Loss of Freeview Channels with 4G Mobile

In article , David Woolley
wrote:
Andy Champ wrote:
On 18/11/2012 13:53, David Woolley wrote:
The Natural Philosopher wrote:

In order to GET a signal - ANY signal no matter how little data it
containsl - to a receicver, you have to have enough peak power to
overcome the noise.

For Gaussian noise, that is impossible. (Peak powers of gaussian
noise are unconstrained.)

Ermmm... won't the error correction deal with the odd dropped bit? (I
write as a SW engineer with only limited RF knowledge)

It will do so, but it doesn't rely on peak power exceeding the noise.
Shannon's law says that if you have a perfect coding scheme, aren't in a
hurry to get the decoded signal out, and the noise is Gaussian, you can
get zero error rates as long as the signal to noise ratio exceeds a
certain value for the bandwidth.

Yes. In fact you can derive Shannon's equation by using either peaks or
averages during the mathematical arguments. The nominal info rate limit
comes out the same. Just that in general people use it on the basis of the
time-averaged signal and noise powers. After that, how far you fall short
of Shannon depends on your coding scheme and if the noise departs from
being 'Normal'. (e.g. ignition interference or 1/f in some cases.)

One of the mathematical results many scientists or engineers either don't
know or avoid talking about is that true 1/f noise has an average value
that rises as you take longer time-averages. (Equivalent to sending a
longer signal.) So can be a problem in some situations. The relevant
integral blows up to infinity when you do the maths. Fortunately it returns
a finite value for Gaussian white noise. :-)

Slainte,

Jim

--
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In article , Bill Wright
wrote:
Woody wrote:


We got some crystal filters made in the States - last order was $240
apiece for a dozen - but they are 40dB down on one side 50KHz away
and 60dB or more down on the other side 200KHz away. Only downside is
6dB insertion loss. They are about 3" long and 1" sq with a BNC on
each end.

FWIW The few '4G' filters I've seen measured results for are apparently
based on ceramic resonators. No idea (yet) what will end up being handed
out like sweeties, though. Not yet been able to get any responses on that.


So yes it can be done - at a price.

Yes, and see my later post about the final solution.

Crumbs! That's a bit drastic, even for OfCom! 8-]

Slainte,

Jim

--
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On Mon, 19 Nov 2012 03:55:53 +0000, Bill Wright
wrote:

Woody wrote:


We got some crystal filters made in the States - last order was
$240 apiece for a dozen - but they are 40dB down on one side
50KHz away and 60dB or more down on the other side 200KHz away.
Only downside is 6dB insertion loss. They are about 3" long and
1" sq with a BNC on each end.

So yes it can be done - at a price.

Yes, and see my later post about the final solution.


In this discussion about filters, we shouldn't forget that with a
duplex spacing of 40 MHz the portable tx's will be further away from
the TV channels than the base tx's.
The filters will hopefully have greater attenation at these higher
frequencies and this should affect the balance of likely interference
from the two sources.
Incidentally I must confess to being a little confused as to the
application of the quoted filter. If it was for a paging system then
it couldn't be fitted to the receivers. Was it installed into the
output of the *offending* transmitter?

In article ,
wrote:
On Mon, 19 Nov 2012 03:55:53 +0000, Bill Wright wrote:


In this discussion about filters, we shouldn't forget that with a duplex
spacing of 40 MHz the portable tx's will be further away from the TV
channels than the base tx's.

Good reminder! Yes, one of the reasons the 'user' 4G devices should be less
of a challenge is that the wider offset in frequency makes decent filters
far easier to make. Translate that to cheaper, more reliable.

FWIW I'd be less concerned if OfCom had either:

1) Only arranged the change on the basis that ch59 and ch60 would not be
used for TV. At minimum, not use ch60.

2) Removed at least the lowest 4G channel.

That would have at least given a pass-reject gap of 5-8 MHz. Still
demanding for inexpensive small filters. But likely to be far more
practical than a gap of about 1MHz.

As it is, it seems crazy to me for OfCom to dream that using ch60 makes
sense when 4G is in operation. Makes the whole issue far harder to deal
with.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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In message , Woody
writes
"Bill Wright" wrote in message
...
The Natural Philosopher wrote:

Yes. Nothing very exciting. A few people will be affected if
they are very close to a base station. Most will be curable by
adding a decent filter to the front end of the TV tuner or
replacing the TV tuner with a better one that has such built
in.

Could you point me to a filter that has a reasonably flat
response and negligible loss across 470 to 789.850MHz and has
40dB of attenuation from 790.00MHz upwards? If so, how much
does it cost?

Bill



A bit tight that, but after a fashion it can be done.

I have a paging customer with a private paging system in the
153MHz general paging band. They suffer horrendous RFI from
another national paging organisation 50KHz away when their Tx's
overheat and go a tad dirty.

We got some crystal filters made in the States - last order was
$240 apiece for a dozen - but they are 40dB down on one side
50KHz away and 60dB or more down on the other side 200KHz away.
Only downside is 6dB insertion loss. They are about 3" long and
1" sq with a BNC on each end.

So yes it can be done - at a price.

153MHz paging systems are narrowband, so it should be relatively simple
to make high-Q bandpass and bandstop filters from readily-available
153MHz crystals (probably 5th overtone). However, for TV, what is needed
is a lowpass filter (well, passing at least down to 470MHz*) with a
vertical cliff edge at 789.850MHz, and that is a completely different
kettle of fish.
* While you're at it, you might as well roll off below 470MHz to kill
Tetra and other things. However, it's the top end which poses the real,
more-or-less insurmountable problem.
--
Ian

"Mark Carver" wrote in message
...
tim..... wrote:

"Mark Carver" wrote in message
...
tim..... wrote:

This is crazy. I thought that analogue t.v. was switched off to
provide frequencies for 4G,

No

Err, Yes really. That was the game plan, called Digital Dividend. 112
MHz worth of spectrum was to be sold off, at the time (year 2003) it was
undecided what for.

so you admit that it wasn't cleared for 4G then

which is what I said

Some of the UHF band has been cleared, and 4G will be using some of that
space. It was always the intention (and has been for 10 years or more) to
sell off liberated frequencies.

Your statement,

Quote:-

"It just happens that now analogue TV has gone there are a few spare
channels available to be sold which may, or may not, be bought up by
telcos to use for 4G services. "

End Quote

Implies the decision to sell was a recent one, (which it isn't).

I don't agree that it implies that, because I did know that it always was
the intention to sell off spare channels

O2 and Vodafone have bought the space, (800 MHz) and will be using it from
next summer, no 'may' about it.

OK, I didn't know that they had actually found a buyer. I've been out of
mobile comms for 5 years.

tim

In message , The Natural Philosopher
writing at 21:34:09 in his/her local time opines:-

what is the point of making them Megawatt level when what they connect
to has at best a 1W device in it to reply with?

Quite right! It's well known that a mobile phone mast can only talk to
one subscriber at a time, and that always in a predetermined direction.

Isn't it?
--
Roy Brown 'Have nothing in your houses that you do not know to be
Kelmscott Ltd useful, or believe to be beautiful' William Morris

Jim Lesurf wrote:

As it is, it seems crazy to me for OfCom to dream that using ch60 makes
sense when 4G is in operation. Makes the whole issue far harder to deal
with.
Why have they done that? It's very strange.

Bill

In article , Bill Wright
wrote:
Jim Lesurf wrote:

As it is, it seems crazy to me for OfCom to dream that using ch60
makes sense when 4G is in operation. Makes the whole issue far harder
to deal with.
Why have they done that? It's very strange.

Beats me. I can only assume that the suits who agreed the details are
innocent of any real understanding of practical RF. So they assume a
1MHz-ish gap will be fine. To an accountant thinking of selling spectrum on
a MHz/quid basis a gap looks like a 'wasted asset' I guess.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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In article , Mark Carver
scribeth thus
Peter Duncanson wrote:

However, TV is probably the main means of informing the population about
catastrophes whether local or national.

Like it or not, 'Social Media' via smartphones is rapidly taking over from TV
and radio broadcasting for that function.

Indeed it is. Our offspring hardly know how to switch the main TV on
preferring to watch and now listen to most everything on their ipads or
phones via the wi-fi!...



There was a major fire near here a couple of of years ago, You Tube etc filled
up with videos of it almost within minutes, several hours before BBC South and
ITV Meridian broadcast the news; oh, and guess where they lifted the pictures
from ?


Lorra wannabee freelancers around nowadays;!...

--
Tony Sayer