all modems and router/modems have seperate power supplies to reduce the chance of mains finding it's way into the phone network

Que ? Separate power supplies, separate from what ? Each other ? The telly ? Next door ? If the power supply for a modem/router etc goes wrong, then the fact that it is usually connected direct to the telephone line via the RJ11 lead would mean it has a very easy way on to the Openreach pair.

Homeplugs and broadband modems both do similar things- they convert the digital networking signals into a form that is more suitable for transmission down the chosen physical link (and convert the signals coming the other way of course). But because they serve different requirements, they have different electrical characteristics and so aren't compatible either with each other or the "original" signal they are carrying.

There's a useful article covering some of the details of how they work here (courtesy of Wikipedia) which might help RobertoS understand why they need to be fed Ethernet frames.

They're actually pretty complex, encrypt the frames, do forward error correction and acknowledgement that the frame has been received as far as I can see.

Even if they worked as RobertoS thought, simply transferring signals from one plug to another without interpreting what the signal represented they probably wouldn't work for VDSL signals. If they behaved purely as a bit of wire they'd need to just connect the Ethernet transmit pin on one side to the receive pin on the other and vice versa using/emuating two pairs - that wouldn't work with VDSL which achieves a full duplex link on one pair by frequency division multiplexing the up&downstream signals and driving from both ends.

Rather more mundanely how would you connect the RJ11 from the faceplate to the RJ45 on the homeplug?If you took and RJ11<->RJ11 lead and plugged it into the central 6 pins of the RJ45 the VDSL signal (central pair) wouldn't actually connect to anything on a 100Mb/s Ethernet interface (that pair isn't used in 100Base-T).

I do confess though that one thing I haven't figured out is whether, when you use three or more of the things, what you get is more akin to an Ethernet hub or a switch - anybody know?

Edited by mr_bean (Sun 15-May-11 22:38:30)

In reply to a post by DarrenNI:

In my case, the extension wiring definitely wouldn't have been up scratch.

Good news though - bought a couple of Devolos, connected the modem to the one downstairs and the Home Hub to the upstairs one, and it worked like a dream, with no configuration whatsoever required. Absolutely negligible drop in speed as well.

Yes, there are undoubtedly neater and cheaper ways, but this was quick and avoided me having to use my non- existent DIY skills. Thanks everyone for the advice.

Which did you end up getting?
200mbps or 500mbps? or something else?

200mbps - fast enough for anything which I need, but probably not ideal if I were to be streaming HD video from the NAS or the like. Tempted to connect my Samknows unit to one end to see what the speed impact actually is.

In reply to a post by DarrenNI:

200mbps - fast enough for anything which I need, but probably not ideal if I were to be streaming HD video from the NAS or the like. Tempted to connect my Samknows unit to one end to see what the speed impact actually is.

I found that my 200Mbps Devolos topped out at just under 30Mbps throughput despite saying that they were connected at approx 100Mbps. They have now been replaced by a long ethernet cable.

In reply to a post by DarrenNI:

200mbps - fast enough for anything which I need, but probably not ideal if I were to be streaming HD video from the NAS or the like. Tempted to connect my Samknows unit to one end to see what the speed impact actually is.

That will be more than fast enough to stream high definition movies - I have a set of the Devolo 200Mbps units and stream 1080p with ease..

The 200Mbps is both directions combined, thus 100Meg either way in perfect conditions, and then as the metres of wiring increases throughput will drop further.

Ethernet cable is still best, but for those not able to run cable or put ends on CAT5e/6 then the homeplugs have represented a solution for some time.

Indeed. Best ones available are the Solwise Gigabit.

http://www.solwise.co.uk/net-powerline-gig-index.htm

The throughput achieved on homeplugs is always well under the headline speed but in a house wired in the last 25 years you should be able to pull 100+ Mbit realistic throughput on the Solwise 1GBit set.

Reading several reviews and benchmarks, this is the highest throughput seen to date.

Still slower than my 5GHz N though... Just.

In reply to a post by MrSaffron:

The 200Mbps is both directions combined, thus 100Meg either way in perfect conditions, and then as the metres of wiring increases throughput will drop further.

Yes the condition and length of the wiring matters, I cannot guarantee where the wiring goes in my house, when an electrician did some wiring in my kitchen he found that three pairs of sockets were spurred off the main ring

Ethernet cable is still best, but for those not able to run cable or put ends on CAT5e/6 then the homeplugs have represented a solution for some time.

I had been using the homeplugs because I was too lazy to do it properly, I decided to cable it in the end as it was cheaper than another set of homeplugs.