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[les-70]

[waltergmw]

@ les-70,

I can confirm that a normal VDSL modem will run quite happily of its power supply connected to a small inverter plugged into a car's cigarette lighter socket.

Kind regards,
Walter

[les-70]

 Thanks,   I am fairly sure the HG612 power supply is not relevant in these tests.   I have done the test with a linear power supply on a BT mains conditioner and get exactly the same changes as when run of the normal switched mode psu on the direct mains.  The mains conditioner and/or linear psu give a quite separate ~0.3db improvement when used.  The linear supply made no difference when I had adsl so I guess the vdsl bandwidth raises the risk of noise.

 In the Ethernet cable swap test the issue really has to be a couple of bad Ethernet cables. They seem to work but can't be fully OK.  I guess the bad Ethernet cables have poor connections/higher impedance on some the wires used. Most cables give No impact,  a few a small impact and a couple (one of which I first used)  a large impact.   

[les-70]

    An update::  The two "bad" cables giving drops of 1-2 db snrm are simply faulty, one shows a high impedance where there should be about an ohm and the other has a loose connection somewhere in its makeup. It took a long while and some waggling to spot the loose connection one.   The other 3 cables giving smaller snrm drops of about 0.2-0.3 db are also in the bin now but nothing was obviously wrong with them.  Below I show the impact each of these 3 poor cables had on the snrm.  The impact of the obviously "faulty" cables was similar but much bigger.  As I noted above the poor cable adds a lot more noise to the highest frequency band

   I have retested all the other cables I have and can't get any effect from them i.e. they just work and don't influence the snrm at all when used on Lan2. They work perfectly in my normal setup and also in the test set up so everything is now as it should be  .  Those thinking it unexpected can be reassured that if the cables are good that is definitely the case. 

   However 5 cables are in the bin (for recycling) and I assume I may not alone in having some duff cables.   

[roseway]

That's an interesting result, and quite surprising. It's suprising that so many cables are faulty in this way, and surprising that the fault only affects the top band.

[les-70]

  I seem to have had 1 in 10 cables with a serious fault and 1 in 5 of those remaining with the "mild issue" seen in the snrm above.  1 in 4 overall does indeed seem very high rate but the collection does include some quite old cables.  One of the serious faults was an "brand new" BT hub cable and the other serious one was an old cable that may have been bent once too often. 

  It is interesting that all bar one of the cables seemed to work perfectly in the sense that all  Ethernet traffic got through OK.  The one with an intermittent open circuit did fail to pass Ethernet from time to time e.g. with router stats running whilst the cable was used and waggled a few samples were lost. 

   It was by pure luck that I noticed the noise and 0.3 db drop when I swapped in new cable on Lan2 when tidying the wiring up - I was only aiming to get the Lan1 and Lan2  cable colours different!

[burakkucat]

I have to agree with Eric. It is a most interesting and unexpected result. Thank you for the precise testing and clear explanation of your findings, les-70. 

[burakkucat]

I can confirm that a normal VDSL modem will run quite happily of its power supply connected to a small inverter plugged into a car's cigarette lighter socket.

Deviating off topic but using Walter's suggestion, above, will add yet another noise-generating device into the circuit! The average small inverter will be a switching based, oscillatory device which generates an approximation to a sine wave. That generated stepped square-wave (~240 V AC) is then transformed back to 12 V DC by the normal switching mode PSU.

For Walter's Wheelbarrow, I would construct an appropriately fused distribution box which takes the ~12 V DC from the car battery (via the cigarette light socket -- until such devices become Verboten) and to which a flying lead can be connected, thus allowing the modem to be directly powered from the car's battery. 

[les-70]

  @burakkaucat   

  On your deviated topic I have resisted batteries as they don't seem a long term connection solution. One day I may try it simply as an experiment.  I started in the direction of mains carried noise with a BT mains conditioner which gave me +0.3db snrm gain with a fixed speed sync.

 I then tried using as well a linear PSU for the HG612.  That gave a tiny extra benefit of ~0.1db.  However leaving out the BT conditioner and just using the linear supply is a very similar benefit to that given by the BT mains conditioner.  A linear PSU should have more mains isolation than a switched one and no issue with "switching noise".  Since the linear PSU did not give much extra  benefit when used with the BT mains conditioner I guess the  main benefit of the linear PSU may be just the isolation and filtering due to the linear PSU transformer.   I find the linear PSU more attractive as it does not hum and only uses an extra 1-2 watts c.f. the switched supply.  The BT conditioner used an extra 10 watts and had a small but noticeable hum.   

 As a further deviation I have been pleased that the DLM seems to have ignored all the testing.  Either it just does not care or it detects and ignores deliberate power downs.

[NewtronStar]

As a further deviation I have been pleased that the DLM seems to have ignored all the testing.  Either it just does not care or it detects and ignores deliberate power downs.

When reading your posts I was wondering to myself how the DLM would react to your testing and think as long as you leave a minium of 15 minutes in the powered off state between tests you should get away without any DLM intervention   

[waltergmw]

@ BKK,

If there are concerns about voltages and spikes etc., I would counsel some caution as car electrics can be quite variable too, depending upon engine / generator on and off, use of self starter etc.

Kind regards,
Walter

[Black Sheep]

Some good fault-finding experiments from Les. The learning curve continues ............... 

[Chrysalis]

this is interesting, now I am probably going to try swapping out both lan cables between my hg and router, both are isp supplied short cables not the usual long high quality ones I use for rest of my lan.

[les-70]

  I think that it is well worth trying the Lan cable swap test but judging by my collection there is only a 1 in 4 chance of any difference and then most probably only a change of a few tenth's of a db snrm -  but you never know unless you try.  It is a nice test as you remain in sync and and can monitor clearly what happens.

[les-70]

 An update.  I have now gained about 0.8 db snrm or 3mb/s of attainable by:-

   1. Replacing a dodgy lan cable  ~0.1-0.2 db
   2. Replacing the flat dsl cable with a homemade dsl cable using twisted pair  ~0.1db
   3  Running the HG612 on Bt mains conditioner ~0.2-0.3db
   4  Using a linear psu for the HG612  ~0.1
   5  Earthing the disconnected pair on the incoming drop wire and internal cable to the master socket ~0.2db

  Note that the last mod is not legal or recommended and has been done so that it can be easily and quickly removed.
  I checked carefully that the unused pair had no connection to earth and was open circuit before adding the earth connection.

  With mods 1-4 all in place the average error rate was reduced by about 30% and odd big crc spikes were reduced in size but still gave about 5 ses/day

  With mod 5 the error rate has halved and over a period of one week no ses or crc spikes have occurred - I believe this is the biggest useful change. I think I have obtained the benefit from the spare pair giving partial screening of the used pair. It may also be significant that the run to my house is underground until it goes up the pole that drop wire comes from.