This topic

SOGEA VDSL without using a filter

Colin_London — Sun, 18 Jun 2023 20:35:12 GMT

I am being (force) migrated to SOGEA Digital Voice over VDSL next week.

My broadband is just on the cusp of full 80/20, but the line capability sometimes drops down to 77Mbps (2.5 to 2dB margin) causing gradual attrition of the profile and eventually an inevitable resynch. If I can get an extra dB or so overhead on the line I think these resynchs can be avoided.

I am thinking that the move to digital voice presents the opportunity to dispose of the faceplate filter altogether and maybe gain a dB or two from removal of the filter insertion loss. I have even bought a standard faceplate to replace the v4 filtered faceplate. I see that Openreach support use of the standard faceplate to pass 'everything', but there is no cable specified.

I understand that there is no issue connecting the SmartHub 2 to the SOGEA line without a filter in place. However, which cable to use? Most of the 'BT plug to RJ11' cables on sale on Amazon are for old VF modem connections. These may be crossover cables. I have also seen 2 and 4 wire cable versions on sale. No idea if these would work for this connection.

Does anyone know of a short (1m) BT to RJ11 cable with the correct pinouts at each end to connect a SmartHub 2 directly to a standard 5c Master Socket faceplate? I don't want to damage the SH2 modem by using a cable with incorrect pinouts.

Re: SOGEA VDSL without using a filter

licquorice — Sun, 18 Jun 2023 20:59:29 GMT

You won't damage anything.

Re: SOGEA VDSL without using a filter

Colin_London — Sun, 18 Jun 2023 22:42:29 GMT

Thanks - but which cable to buy?

A two wire crossover?

A two wire non-crossover?

A four wire crossover?

What is a 'rollover' spec? Or will literally any old fax/modem cable work??

Re: SOGEA VDSL without using a filter

pippincp — Mon, 19 Jun 2023 01:13:28 GMT

Any old Fax/Modem cable. The only reason for the filter was to be able to use the voice service without interference from the broadband signal.

Re: SOGEA VDSL without using a filter

licquorice — Mon, 19 Jun 2023 06:52:45 GMT

Broadband (and telephony for that matter) only uses 2 wires and isn't polarity conscious.

Re: SOGEA VDSL without using a filter

Colin_London — Mon, 19 Jun 2023 07:18:24 GMT

Excellent. I have found a supplier who I have used before that makes high quality CAT5 cables including an option for BT to RJ11. So hopefully all set now for when the dial tone disappears.

I know that the ‘replacement’ SmartHub 2s are sent out without cables to reduce waste and I guess that the approach of just using the existing filtered faceplates is to reduce confusion for digital voice switchover. But keeping all those old filters in-situ is not the best technical solution and is diminishing the benefit of the migration to SOGEA.

Re: SOGEA VDSL without using a filter

licquorice — Mon, 19 Jun 2023 07:25:02 GMT

The broadband signal passes straight through the filter, it is the phone signal that is filtered.

Re: SOGEA VDSL without using a filter

Colin_London — Mon, 19 Jun 2023 08:10:06 GMT

If you remember your filter theory you will recall that any filter will introduce some loss in the passband - maybe only 0.5dB but it is there. This becomes more significant at the edge of the passband. If you don’t need a filter, get rid of it.

edit: just googled some micro filter specifications. They all have an insertion loss of between 0.5 and 1dB. That will be enough to reduce my resynchs.

Re: SOGEA VDSL without using a filter

Anonymous — Mon, 19 Jun 2023 08:00:39 GMT

I'm afraid previously replies aren't necessarily correct. While the BT plug always uses pins 2 & 5, some RJ11 sockets are wired 3 & 4. Hence why there is the choice between straight & crossover cables. So "Any old fax/modem cable" only has a 50:50 chance of working. You need a straight two wire cable, although four wire would do as the spare wires would simply be ignored.

But @licquorice is correct in that the filtering is only applied to the BT socket & not the RJ11. So unless you're faceplate is faulty, what you're proposing is a waste of time. If anything you want an old style extension socket that wires directly to the BT socket without a test socket.

Re: SOGEA VDSL without using a filter

Colin_London — Mon, 19 Jun 2023 08:15:24 GMT

Of course the intent is to pass the signal straight through but there is an insertion loss - as I quoted between 0.5 and 1dB. Is this not worth removing?

Thanks for the confirmation that a straight cable is required. Thankfully the one I have ordered is straight.

Re: SOGEA VDSL without using a filter

iniltous — Mon, 19 Jun 2023 09:05:54 GMT

Arguably the insertion loss refers to the voice frequency (0.3-3.4Khz ) the band pass filter is designed to allow, as stated the idea is to disallow ADSL/VDSL frequencies onto the voice path , so you may find your noise margins are unaffected by removing the filter on the ‘data’ side , but obviously it’s going to be fairly simple to check once you have removed the filter from your line.

Re: SOGEA VDSL without using a filter

licquorice — Mon, 19 Jun 2023 10:27:52 GMT

Re: SOGEA VDSL without using a filter

Colin_London — Mon, 19 Jun 2023 11:31:02 GMT

There is a bit more inside a VDSL filter than that!

Re: SOGEA VDSL without using a filter

licquorice — Mon, 19 Jun 2023 11:44:28 GMT

No there isn't, and in any case the broadband signal doesn't pass through it, the voice signal does.

Re: SOGEA VDSL without using a filter

pippincp — Mon, 19 Jun 2023 16:42:13 GMT

@Colin_London you'd be wrong. @licquorice is quite correct. Also there is no difference between an ADSL, VDSL or G.Fast filter. They all do the same thing.

Re: SOGEA VDSL without using a filter

Colin_London — Tue, 20 Jun 2023 09:49:28 GMT

They do the same thing, but the design has changed. Why do you think the faceplate went through different versions? The latest faceplate has a REIN filter in it as well which isn’t shown on the little sketch above.

Re: SOGEA VDSL without using a filter

Colin_London — Tue, 20 Jun 2023 21:38:42 GMT

So for the doubters - removing the filter, replacing with a standard faceplate and putting the BT<>RJ11 cable in place has given me an extra 0.5dB as predicted, and an extra 3Mbps overhead on my maximum data rate. This is even before the POTS service has been removed from the line.

Also took the faceplate apart (don't worry, not Openreach property I bought it online). It has:

4 x induction coils

8 x Surface Mount Capacitors

2 Electrolytic Caps

REIN filter

Surge Arrestor

6 resistors

So quite a bit more than that sketch......