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RECEPTION PROBLEMS

Introduction

 

Nearly half of all reception problems are due to deficiencies or faults in the television/digital receiver, the aerial lead or the aerial. The following information will help you to check whether the problem you are having is due to one of these causes.

Portable television sets fitted with an inbuilt aerial or a set-top aerial are prone to reception problems. Where these reception problems are experienced, the set should be fitted with an externally mounted aerial. Many of the existing cures to solve analogue reception problems can also be adopted to cure digital problems. The following advice applies to an external aerial installation.

 

Initial checks of your equipment

 

  • Check that your mains plug is wired correctly with tight electrical connections, and that it is pushed firmly into the socket.
  • Check that you are able to get a good steady picture at the times when the reception problem is not present.
  • If any reception problems are apparent ask your neighbours if they have the same or similar type of problem.
  • If a new aerial has been installed, it may be wise to adjust the tuning of each channel manually on the TV, or rescan for digital channels via the appropriate menus on the set top digi box.
  • Check that your aerial lead appears to be in good condition, with its plug firmly attached to the lead and making good contact when pushed into the aerial socket on the back of the TV set or digi box.
  • Also check that the cable is of the best quality, copper braid with copper or aluminium foil type cables are generally a minimum requirement, especially for digital reception.
  • Ensure that there are no tight bends or kinks in the coax cable and also ensure that the cable is not routed close to any electrical cables or items such as thermostats or motors etc.
  • Check the wind or wildlife i.e. large birds (perching) have not moved your aerial. A glance at neighbouring aerials will generally show an approximation of the correct direction of the local transmitter.
  • Check that you have the right aerial for your area. If you are in doubt, consult your local dealer or aerial installer.
  • Hotels, blocks of flats and some housing estates use a communal aerial, which you cannot check yourself. You should contact the landlord or his nominated contractor.

The following are typical examples of reception problems and help in curing such problems

Questions

 

I have tried all of the above suggestions and its still not right what now?

 

Q.     The aerial range is extensive, is there a guide to selection?

A.     The site search also includes the facility to enter a postcode search for your location. This will gives details of possible transmitters and the recommended products.

 

 


Q.    How do I order your products?

 

A.    Products can be ordered by one of the following methods:-

  • If you are an end user then either contacting your local professional installer or select the buy icon on the product pages.
  • If you are trade installer and wish to find details of your local wholesaler,  please fill in the appropriate details on our contact.

 


Q.    Digital TV Reception Problems

Poor Digital

Very Poor

Poor Digital Reception (notice break-up at bottom of picture)

Very Poor Digital Reception (this could be due to weak signal or interference)

Unlike the old analogue reception problems where the various patterns tell us what the problem is, digital reception generally has the same screen output for all reception problems be it weak signal or radio interference. Usually, cures for the old analogue reception issues will also work for digital reception problems.

Essentials for Good Quality Digital Reception

 

  • Use a good quality benchmarked aerial (follow the aerial manufacturers cable route recommendations) or as a minimum, an aerial with a corner type reflector with fitted Balun.
  • Use good quality double-screened coaxial cable (preferably benchmarked types) and good quality connectors.
  • Avoid splitting the signal, use distribution amps if reception in more than one room is required.
  • Use masthead type amplification; avoid set back type amplification as the main method of distribution (the signal will have degraded by the time it reaches the set back, if it is not pre-amplified).
  • Take care when running the cables, avoid tight bends (kinks) and do not run the cable alongside any other cable, especially mains/electrical cables.
  • Keep cable connections and lengths to an absolute minimum; if possible take the cable through the wall and directly into the receiver rather than connecting via a wall plate. (If wall plates are to be used, use screened versions).

 

A.     What you can do?

  • If the picture is breaking up constantly or no channels are found, the signal is too weak and will need attention, try the following:
  • Ensure that the aerial is benchmarked, or as a minimum, is the corner reflector type with a Balun fitted.
  • Check the aerial polarity (horizontal or vertical).
  • Ensure that the aerial is aligned to the transmitter.
  • Ensure that no obstructions are directly in front of the aerial, i.e. trees, chimneystack (or water tanks in loft installations).
  • If necessary increase the installed height of the aerial to avoid obstructions.
  • If loft mounting is unsuccessful, try installing the aerial outside as high as possible.
  • Check all cable connections and ensure that the cable is good quality double-screened type.
  • Ensure that interconnecting leads i.e. fly leads and Scart leads are good quality screened types.
  • Ensure that the aerial is of the correct group type i.e. A, B, CD or WB. (For example, if a group ‘A’ aerial is installed, digital channels within group ‘CD’ may break-up or may not be received at all).
  • If after everything has been checked, the signal is still weak, try a higher gain aerial and/or a pre-amplifier.
  • If the picture breaks up when an electrical switch is made, i.e. thermostat or light switch, the problem could be the shielding effectiveness of the coax cable.
  • If the cable is old, replace it with good quality double-screened cable (preferably benchmarked versions) on all cable routes.
  • Ensure that the cable is not running alongside other cables especially electrical cables.
  • If the picture breaks up intermittently with no electrical switching taking place, the cause could be radio interference i.e. Tetra or PMR (Private mobile Radio)
  • Again, use good quality double-screened cable (preferably benchmarked versions), again this includes interconnecting cables, i.e. fly leads and Scart leads.
  • Check all cable connections.
  • Try re-positioning the aerial to a position that could be shielded from potential interference but will still be able to receive the TV signal.
  • Install a Tetra filter or an amplifier with inbuilt Tetra filtering.
  • Inline passive filters and amplifiers are now available with Tetra filtering.
  • If after attempting all relevant cures the problem still exists, the problem could be the TV, especially if it is an old model (older models may not have the screening effectiveness as that which is found on modern units).

The above recommendations will in most cases most digital reception problems.

 


Q.   

What is Ghosting?

Ghosting

Normal Picture

An example of "Ghosting"

Why Ghosting Occurs

This is the sort of picture you may have seen with analogue TV signals is reflected from a large building or other structure in your locality.

The problem is caused because both the direct signal and a reflected signal from the transmitter are being received. Because the reflected signal travels a greater distance before it arrives, it produces a picture shifted to the right of the normal picture.

Digital television uses a modulation system that has a lot of protection against multipath reception (ghosting). In most cases where ghosting occurs on an analogue picture, the digital reception will be ok. However, if the digital reception seems be affected due to the ghosting seen on the analogue pictures, the cures below for analogue ghosting should in turn cure the digital reception too.

 

A.       What you can do?

  • A better picture can usually be obtained by altering the direction in which the aerial is pointing.
  • Adjusting the height of the aerial is usually the best method to adopt.
  • If ghosting is severe and persistent, a more directive aerial such as a high gain aerial or a log periodic type could be used. Another aerial that has been known to eliminate ghost signals is a Grid type aerial.

 


Q.    I have a poor picture (Weak signal) on Digital

Weak Signal
Normal Old Analogue Picture
Progessively Weaker Old Analogue Signal
Weak Signal

A normal Digital Picture

A Weak Digital Signal

The picture on the left shows a normal picture for comparison. The pictures on the right are the type you will receive if you are far away from the TV station or if there is a building or hill between you and the TV station. The same effect may be caused if you live in a valley where you are shielded from the signal.

Each TV station has a defined service area where the strength of the TV signal is adequate to give good reception. Just beyond the boundary of the service area is a fringe area where the signal will be weaker and reception quality will be poorer.

 

A.     What you can do?

  • Once you have checked that your weak signal is not due to a defective or badly pointed aerial, poor connection, broken or disconnected lead, you could improve the signal strength by:
  • Changing the coax cable to a double-screened type.
  • Increase the height of the aerial if possible.
  • Install a higher gain aerial.
  • Installing a masthead or setback amplifier to boost the signal.
  • If there are many splits of the signal around the home using standard coaxial cable splitter units, it could be that the signal has been reduced too much, in cases where 2 or more TV sets are to be fed it is recommended that a distribution amplifier be used rather than splitting the signal. This method is especially essential for digital reception.

 


Q.    I have two channels or two images at the same time on my TV (co-channel interference.)

Cochannel Interference

Two Examples of Co-channel interference

A distant transmitter usually causes co-channel Interference, because it is transmitting on the same channel as the local transmitter where the main signal is being received from. This problem is rare, but unfortunately can happen due to the channel allocations of the vast amount of transmitters nationwide.

 

Co-channel interference can affect digital reception by overloading; in this case the following analogue cures could cure the problem.

 

A.     What you can do?

  • It can be that the aerial installed has a very large viewing angle/beam width; an aerial such as a high gain that has a narrow viewing angle could solve the problem.
  • Adjustments in height and left to right (azimuth) as per the ghosting example could solve the problem.
  • If the problem is severe, it could be that the location of the property is on a bearing with the required transmitter that will always have the problem. In a case like this it is often required that the aerial be pointed in a different direction to receive from an alternative transmitter. This alternative transmitter could be further away from the original; therefore amplification or a higher gain aerial may be required.
  • Monitor the polarity of the aerial when searching for an alternative signal as the alternative transmitter may transmit a vertically polarised signal; this means that the orientation of the aerial will need to be vertical.

 

Q.    I have lines or squares appearing across my screen. (Electrical interference)

Lines

Two Examples of Electrical/Impulse Interference

Because nearly half of all TV reception problems are due to deficiencies and faults in the TV set, the aerial lead or aerial, you should ensure your equipment is in good working order before checking for interference.

Many interference problems, however, can be traced to domestic electrical equipment or appliances in your own home or a neighbouring property.

Electrical/impulse interference is usually more noticeable with digital reception. The reception will appear to be breaking up or look like a mosaic pattern. If this occurs the best solution is an aerial with a balun and a double screened coaxial cable. Analogue cures below could cure the problem. If this type of interference appears on digital reception all the time, and also freezes, the reason is that the signal is not strong enough.

 

Some causes of electrical/impulse Interference - Type 1

  • Vacuum cleaners
  • Fans
  • Electric drills
  • Electric trains
  • Electric razors
  • Sewing machines

 

Some causes of electrical/impulse Interference - Type 2

  • Automatic switches
  • Central heating thermostats
  • Refrigerators
  • Freezers

 

This type of interference is normally caused by switches or thermostats especially thermostats in central heating systems. It appears on the screen as a dense white band of spots or on digital pictures as a mosaic effect, but only for a short period of time.

 

How to find the source of interference

 

In many cases the source of the interference will be obvious because the interference appears when an item such as an electric drill is being used. Where the source of interference isn't obvious, try to locate it by switching off everything in the home one item at a time while another person monitors the effect on the TV screen.

Alternatively, if you have a portable radio and can hear the interference on it, take the radio from room to room to find where the interference is loudest.

All modern electrical equipment is manufactured to regulations requiring that interference suppressors be fitted. If you find an appliance causing interference and the appliance is still under guarantee, send it back with a request that it be put right. Otherwise, ask an electrical dealer to fit a suppressor to it. Under no circumstances should you attempt this internal modification yourself.

 

A.       What you can do?

  • Always install an aerial with a balun.
  • Combine a balun fitted aerial to good quality double-screened type coaxial cable.
  • Avoid coupling joints in the cable; always aim to have one solid piece of cable to each outlet point.
  • Install screened accessories such as wall plates.
  • Do not run coaxial cable near to any source of electrical interference such as a thermostat or a motor.

 


Q.    There is a strange pattern on my TV. (Radio interference)

Radio Interference

 

Radio transmitters are used for communication by radio amateurs, radio taxis and many other licensed and authorised services. Strong transmissions from any of these sources could affect your TV reception.

In many cases there is no fault with the radio transmitter and the radio operator is not to blame. The problem could occur because the TV set is not designed well enough to resist signals that it should not receive. In such cases, the TV set is said to be lacking in immunity.

 

A.    What you can do?

  • You can cure many cases by fitting a simple plug-in high-pass filter between the plug on the end of the aerial lead and the aerial socket on the back of the TV set. A variety of suitable filters are available and your dealer will advise you which ones to try.
  • If the filter does not work, the TV set could require an internal modification to improve its immunity to interference.
  • Many aerials have good out of band rejection performance, so a change of aerial to one with good out of band rejection may be worthwhile.
  • Also many masthead and distribution amplifiers have filters fitted, so a change of amplifier to one with included filters could also help.

 


Q.    TETRA interference

TETRA Interference

This image shows how a strong TETRA transmission could affect your TV reception. TETRA interference on Digital pictures would look like the mosaic effect often found with other types of interference.

 

A.    What you can do?

  • Many aerials have good out of band rejection performance, so a change of aerial to one with good out of band rejection may be worthwhile.
  • Re-positioning the aerial would also be a good idea, even if it were only the height and azimuth that can be adjusted.

 

Install a simple passive TETRA filter or if an amplifier is required install one with TETRA filtering included.

Refer to the FAQ on TETRA Interference

 


 

Q.   

 

This image shows an LTE interference on Digital pictures would look like the mosaic effect often found with other types of interference.

 

A.    What you can do?

 


Q.    Do It Yourself

         In areas of weak signals the use of Double Screened cables may be beneficial, as this will help to reduce signal loss and degradation of picture quality.

  • Popping and Crackling on Nicam Stereo sound can be caused by lack of signal. Changing to a a higher gain aerial such as a Super Range 18 element or a high gain multibeam aerial such as one from the DMX or JBX range may resolve this problem.
  • Mounting aerials indoors in your loft will reduce the available signal. Always try to mount an aerial outdoors for the best results.
  • Trees can cause a signal to be reduced when the leaves return in spring. They have a slow, gradual weakening effect to the picture. The picture may "Come and Go" as the tree sways in the wind. An aerial should be positioned so as to look around or over any trees.
  • If fitting more than one aerial to a mast always keep them as far apart as possible. Aerials mounted too close together may interfere with each other.
  • For optimum results it is advisable to fit an aerial which is designed to work specifically on the appropriate group for your area. Transmitters are normally polarised horizontally for a main transmitter, or vertically for a relay transmitter.

 

UK UHF TV Channel Groups

 

Band

Pre LTE:800

Channels

 Pre LTE:800

Frequency (MHz)

Post LTE:800

Channels

Post LTE:800

Frequency (MHz 

Colour Code
A
21-37
470-606
21-37
470-606
RED
B
35-53
582-734
35-53
582-734
YELLOW
C/D
48-68
686-854
48-60
686-790
GREEN
E
35-68
582-854
35-60
582-790 
BROWN
K
21-48
470-694
21-48
470-694 
GREY
W/B
21-68
470-854
-
 -
BLACK
-
 -
21-60
 470-790
WHITE 

 

Q.    I have tried all of the above suggestions and its still not right what now?

In most cases problems can be cured with slight adjustments to the installation. However it is possible to get carried away with all the little tweaks here and there. If it is proving difficult to achieve the best reception possible and everything has been tried, it may be worthwhile to call out an experienced engineer, it is recommended that a CAI (Confederation Of Aerial Industries) registered engineer be used. It may be that the problems you are having are common in the area and the engineer may know a common cure.

Also in most cases, digital reception problems can be cured by the same methods adopted for analogue reception problems, key components for a successful digital installation are a good quality high gain aerial (preferably a CAI benchmarked model), good quality double screened cable and good quality screened outlet plates (if used). In addition to this all cable connections should be kept to a minimum and be tight and correct.