KILMORE & DISTRICT TV ANTENNAS

Now that I have provided a brief précis and my “gripe” re the licensing of TV antenna installers - I welcome you to my revised WEB site; trust that my humor, contents and comments are appreciated.

spectrum view

I tell ya it was having a bath!

cartoon ode

Fantastic - You’ve found me!

Tree near Heathcote

Roadside tree near Heathcote

I have 4 key items that you may find of interest – Digital Cliff, Invisible R.F.I. , Sporadic E Propagation (E-Skip) & Concealed Galvanic Corrosion of Coaxial Cable “F” Connections

These four topics provide technical explanations for common “mystery” interference issues that affect your digital TV reception.

Topic 1: Digital Cliff – A frequent cause of Pixelation and loss of signal.

The below analyzer screen captures (A - C) display a client’s TV antenna system that was not affected by common R.F.I issues. Yet - owing to a low Modulation Error Ratio (M.E.R.) frequent pixelation of the ABC channels was due to the TV antenna site.

Whilst the TEN (219.50MHz) channels had infrequent pixelation issues – my client’s favorite ABC channels were un-watchable.

Roverinstruments HD TAB7 EVO Analyzer’s Spectrum, Measurement & Constellation Screens (A - C) screen captures display the classic affects of the digital cliff.

spectrum view

A


Spectrum View indicating imperfection of the TEN & ABC multiplexes with a slope & drop of the ABC input level.

Card image cap

B


Extremely low M.E.R, S.N.R levels, Failed NsMAR, & b-BER : 1x10-2, + a-BER: 3x10-4 ratios = Pixelation.

Constellation capture

C


Constellation scan indicates excessive noise levels resulting in indistinguishable constellation points.

Technical remarks:

• When a TV carrier is close to the “Digital Cliff” edge - M.E.R. levels less than 24dB will drop below an unusable safety margin.

• The received data then fails to be decoded resulting in pixelation (breakup) of audio and video to a complete loss of signal.

• Low M.E.R. levels also increase extra noise levels – hence screen capture (C) the constellation points are indistinguishable.



Solution:
Re-positioning or the re-placement of the antenna by an experienced installer is vital to obtain near-equal M.E.R. levels that are greater than 28dB for all carriers measured at TV outlets. M.E.R. levels less than 24dB will guarantee reduced safety margins.
perfect constellation scan

A Perfect Constellation Scan

diagram of cliff edge comparison

Diagram of the Digital Cliff compared to Analogue transmission

Topic 2: Digital Reflections (Echoes) – the “Invisible” cause of Interference:

During the launch of terrestrial digital TV in Europe it was revealed that some channels failed to be stored after a scan of a digital TV/PVR tuner. European Research and Design engineers of TV signal analyzers identified an invisible type of interference existed.

Prior to digital TV transmissions analogue TV could be affected by reflections (Ghosting) that displayed images to the right of the main picture. Regrettably these same reflections also affect digital TV reception, but there are no images to the right of the picture. These reflections are known as Echoes, may cause pixelation plus (if strong enough), result in loss of signals, and are only detected by utilizing a modern Digital TV Signal Analyzer that incorporates the Echo Detection feature.

Due to the importance and technical content details involving the Detection and Management of Echoes please refer to the Technical Information section Part “B” Item 2. This section also includes a pdf document that can be downloaded.

Topic 3: Sporadic E Propagation (E-Skip) a seasonal & invisible cause of Pixelation & loss of signal.

Sporadic E, also called E-skip, is the phenomenon of irregularly scattered patches of relatively dense ionization that develop seasonally within the E region of the ionosphere and reflect TV and FM frequencies, generally up to about 150 MHz. When frequencies reflect off multiple patches, it is referred to as multi-hop skip. E-skip allows radio waves to travel thousand miles or far beyond their intended area of reception. E-skip is unrelated to tropospheric ducting.

Television and FM signals received via Sporadic E can be extremely strong and range in strength over a short duration from just being detectable to overloading. Short-skip (400–800 miles or 640–1,290 kilometres) signals can have a tendency to be reflected from more than one part of the Sporadic E layer, resulting in multiple images and ghosting, with phase reversal at times. Viewers will then begin to experience picture degradation with associated pixelation to loss of signal episodes as a result of each increasing and succeeding Sporadic E hop.

NASA Solar

Fig 1


NASA Solar Cycle Prediction

cartoon bird

Fig 2


Dam! - Skip has flipped my brain’s compass upside down

layers of the Ionosphere

Fig 3


Layers of the Ionosphere

Fig. 1 - Is a graphic Solar Cycle Prediction courtesy of the NASA Ames Research Center – California.

Fig. 1 is a result of Dr David Hathaway’s research into Solar Cycle Prediction. Every 11 years or so, the Sun's magnetic field completely flips, and the Sun's north and south poles switch places. Thereafter it takes about 11 years for the Sun’s north and south poles to flip back again.

After 29 years of service Dr Hathaway retired in 2016, and was Member of MSFC Solar Physics Group in California.

Fig. 2 - Depicts a humorous version of the Sun’s magnetic field effects.

Fig. 3 - Is the layers of the Ionosphere surrounding our Earth’s surface.

Summary:

E-Skip conditions and Solar Cycles (Solar Outages) are R.F.I. factors that can affect thousands (or more) of digital TV receivers, can impact upon one or more VHF channels, may exist for a brief period or persist for hours, and cannot be resolved by altering the direction of a TV antenna or installing a special filter.

E-Skip conditions (in the past) commonly develop seasonally - typically in late spring, summer, and early autumn. Sadly there are no advantages to be gained by retuning digital receivers whilst E-Skip conditions exist or requesting the services of a TV antenna installer. As a rule E-Skip conditions are known to suddenly disappear or will (in time) cease to exist allowing digital TV reception to recover to good viewing qualities.

I am also aware that UHF TV frequencies can be affected by Tropospheric Propagation (ducting). This occurs when local digital transmission can be affected by co-channel interference, with some local channels pixelating. If co-channel interference becomes frequent – an experienced TV antenna installer may be able to resolve issues by utilizing an alternative (highly directional) TV antenna.

Topic 4: Concealed Galvanic Corrosion of Coaxial Cable “F” Connections


Galvanic Corrosion (rusting) of coaxial cable “F” connections has rarely caused complaints of increasing episodes of pixelation to a complete loss of signal. However the incidence of Galvanic Corrosion appears to be on the increase, and tends to exist in TV antenna systems located in variable coverage areas that utilize D.C. voltage for masthead amplifiers, “F” splitters and joiners, plus coaxial cables that are manufactured with copper-coated centre conductors.

So what is Galvanic Corrosion?

The following link Galvanic Series Table provides a basic scientific explanation for the development of Galvanic Corrosion. Galvanic Corrosion is fundamentally a result of self-induced electrical potential of two dissimilar metals, plus an electrolyte. During the oxidation of dissimilar metals within an “F” connection - a vapor is created, and converts to an electrolyte.

NB Concealed Galvanic Corrosion is NOT the result of sea-air or rain-water entry via aged or damaged outer covers of coaxial cable, and is easily disregarded by D.I.Y. and in-experienced installers. When two dissimilar metals combine e.g. aluminum “F” connections, copper-coated center conductors of coaxial cable, D.C. power voltage, the existence of an electrolyte, plus oxygen – is (in my opinion) an ideal “combination of the above basic essentials” for the first stage of Galvanic Corrosion to begin the oxidation of the two dissimilar metals (“F” connections and copper coated steel centre conductors) that results in an open circuit.

Galvanic Corrosion is often confined to within the center of an “F” connection, and is not visible until the “F” connection is completely removed exposing the internal corroded components. The below example was in a ceiling cavity, and is displaying air-spaced coaxial cable minus the centre conductor, an “F” joiner, and RG6Q coaxial cable that was providing 14 volts D.C. to a masthead amplifier.

The use of a TV signal analyzer with a Reflectometer option or a multi meter is unlikely to reveal galvanic corrosion, until the oxidation of the dissimilar metals becomes an open circuit. Prior to an open circuit – a notably reduced D.C. voltage level at the masthead amplifier may suggest a cable fault. Given that the problem is not caused by radio frequency interference or other issues – a physical inspection of all cable connections becomes necessary. Conversely should there be an open circuit a Reflectometer option (see the below screen capture) will rapidly estimate the distance from your analyzer to the cable fault.

NB A helpful hint: From my personal experience if your investigations fail to provide an answer for a reception complaint, and the coaxial cable from the masthead amplifier outer jacket is not damaged by cockatoos or other factors – then a client’s verbal history of increasing episodes of erratic pixelation and loss of signal - may suggest that Galvanic Corrosion is likely.

Summary: Copper-coated steel centre conductors of coaxial cable plus Aluminum are both rated as being a less Noble Metal.

     Galvanic Corrosion Example

Galvanic Corrosion Example

        Reflectometer Indicating distance from Analyzer to Cable Fault

Reflectometer Indicating distance from Analyzer to Cable Fault