ATV RESEARCH Inc. MATV-SMATV Systems Design

Basics of
MATV - SMATV SYSTEMS DESIGN

The purpose of this site is to assist the typical electronic technician through the basic fundamentals of commercial and residential Master Antenna and Satellite Master Antenna TV headend design and distribution principles.

This is not intended to replace the many well written technical books on the subject but rather it is a practical, down-to-earth approach for the busy tech who needs some quick assistance in defining and refining some of the fine details of MATV/SMATV installations.

Our primary goals will be to walk you through some typical headend systems explaining the whys and wherefores of each piece of equipment as well as possible options that may be required, either for budgetary or technical reasons. In addition, we will discuss the different methods of distributing the TV signals through the complex, once the headend has been completed.

LET'S GET STARTED.

Let's first divide out some of the more common headend systems and attempt to rank them as to cost and performance. Let's call them;

1. BASIC -- Systems using broadband amplifier techniques
2. STANDARD COMMERCIAL -- Systems using single channel AGC type amps
3. DELUXE COMMERCIAL -- Systems using single channel processors

FIG. 1 - Typical Standard Commercial headend System Incorporating Single Channel "Strip" Amplifiers.

A Plain Vanilla System to get us started!
Since most techs have handled dozens and dozens of the basic broadband amplifier systems, that are so typical in most residential installations, let's pass over these systems (at least for now) and get right to the meat of the typical headend that makes up the bulk of most mid-range motel, apartment complexes, retirement homes and the like. (Note: The fact is, some of the more elaborate residential systems may even take on similarities of this "standard" type system.)

Using Fig. 1 as a sample, let's walk through the system from antenna to trunkline output and briefly look at each component.

Selecting the antenna(s)
Most systems involve both VHF and UHF that can be received from a single broadband U/V antenna. This, of course, assumes that the signals all come from basically the same direction. If not, or, if some signals are local and others are fringe, then more than one antenna is necessary.

Whether we are dealing with one or several antennas, the basic idea is to get the signals properly divided out to feed the individual pieces of equipment. It goes without saying, that multiple antennas greatly simplify the headend since we have a feed for each channel. In our case (shown in Fig. 1) we have chosen to use only one antenna in order to show the procedure that works nicely for dividing out each signal with the least amount of db loss.

Separating the UHF from the VHF
Our first task is to divide the UHF from the VHF...this is accomplished with a UVSJ (Uhf/VHF separator/joiner). This item is a passive device and is manufactured by Pico-Macom. Similar units are available from other manufacturers. Incidentally, it also works equally well in the opposite direction for joining UHF and VHF signals. The reason the UVSJ is chosen over a standard 2-way splitter is the reduced losses...typically less than 1 db as compared to 3-4db for a 2-way splitter.

Separate the LOW-VHF Band from the HIGH-VHF Band
Next we need to separate out the low band(2-6) VHF signals from the high band (7-13)...this is done with an HLSJ (Hi/lo VHF separator/joiner). Again, this item is manufactured by Pico. It also works in a bi-directional fashion and is equally popular as a hi/lo VHF joiner.

Making certain we have adequate signal levels after separating bands
If we have more than one signal in any one of the three bands (UHF, HI VHF, LO VHF) then we use a 2-way, 3-way or other appropriate value of splitter to further break out our signals so that we have a separate feed for each related amplifier or converter. There may be times when the levels of the signals will not be strong enough to offer adequate levels once they are split. If this is the case, a small amplifier (say 10db) may be required prior to making the split-out.

The Single Channel Amplifier (known as the "strip-amp")
Pico-Macom appropriately has named their single channel amplifiers according to the band they operate in...for example, a Low Band Single channel amp is called an LBS...High Band is HBS and Mid Band is MBS. As shown in Fig. 1, once the vhf signals are properly divided out they are next fed into the single channel amps (also referred to by most technicians as "strip amps").

Down Converting UHF signals to VHF or Midband channels
Note that the UHF signals do not go directly into the strip amps...but instead go through a crystal controlled UHF to VHF converter (in our example this is the Pico Model XUV). The reason for this is that most commercial systems have fairly lengthy trunklines and to attempt to distribute both VHF and UHF signals throughout the complex posses numerous problems in maintaining proper signal balance between the two extreme ends of the bands. It is much easier to convert the signals down to UHF and is a very normal practice. Once the signals have been converted to VHF they are then sent into the same type of single channel amps as we used for the VHF channels.

The real reasons for single channel amps
One of the main attributes of single channel amplifiers is that they incorporate AGC (Automatic Gain Control) which assists in maintaining a "balanced" system. This is extremely vital when working with a large distribution system and especially if you are working with "adjacent" channels. In addition to the AGC feature, they also incorporate single channel input and output filtering for the cleanest performance. In the past these amplifiers were many times "looped" from one amp to the next like Christmas lights...thus eliminating the high losses of a passive combiner or the necessity of a separate trunkline amp.

Combining the signals...and watching our signal levels!
Today, we see less and less looping of strip amps and less use of passive combiners. More systems are being designed today with the "active" combiner...one with actual gain, rather than loss. However, when feeding active combiners it is necessary to be aware of the maximum level that can be fed into the unit. This will vary from manufacturer to manufacturer and also will depend on the total number of channels involved.

Since the smallest single channel strip amps are typically 66db units, you will need to reduce the level more into the range of 30-40db to feed most active combiners. We have chosen the CHC-16 by Pico. It is a 16-channel unit with approximately 12db of gain.

Adding the Modulator for in-house VCR, bulletin channel, satellite channels and the like...
Many MATV systems also have separate modulated inputs for a variety of reasons...it could be a poolside camera, a bulletin board channel or a VCR channel. In the case of an SMATV system, it obviously would include one or more channels to carry the satellite programming. We show a very common modulator made by Pico, their model PCM-55-(ch). It is a single channel, filtered and crystal controlled unit with 55 db maximum output. Again, some padding is generally required before feeding it into the combiner.

Planning for future expansion
In our example, we have lots of spare inputs on the combiner. From this standard system it is easy to expand either modulated channels and/or off-the-air channels. Once the basics are down pat, it's just a matter of wiring in more of the same.

FIG. 2 - Typical Deluxe Commercial headend System Using Channel Processors

The Deluxe System ...sometimes even simplier than the "standard" systems!
Compare Fig. 2 with the previous "Standard" system and you will note very few changes actually have transpired between the two layouts. The "Deluxe" system in Fig. 2 has actually become less involved. Note that we no longer require a separate UHF/VHF converter for down converting the UHF signals since the processors are "any channel in" and "any channel out".

Why a Processor over a "strip amp"??
As just mentioned, one thing that a processor will do for you is provide a quick and easy way of converting any input channel to any output channel. This is probably one of the big reasons for processors...especially when working with channels that need to be shifted.

In addition to down converting UHF, it's sometimes also necessary to convert certain strong, local off-the-air VHF channels to a different VHF channel. If these channels are left on the same channel they will occassionally cause an undesireable ghosting caused by some direct ingress of signal into the TV set that is not timed the same as the cable signal.

When using processors to do the V/V conversions, it's all done in one unit rather than a VHF/VHF converter feeding a single channel "strip" amp.

Other reasons for the more costly processors includes improved circuitry for optimum AGC gain control, better rejection of off channel signals through the use of SAW type filtering, better signal-to-noise ratio and so on. The old adage is certainly valid when it comes to the processor vs the single channel amp...you get what you pay for!

An upgraded modulator is now in order...
It seems only logical that if we go with the technically better processors that incorporate SAW (Surface Acustical Wave) type filtering then we should also use a comparable grade modulator that also incorporates this type of filtering. The Pico model M600 was chosen for this illustration, however numerous other models from Pico, BT and Holland are also available, each with it's own particular attributes that may or may not be important in a specific installation. The most important issue for us to consider in this discussion, is not the exact brand but to keep in mind that when working with a higher class of clientele, you generally upgrade the entire system...processors, modulators, antennas, etc. The goal is to give a substantially improved system with greater performance and higher long term reliability. Whether we use agile or fixed channel processors and modulators is primarily a budgetary consideration. Obviously the more field agility in this type of system, the easier it is to maintain, modify or update.

The rest of the story...
As is evident from the comparison of Fig. 1 and Fig. 2 ...there really isn't much difference between a "standard" and a "deluxe" system other than the processors in place of strip amps and converters and the general overall quality of equipment used. Basically, all the same items are required in both cases...it's just that with a bigger budget we can go with technically better equipment. Even the basic method of handling the dividing out of the antenna signals and the balancing of levels prior to combining all remain pretty much the same.

Minor little things do, however, make a big difference in the more premium systems. For example, the addition of channel deletion filters, FM traps, audio modulators, etc all add to the overall value of the system. Each situation usually has to be approached on a one-to-one basis, depending on the individual customer's requirements.

It's beyond the scope of this site to cover all situations but we do maintain a consulting division here at ATV Research for special situations. Just contact our sales office...they will be more than happy to consult with you and show you your options.

FIG. 3 - THE BASIC BROADBAND AMPLIFIER SYSTEM

Last but not least...The Basics of a BASIC SYSTEM!!
When it comes to many residential systems (as well as some of the extremely small budget-minded commercial systems) about all that a tech can work with is the simple basic broadband amplifier approach like the one shown in Fig. 3. We've purposely left this system till the last...after all, it's so down-right simple, why should we give it top billing...right? ...Who are we trying to kid? Sometimes the so-called "simple system" is really the hardest...especially with regards to the technician's time and energy in getting it up and running in a satisfactory fashion!

The "Do-Everthing" Amplifier
Just stop and think what we are asking of this one-amp system...consider the number of TV channels in many areas; think about the wide range of signal levels and the tremendous span of frequencies from channel 2 to UHF channel 69. I'm sure you'll agree, these three factors alone make it quite a challenge to obtain anywhere near ideal performance out of a single amplifier system! Yet, it's done, over and over again throughout the country everyday.

Nevertheless, when that's all the customer can afford or will allow, then that's what you the tech has to attempt to work with. Fortunately, we have a number of amplifiers that make our jobs a little easier than past times.

Dealing with two antennas.
To illustrate how a UVSJ can be used equally well as a joiner, we've created this system with a separate UHF antenna. The two signals are joined with the UVSJ (wired as a joiner). The VHF and UHF are fed into the broadband via a single cable.

We could have been dealing with low and high VHF antennas...if so, we would have used the HLSJ as a joiner. Also, there are times when an undesireable signal will be picked up from the back side of the unwanted antenna and thereby cause ghosting in the picture. To prevent this a special trap can be ordered to place in the antenna line to prevent this ingress. Likewise, unwanted FM signals can be trapped, when necessary.

Inserting a local modulated channel

One additional situation that occurs regularly, even in the simpliest of systems is the necessity to insert a modulator...for a satellite, VCR, door camera, etc. Again, referring to fig. 3 we have shown the insertion of a UHF modulator of the popular BT HAVM series or Holland HMM-10 series.. These modulators put out about 25db and generally can be inserted after the broadband amp simply by using a splitter backwards as a joiner. (When using a splitter backwards, of course, be certain to mentally relabel all ports so that the two outputs become the two inputs and the former input is now the combined output.)

Some Favorite Amps...
A couple favorite choices for good broadband amplifers is the Channel Plus DA500 series, BT ACA-35-1000 and the Pico PDA-30PR. These amps have extremely good dynamic range and can handle signals from both extremes...from very weak to VERY STRONG! The DA500 is an 18db fixed gain, 1000 Mhz amp. The ACA-35-1000 is 35db and the PDA-30PR is 30db....all are capabile of handling signals up to 1000 Mhz. If you have a wide range of signals (i.e. -20db to +30db) you would be wise to consider one of these amplifiers. If you go with a "nickel-and-dime" type of amp you may easily waste a ton of time on the job site and still never have the customer very happy.

If you need something a little more economical and with separate gain controls for each band then why not try the Pico-Macom TA-36. It's really more gain than many jobs need but it does have individual low VHF, high VHF and UHF band gain adjustments...something that is very helpful in preventing overdrive and cross-modulation. Also it has two switchable FM traps...a very important feature should you encounter strong FM signals (especially in the low end of the band) along with a channel 6 TV signal that you are trying to also receive.

Next in line for amplifiers include some of the Blonder Tongue Vaulter and Suburban series of antenna mast-mounted amplifiers that typically are in the $50-$60 range. These antenna type pre-amps offer reasonable performance over a moderate range of signal levels and come complete with the power inserter and power supply. This approach is particularly nice when the antenna is phycially located some distance from the distribution point.

Low Cost Broadbands...your last resort!
Of course, we can't completely discount the low-end amplifiers. There are parts of the country that are blessed with very few channels and those may even be in the ideal db level range. If you are this fortunate you can easily get by with many of the $15-30 type amps. Typical models might include the Pico-Macom TA-12, TA-15 and TA-25 amplifier series. These amps exhibit 12db, 15db and 25db respectively. Don't attempt to use these amps however, if you are working with a lot of channels, some of which are strong enough to cause overload. Cross-modulation and other instability problems will probably plague your installation and make it less than ideal. Use these lower cost amplifiers judiciously and you can occasionally fair out okay.

NEXT - Click here to learn how to distribute signals throughout a commercial establishment or a residence using the principles of drop-tap or home-run wiring.

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