# OTA Hook-up with Multi-Switch & Diplexer



## sweetchloe (Aug 23, 2009)

I'm trying to hook-up OTA to get local channels (DirecTV does not have local channels in my area). If I hook-up my unidirectional antenna directly into my TV I get reception. When I set the antenna in the attic and use a DTV 3x 4 Multi-switch with the antenna and DirecTV satellite inputs and then sent an output down the single wire in the wall to a Diplexer with the Sat out to my DirecTV box and ANT out to my TV, I do not get a TV signal. I do get the satellite signal and reception.

Can anyone tell me why and what else I can try to get this arrangement to work.

Thanks


----------



## BattleZone (Nov 13, 2007)

Likely the insertion loss from the diplexing is causing enough signal loss to fall below the threshold needed to get a picture. You either need a pre-amp or run a straight line to the tuner.


----------



## dave29 (Feb 18, 2007)

Jim5506 said:


> Satellite multi-switches do not pass OTA frequencies.


Some older Multiswitches did. They even had an input for ota.


----------



## Jerry Springer (Jun 24, 2009)

Over the air television is mostly UHF. Some stations that were UHF were moved down into the VHF while other VHF stations were moved up into the UHF.
To complicate matters, some VHF stations were moved up to the UHF - for their temporary transmitters and then moved back down to the VHF once the analog transmitters were shut off.

In the analog days, there was 2 effective transmitters for television.

1- the video was AM - amplitude modulation, at a high amount of power. They did this because AM will travel long distances and it requires more power to over come noise generated by electrical devices and storms.

2 - the second was FM for the audio, which was at a lower level of transmit power, because FM will travel long distance with less interference from electrical noise.

When they switched the signal to digital, the allowable amount of transmit power was lowered for the VHF stations and raised for the UHF stations.

UHF needs 4 times the power to transmit 80% as far as VHF. 

Instead of taking away the VHF section of frequency's,' the FCC took away the high UHF frequency's. What this did was instead of us only needing one antenna, now we need two. One for the UHF and one for the VHF.

To complicate matters, UHF is mostly line of sight. Use a flashlight as a example. If you shine a flashlight up in the air, it does not shine down into a hole - valley. If you shine it at the center of a building, it does not come out the other side, nor does it go around corners.

Like a beam of light, sooner or later it stops bouncing off the atmosphere and travels out into space. Which means that once you get past the normal line of sight, say - 40 miles. Then the only way you can receive it is if it bounces off the atmosphere. When it quits bouncing - it goes out into space and you have no more signal.

VHF was ground following. It did go up one hill and down the next. It did go through buildings, it did go around corners. It did travel long distances with the right amount of transmit power and the right height of the transmit antenna. You didn't even need much of a antenna to receive it.

To receive UHF signals properly, you need a good directional UHF antenna, mounted outside as far away from anything that makes electrical noise. 10 feet above the roof is the most common install. UHF signals are blocked not by the building materials - unless that building material is made out of metal.

Metal roofs and metal walls blocks UHF signals. Asphalt shingles and wood do not block signals, but the flashing as narrow as a piece 6 inches wide can.
As can the moisture under your shingles and the moisture inside of the wood.

Trees will also block your signal and the leaves will block your signal, due to the fact that there is moisture inside of the leaves. Hills and mountains will block your signal as will a building 4 or more stories high.

Moisture inside of your coax or connector wire will also block or ground out your signals.

Just like a beam of light, if you shine your light north, it will not shine south.

If you point your antenna in the wrong direction, by even so much as 10* degrees in the wrong direction, you will have little or no signal from a fringe station.

The question then becomes, how much is 10*

One day I was working on my antenna and I had to take it down. I used a Sharpie Marker to make witness marks so I could re install the antenna in the exact same location as before. Due to the fact that I used a digital rotor and I wanted my memory to remain the same for the programmed buttons.

Just half the thickness of the line drawn by a new Sharpie marker was 10*

A really good antenna might get you as much as 30* in either direction from the center of a signal for a fringe channel. That means that it has to be pretty durn close to being pointed in the right direction to receive the signal you wish to watch.

If the station is less than 40 miles and if it is on a low enough UHF and if it transmits on lot's of power, say 5000 Kw, you might be able to get a good signal 280* around the antenna.

But putting a Omni Directional antenna inside of the attic, is like putting a lamp under a bushel basket and expecting it to shine light out into a room.

Omni directional antenna's only works if the signals you wish to receive are less than 20 miles from your location and if you keep your wire runs as short as possible and if you mount it outside with a clear unobstructed view of the horizon in the direction you wish to receive..

Diplexers are inefficient and loose as much as 50% of the signal just inside of the Diplexer. Add to that the line loss of all the wire going throughout the house and pretty soon, even a good signal will be deteriorated down to nothing.

I would recommend a amplifier, The best is to only use a amplifier as close to the antenna as possible with the highest gain in the area that you are interested in receiving (UHF) with the lowest possible noise and both at a reasonable cost.

The KEY is that you want a relative "good" level of input at your receiver 
(TV) with the minimum noise.
A mast mounted amplifier (doesn't matter if it is called a amplifier or 
preamplifier) is the best when you are in a remote area.
In theory it is best if you amplify a "good" signal to a higher level than 
a "poor noisy" signal to a higher level. When you start out with crap and 
amplify it you just end up with more crap.
All cable has loss and the higher up that you go in frequency (VHF to UHF) 
the more loss that the cable has.
If you start with a low level signal at the antenna and then butt it into 
coax cable you are going to have less come out at the end than went into it 
from the antenna. The amount of loss depends upon a number of factors, 
cable type and cable length are the two most important. Cable is rated in 
db loss per 100' at X MHz (frequency). RG-6 cable is the cable most used 
in TV use. Like all things there is good RG6 and not so good. Belden 
1829AC Coax - Series 6 has a loss of 4db/100 feet at 500 MHz (TV Channel 
18)
Channel 32 is 580 MHz Channel 52 is 700 MHz a 5 db loss At TV channel 2 
the cable would have a loss of 1.4db. So at channel 18 you loose more than 
1/2 the power in 100' of cable between the antenna and the TV.

Duplexers by design have a 3.7 db loss (a little more than 1/2 the power lost). If your were in a high signal area for the over the air TV a duplexer would be fine, but where you are you need all the signal at the receiver (TV) that you can get. If you have a mast mounted pre amp that will compensate for the loss of the cable and the splitter you might still be ok.


----------



## harsh (Jun 15, 2003)

Is your antenna amplified? If so, it is likely that the diplexers are cutting off the amplifier power.

It wasn't entirely clear from the original post that the diplexers are between the multiswitch and the satellite input on the D* receiver. Is this the case? The inserting diplexer must be installed on the corresponding multiswitch output and the extracting diplexer must be installed at the D* receiver satellite input.


----------

