FM and TV Propagation and Reception

Question: What conditions need to exist for SPRTV's new TV channels to be available in my home or business?

FM radio and television signal reception is highly variable dependent upon location and terrain.  While a line of sight between a high VHF band television transmitter antenna and a television receiver antenna will assure the optimum signal strength, this is not an absolute requirement. 

Regarding the quality of digital television transmissions in general, unlike the old analog TV signals that were usable even when very weak, digital TV (DTV) signals seem like they are either there or they are not.  Also, digital TV translators are not as powerful as primary TV station broadcast transmitters so a traditional indoor rabbit-ears antenna may not work.  The effective radiated power of SPRTV's Channel 8, 10 and 12 TV translators on Baldy is about 270 watts each.  The KCNC/CBS transmitter at Lookout Mountain, for example, is 1,200,000 watts and many viewers need an outside high-gain directional antenna to get their signal.  It stands to reason that TV translator users in Summit County will probably require an outside TV antenna as well.

Knowing that SPRTV's three digital TV translators are much less powerful than typical broadcast television station transmitters, an unamplified rabbit-ears antenna positioned inside of your home will probably not work.  While it is possible an indoor rabbit-ears antenna at a location close to Baldy may perform properly, given the uncertainty of FM radio and TV signal propagation here in the mountains it is prudent for the prospective TV translator user to adopt an outside TV antenna.

An SPRTV technician is available to visit your location free of charge to determine if over-the-air antenna TV reception is possible.  While the performance of other TV antennas in your neighborhood provide useful data, the best way to know which one will work best for you is to have a technician visit your location and evaluate reception with a standard reference antenna.  For assistance tuning in our TV translators call one of the SPRTV Help Lines, (970) 485-2188 or (970) 453-9293, and ask for Gary Peterson.

Question: What equipment is required to receive SPRTV's DTV signals?

In order to receive SPR's television signals you need a digital-to-analog TV set-top converter box or a digital television set plus a good TV antenna that is pointed toward the Bald Mt. Electronics Site.

While it may be found that an indoor antenna will work for people fairly close to our FM and TV translator site on Bald Mt. (within 4 miles or so) SPRTV recommends a high-gain directional TV antenna mounted outside of the building.  A combination high VHF band + UHF band TV antenna may prove useful if SPRTV adds a UHF TV translator or low power (LPTV) station at some point in the future.

For TV reception using an analog television plus a DTV converter box or a new digital television:

1. Connect the TV antenna to the antenna input on the back of your television or digital-to-analog converter box and then scan for the block of DTV channels.

2. Move the TV antenna to different locations inside and outside of your home searching for the best reception.

3. If your scan locates one or more of the three DTV translators but the pictures are broken up or pixilated you will need a better antenna before you can start enjoying over-the-air digital TV.  You may wish to consult the SPRTV FM and TV Antenna Selection and Installation Guide.

4. If repeated scans find no DTV signals, an SPRTV technician is available to visit your location to determine if over-the-air digital television signal reception is at all possible.  For assistance call (970) 485-2188 or (970) 453-9293 and ask for Gary.

On FM and TV antennas in general, all of the following will usually result in better reception, listed roughly from most important to least important:

1. Point the antenna towards the translator (the importance of this depends on how directional the antenna is). 

2. Move the antenna higher. 

3. Use a longer, higher gain directional antenna.

4. Mount the antenna outside.

5. Use a single run of new RG-6 coaxial cable that's no longer than necessary.

6. Use an antenna preamplifier if you are far away from the TV translators.

7. Use an amplifier if the coaxial cable run between the antenna and TV is longer than 100' and or if a splitter is used to feed multiple television sets.  Make sure the amplifier is a high quality low noise type.

It's not strictly necessary to do all of these things, but each one will help.  For example, if you cannot mount the antenna outside it still helps to have a directional antenna and put it as high as you can, like in an attic.

A Bit More About Radio-frequency Propagation

Reflection and diffraction play a role in electromagnetic space-wave propagation allowing reception to occur even when a line of sight does not exist.  In regards to distance, when this is doubled the strength of the signal is reduced to one-quarter of its former value.  In other words, the radiated power from an antenna is reduced as the square of the distance from its source.  This is known as the inverse square law.

The lines represent the flux emanating from the source.  The total number of flux lines depends on the strength of the source and is constant with increasing distance.  A greater density of flux lines (lines per unit area) means a stronger field.  The density of flux lines is inversely proportional to the square of the distance from the source because the surface area of a sphere increases with the square of the radius.  Thus the strength of the field is inversely proportional to the square of the distance from the source.  Source: http://en.wikipedia.org/wiki/Inverse-square_law .

Another factor that effects signal strength is antenna shielding.  Simply stated, when an antenna is positioned indoors the surrounding structure forms a barrier that the incoming FM or TV signal must penetrate.  The degree of attenuation depends upon the structural material.  (See Shielding Theory and Transfer Functions in EMC Shielding Design for additional words on this subject.)