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TopTapper
Posted: Fri Apr 20, 2012 2:35 pm Reply with quote
Frequent contributor Joined: 29 Jan 2006 Posts: 234
Signal Monitor is showing dubious quality on COM6 since Crystal Palace DSO. The sample always ranges from 0 to 100 with the average usually in the 80s or 90s, fairly often 100. The low-level quality reading on COM4 shown below looks like a one-off (possibly due to heavy toggling of sampling options at the time).

Code:
Signal Monitor 0.54 RC3 Results

Measured on 20/4/2012 at 12:30

Data format (Min:Av:Max %):    T1 Levels     T1 Quality    T2 Levels     T2 Quality
PSB1 BBC ONE   on RF Ch 23   | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
PSB2 ITV1      on RF Ch 26   | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
COM4 ITV3      on RF Ch 25   |  89: 99:100 | 100:100:100 | 100:100:100 | 100:100:100
COM5 Pick TV   on RF Ch 22   | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
COM6 Yesterday on RF Ch 28   | 100:100:100 |   0: 78:100 | 100:100:100 |   0: 63:100

Settle time: 500 milliseconds - Sample time: 10 seconds


Does this look like excessive signal strength? There's a good unbroken cable to Toppy but from a wideband aerial which was set up by roughly following neighbours' kit. It's roughly 8 miles from the transmitter and has worked well pre-DSO, even when it found a new position in a storm - probably because I over-tightened an alloy masthead clamp.

Viewing the COM6 channels always appears fine - there's no hint of audio or visual glitch so I'm wondering if I can ignore the reading - at least until the summer when scaffolding will be up - or is that asking for a Topfield disk-wipe?

Any opinions appreciated.

MyInfo channel data:
Code:
Found 28 TV channels and 7 Radio channels
No channel problems detected
LCNs of programme channels found on Tx Ch 22 are: 11, 19, 20, 29,
LCNs of programme channels found on Tx Ch 23 are: 1, 2, 7, 9, 80, 301, 302, 702, 703, 704, 705, 706, 707, 708,
LCNs of programme channels found on Tx Ch 25 are: 10, 27, 30, 31, 38, 44,
LCNs of programme channels found on Tx Ch 26 are: 3, 4, 5, 6, 13, 14, 28, 33,
LCNs of programme channels found on Tx Ch 28 are: 12, 15, 24,

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andyfras
Posted: Fri Apr 20, 2012 3:19 pm Reply with quote
Frequent contributor Joined: 25 Jul 2005 Posts: 3463
I advise a 12dB attenuator.

Since DSO at Hannington, I have removed a 15dB mast-head amplifier and replaced it with a 4-way passive splitter. My signal strengths are between 70% - 90% and quality is 100% on all muxes.

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TopTapper
Posted: Fri Apr 20, 2012 4:20 pm Reply with quote
Frequent contributor Joined: 29 Jan 2006 Posts: 234
Thanks for the advice, andyfras. It looks like my inappropriate aerial isn't going to save me Wink so I'll see how I get on with a variable attenuator...
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mstombs
Posted: Sat Apr 21, 2012 9:06 am Reply with quote
Frequent contributor Joined: 31 Dec 2006 Posts: 938
Interesting plots of before/after broadcast signals here:-

http://www.bbc.co.uk/blogs/researchanddevelopment/2012/04/goodbye-analogue-telly-hello-d.shtml





surprisingly COM5 should now be strongest, but how your reception and distortion maps into COM6 anyones guess!
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alan_m
Posted: Sat Apr 21, 2012 9:45 am Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3523
andyfras wrote:
I advise a 12dB attenuator.

I have removed a 15dB mast-head amplifier and replaced it with a 4-way passive splitter.


Thats a extra 21dB of attenuation so if a system was close to overload before DSO then 12dB may be too low. If purchasing at 1 [1] it may be worth buying a few of different values. Although not a mechanically stable arrangement, in-line attenuators can be plugged into each other. A set comprising 6, 9 and 12dB can give you 6, 9, 12, 18, 21 and 27dB for test purposes.

[1]
http://www.beststuff.co.uk/store/TV-Attenuator.htm

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alan_m
Posted: Sat Apr 21, 2012 9:54 am Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3523
mstombs wrote:

surprisingly COM5 should now be strongest, but how your reception and distortion maps into COM6 anyones guess!


The Toppy doesn't show a level figure above 99% (100% reported by Signal Monitor) so if the level on COM6 was 10% or 500% higher than the threshold for overloading the Toppy's tuner the Toppy would still only report 99%. 100% signal level and near zero quality can be seen under certain weather conditions but if remains like this 24/7 then it suggests too much signal.

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andyfras
Posted: Sat Apr 21, 2012 9:58 am Reply with quote
Frequent contributor Joined: 25 Jul 2005 Posts: 3463
alan_m wrote:
Thats a extra 21dB of attenuation...

Our situation was a bit unusual as the Hannington signal was deliberately reduced in our direction to prevent interfering with Guildford analogue (shared many of the frequencies). This meant that after DSO, not only did we get the normal power increase, but the directional attenuation was also removed, leading to about 24dB increase (estimate) in our direction.

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TopTapper
Posted: Tue Apr 24, 2012 4:35 pm Reply with quote
Frequent contributor Joined: 29 Jan 2006 Posts: 234
Many thanks for the replies, all but one I've only just noticed! I don't know what to make of the results I'm now getting with a variable attenuator. Signal Monitor 0.54 RC3, all at 500ms settle & 5s sample gives:
Code:
  Min:Average:Max%               T1 Levels     T1 Quality    T2 Levels     T2 Quality
1 Min (~0dB)
  PSB1 BBC ONE on RF Ch 23    | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  PSB2 ITV1 on RF Ch 26       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM4 ITV3 on RF Ch 25       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM5 Pick TV on RF Ch 22    | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM6 Yesterday on RF Ch 28  | 100:100:100 |   0: 22:100 | 100:100:100 | 100:100:100
2 Max (~20dB)
  PSB1 BBC ONE on RF Ch 23    |  75: 76: 80 | 100:100:100 | 100:100:100 | 100:100:100
  PSB2 ITV1 on RF Ch 26       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM4 ITV3 on RF Ch 25       |  98: 99:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM5 Pick TV on RF Ch 22    |  75: 75: 77 | 100:100:100 | 100:100:100 | 100:100:100
  COM6 Yesterday on RF Ch 28  |  94: 99:100 | 100:100:100 | 100:100:100 |   0: 72:100
3 Mid-range (~11dB)
  PSB1 BBC ONE on RF Ch 23    | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  PSB2 ITV1 on RF Ch 26       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM4 ITV3 on RF Ch 25       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM5 Pick TV on RF Ch 22    | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM6 Yesterday on RF Ch 28  | 100:100:100 | 100:100:100 | 100:100:100 |   0: 43:100
4 Max (~20dB) input to T2
  PSB1 BBC ONE on RF Ch 23    |  87: 97:100 | 100:100:100 |  80: 80: 81 | 100:100:100
  PSB2 ITV1 on RF Ch 26       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM4 ITV3 on RF Ch 25       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM5 Pick TV on RF Ch 22    |  84: 92:100 | 100:100:100 |  76: 78: 80 | 100:100:100
  COM6 Yesterday on RF Ch 28  | 100:100:100 | 100:100:100 | 100:100:100 |   0: 34:100


Is something's askew with the hardware or results? In test 3, how can T2 signal strength be higher than T1 (over ~5 minutes on the max test)? It's the same story in test 4, where the attenuator output goes direct to T2. Oddness and despite test 4, I'm guessing that a faulty attenuator isn't likely to explain the results.

It's probably a good time to check the PSU voltages...

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alan_m
Posted: Tue Apr 24, 2012 7:52 pm Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3523
TopTapper wrote:

Is something's askew with the hardware or results? In test 3, how can T2 signal strength be higher than T1 (


The tuner outputs will have some gain. It will be nominally x1 into 75 ohms but it could be x0.9 or x1.1 (or more) If you have used the the short cable to join the two tuners then one tuner will be getting the aerial signal and the other will be getting the aerial signal x the tuner output stage gain.

If something is being overloaded at one frequency the output stages could be doing something unpredictable.

The signal level monitoring is also likely to be rather crude in implementation and so +/- 5% shouldn't cause to much worry.


With 20dB in circuit you are still getting 100% signal levels. Are you sure that you haven't got any amplifiers in line?
As one of the tuners gets you back to near 100% quality when you reduce the input by 20dB (x10) it suggest that you still have two much signal.

If you have a two way passive aerial splitter to hand this would give some more attenuation.
Aerial lead -> 20db attenuator -> aerial splitter -> two separate aerial fly leads.
The 20dB attenuator plus the splitter would give a total or around 24dB (x16) so you may have to back off the variable attenuator. Otherwise, a larger attenuator.

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TopTapper
Posted: Tue Apr 24, 2012 8:55 pm Reply with quote
Frequent contributor Joined: 29 Jan 2006 Posts: 234
Thanks for the advice, alan_m. There's no amp in the chain - I fitted the aerial and cabling a few years ago ... there's an unbroken cable from aerial to toppy or attenuator. (That's not the whole story as T2 feeds an amp, which is never powered, which in turn feeds a cheap FM/TV splitter which is used for a radio [and the TV, pre-DSO]). I should be able to re-jig the kit to reduce the signal further but there may be hardware issues at play...

PSU voltages, after a few hours time shifting (and a brand new multimeter battery):
Code:
-------------------
 5     5.00 - 5.01
12    12.46 - 12.49
-------------------
30    31.1
22    24.9
17    17.61 - 17.62
 8     7.60 - 7.62 
 5     5.00
 3.3   3.31 - 3.32
15    15.76 - 15.78
-------------------

Perhaps, more significantly, the U20 reading is very low @ ~0.03 measuring from chassis to top of capacitor. Is this likely to screw reception? (I didn't know what else to check).

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alan_m
Posted: Tue Apr 24, 2012 9:09 pm Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3523
TopTapper wrote:

Perhaps, more significantly, the U20 reading is very low @ ~0.03 measuring from chassis to top of capacitor. Is this likely to screw reception? (I didn't know what else to check).


Chassis and 0V are not the same thing. Instead of chassis use a 0V line on the power supply connector.

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alan_m
Posted: Tue Apr 24, 2012 9:23 pm Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3523
TopTapper wrote:
(That's not the whole story as T2 feeds an amp, which is never powered, which in turn feeds a cheap FM/TV splitter which is used for a radio [and the TV, pre-DSO]).


Are the Signal Monitor figures you posted previously with this extra equipment on T2 removed?

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andyfras
Posted: Tue Apr 24, 2012 10:48 pm Reply with quote
Frequent contributor Joined: 25 Jul 2005 Posts: 3463
TopTapper wrote:
Perhaps, more significantly, the U20 reading is very low @ ~0.03 measuring from chassis to top of capacitor. Is this likely to screw reception?

Measure the wide tab of U20 (relative to chassis is fine).

If U20 was giving out such a low voltage, the main processor would not work at all and there would be no reception.

The PSU voltages are OK.

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TopTapper
Posted: Wed Apr 25, 2012 2:19 am Reply with quote
Frequent contributor Joined: 29 Jan 2006 Posts: 234
alan_m wrote:
Are the Signal Monitor figures you posted previously with this extra equipment on T2 removed?


Probably not - sorry if this should have been mentioned before. Tests 5-8 below are run with nothing attached to T2 out. Test 5 is a re-run of the standard set-up, 6-8 use the unpowered amp to provide single or dual feeds to the Toppy. (The quality of the cable used from amp to T2 is slightly suspect).

Code:
  Min:Average:Max%               T1 Levels     T1 Quality    T2 Levels     T2 Quality
5 Max (~20dB) no T2 output
  PSB1 BBC ONE on RF Ch 23    |  75: 77: 80 | 100:100:100 | 100:100:100 | 100:100:100
  PSB2 ITV1 on RF Ch 26       |  86: 97:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM4 ITV3 on RF Ch 25       | 100:100:100 | 100:100:100 | 100:100:100 | 100:100:100
  COM5 Pick TV on RF Ch 22    |  75: 76: 77 | 100:100:100 | 100:100:100 | 100:100:100
  COM6 Yesterday on RF Ch 28  |  86: 92:100 |   0: 41:100 | 100:100:100 |   0: 95:100
6 Max Att->Amp->T1->T2
  PSB1 BBC ONE on RF Ch 23    |  55: 56: 57 | 100:100:100 |  63: 63: 64 | 100:100:100
  PSB2 ITV1 on RF Ch 26       |  57: 57: 60 | 100:100:100 |  62: 62: 63 | 100:100:100
  COM4 ITV3 on RF Ch 25       |  60: 60: 60 | 100:100:100 |  65: 65: 65 | 100:100:100
  COM5 Pick TV on RF Ch 22    |  56: 57: 58 | 100:100:100 |  62: 62: 63 | 100:100:100
  COM6 Yesterday on RF Ch 28  |  56: 56: 56 |   0: 79:100 |  62: 62: 62 |   0: 79:100
7 Max Att->Amp-|->T1
               |->T2
  PSB1 BBC ONE on RF Ch 23    |  54: 54: 54 | 100:100:100 |  54: 54: 55 |  97: 97: 98
  PSB2 ITV1 on RF Ch 26       |  55: 55: 56 | 100:100:100 |  56: 56: 57 |  96: 96:100
  COM4 ITV3 on RF Ch 25       |  56: 57: 60 | 100:100:100 |  58: 58: 60 | 100:100:100
  COM5 Pick TV on RF Ch 22    |  54: 54: 54 | 100:100:100 |  55: 55: 55 |  99: 99:100
  COM6 Yesterday on RF Ch 28  |  55: 55: 55 |   0: 51:100 |  55: 55: 56 |   0: 34:100
8 Mid-Range (rest as 7)
  PSB1 BBC ONE on RF Ch 23    |  69: 69: 70 | 100:100:100 |  69: 69: 69 | 100:100:100
  PSB2 ITV1 on RF Ch 26       |  71: 71: 72 | 100:100:100 |  70: 71: 72 | 100:100:100
  COM4 ITV3 on RF Ch 25       |  72: 72: 73 | 100:100:100 |  72: 72: 73 | 100:100:100
  COM5 Pick TV on RF Ch 22    |  70: 70: 71 | 100:100:100 |  69: 69: 70 | 100:100:100
  COM6 Yesterday on RF Ch 28  |  70: 70: 71 |   0: 80:100 |  69: 70: 71 |   0: 48:100 

It's still proving difficult to get reliable quality on COM6 but I'll keep trying.

@andyfras & alan_m: On U20, after further tests with various grounds and much head scratching, it looks like my multimeter only does >2V DC. The packaging states "DC: 2V - 600V". Previously, I assumed the 2V band was 0-2V, not 2+. It seems like a mighty whacky place to start, Maplin "Precison Gold" PG 010.
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andyfras
Posted: Wed Apr 25, 2012 7:40 am Reply with quote
Frequent contributor Joined: 25 Jul 2005 Posts: 3463
TopTapper wrote:
...it looks like my multimeter only does >2V DC. The packaging states "DC: 2V - 600V". Previously, I assumed the 2V band was 0-2V, not 2+. It seems like a mighty whacky place to start, Maplin "Precison Gold" PG 010.

Try measuring a 1.5V battery (AA, AAA, C, D).

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