

One more thing…

If you are shopping for a new printer you will see resolution specs that look something like, 4800 x 2400 dpi

Not going to go into a long discussion on this but I will say that everything said above has very little to do with this spec.

Simply said, most all printers that one would use to print a photograph are capable of putting 300 dots, (pixels) in one linear inch of paper. In keeping with the dummied-down 10th grade, (not picking on you Sophomores) explanation, one can think of printer resolution specs as how many dots a particular printer can fit inside one pixel.

This has more to do with reproducing good tones and colors than it has to do with the actual resolution we discussed above.

In Closing,

This is a very simple explanation of what can be a complicated subject. Visit any photographer's forum on the Web and you will find plenty of debate and discussion. However, I think this covers the basics…

DTV Antenna System Design

DTV Over-the-Air Antenna System Design
Patrick Ziegler Wholesale Electronics Inc.

The advent of DTV has left antenna installers in fringe areas sometimes scratching their heads.

We welcome any RF engineers or subject matter experts to share your thoughts on this subject by emailing us at info@weisd.com

In the past antenna system design was a pretty straight forward procedure. Estimate or measure the field strength of the transmitting stations, choose an appropriate antenna or antennas, calculate your losses in the down lead and choose an appropriate preamplifier to compensate.

If you needed a distribution system, you designed that and picked the appropriate distribution amplifier to maintain adequate signal strength to all receivers on the system.

DTV problem #1: Because of the nature of the DTV signal, you cannot measure the field strength of the transmitting station. So, you have to make the assumption that your favorite station is providing similar service as they did with analog TV.

Some stations have migrated away from their old frequencies. Others, who were previously transmitting DTV on temporary frequencies, have moved back to their original frequencies. Some will make these changes in June of this year.

Many low-band TV frequencies, (Chnls 2 through 6) have been abandoned for fear of issues with electrical interference.

To add to the confusion, we now have both, “Virtual Channels” and "Actual Channels, normally the channel you are use to referring to your favorite station as and what appears on you DTV receiver, and “Actual Channels”, the actual bandwidth and frequency that the station is transmitting on. Many times these two are not only different but in different bands.

You may think you are watching Chnl 5 but really be tuned to Chnl.23.

The so called, “Signal Level Meter” imbedded in most digital TV's and Digital Converter boxes is really not a “Level” meter but a measure of signal quality or readability. It is possible to have good signal level and poor signal quality. In analog we had, "Signal to Noise" ratio in the DTV world we have, "Bit Error Rate" or BER. Noise, interference and ghosting, (multipath interference) cause "bits" of data to be lost. When enough data is lost your receiver simply stops showing you the video stream.

DTV problem #2: Trouble shooting receiver problems with analog signals was very easy. Your receiver showed you the trouble. If you had a lot of noise in the picture that meant you had either no signal at the antenna or you where losing too much via the down lead or distribution system.

Multipath, skip and other atmospheric issues were evident in the picture..

With DTV, you cannot see these issues. They do not manifest themselves in the picture at all. The picture simply goes away or becomes too intermittent to watch.

People who live in out lying areas have become accustomed to watching less than perfect reception. Snowy pictures, multipath and electrical interference are things that people learned to live with. With DTV, these issues cause complete loss of the picture.

DTV Problem number 3: Digital TV's and Digital to Analog converters do not tune on the fly, as did analog TV's.

If you make changes to the antenna system or if the transmitting station has changed, you need to rescan the channels with your TV or converter box.

This is important if your antenna system includes a rotator. After turning your antenna, you will need to rescan.

So, What can we do?

From the output of the receiving antenna down, we can still go about things the old-fashion way. We can determine the highest frequency on our down lead, (using the “Real Channel”) and use this to calculate our cable loss and choose the appropriate preamplifier to compensate. We can do the same for our distribution system.

Calculating Cable Loss:

I think a good rule of thumb to use here is, (UHF –6dB/100') & (VHF –3dB/100ft). However you can look at the exact numbers for your particular cable on the manufacturer's data sheet.

For any hardware on the line add –1dB insertion loss plus whatever loss or gain that device may have at the frequency of the receive signal.

Add up all your losses and then choose a preamplifier to offset these losses.

Choosing the Antenna:

As a former Broadcast Engineer this is where things begin to depart from the old for me. It used to be easy to estimate what one could expect for field strength at the receiving end using propagation models and any free online service such as tvfool.com

Now we really have no numbers to work with. Signal strength and signal-to-noise ratio are impossible to measure with DTV today.

At this point, the best we can do using what we already know about antennas and TV reception and what we have learned about DTV reception is make an educated guess.

Metro Areas:

It is possible to have too much signal. If you are located close to a transmitting tower, you may need to attenuate these near stations. Overdriving the front end of a receiver creates noise; DTV and noise are a bad combination.

Multi Path in metro areas can also lead to issues. DTV receivers will not tolerate a strong Multi Path signal.

Rural and Deep Fringe areas:

Multi path is a problem here also as in metro areas as well as low signal. These with the addition of any other interference can result in a “Bit Error Rate” that your receiver will find unacceptable.

High-Gain Directional antennas and stacked antenna arrays can help. The more directional the antenna the less susceptible it is to ghosting (Multi Path) and the higher gain will give you more signal strength.

Vertically stacked antennas need to be ½ wavelength of the lowest receive frequency apart on the mast and the interconnect cables need to be exactly the same length. This allows the signal from both antennas to add together in the combiner.

Two vertically stacked antennas will give you near +3dB of gain over a single antenna.

Transmitting Stations in Multiple Directions:

In many rural areas you may find yourself between transmitting stations. You might have stations located in two or three different directions.

In this event, you may need to install two or three different antennas orientated in different directions.

Or, you might want to install a rotator to rotate a single antenna. The trouble here is, every time you rotate your antenna, you will need to re scan the channels with your TV or converter box.

A multiple antenna system might be a better alternative.

However, multiple antennas on the same down lead can lead to multi-path or ghosting issues.

To minimize this, antenna spacing is critical. Space antennas no less than 1/2 wavelength apart using the lowest frequency on the system. It might also be necessary to install traps or filters between antennas and combiners to attenuate multi-path signals.

Band-Pass filters built for NTSC or Analog Television may be problematic when used with DTV. Band-Stop filters might work better until the industry brings DTV filters to market.

In my opinion, many viewers on the fringes have lost Free-Over-The-Air television. As said above, they have watched snowy or otherwise marginal pictures for years and grown use to it. Now, on the fringes, they have lost reception.

Some can get it back with a new re-designed antenna system and others we will just not be able to help.

The FCC has always been an advocate for free over the air TV largely because of the Emergency Broadcast Network now known as EAS.

It will be interesting once all the broadcasters have made the switch what will happen and or adjustments will be made to our new DTV transmission system.

Hello and Welcome to Wholesale Electronics new blog. This is our first post and we are looking forward to hearing from you...

Wholesale Electronics is located in Mitchell, SD and has been in business here for over 30 years. We launched www.weisd.com eight years ago and have since found customers all over the world.

We are very excited to now have a forum for our visitors and customers to share their thoughts and ideas.