Journalists again...

BeerNut

From BBC NI News:

A new wind turbine in Bangor has been causing interference to some people's television reception.

So to compensate for the TV nightmares, North Down Borough Council are handing over cheques for £150 to those affected.
<snip>
The council agreed to pay a fixed price so that people suffering from the 'wind effect' can get their terrestrial aerial replaced with a digital one or a satellite dish.

You have to wonder how much Natalie paid for her digital aerial when she bought her Freeview STB.

watty

If it affects Analogue, it's likely to affect Freeview.

£150 is a bit slim for a decent freeSat box AND professional installs, unless that is now the bundle price inc. install in Co. Down now.

There are no such thing as Digital Aerials.

BeerNut

watty wrote: »

There are no such thing as Digital Aerials.

:eek: But it's on the BBC. I think you'll find they know a thing or two about broadcasting.

Wouldn't it be tempting to bring a "digital aerial" back to the shop that sold it and complain it was only picking up ones?

danjo

watty wrote: »

There are no such thing as Digital Aerials.

++
Saying there is an analogue and a digital aerial is similar to saying you have an essay pen and a letter pen. The pen is the same, only the application differs.

The Cush

watty wrote: »

There are no such thing as Digital Aerials.

The ‘digital aerial’ myth

The myth says that you need a special aerial for digital. There is no such thing as a digital aerial. All aerials receive digital and analogue signals.

Beware of the shark!
If you do replace your aerial the installer might point to a neighbour’s roof and show you a large aerial with a lot of funny shaped prongs, and say, “That’s what you need. That’s a digital aerial!” He might show you such an aerial in a catalogue. However, as you should know by now, there is no such thing as a digital aerial!

watty

Spark Transmissions and Morse / CW are digital as the Transmitter either transmits something or nothing.

Though Morse is NOT binary as it has at least 5 symbols: dash, dot, gap for dot/dash, letter gap and word gap.

Digital data is carried on specially coded Analogue signals. If there is a poor quality aerial preamp the distortion, intermodulation or interference may not be very noticable on analogue TV to a casual viewer, but may distort the signal so the symbols used to carry the digital information can't be told apart from each other or interference.

It's really a very very fast Modem. Old Dialup computing is Digital, and the Modem then passes an analogue signal up to 3kHz on the phone line. DSL needs very good line as its modem uses 4kHz to 22MHz approximately, though it's adaptive using 100s or 1000s of simultaneous slower channels, depend on if ADSL, ADSL2+ or VDSL.

Digital Terrestrial TV uses a similar modulation scheme to DSL (OFDM) and Satellite uses a similar scheme to old 9600 baud modems (QPSK), except at millions of times faster. Cable Digital uses a very fast complex version of how a 33K baud modem works (256 QAM).

DSL is just as much an "analogue" Modem as an old Dialup modem, just different frequency band and coding.

danjo

watty wrote: »

Though Morse is NOT binary as it has at least 5 symbols: dash, dot, gap for dot/dash, letter gap and word gap.

Could not agree with this statement. There are two states either on or off therefore it is binary. Because the pulse duration or repetition frequency varies does not mean it is not binary.

BeerNut

So you could represent "SOS" in binary as:
1010100110110110010101

Where:
1 = dot
11 = dash
0 = dot/dash gap
00 = letter gap
000 = word gap

Does that work?

watty

Morse can be coded in binary, as I orginally said, tx on = 1 and off= 0

Spark Transmissions and Morse / CW are digital as the Transmitter either transmits something or nothing.

i.e. 1 or 0

but Morse itself obviously is not binary, it has five states, not two.

Text uses 8 bits to encode one character.

@beerNut, your scheme is not quite the right timing, but you have the idea of it. Morse does normally use Binary or Digital transmission, encoding its 5 symbols appropriately,

ASCII can be represented in Decimal, hex, octal or binary coding.


Digital transmission takes the serial binary representation of the data and then encodes it using different (analogue) symbols. A symbol can carry 2 to 10 binary bits.

Morse is obviously more complex than it looks as the number of dots, dashes and spaces varies per character. But machine sent morse, or computer decoded morse doesn't directly use binary. You need 5 different symbols that are then translated to or from binary at the last stage of transmission or first stage of reception.

Writing a program to take a line of text and "send it" as morse with the final code as binary and thus turn transmitter on/off is easy.

Writing a program to detect silence or carrier reliably and track it as the frequency drifts is basic enough DSP these days.

Then you have a binary stream where you don't know the clock speed, so you can't easily recognise it as binary as per beernut's approximation. Instead I wrote software to recognise the 5 symbols directly, by incrementing a high speed timer every time a change occurred then looking back over the time of each "on" to decide if dot or dash and each "off" to decide if internal dot/dash dot/dot, dash/dot or dash/dash separator or else a character gap or word gap.

It doesn't matter much if you make some error on letter/word timing. But internal time vs external time is the vital one.

RS232 in contrast is solely binary but with a framing signal. As such if you know the clock speed it is very easy to get the binary serial data.

All types of digital electronic transmisson do go through an intermediate low level serial binary data phase.

watty

Some fragments of a working Morse reception decoder.

The DSP returns an event with signal duration every time a signal ends.

Another event occurs at start of a signal. Thus "on" =1 and "off" =0 are timed. But these don't relate in any direct way to Morse, sadly.

"Standard" Morse to "binary bit " timings
dot = 1 * speed
dash = 3 * speed
gap = 1 * speed
gapChar = (3 * speed) - gap
gapWord = (7 * speed) - gapChar

Private Sub ToneDecoder_OnFrequencyDetected(ByVal Frequency As Double, ByVal secondFreq As Double, ByVal duration As Long, ByVal StartPos As Long)
 'txtLog.Text = "Freq =" + CStr(Frequency) & Chr(13) & Chr(10) & txtLog.Text
 If rigMode = modeRX Then
 If ((Frequency > (udFrequency.Value - 150)) And (Frequency < (udFrequency.Value + 150))) Or _
    ((secondFreq > (udFrequency.Value - 150)) And (secondFreq < (udFrequency.Value + 150))) Then
   
    If averageDida > 5 * duration Then
        averageDida = 4 * duration / 5
        textDida = textDida + "."
    ElseIf duration > 5 * averageDida Then
        averageDida = 5 * duration / 4
        textDida = textDida + "-"
    Else
       averageDida = (averageDida + duration) / 2
        If duration < averageDida Then
            textDida = textDida + "."
        Else
            textDida = textDida + "-"
        End If
    End If
    lblRXDida.Caption = textDida
End If

 End If
End Sub

Private Sub ToneDecoder_OnSilenceEnd(ByVal EndPos As Long, ByVal duration As Long)
 On Error GoTo DONE
    If rigMode = modeRX Then
        timerCW.Enabled = False
        If (duration > 1) And (duration < 5000) Then
        
            timerCW.Interval = duration * 20
        Else
            timerCW.Interval = 2000
        End If
        If (duration) > (4 * averageDida) Then
            ' WriteCh CwToText(textDida) + " "
             txtLog.Text = txtLog.Text + CwToText(textDida) + " "
             lblRXDida.Caption = textDida
    
             textDida = ""
         
        ElseIf (duration >= averageDida) Then
           
             txtLog.Text = txtLog.Text + CwToText(textDida)
            lblRXDida.Caption = textDida
    
             textDida = ""
        End If
DONE:
        timerCW.Enabled = True
    End If
  
End Sub

Transmission is easy

Private Function TextToCW(ch As String) As String
Dim dida As String

    ch = Format(ch, "<")
    Select Case ch
    Case "a"
        dida = ".-"
    Case "b"
        dida = "-..."
    Case "c"
        dida = "-.-."
    Case "d"
        dida = "-.."
    Case "e"
        dida = "."
    Case "f"
        dida = "..-."
    Case "g"
        dida = "--."
    Case "h"
        dida = "...."
    Case "i"
        dida = ".."
    Case "j"
        dida = ".---"
    Case "k"
        dida = "-.-"
    Case "l"
        dida = ".-.."
    Case "m"
        dida = "--"
    Case "n"
        dida = "-."
    Case "o"
        dida = "---"
    Case "p"
        dida = ".--."
    Case "q"
        dida = "--.-"
    Case "r"
        dida = ".-."
    Case "s"
        dida = "..."
    Case "t"
        dida = "-"
    Case "u"
        dida = "..-"
    Case "v"
        dida = "...-"
    Case "w"
        dida = ".--"
    Case "x"
        dida = "-..-"
    Case "y"
        dida = "-.--"
    Case "z"
        dida = "--.."
    Case "0"
        dida = "-----"
    Case "1"
        dida = ".----"
    Case "2"
        dida = "..---"
    Case "3"
        dida = "...--"
    Case "4"
        dida = "....-"
    Case "5"
        dida = "....."
    Case "6"
        dida = "-...."
    Case "7"
        dida = "--..."
    Case "8"
        dida = "---.."
    Case "9"
        dida = "----."
    Case "."
        dida = ".-.-.-"
    Case ","
        dida = "--..--"
    Case ":"
        dida = "---..."
    Case "?"
        dida = "..--.."
    Case "'", "`"
        dida = ".----."
    Case "-"
        dida = "-....-"
    Case "/"
        dida = "-..-."
    Case "(", ")", "{", "}", "[", "]"
        dida = "-.--.-"
    Case """"
        dida = ".-..-."
    Case "&#233;"
        dida = "..-.."
    Case "&#225;"
        dida = ".-.-"
    Case " ", "_"
        dida = " "
    Case Else
        dida = "..--.."
    End Select
    TextToCW = dida
End Function



Private Sub cwGen(textCW As String)

Dim dot As Integer
Dim dash As Integer
Dim gap As Integer
Dim gapChar As Integer
Dim gapWord As Integer
Dim speed  As Integer
Dim times As Integer
Dim dlen As Integer
Dim dida As String
Dim temp As String
'50 is very slow about 9 wpm,  15 about 18wpm
'  60 is about 25 wpm
'  about the fastest. Works better with 256 or 512 than 1024 buffer
' 160 about 8wpm
' 100 about 10wpm ?
' 80 about 15 wpm
' 75 about 16wpm
    speed = 1100 / udWPM.Value
    dot = 1 * speed
    dash = 3 * speed
    gap = 1 * speed
    gapChar = (3 * speed) - gap
    gapWord = (7 * speed) - gapChar
    
    
    For times = 1 To Len(textCW)
        temp = Mid(textCW, times, 1)
        dida = TextToCW(temp)
      
        For dlen = 1 To Len(dida)
            temp = Mid(dida, dlen, 1)
            If temp = "." Then
                ToneEncoder.GenerateTone dot, gap, udFrequency.Value
            ElseIf temp = "-" Then
                ToneEncoder.GenerateTone dash, gap, udFrequency.Value
            Else
                ToneEncoder.GenerateSilence gapWord
            End If
        Next dlen
        ToneEncoder.GenerateSilence gapChar
    Next times
    
End Sub

Normally transmitters are not directly "keyed" on and off anymore as that makes nasty clicks. They are used in SSB mode so the frequency transmitted is "ToneEncoder" frequency (often 800Hz) added to or subtracted from the RF "tuned" frequency.

Mike 1972

But it's on the BBC. I think you'll find they know a thing or two about broadcasting.

Tbe Beeb are a big organisation. I doubt the journalists tie up with the engineering staff for each broadcasting related story (even if they should)

If it affects Analogue, it's likely to affect Freeview.

Given that the DTT system was developed in the 1990's was it not rather short sighted of the designers not to provide for more multipath immunity ?

How does DTT cope with aircraft reflections (can be a bugbear for analouge viewers living near airports)

watty

DTT is OFDM so it's very very good for multipath,
But OFDM is poorer than cable or satellite for Doppler Shift. Not that doppler shift is a problem for cable, nor DTH TV on Clarke Belt. LEO sats have huge doppler shift. It only takes the ISS about 15mins to woosh from horizon to horizon. But you can hook up tuning to TLE based tracking SW and "track" the doppler shift. That wouldn't work for OFDM. So only Terrestrial uses OFDM.

The blades are moving


It's one advantage of the US ATSC / 8VSB system, it's not so much affected by moving blades. Originally it was poorer at ordinary multipath than OFDM, but they claim to have improved it some how.

The BBC used to know a lot about broadcasting. I worked as a Communications Engineer there. The Government forced them to sell the TX network.
Automation did away with a lot of non-studio technical staff.
They outsourced IT
They cut back savagely the R&D

The journalists never ever did ask any one technical about their stuff when I was there.

BeerNut

Mike 1972 wrote: »

Tbe Beeb are a big organisation. I doubt the journalists tie up with the engineering staff for each broadcasting related story

I think my irony Tx may need some recalibration.

fat-tony

BeerNut wrote: »

I think my irony Tx may need some recalibration.

Rx'd here ok:)

In the wider context, though, we got interesting side discussions on:

• what constitutes digital transmission
• the five states of the Morse Code
• a lesson in programming
• stories from the trenches on the effects of outsourcing IT and R&D

Antenna

watty wrote: »

The blades are moving

Is there any non-conductive material strong enough that could be used for the blades on these turbines!?