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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

The Terminator - I'll not be back



 
 
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  #31  
Old June 22nd 17, 11:26 AM posted to uk.tech.digital-tv
Dan[_3_]
external usenet poster
 
Posts: 8
Default The Terminator - I'll not be back

On Tue, 20 Jun 2017 16:43:18 +0000 (UTC), Tweed wrote:

A
colleague had a problem with sudden loss of performance at random times,
and came across a Virgin van in the area and the technician said they were
trying to trace the uncapped modem.


A few years back I briefly worked for Kuhne & Nagel at a VM Media engineer
field store. VM & their installers (Kelly then now MAP) also used the
building. There were lots of notices & warnings around about chipped boxes.

I don't think the problem is as bad now, but I heard that huge areas were
full of chipped TV boxes. I think the cable modems used MAC spoofing BICBW,
a valid MAC code from another area was cloned & used in another area.

I was an early user of their Cable Modems in the Diamond Cable days, they
dropped the price from 40 to 20 a month for 512Kb, lighting fast back
then, if you purchased the modem for 150, 25 a month if not.
There was no automation on install, I had to ring DC with my MAC code &
they activated it before the Kelly guy came to put the point in. I did
still have a (unterminated) TV point, so plugged it into that & it worked
fine.
I had a techie workmate who also signed up, he told me that the speed you
got was set by the modem firmware & he had hacked it to get 2Mb. He was
prone to extreme bull**** though.

D
  #32  
Old June 22nd 17, 01:03 PM posted to uk.tech.digital-tv
Ian Field
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Posts: 125
Default The Terminator - I'll not be back



"Terry Casey" wrote in message
...
In article -
september.org, lid says...


Probably needs a better brain than mine to give a detailed
explanation ...


A fellow member of the
http://golbornevintageradio.co.uk/
forums has pointed me to this:

http://www.antenna-theory.com/defini...eciprocity.php

which says:

"Reciprocity

Reciprocity is one of the most useful (and fortunate)
property of antennas. Reciprocity states that the receive
and transmit properties of an antenna are identical. Hence,
antennas do not have distinct transmit and receive radiation
patterns - if you know the radiation pattern in the transmit
mode then you also know the pattern in the receive mode.
This makes things much simpler, as you can imagine."

So, if a poor SWR - such as might result from an
unterminated feeder - can cause it to radiate, the
reciprocity property means that it must be able to receive
as well - screening or no screening.


Co ax outer screens the inner - but nothing screens the outer and it can
radiate. Twin feeder allegedly cancels out.

  #34  
Old June 22nd 17, 03:30 PM posted to uk.tech.digital-tv
Ian Jackson[_7_]
external usenet poster
 
Posts: 59
Default The Terminator - I'll not be back

In message , Ian Field
writes


"Terry Casey" wrote in message
...
In article -
september.org, lid says...


Probably needs a better brain than mine to give a detailed
explanation ...


A fellow member of the
http://golbornevintageradio.co.uk/
forums has pointed me to this:

http://www.antenna-theory.com/defini...eciprocity.php

which says:

"Reciprocity

Reciprocity is one of the most useful (and fortunate)
property of antennas. Reciprocity states that the receive
and transmit properties of an antenna are identical. Hence,
antennas do not have distinct transmit and receive radiation
patterns - if you know the radiation pattern in the transmit
mode then you also know the pattern in the receive mode.
This makes things much simpler, as you can imagine."

So, if a poor SWR - such as might result from an
unterminated feeder - can cause it to radiate, the
reciprocity property means that it must be able to receive
as well - screening or no screening.


Co ax outer screens the inner - but nothing screens the outer and it
can radiate. Twin feeder allegedly cancels out.


Coax does not radiate provided that the current in the screen stays on
the inside of the screen.

It held on the inside of the screen by the attraction of the electrical
charge of the equal-and-opposite current flowing in the inner conductor,
but because of the Faraday Pail effect, its natural desire is to try to
flow on the outside of the screen - which it does increasingly as the
frequency is lowered.

It is only at the higher frequencies that the skin effect prevents the
current in the screen penetrating from its inner side to its outer side
- so in consequence, it's only at the higher frequencies that the screen
provides a proper screen. This is particularly true if the screen is
very thin, or does not provide 100% cover.

Things do not really change if the coax is mis-terminated (resulting in
a less-than-perfect 1:1 SWR) - although I guess that if the coax was
radiating when correctly terminated, when mis-terminated current high
spots might locally radiate more, and (conversely) current low spots
might radiate less.
--
Ian
  #35  
Old June 22nd 17, 04:09 PM posted to uk.tech.digital-tv
Dan[_3_]
external usenet poster
 
Posts: 8
Default The Terminator - I'll not be back

On Thu, 22 Jun 2017 14:15:29 +0100, Terry Casey wrote:

... and you are almost certainly right there!

I don't know what sort of kit Diamond Cable used to start
their service but Cable & Wireless Communications, later
ntl: (as was Diamond) used the same Cisco headend kit and it
is probable that Diamond, like ntl: etc only sold their
512kb service - it was, after all, nearly 10 times the
maximum speed available on dial-up!

Thus the Cisco router in the headend or hub determined the
transmision speed and I very much doubt that your mate had
any way of interfering with that!


The modems were the surfboard 3100, from distant memory I think he said
different profiles were put on the modem by the headend. This is what he
supposedly changed to speed things up.A quick google does find links for
hacking the surfborad for faster speeds.

https://www.slideshare.net/NaciConSo...acking-how-to2

But as I say, a serial bul****ter, to embarrasing levels at times, but he
was a senior PM & he did know his networking stuff.
 




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