82 replies to this topic

[buma567]

Hi all,
Have been involved in the cabling industry for sometime now and read this forum quite regularly.
Have been installing antennas for around a year so am still learning every day, have found this site to be a huge help with my work.
I came across something i don't understand whilst on a job yesterday.

Double storey tin roof house behind a very large hill in outer southeast suburb of Melbourne using mt Dandenong transmitter .
After testing the roof space at varying heights found a location for best signal using a Unaohm T40.
Installed Fracarro log periodic antenna, used quality Rg6 and compression F connectors.
I then tested my signal levels at the output of the 4 way splitter and noticed a large change in Chber.
I then tested signal level on the RG6 coming from the antenna and its all OK.
I tried 3 different splitters all with the same result.

CHBER at Antenna.

Ch 06 : 4e5
Ch 08 : 4e5
Ch 11 : 0e0
Ch 12 : 1e6
Ch 29 : 0e0

At cable from antenna.

Ch 06: 68db, 28mer, 2e5
Ch 08: 68db, 28mer, 3e5
Ch 11: 65db, 35mer, 0e0
Ch 12: 65db, 34mer, 1e6
Ch 29: 61db, 36mer, 0e0

Signal levels taken at output of 4 way splitter.

Ch 06: 61db, 26mer, 1e4
Ch 08: 61db, 27mer, 9e5
Ch 11: 58db, 28mer, 3e5
Ch 12: 59db, 28mer, 2e5
Ch 29: 54db, 31mer, 1e5

I am hoping someone can help me to understand what is happening here as i believe the Chber should not change that much.

Thanks Buma

[mtv]

Are you sure those DCP readings are dB... not dBuV?

It's common for some increase in chBER with splitters, but I agree some figures are a little high.

MER is fairly consistent and based on those figures, should still provide fairly reliable reception.

Important.... did you take the measurements from the splitter with each port terminated?...... eg: either with a tuner connected or a 75ohm load?

If not, you will probably get different results when you do.

[M'bozo]

buma567, on Aug 4 2011, 10:35 AM, said:

Ch 11 : 0e0

Ch 29 : 0e0

I've always considered "CHBER: 0.0e +00" readings on my T40 to be an overange indication, so I increase meter attenuation to get what I feel to be a more realistic reading.

(assuming I'm interpretating that part of your post correctly)

[mtv]

M'bozo, on Aug 4 2011, 12:47 PM, said:

I've always considered "CHBER: 0.0e +00" readings on my T40 to be an overange indication, so I increase meter attenuation to get what I feel to be a more realistic reading.

I wondered about that figure too.

You should always check with increased attenuation, as even just slightly overange can give false readings.

You (should) pick it up when attenuating to check for operating margin any way, but I always check attenuation with readings to begin with.

[bellotv]

buma567

Good to see someone actually thinks about the readings they get.

The reality is that with  all digital meters  the CHBER reading will vary with the DCP level .

Typically  ChBER will increase as  the DCP is increased up to around 55-60dBuV after which point it tends to level off and increases only slightly as DCP is increased.

This will explain why your 68dBuv input to the splitter has a higher BER than the output at 61dBuV. (68dBuV is in the more level part of the meters "DCP verses ChBER curve "whereas  61dBuV is around where the curve tends to begin to level off)

Its a quirk that we all live with.

You probably have noticed that when measuring signals  with DCP less than around 40dBuV that the ChBER reading is always pathetically low.

The trick here is to use a masthead amp ( powered by the meter) to lift the levels to around 65-70dBuV. This gets the signal into that "flat" measurement point where the meter will read ChBER for what it is without the DCP effecting the reading so much.

BTW . All those ChBER readings you have given look fine .
personally I'd be worried about the SBS reading of 54dBuV though as this could get boarderline  low by the time it gets through the coax to the wall plate,flylead to the TV input socket.

Bellotv  ( used a T40a for over six years) Have two now  

Edit : I also agree with other comments about attenuating ( usually manually on the meter by 10dB is enough) to get a true reading if Ch BER is over range ,but realistically if its that close to perfection I'm not that concerned. ( so long as the DCP isn't excessive and likely to cause tuner overload (higher than about 75dBuV))
Then obviously I'd fit a real attenuator

Edited by bellotv, 04 August 2011 - 07:00 PM.

[debruis]

buma567, on Aug 4 2011, 10:35 AM, said:

Hi all,
Have been involved in the cabling industry for sometime now and read this forum quite regularly.
Have been installing antennas for around a year so am still learning every day, have found this site to be a huge help with my work.
I came across something i don't understand whilst on a job yesterday.

Double storey tin roof house behind a very large hill in outer southeast suburb of Melbourne using mt Dandenong transmitter .
After testing the roof space at varying heights found a location for best signal using a Unaohm T40.
Installed Fracarro log periodic antenna, used quality Rg6 and compression F connectors.
I then tested my signal levels at the output of the 4 way splitter and noticed a large change in Chber.
I then tested signal level on the RG6 coming from the antenna and its all OK.
I tried 3 different splitters all with the same result.

CHBER at Antenna.

Ch 06 : 4e5
Ch 08 : 4e5
Ch 11 : 0e0
Ch 12 : 1e6
Ch 29 : 0e0

At cable from antenna.

Ch 06: 68db, 28mer, 2e5
Ch 08: 68db, 28mer, 3e5
Ch 11: 65db, 35mer, 0e0
Ch 12: 65db, 34mer, 1e6
Ch 29: 61db, 36mer, 0e0

Signal levels taken at output of 4 way splitter.

Ch 06: 61db, 26mer, 1e4
Ch 08: 61db, 27mer, 9e5
Ch 11: 58db, 28mer, 3e5
Ch 12: 59db, 28mer, 2e5
Ch 29: 54db, 31mer, 1e5

I am hoping someone can help me to understand what is happening here as i believe the Chber should not change that much.

Thanks Buma

I have had a similar problems with CH 8 like this when installations have been close to the towers on the lower Nth Shore. I have found that attenuation at the antenna has helped to improve SNR & BER. Try antenuating to 50-55db incoming at the antenna on CH8 and hopefully this will improve BER. The only problem with this can be distribution to multiple outlets with the signal loss but of course this can be compensated by using the a distribution amplifier. The only thing that is a pain is that Kingray etc do not make a distribution with a low gain range as usually minimal gain is only required. Hopefully this may be of some help

[andrewlace]

Hi Buma, an interesting feature of the T40 and one that makes me particularly fond of the guy is the attenuation feature.  If you are doing a job where you allow for a 10dB loss, just vary the attenuation in the BER mode.  It then varies the measurement accordingly.  Will signal strength make a large difference to BER?: yep.  The BER you report are excellent, so I wouldn't worry too much.

debruis, on Aug 4 2011, 08:52 PM, said:

I have had a similar problems with CH 8 like this when installations have been close to the towers on the lower Nth Shore. I have found that attenuation at the antenna has helped to improve SNR & BER. Try antenuating to 50-55db incoming at the antenna on CH8 and hopefully this will improve BER. The only problem with this can be distribution to multiple outlets with the signal loss but of course this can be compensated by using the a distribution amplifier. The only thing that is a pain is that Kingray etc do not make a distribution with a low gain range as usually minimal gain is only required. Hopefully this may be of some help

[Tazzy2Heads]

buma567, on Aug 4 2011, 10:35 AM, said:

Hi all,
Have been involved in the cabling industry for sometime now and read this forum quite regularly.
Have been installing antennas for around a year so am still learning every day, have found this site to be a huge help with my work.
I came across something i don't understand whilst on a job yesterday.

Double storey tin roof house behind a very large hill in outer southeast suburb of Melbourne using mt Dandenong transmitter .
After testing the roof space at varying heights found a location for best signal using a Unaohm T40.
Installed Fracarro log periodic antenna, used quality Rg6 and compression F connectors.
I then tested my signal levels at the output of the 4 way splitter and noticed a large change in Chber.
I then tested signal level on the RG6 coming from the antenna and its all OK.
I tried 3 different splitters all with the same result.

CHBER at Antenna.

Ch 06 : 4e5
Ch 08 : 4e5
Ch 11 : 0e0
Ch 12 : 1e6
Ch 29 : 0e0

At cable from antenna.

Ch 06: 68db, 28mer, 2e5
Ch 08: 68db, 28mer, 3e5
Ch 11: 65db, 35mer, 0e0
Ch 12: 65db, 34mer, 1e6
Ch 29: 61db, 36mer, 0e0

Signal levels taken at output of 4 way splitter.

Ch 06: 61db, 26mer, 1e4
Ch 08: 61db, 27mer, 9e5
Ch 11: 58db, 28mer, 3e5
Ch 12: 59db, 28mer, 2e5
Ch 29: 54db, 31mer, 1e5

I am hoping someone can help me to understand what is happening here as i believe the Chber should not change that much.

Thanks Buma

Hi Guys,  Signal 68 db, 2e5, Luxury ! every second job I seem to get these days I have put an Amp on the T40 to find a signal.It all looks ballpark OK to to what I find in the hills .Tazzy.

[beeblebrox]

buma567, on Aug 4 2011, 10:35 AM, said:

Ch 06: 68db, 28mer, 2e5
Ch 08: 68db, 28mer, 3e5
Ch 11: 65db, 35mer, 0e0
Ch 12: 65db, 34mer, 1e6
Ch 29: 61db, 36mer, 0e0

Signal levels taken at output of 4 way splitter.

Ch 06: 61db, 26mer, 1e4
Ch 08: 61db, 27mer, 9e5
Ch 11: 58db, 28mer, 3e5
Ch 12: 59db, 28mer, 2e5
Ch 29: 54db, 31mer, 1e5

I am hoping someone can help me to understand what is happening here as i believe the Chber should not change that much.

Thanks Buma

As MTV Says unterminated ports will generate impedence imbalances and increase your error rate so this could be a factor.  This has been discussed at some length in the past here.

There's an interesting report on unterminated ports in matv systems here that doesn't specifically talk about BER but highlights some of the problems.

[beeblebrox]

Tazzy2Heads, on Aug 4 2011, 11:00 PM, said:

Hi Guys,  Signal 68 db, 2e5, Luxury ! every second job I seem to get these days I have put an Amp on the T40 to find a signal.It all looks ballpark OK to to what I find in the hills .Tazzy.

tazzy you think that's luxury.. did a job yesterday... 79-89dbuv off the antenna on every channel  had to attenuate the buggery out of it for the one point I was hooking up.

[debruis]

beeblebrox, on Aug 5 2011, 09:49 AM, said:

tazzy you think that's luxury.. did a job yesterday... 79-89dbuv off the antenna on every channel  had to attenuate the buggery out of it for the one point I was hooking up.

Did you have to knock 16-20db of the incoming signal to clean up the noise? I have had to do this from time to time with incoming readings like the ones you have mentioned and higher. Installations are generally lot easier when located close to the towers but high signals have there own issues as well especially within 5-10klms of the towers. If the terrain is undulating and  reflected signal come into play I have found the incoming channel signal levels can be uneven and require different signal levels for optimum SNR and BER eg an installation on the Lower Nth Shore CH8 had to be no greater than 52dbuv CH12 no greater than 56dbuv while CHs 6,11 29 & 34 could be 60-70dbuv and not have any BER issues.

[buma567]

Wow, thanks for the input guys and from all the names i have come to respect its greatly appreciated.

I believed the signal was OK to give good reception and can understand a small increase in Chber along all of the components just didn't want to see all my good signal being wasted by what i thought was a splitter.

Yep sorry bit lazy there with my terminology, is dBuV.

I explained the lowish DCP level on SBS to the customer but even though they could see all the tall masts and masthead amplifiers on nearly all the houses surrounding them they did not want to pay for an an amplifier.

The readings were taken with no load connected to the splitter.

I did test the 2nd 4 way splitter installed with 75 ohm terminators on the spare outlets to see if that was my problem but didn't get a noticeable amount of change, didn't record readings though. Will test this on my next job.

I purchased my T40 after reading reviews from this site, there's still a lot for me to learn about many of the features this meter has.

Never used the attenuation feature before today.
Had a play with the attenuation this afternoon and can now see the Chber clearly increase as the DCP lowers.

I assumed that 0e0 meant that the meter was receiving as good a signal as it could get, my bad.

Have noticed very bad Chber readings with low DCP, i put this down to not enough DCP to test correctly. Obviously when amplified the ChBer has improved but i had never watched the ChBer while increasing the gain to see at what level or how it improved.

Am i understanding operation margin correctly to be how low you can attenuate the signal too to find out where the signal will start to fail?

[mtv]

buma567, on Aug 5 2011, 10:40 PM, said:

Am i understanding operation margin correctly to be how low you can attenuate the signal too to find out where the signal will start to fail?

Yep... a minumum of 9dB above the threshold is desireable.

[buma567]

Thank you very much for answering my question, will try a few things out tomorrow and I'm sure to have a few more queries.

[charlesc]

buma567, on Aug 5 2011, 10:40 PM, said:

Am i understanding operation margin correctly to be how low you can attenuate the signal too to find out where the signal will start to fail?

There are a couple of good guides linked to in my sig below.  They're fairly old now, but basically still relevant.  I'm not sure if you've seen them, but perhaps grab them and have a read.
Operating margin is one aspect that is covered.

Good to see you have a T40, that meter should serve you well.

[Tazzy2Heads]

beeblebrox, on Aug 5 2011, 09:49 AM, said:

tazzy you think that's luxury.. did a job yesterday... 79-89dbuv off the antenna on every channel  had to attenuate the buggery out of it for the one point I was hooking up.

Hi beeblebrox,

I don't get many jobs in big signal areas even though where I am I can get 85- 90+ dbuv holding a 4 element Band  3 antenna on all channels. Most of the  
jobs are done by electricians and DIY's that think the bigger the tv the bigger the antenna has to be . I can go up the road and look at 10, 14, and 18
element B3 yagi's on cottages all with line of sight to 50kw transmitters.There's even a couple of places with EE 06's on the roof , after all it does have the
word DIGITAL on the box so it must be right ,don't need a meter !!.
Keep on attenuating, Tazzy.

[beeblebrox]

that digital word again.... gee it must be ok coz it says digital on the box!!!  ... at one stage tricky dicky was selling amplified rabbit ears with a digital clock on the front... that was the ultimate in digital antenna!!!!!   similar to this http://www.wahardwar...id_product=1014


I think the best one I've seen recently and there are some absolute doozys out there is this http://www.arlec.com...ntCatalogueID=1

as for sparkies...   I have a lot of respect for some sparkies... the ones who know not to touch MATV systems and get a professional in.. the rest are just downright cowboys!

[DrP]

beeblebrox, on Aug 18 2011, 07:16 PM, said:

I think the best one I've seen recently and there are some absolute doozys out there is this http://www.arlec.com...ntCatalogueID=1

At least you'll know there'll always be a picture to watch.  

[mtv]

DrP, on Aug 19 2011, 05:33 AM, said:

At least you'll know there'll always be a picture to watch.

A new meaning to 'digital picture frame'.  

Did you also note their 'current' catalogue, even on the home page is 2009?

[Tazzy2Heads]

beeblebrox, on Aug 18 2011, 07:16 PM, said:

that digital word again.... gee it must be ok coz it says digital on the box!!!  ... at one stage tricky dicky was selling amplified rabbit ears with a digital clock on the front... that was the ultimate in digital antenna!!!!!   similar to this http://www.wahardwar...id_product=1014


I think the best one I've seen recently and there are some absolute doozys out there is this http://www.arlec.com...ntCatalogueID=1

as for sparkies...   I have a lot of respect for some sparkies... the ones who know not to touch MATV systems and get a professional in.. the rest are just downright cowboys!

Hi beeblebrox,

That's one dam fine looking digital clock for the money, has antennas and all !! , must be a tv in there somewhere ?!!.
The link to the ceiling fan spare parts company is pretty scarey too, they are advertising fixed price ceiling fan installations.I guess thats a job for 'Jm's' Electricians etc. Can't wait for 'Jm's' Polititions what a franchise that would be!.Tazzy.

[mtv]

Tazzy2Heads, on Aug 19 2011, 11:42 PM, said:

Can't wait for 'Jm's' Polititions what a franchise that would be!.Tazzy.

This is starting to go OT.... but it's probably one area where they couldn't do any worse than most current politicians.  

[The Baja]

buma567, on Aug 5 2011, 08:40 PM, said:

I purchased my T40 after reading reviews from this site, there's still a lot for me to learn about many of the features this meter has.

I think you may have been Reading the wrong Reviews   When was the last time your T40 was Calibrated????

And What features would these be in the T40 that you mention????     can it detect an Echo within the Guard Interval??????

If you are serious about getting into this industry then you need to upgrade your meter. If you don't intend to do satellite work then a Good FTA Analyzer is not that expensive. If you are only in it to Cash-in on the trade.....................Then good luck


Cheer's


Baja

[clipper]

Baja_Dave, on Aug 20 2011, 01:42 AM, said:

If you are serious about getting into this industry then you need to upgrade your meter. If you don't intend to do satellite work then a Good FTA Analyzer is not that expensive. If you are only in it to Cash-in on the trade.....................Then good luck
Baja

Give him a break Baja- he's just starting out, at least starting to get serious, and the older model T40 will serve him well for the time being.

[jrp001]

Baja_Dave, on Aug 20 2011, 01:42 AM, said:

I think you may have been Reading the wrong Reviews   When was the last time your T40 was Calibrated????

And What features would these be in the T40 that you mention????     can it detect an Echo within the Guard Interval??????

If you are serious about getting into this industry then you need to upgrade your meter. If you don't intend to do satellite work then a Good FTA Analyzer is not that expensive. If you are only in it to Cash-in on the trade.....................Then good luck


Cheer's


Baja

Calibration on these installer meters only calibrates dB level, it doesnt calibrate MER's and BER's....Plug it into a known modulated output of a STB If is around 70dB and the attenuator drops in 10 dB steps thats good enough.

The T40 is a very simple meter and can be upgraded to do echo's but there is no need for this function in SFN's..Analyze your readings (MER, PRE & POST BER's) and see how they behave because this will tell you whats going on.

If you cant do a FTA (digital) install with this simple meter, then a high end meter isnt going to help you.

[bellotv]

jrp001, on Aug 21 2011, 05:57 PM, said:

Calibration on these installer meters only calibrates dB level, it doesnt calibrate MER's and BER's....Plug it into a known modulated output of a STB If is around 70dB and the attenuator drops in 10 dB steps thats good enough.

The T40 is a very simple meter and can be upgraded to do echo's but there is no need for this function in SFN's..Analyze your readings (MER, PRE & POST BER's) and see how they behave because this will tell you whats going on.

If you cant do a FTA (digital) install with this simple meter, then a high end meter isnt going to help you.

Spot on jrp001. I  was just about to say the same..

Going out on a limb here ,but I'd say there is nothing that a T40a (with the AER upgrade)  can't tell you that a more expensive "bells and whistles" analyzer can.

Edited by bellotv, 21 August 2011 - 06:21 PM.