Digital Signal Meter

The Cush

With signal quality being more important than signal strength with DTT I came across this interesting graphic



Anyone with a Sony TV may be familiar with pre-Viterbi (CH-BER / pre FEC) and post-Viterbi (aBER / post FEC) error correction information and their 5s averages e.g. 2.00 e-6 (2/1,000,000 or 0.000002 = 2 x 10-6 or 2.0E-06) - 2 bits out of the 1,000,000 bits received are errored.

Souriau

Just update my unit to Emitor DigiAir Pro for having BER and MER on it

When I done a spectrum scan, I see some activity at 450MHz

Can anyone tell me what is using this frequency?

Ronnie Raygun

Tetra?

Rippy

Ronnie Raygun wrote: »

Tetra?

Nope, Tetra is 380-40Mhz.

STB

Souriau wrote: »

Just update my unit to Emitor DigiAir Pro for having BER and MER on it

When I done a spectrum scan, I see some activity at 450MHz

Can anyone tell me what is using this frequency?

Do you have a wireless phone ?

Could also be HAM.

watty

PMR 446 walkie talkies?

There is also a Mobile Data licence around 450MHz, but I think nothing rolled out.

Tetra is indeed some place between 446 and 470MHz, but I forget where. It's buried on Comreg's site somewhere. Their site is a disgrace for searching.

"Ham" is 430 to 440 and not very active.

Lots and lots of 433MHz (Doorbells, Baby alarms, Remote channel on Video Senders, Wireless weather stations, wireless alarms etc)

STB

watty wrote: »

PMR 446 walkie talkies

"Ham" is 430 to 440 and not very active.

Lots and lots of 433MHz (Doorbells, Baby alarms, Remote channel on Video Senders, Wireless weather stations, wireless alarms etc)

I thought 70cm covered up to 450megs ? Well it seems it could be amateur radio. Fairly near is a repeater on 439.6mhz - digital just outside Newry.

Souriau

I have this meter a week now and been testing it and making adjustments to the aerial and amp distribution system

Firstly the signal reaching the TV was over power
BBC and UTV mux where breaking up

Now after the adjustment and now see rock steady pictures

First I check for aerial alignement to get peak reading,
The aerial was off by 10 deg
then I took reading and see chart 1
made adjustment with reducing signal strenght with 10db attenutor
took another reading and see chart 2

I am quite please with this meter as it help me to pin-point the problem quickly.

Ronnie Raygun

So the meter is at the tv & the attenuator is at the distribution input? What's the gain & maximum input signal level for the distribution amp? Those signal levels (especially considering the dist. amp. has applied its gain) shouldn't overload anything.

What is used to receive the Saorview signal & how is it combined with the others?

Peter Rhea

The readings for the analogue channels mightn't be accurate, probably should be higher.

Souriau

Peter Rhea wrote: »

The readings for the analogue channels mightn't be accurate, probably should be higher.

When set to digital mode, signal are, in dBµv.
21=72.8, 24=71.1, 27=72.2, 31=74.1, 37=55.3
from Divis and Black mountain for Ch.5

40=46.2, 43=52.1, 46=56.2, 50=43.5 from Cairn Hill

When set to analouge mode, signal are, in dBµv.
21=66.0, 24=67.1, 27=66.6, 31=67.8, 37=50.3
from Divis and Black mountain for Ch.5

40=38.8, 43=47.0, 46=50.2, 50=37.3 from Cairn Hill

Souriau

Ronnie Raygun wrote: »

So the meter is at the tv & the attenuator is at the distribution input? What's the gain & maximum input signal level for the distribution amp? Those signal levels (especially considering the dist. amp. has applied its gain) shouldn't overload anything.

What is used to receive the Saorview signal & how is it combined with the others?

Group B aerial with B amp at 14db gain
diplex into Group A to E
Group A from Divis and E from Cairn Hill
the attenutor is just on group A from Divis.
This is why 48 from Divis is weak as it is out of band with the diplexer, but that will change in October.

Ronnie Raygun

Souriau wrote: »

Group A from Divis and E from Cairn Hill
the attenutor is just on group A from Divis.

And the meter readings were taken at the tv point?

Is there also a masthead amp on the group A aerial?

What's the "power distribution in attic" referred to in the 2nd attachment?

It's misleading to state that the meter helped you find the problem if in reality you just got lucky with the attenuator.

Souriau

Without the meter, I would be working blind, not knowing is too much to too little.
The meter is a tool to help to see what is going on and help to make correct adjustment to gain good quality signal.
without it, I be spending a lot of time trying this and that.

The signal meter on the TV is not much help
one need to see the BER, Pre and Post to check the quality of incoming signal

Ronnie Raygun

Yes, but where in the system was the meter connected when you took those readings shown in the attachments? Simple question.

Souriau

At the end of the co-ax cable before plugging into the TV
taking into conderstion the cable db loss. the distrubition amp gain.
The final measurement was taken at the site where the TV is

Ronnie Raygun

The improvements in SNR & BER on mux 1 & mux B are plain to see, I suppose. Still doesn't explain why attenuating the signal led to an improvement.

Souriau

Ronnie Raygun wrote: »

The improvements in SNR & BER on mux 1 & mux B are plain to see, I suppose. Still doesn't explain why attenuating the signal led to an improvement.

I am not a qualified electronic engineer or have good understanding of the working of signal transmission or how the box decode the signal.
All I was showing is how the BER and SNR improved by reducing the strength of the incoming signal.
I took reading of before and after
What I did was to take the reading at the TV end of the co-ax lead, had a variable attenutor and adjust it till I see the highest reading I can get.
this was all done in the living room where the TV is
once I find the best SNR and BER, I then went to see the signal strength was, again with the variable attenutor and then without it,
this show me the different in dBµv. I subtract the lowest dBµv from the highest dBµv and was 10dB.
Then I went up to the attic and fit a 10dB attenutor at the distrubition unit

I came into this site a few years back with little knowledge of this
others members in here had help me and point me in the right direction
now I having more knowledge but still I am no expert
I am now just showing others of my finding and I also would like to thanks everyone for helping me to understand most of this.

Is this site not for seeking and sharing informations?

Ronnie Raygun

Souriau wrote: »

Is this site not for seeking and sharing informations?

It is indeed, but you have to get your story straight & explain exactly what you did & the layout of your system.

The reason I ask these questions is because I was interested to find out what was going on with your readings but I'm still mostly none the wiser as your replies regarding placement of the attenuator are confusing; is there a masthead amp on the aerial receiving from Divis?

The Cush

Souriau wrote: »

Just update my unit to Emitor DigiAir Pro for having BER and MER on it

Souriau wrote: »

I have this meter a week now and been testing it and making adjustments to the aerial and amp distribution system

Hi Souriau

Where did you purchase the meter and how much?

Souriau

Ronnie Raygun wrote: »

It is indeed, but you have to get your story straight & explain exactly what you did & the layout of your system.

The reason I ask these questions is because I was interested to find out what was going on with your readings but I'm still mostly none the wiser as your replies regarding placement of the attenuator are confusing; is there a masthead amp on the aerial receiving from Divis?

I will sit down later to review and rewrite it again

Souriau

The Cush wrote: »

Hi Souriau

Where did you purchase the meter and how much?

I ordered it directly from Sweden and they charged me €259

The Cush

Souriau wrote: »

I ordered it directly from Sweden and they charged me €259

Link? Emitor or online retailer?

Souriau

The Cush wrote: »

Link? Emitor or online retailer?

Sorry, direct with Emitor, cost of unit and p&p, exc VAT

Souriau

Took some snapshot of the DigiAir Pro when BBC change from BBC 2 to BBC A

The Cush

Souriau wrote: »

Took some snapshot of the DigiAir Pro when BBC change from BBC 2 to BBC A

Do you have a pic of the pre/post BER?

Souriau

Sure

lucernarian

I think a vague estimate of how good the pre-viterbi error rate can be made by looking at the plot of dots inside the square on the MER information screen. I'm guessing this is a representation of the QAM constellation in realtime and the less it represents the kind of plots seen on the likes of this page (http://www.radio-electronics.com/info/rf-technology-design/pm-phase-modulation/8qam-16qam-32qam-64qam-128qam-256qam.php) then the higher the expected bit error rate.

Either way, it does look like the old Mux 1 was on the edge of reliable reception.

Souriau

it is just a quick look to see how well the signal is, the smaller and tighter the dots are together, the better the quality of the signal
compare to Mux 2 which is poor, signal scatter all over the place
see attach pic

Souriau

Someone asked how good is the signal meter on Sony TV
So I took reading of both and shown below
First is the BBC A, highpower output from Divis. E27

BBC A E37 high power. aerial with amp, Wideband
Digiair Pro signal meter
Signal strength 68.1 dbµv
SNR

---

>31.0 dbµv
Pre Ber

---

6.6E-04
Post-BER

---

>1.0E08
MER

---

>31 db

Sony TV with signal meter
Signal Quality- 100
Signal Strength 100
Pre-Viterbi---- 7.30 e-5
C/N

---

30
UEC

---

0
Post Viterbi--- 0
5s

---

0
AGC

---

118

BBC A E37 high power. aerial w/o amp, Group K, 18 elements
Digiair Pro signal meter
Signal strength 46.4 dbµv
SNR

---

30.0 dbµv
Pre Ber

---

1.0E-04
Post-BER

---

>1.0E08
MER

---

29 db

Sony TV with signal meter
Signal Quality- 100
Signal Strength 90
Pre-Viterbi---- 1.45 e-4
C/N

---

29
UEC

---

0
Post Viterbi--- 0
5s

---

0
AGC

---

163