Rover HD TAB 7 Evo "Tablet" Analyzer
Rover HD TAB 7 Evo "Tablet" Analyzer
An analogue field strength analyzer will not resolve complex digital TV reception issues. For example an analogue C/N ratio is simply a measure of the ratio of the peak video carrier over the noise in the channel, over the system's bandwidth that is expressed in dB. This type of measurement (via an analogue analyzer) may be achieved on a digital channel – but an analogue analyzer will never provide vital measurements of digital TV signals.
Unlike analogue video, QAM modulation not only utilizes Amplitude Modulation, but also Phase Modulation. Simply measuring the carrier level relative to the noise level does not take into account any phase noise that may also be present in the digital signal. The Modulation Error Ratio (MER) is a crucial measurement, and without knowing the MER level - an installer will fail to gain personal satisfaction, including loss of sales and community standing.
For some digital TV antenna installers achieving good before and after Error Correction levels is their main objective. From my experiences stable before and after error correction levels e.g. less than 10-8 being observed for five minutes may suggest good MER levels. However I have never relied upon error correction levels whilst conducting a site test. What I rely upon is gaining the best possible safety margin by achieving MER levels that average at least 28 – 32 dB for all received carriers.
From time to time distributors of digital TV signal analyzers offer significant discounts for a quality analyzer that provides data measurements such as Digital Power, Noise (Safety) Margins, MER levels, Spectrum & MER scans, Echo Detection, and Constellation Scans that are all vital features of an installer’s field strength analyzer if you wish to solve complex reception issues, gain credibility, and promote your business status. These offers frequently arise near the end of the financial year as an asset write-off, and when there is an upgrade of analyzers that feature improved technology, micro surface-mounted components, and range from $2,500 to $5,000.
Unfortunately Terrestrial Digital Television R.F.I. is a common issue that will test the skills of a TV antenna installer. By now experienced installers should be aware of the types of R.F.I. that exist, be able to recognize the possible source, and rectify such issues. However there will always be digital reception complaints that will require your supreme skills.
Should you receive an R.F.I. complaint that is being emitted from outside your client’s property, it is difficult to rectify and your client plus yourself decide to request the help of the A.C.M.A Investigation Services - an on-line form is to be completed. It is best that the installer prepares the on-line form, provides all details including the name etc of the client, plus your analyzer’s data level measurements e.g. digital power, MER, SNR/CNR, before & after BER levels.
TV antenna installers will be aware that distributors of TV antenna equipment stock Band Pass filters to minimize the input levels of Telco 4G frequencies. The filters are either included in masthead amplifier circuits or are available as specific filters for Blocks A to E (174 to 694MHz). However Band Pass filters do not prevent the ingress of banned 4G repeater or booster frequencies. The following example was detected in Kilmore.
Four months ago I was requested to investigate R.F.I. issues at a block of units whereby I had installed the M.A.T.V. system four years ago. The antenna is utilizing the Bendigo (Mt. Alexander) transmitter, is fitted with a low bandpass (4G) filter, and was fully operational without any reception problems; that is - until I received a request to investigate frequent pixelation episodes.
The R.F.I. was affecting all four units, frequently began at 5pm until 10:30pm on week-nights, and most weekends. To identify the R.F.I. issue I jointly monitored my Rover spectrum screen, plus a resident’s TV. The interference was of an extremely brief duration (less than 1.5 seconds), and the spikes appeared between 700 to 720MHz, with input levels frequently beyond 90dBuv. To screen capture the activity I activated the maximum hold feature of the spectrum screen. The high input levels of the spikes caused the masthead amplifier to overload resulting in the resident’s digital reception to pixelate plus a temporary loss of signal.
Given my analyzer has the LTE option I was able to confirm that the frequencies captured were that of an Uplink 4G appliance. To temporarily satisfy the residents I modified an adjustable UHF notch filter to reduce the unwanted frequencies by 6o dBuv, then installed the modified filter between the antenna and masthead amp. By reducing the interference input I was able concentrate upon locating the source of R.F.I. My search for the cause resulted in locating a banned 4G repeater/booster device 500m from the units. This issue was referred to A.C.M.A. for further investigation and removal of the banned 4G repeater.
The below modified screen captures display the above findings prior to installing the adjustable UHF notch filter. The M.A.T.V. system had a low bandpass (ch. 28 – 34) 4GX filter, but the strong LTE uplink frequencies still managed to cause the masthead amp to over-load resulting in excessive floor noise levels that affected the received Bendigo (Mt. Alexander) UHF digital carriers.
There are only two approved 4G repeaters or boosters approved for use in Australia. They are Telstra & Optus Smart Repeaters. Banned 4G repeaters not only corrupt digital TV reception but also Telco Mobile tower installations. The Federal Government’s Telecommunications Act 1997 provides for the Prohibition of Mobile Phone Boosters, and the penalty fine for operating a banned 4G repeater can be $220,000. The need to buy a banned 4G booster is chiefly due to limited coverage of 4G transmissions.
Below are screen captures that demonstrate the effect and existence of Echoes
Observe the reduced MER, SNR, NaMAR, b and a BER levels
Typical Echo Detection screen indicating Post Echoes Inside and Outside the Guard Interval **(Green area)
Digital echoes are an inexperienced TV antenna installer’s “nightmare” unless they can detect them.
As a rule inexperienced installers can waste many hours by raising the antenna higher or adding a stronger masthead amplifier. Both actions will only cause further problems, but lowering or shielding the antenna from the echo/es is an option; unless another transmitter is available. Therefore an up-to-date TV signal analyzer is a must have item.
There are two versions of an Echo – Pre Echo or Post Echo. Pre Echoes exist before the carrier, and Post Echoes are those after the carrier. The carrier is the yellow/red broken line above the 0.00Km marker.
An Echo is a reflection of a terrestrial digital TV transmission reflecting off a mountain, a building, exist in rural and metropolitan areas, and have the ability to cause pixelation and or a complete loss of signal/s.
An Echo can be singular or multiple, may affect a channel or channels, and may be either constant or unpredictable. Depending upon the local terrain an Echo may be weak or strong, and exist in the VHF / UHF spectrums.
An Echo or Echoes are “invisible” as they can only be detected by a digital signal analyzer that is equipped with the Echo Detection feature. The initial hint of an Echo’s existence is a very low MER level. Whilst low MER levels can also suggest other R.F.I. factors my first course of action is to check the Echo Detection screen then the spectrum screen, and in particular - closely inspect the multiplexes for the existence of a saw tooth top or similar irregularities.
All digital TV tuner appliances feature a G.I. that provides for Error Correction of the received channel. There are two vital Error Correction processes -: • Viterbi – Viterbi decoding was developed by Andrew J Viterbi, and is the first stage of Error Correction. • Reed-Solomon – In decoding theory Reed-Solomon codes are non-binary cyclic error correcting codes invented by Irving S. Reed and Gustave Solomon, and is the second stage of Error Correction.
Installers who are acquainted with the Error Correction process will be aware that the G.I. has its limitations to remove redundant data (R.F.I.) e.g. Echoes within or outside the G.I. that can cause pixelation and loss of signal/s. The Echo Detection display (above) shows an Echo inside the G.I. that is minus 23dB. This Echo is likely to cause pixelation, but the Echoes outside the G.I. will cause constant pixelation, and loss of signal episodes.
It is vital to remember that an Echo’s strength will fluctuate resulting in a swift decline or rise of input levels.
In the above Measurement screen low MER, SNR levels resulted in failed NsMar, bBER, and aBER levels that when combined with a history of pixelation, the type of terrain surrounding the site - suggests the presence Echoes.
I have created a pdf document on the Detection and Management of Echoes. My document is also utilized by TV Antenna installers in Italy, Spain, and the U.K. and may be accessed via Roverinstrument’s WEB site under their Service heading, then scroll down to TV-LTE-GSM tutor sub-heading.