Galvanic isolators - insertion losses?

[SimonM]

Truthfully, this is a co-ax broadband question,
but the people who are most likely to know what's
what read this forum :-)

Virgin recently fitted a galvanic isolator to our
BB. The technician didn't do it very well, and I
found out last week it was the cause of the
performance problems we had (because he didn't
tighten up an F-connector properly, then hid it
inside a plastic cover).

So that one is now sorted, but it made me wonder
about the impedance matching of the things. I
couldn't find impedance graphs for the model
Virgin used, but a similar one I did find had a
whole lot of nasty notches in-band (comb filter
effect), implying it was causing reflections, and
thus not properly matched.

The one we have arrived with a 10-inch tail, which
experience tells me isn't a very good thing if
it's not matched (reflections going both
directions). So I've replaced that with
back-to-back F connectors, straight onto the pad
on the back of the modem. It doesn't eliminate the
mismatch, but it might (I hope) mitigate the
problem a bit.

So far it's all working really well, but are there
any thoughts from the RF experts?

S.

[Brian Gaff]

Which leads me to a not unrelated query. If I want my bb router from Virgin
in the next room is it feasible to buy cable and male and female connectors
and just extend it or is this likely to fail due to the effect of the longer
cable run?
Brian

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"SimonM" <some...@large.in.the.world> wrote in message
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[Phi]

I have a twisted pair running between my downstairs telephone incomer box
and the alternative connection box upstairs. In fact I had to break the
wires and rejoin them by just twisting the wires together when I had a new
front door fitted.

"Brian Gaff" <bri...@blueyonder.co.uk> wrote in message
news:otn9fj$17v$1...@news.albasani.net...

[SimonM]

On 05/11/17 15:07, Brian Gaff wrote:
> Which leads me to a not unrelated query. If I want my bb router from Virgin
> in the next room is it feasible to buy cable and male and female connectors
> and just extend it or is this likely to fail due to the effect of the longer
> cable run?
> Brian

The usual rules apply: impedance matched joints as
much as possible and appropriate co-ax. If you do
that you will be fine.

They use F connectors, which are the sort that use
the signal core of the co-ax as the connector pin.

I use the ones with a very coarse thread inside,
that you can screw onto the plastic sleeve (with
the braid turned outewards over the top. It's like
making off a traditional PO 316 jack plug.

You will need a barrel for the middle-of-cable
joint (remember them), but otherwise it will all
go together easily, and should work fine.

In our house there is already a joint, where the
cable comes into the house. That's about 25% along
the run from the amp in the pavement box (almost
right outside). As far as I can tell it causes no
problems.

[Bill Wright]

On 05/11/2017 15:33, Phi wrote:
> I have a twisted pair

Yes we've got one on our street

Bill

[Bill Wright]

On 05/11/2017 15:49, SimonM wrote:

> The usual rules apply: impedance matched joints as much as possible and
> appropriate co-ax. If you do that you will be fine.
>
> They use F connectors, which are the sort that use the signal core of
> the co-ax as the connector pin.

I've been unable to detect significant VSWR problems at UHF caused by
two fs and a barrel.

Bill

[SimonM]

Good-oh.

What about galvanic isolators? I'd never seen one
in the flesh before this one (so to speak), but
Googling suggests you have to use them in
distributed aerial systems between buildings, to
avoid earth currents, etc.

I know, "don't trust Google!" But anyway, have you
had them be more of a nuisance than just the faff
of fitting them?

[Brian Gaff]

Virgin use a coaxial cable of very big and stiff construction.
Its not like BTs silly semi broadband.

Brian

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"Phi" <phi...@inbox.com> wrote in message
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[Brian Gaff]

I've often wondered why they use the inner as the pin, I'm used to N
connectors when I was working lots of chunkyness!

Brian

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"Bill Wright" <wrights...@f2s.com> wrote in message
news:otnons$os$1...@gioia.aioe.org...

[Brian Gaff]

There will always be losses of course when you attempt to isolate both
conductors, DC wise however its done. I suppose the trick is to make sure
the levels are good and the s/n is good.
Not had much to do with between building systems. Why should this matter
these days?

Brian

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"SimonM" <some...@large.in.the.world> wrote in message

news:dcKLB.157$Er1...@fx11.am4...

[Robin]

I recommend you leave the connection to their cable accessible if you
can. I say that because Virgin can blame you for problems when they
find you have their modem connected to cable which they don't own.

I am not saying they will do so. But it is best if you can, if they get
sniffy, move the modem back temporarily.

Subject to back, what you propose will work. I moved our modem about 8m
when I had the floorboards up. But I had the benefit of 25m of spare
white coax left for me for that purpose by the Telewest installer :)

On 05/11/2017 15:07, Brian Gaff wrote:
> Which leads me to a not unrelated query. If I want my bb router from Virgin
> in the next room is it feasible to buy cable and male and female connectors
> and just extend it or is this likely to fail due to the effect of the longer
> cable run?
> Brian
>


--

Robin
reply-to address is (intended to be) valid

[Dave Liquorice]

On Mon, 6 Nov 2017 09:04:24 -0000, Brian Gaff wrote:

> Not had much to do with between building systems. Why should this
> matter these days?

Exporting earths. You don't want to connect the earth of one building
to the earth of another the chances are they will be at different
potentials leading to earth loop currents and induced hum.

--
Cheers
Dave.

[Dave Liquorice]

On Mon, 6 Nov 2017 09:01:26 -0000, Brian Gaff wrote:

> I've often wondered why they use the inner as the pin, I'm used to N
> connectors when I was working lots of chunkyness!

A way of producing a very cheap, quick to fit, solderless, connector
with a constant impedance.

--
Cheers
Dave.

[Bill Wright]

On 05/11/2017 20:07, SimonM wrote:

> What about galvanic isolators? I'd never seen one in the flesh before
> this one (so to speak), but Googling suggests you have to use them in
> distributed aerial systems between buildings, to avoid earth currents, etc.

Google speaks the truth. Well, sort of. I've only had to do that once,
in all my years before the mast.

Bill

[Bill Wright]

On 06/11/2017 09:04, Brian Gaff wrote:
> There will always be losses of course when you attempt to isolate both
> conductors, DC wise however its done. I suppose the trick is to make sure
> the levels are good and the s/n is good.
> Not had much to do with between building systems. Why should this matter
> these days?
> Brian
>

The losses are minimal. Much depends on the construction of course.

Bill

[Bill Wright]

The one I had with that problem was OK until a projector was connected
to the RF system. Then we had the coax outer providing a moving ground
potential. The effect was much like when there's a faulty capacitor in a
PSU and the gain of the RF amps is moving up and down.

I've always been surprised that this doesn't happen more often. We have
a lot of systems with earthed amps in different buildings but there
doesn't seem to be a problem.

Bill

[Bill Wright]

Cheap unless you go to Maplins

Bill

[J. P. Gilliver (John)]

In message <otplgb$1m6p$1...@gioia.aioe.org>, Bill Wright
<wrights...@f2s.com> writes:
[]

>in all my years before the mast.
>
>Bill

<chuckle>
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

My mission in life is not merely to survive, but to thrive, and to do so with
some passion, some compassion, some humour, and some style. - Maya Angelou,
quoted by Annabel Nnochiri, in RT 2017/5/13-19

[Graham.]

On Mon, 6 Nov 2017 12:52:24 +0000, Bill Wright
<wrights...@f2s.com> coalesced the vapors of human experience into
a viable and meaningful comprehension...

The one I remember was the betting shop that expanded into the shop
next door. While both electricity supplies were available, the
satellite receiver and decoder were plugged into one, and the audio
amp and the tellies were on the other. The hum-bars and audible hum
were a sight to behold.
--

Graham.
%Profound_observation%

[John Williamson]

On 06/11/2017 19:45, Graham. wrote:

> The one I remember was the betting shop that expanded into the shop
> next door. While both electricity supplies were available, the
> satellite receiver and decoder were plugged into one, and the audio
> amp and the tellies were on the other. The hum-bars and audible hum
> were a sight to behold.
>

I'm surprised the magic smoke didn't escape. Adjacent shops (And houses)
are normally on different phases unless they need enough amps to need 3
phase.

--
Tciao for Now!

John.

[J. P. Gilliver (John)]

In message <f6btir...@mid.individual.net>, John Williamson

The audio and video signals would have been nominally isolated from the
mains: obviously not enough to prevent hum and hum bars, but enough for
electrical safety. (Though I would be wary too.)

--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Our thorny national debate about Brexit could turn out to be irrelevant.
Sooner or later the EU as we know it may no longer be there for us to leave.
- Katya Adler, BBC Europe editor (RT, 2017/2/4-10)

[SimonM]

On 06/11/17 22:49, J. P. Gilliver (John) wrote:
> The audio and video signals would have been
> nominally isolated from the mains: obviously not
> enough to prevent hum and hum bars, but enough for
> electrical safety. (Though I would be wary too.)

It's not live and neutral that are the issue here
(although 415V between won't help), it's the way
earths are derived or otherwise.

IIRC, common practice is to bond cable armouring
to the laminations of the 11kV Xfmr, but that
encourages corrosion, which in turn lifts
resistance and thus potentials.

I don't think streets go R,B,Y,R,B,Y,R,B,Y, etc.
any more either, especially not High Streets. The
more unbalanced the phases, the more "fun" to be
had, as it affects the neutral current and the
neutral-to-earth PDs.

I can't remember what happens upstream of the 11kV
Xfmr, but I think it's a virtual neutral back to
the (nominal) power station. I know the higher
voltage lines have an earth wire along the top of
the pylons.

In Virgin's case they had DAs in die-cast
aluminium housings that doubled as heatsinks. The
ones they put underground (in manholes) rotted
fairly fast, as their power was DC on the trunk
co-ax. They're now in the pavement boxes, and I
think V. doesn't want to have to renew them again
too soon.

It's a mess really - they buy the cheapest modems
for the properties, then waste a lot of resource
supporting them (e.g. they could have built the
isolation (and signal pads) into the box). I
recently bought my own firewall/router as Virgin's
latest "super hub" is far from super.

[tony sayer]

>
>In Virgin's case they had DAs in die-cast
>aluminium housings that doubled as heatsinks. The
>ones they put underground (in manholes) rotted
>fairly fast, as their power was DC on the trunk
>co-ax. They're now in the pavement boxes, and I
>think V. doesn't want to have to renew them again
>too soon.

I think a lot depended on the original builders, remember different
companies came and did different locations. We had Comcast do our area
and AIUI from a friend who works for them it was well done.

>
>It's a mess really - they buy the cheapest modems
>for the properties, then waste a lot of resource
>supporting them (e.g. they could have built the
>isolation (and signal pads) into the box). I
>recently bought my own firewall/router as Virgin's
>latest "super hub" is far from super.

What's wrong with it?.

--
Tony Sayer

[Dave Liquorice]

On Wed, 8 Nov 2017 09:22:57 +0000, SimonM wrote:

> I don't think streets go R,B,Y,R,B,Y,R,B,Y, etc. any more either,

No they go B,B,G,B,B,G,B,B,G these days. B-)

> I can't remember what happens upstream of the 11kV
> Xfmr, but I think it's a virtual neutral back to
> the (nominal) power station.

Well the 11 kV side of our transformer just has two phases. One
assumes that the 11 kV star center point is rather well bonded into
the real earth at the primary substation (33 kV to 11 kV) like wise
the source fo the 33 kV. Our supply side has one leg of the
transformer bonded into the real earth, which forms the shared
neutral earth. The other leg is the live.

> I know the higher voltage lines have an earth wire along the top of
> the pylons.

Yeah but it's tiddly compared to the power lines. I think it's there
for lightning protection rather than anything to do with providing an
"earth".
Oh and for wrapping fibre optic cables a round.

--
Cheers
Dave.

[Roderick Stewart]

On Wed, 8 Nov 2017 18:40:39 +0000, tony sayer <to...@bancom.co.uk>
wrote:

>>It's a mess really - they buy the cheapest modems
>>for the properties, then waste a lot of resource
>>supporting them (e.g. they could have built the
>>isolation (and signal pads) into the box). I
>>recently bought my own firewall/router as Virgin's
>>latest "super hub" is far from super.
>
>What's wrong with it?.

When I had to deal with the VM Superhub (a few years ago now), it got
a lot of criticism for its allegedly poor wireless performance. I
didn't get much of an opportunity to play with one myself so I don't
know if it really was as bad as some people said it was, but I've
often wondered if a lot of its wireless problems could be the result
of there being generally less freedom of placement within houses on
account of it using a more awkward cable type than a BT phone line.
Not only that, but the initial placement might in many cases be
optimised for their TV box, which uses the same cable. A corner of the
front room near where the main cable enters the building might be an
easy place to install a superhub, and it might suit a connection to
the TV box, but it's not the best place for wireless coverage for the
whole house.

Rod.

[Stephen]

The Grid is busy replacing those with a combined ground wire and fibre
cable
- the "wrap" cable was rated for 15 years, so now past the original
projected dates.

Wiki has some info on OPGW -
https://en.wikipedia.org/wiki/Optical_ground_wire

--
Stephen

[tony sayer]

In article <tg080d1iipdpr9eg3...@4ax.com>, Roderick
Stewart <rj...@escapetime.myzen.co.uk> scribeth thus

And prolly left like they all are round here on the default channel 6
and interfering with each other!...
--
Tony Sayer

[SimonM]

I have the latest Virgin Modem/router model.
"Super"-anything it most definitely isn't. The
previous one was far better (heck I only wanted
them to replace a glowing PSU!).

Because of its location on the property, the WiFi
performance has always been irrelevant. The
biggest issue is that the firmware is dreadful and
it can't be properly managed.

I have never, ever before come across any sort of
modem that doesn't let you set its LAN IP address.
You can only do it with this one via an SNMP (SSH)
hack, and it's not persistent - any pushed
firmware update will override it. Staggeringly
annoying: "Yes, Virgin, of course I don't mind
reconfiguring ALL the static devices on my network
(and there are a few) just because your
acceptance-testing QC is garbage".

Also, in use I discovered that its web interface
was slow and emitted broken HTML/CSS/Javascript
(as far as I can tell), and didn't manage state
cookies properly (or something). And a lot of
other useful bits of the system were made
inaccessible by the custom firmware for Virgin,
including causing extreme annoyance trying to set
up MAC address tables, the use of node names
(inconsistent and erratic), and so on.

Frankly it was a time-wasting menace, because of
the risk of not locking-down something properly
(because the GUI lied about status of certain
functions).

I bit the bullet and bought an industrial-grade
very fast firewall router* and shoved the Virgin
thing into modem mode. The new kit is a delight in
comparison, and apparently bomb-proof.

And several security firmware updates since early
summer indicates that somebody cares about their
customers, too.

Final thought: the new "Sooper" hub and its PSU
actually run hotter than the predecessors,
although doing less work. I wonder how long this
one will last...

S.

*Ubiquity, in case anyone is interested. Not cheap
but bril and very quick. It will also integrate
with a managed net of their WiFi APs in due
course, allowing the whole lot to be controlled
from one URL.

And for the first time ever I can put IoT garbage
(like the Panasonic TV - not a single firmware
update since 2013!) on a "dangerous" subnet
(physically separate if I want) that really is
properly isolated from the important kit.

[Dave Liquorice]

On Sat, 11 Nov 2017 08:54:02 +0000, SimonM wrote:

> *Ubiquity, in case anyone is interested. Not cheap but bril and very
> quick. It will also integrate with a managed net of their WiFi APs in
> due course, allowing the whole lot to be controlled from one URL.

Not bad kit Ubiquity, (Chinese of course, back doors?) Be aware that
they have a habit of refering to PoE but it's not real 802.3af or
802.3at PoE but 24 V passive and I don't think there is any interlock
to prevent the full benefit of 24 V with a reasonable current
capabilty being applied to something that won't appreciate such
benefit. B-)

> And for the first time ever I can put IoT garbage (like the Panasonic TV
> - not a single firmware update since 2013!) on a "dangerous" subnet

Slightly more paranoid than me but then everything here apart from
the VOIP is behind two or three layers of NAT.

--
Cheers
Dave.