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4G filter measurement



 
 
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  #11  
Old March 10th 13, 09:12 AM posted to uk.tech.digital-tv,uk.tech.broadcast
Scott[_2_]
external usenet poster
 
Posts: 1,344
Default 4G filter measurement

On Sat, 09 Mar 2013 18:09:08 +0000 (GMT), Jim Lesurf
wrote:

I've just done a quick measurement on the SAC AE5100 filter that I bought
from CPC as a "4G filter". Results at...

http://jcgl.orpheusweb.co.uk/temp/AE5100.png

I wonder how representitive this will be of all the other filters that will
now doubtless flood onto the market... Not an encouraging thought...

Have any other countries tried this, or are we the first? There may
be lessons to be learned.

Any idea when filters will become readily available? I imagine
eventually they will go on sale at supermarkets for a fiver or so.
Ads
  #12  
Old March 10th 13, 09:21 AM posted to uk.tech.digital-tv,uk.tech.broadcast
Jim Lesurf[_2_]
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Posts: 4,326
Default 4G filter measurement

In article , Bill Wright
wrote:
Jim Lesurf wrote:
I've just done a quick measurement on the SAC AE5100 filter that I
bought from CPC as a "4G filter". Results at...

http://jcgl.orpheusweb.co.uk/temp/AE5100.png

Useless then, on either graph. But why are they different?


All I did was expand the vertical scale. One graph lets you see the loss
does go to about -60dB once you are well above 790 MHz. The other shows the
small changes arounf 790 more clearly so you can see how lousy the filter
would be for rejecting the 4G just above ch60.



I wonder how representitive this will be of all the other filters that
will now doubtless flood onto the market... Not an encouraging
thought...


There's going to be a run on snake oil. Stock up now.


Here's a bit of background:


https://dl.dropbox.com/u/11023364/Fi...%201%20Feb.pdf
https://dl.dropbox.com/u/11023364/Fi...02%20March.pdf


Noted. I'll have a read. I've been thinking we need a simple 'standard
measure' to make this simple enough for people who want to compare filters.
The graphs show the technically literate when a filter is worthless for a
given task. But a one or two numbers may be easier for punters (and
riggers) to steer towards suitable items amongst the probably tide of
rubbish.

My thoughts so far are to quote two standard values in addition to the
usual ones people bandy.

1) Insertion loss at the middle of ch60.

2) rejection *relative* to that at the middle of the 4G downlink channel
closest to ch60.

So a given filter might have a 'ch60 loss' of, say, 3dB. That's the first
value.

If the loss at the middle of the first 4G ch ('4G adjacent channel
rejection') is, say, 5dB, then the 4G rejection is 5 - 3 = 2 dB. i.e. a
value that shows clearly that such a filter is near-useless.

If one filter has:

ch60 loss = 3dB ; 4G adjacent channel rejection = 2dB, then people can tell
it is poor.

However if a filter with a stated 'in band loss' of 3dB has

ch60 loss = 10 dB ; 4g adjacent channel rejection = 20 dB, then people can
know it will be useful for those who *don't* need to pick up ch59/60. So OK
for some areas but not others.

If anyone finds a five quid filter with

max loss in band 3dB ; ch60 loss 3 dB; 4G adjacent channel rejection =
20 dB, then let me know! I'll go searching for the magicians who provided it! :-)


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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #13  
Old March 10th 13, 09:24 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,326
Default 4G filter measurement

In article ,
wrote:
On Sat, 09 Mar 2013 19:43:12 +0000, Bill Wright wrote:


Jim Lesurf wrote:
I've just done a quick measurement on the SAC AE5100 filter that I
bought from CPC as a "4G filter". Results at...

http://jcgl.orpheusweb.co.uk/temp/AE5100.png

Useless then, on either graph. But why are they different?


That's the same plot isn't it? Just an expanded axis.


Yes.

Not a very effective filter but nonetheless there will be many marginal
locations where it will be adequate.


I'd suspect about as many people will have their problem fixed by a 6dB
pad!

An employee of a well-known site operator tells me that 4G test
transmissions have been going on for many weeks. But he couldn't or
wouldn't say which sites were involved so I don't know if they were in
ch.60 areas.


I'll do a scan here occasionally and keep alert. I'd welcome others doing
scans if they have any RF kit and reporting results. In fact I may raise
this on the FUNCube email list as well! :-)

Hands up who wants to join the new branch of 'Y service' then?... ;-

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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #14  
Old March 10th 13, 09:26 AM posted to uk.tech.digital-tv,uk.tech.broadcast
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,326
Default 4G filter measurement

In article , Brian Gaff
wrote:
In the olden days, people designing services and where to put them in
the spectrum knew what they were doing and the limitations of equipment
for domestic use. it seems to me that recently, and possibly starting
around when pagers first appeared, this talent has been lost in favour
of the idea that we will allocate where we want to and let the industry
fix the issues.


Actually it seems more like, "let industry *not* fix the issues, but just
hand out spin and sweeties."

As PE would say: So that's allright, then!

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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #15  
Old March 10th 13, 09:54 AM posted to uk.tech.digital-tv,uk.tech.broadcast
SpamTrapSeeSig[_2_]
external usenet poster
 
Posts: 34
Default 4G filter measurement

In article , Jim Lesurf
writes
I've been thinking we need a simple 'standard
measure' to make this simple enough for people who want to compare filters.
The graphs show the technically literate when a filter is worthless for a
given task. But a one or two numbers may be easier for punters (and
riggers) to steer towards suitable items amongst the probably tide of
rubbish.

My thoughts so far are to quote two standard values in addition to the
usual ones people bandy.

1) Insertion loss at the middle of ch60.

2) rejection *relative* to that at the middle of the 4G downlink channel
closest to ch60.

So a given filter might have a 'ch60 loss' of, say, 3dB. That's the first
value.

If the loss at the middle of the first 4G ch ('4G adjacent channel
rejection') is, say, 5dB, then the 4G rejection is 5 - 3 = 2 dB. i.e. a
value that shows clearly that such a filter is near-useless.

If one filter has:

ch60 loss = 3dB ; 4G adjacent channel rejection = 2dB, then people can tell
it is poor.

However if a filter with a stated 'in band loss' of 3dB has

ch60 loss = 10 dB ; 4g adjacent channel rejection = 20 dB, then people can
know it will be useful for those who *don't* need to pick up ch59/60. So OK
for some areas but not others.


I assume if you cascade filters, the basic loss (insertion loss) is too
high, so that you don't gain anything. And what about phase shifts below
the nominal cut-off - do they cause issues?

I realised it's almost 35 years since I rushed through this stuff at
Evesham - haven't used it since, probably to my shame.

S.
--
SimonM
  #16  
Old March 10th 13, 10:16 AM posted to uk.tech.digital-tv,uk.tech.broadcast
[email protected]
external usenet poster
 
Posts: 1,245
Default 4G filter measurement

On Sun, 10 Mar 2013 10:24:04 +0000 (GMT), Jim Lesurf
wrote:

In article ,
wrote:
On Sat, 09 Mar 2013 19:43:12 +0000, Bill Wright wrote:


Jim Lesurf wrote:
I've just done a quick measurement on the SAC AE5100 filter that I
bought from CPC as a "4G filter". Results at...

http://jcgl.orpheusweb.co.uk/temp/AE5100.png
Useless then, on either graph. But why are they different?


That's the same plot isn't it? Just an expanded axis.


Yes.

Not a very effective filter but nonetheless there will be many marginal
locations where it will be adequate.


I'd suspect about as many people will have their problem fixed by a 6dB
pad!

Possibly, but not necessarily the exact same locations. An intelligent
installer would have both options (and others) available.
  #17  
Old March 10th 13, 11:09 AM posted to uk.tech.digital-tv,uk.tech.broadcast
J. P. Gilliver (John)
external usenet poster
 
Posts: 298
Default 4G filter measurement

In message , SpamTrapSeeSig
writes:
[]
I assume if you cascade filters, the basic loss (insertion loss) is too
high, so that you don't gain anything. And what about phase shifts


Well, the dB losses do just add, so whether you gain enough _relative_
rejection before you lose too much of the wanted signal will depend on
your situation (how strong the wanted signal is, how deaf your
receiver).

(Are most domestic FreeView receivers - in tellies, STBs, recorders -
similar, as regards sensitivity and overload handling, or do they vary
widely?)

Another problem with cascading filters is potential loss - and
instability - in the connector chain; the Belling-Lee connector is not
famous for its robustness (or, at least, there are plenty of shoddy ones
about), and certainly hanging filter boxes on them won't be a good idea.
(Even if the filter has a little bit of lead on one or other side rather
than using box-mounted connectors, there's still the weight of the
boxlet to add to the strain and thus unreliability.)

below the nominal cut-off - do they cause issues?


I wouldn't be surprised (-:. It's a multicarrier system; there is some
guard space that allows for a little group delay variation, but not a
lot. Especially with the switch to 8-phase (was it?) that we got at
switchover. (_Are_ there any multiplexes in the country that still use
the old phase count?)

I realised it's almost 35 years since I rushed through this stuff at
Evesham - haven't used it since, probably to my shame.

S.


(-: - I'm shooting from the hip too!
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)[email protected]+H+Sh0!:`)DNAf

We have a huge scare over BSE when it is only killing the same number of people
as alarm clocks. Shouldn't we be having an alarm clock scare, too? ("Equinox"
on
Risk, April 1999, paraphrased by Polly Toynbee in Radio Times.)
  #18  
Old March 10th 13, 11:14 AM posted to uk.tech.digital-tv,uk.tech.broadcast
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,326
Default 4G filter measurement

In article , David Woolley
wrote:
Jim Lesurf wrote:
I've just done a quick measurement on the SAC AE5100 filter that I
bought from CPC as a "4G filter". Results at...

http://jcgl.orpheusweb.co.uk/temp/AE5100.png

I wonder how representitive this will be of all the other filters that
will now doubtless flood onto the market... Not an encouraging
thought...


Will LTE base stations necessarily be site cleared for the whole LTE
allocation? It might be that those in marginal areas for the higher DTT
channels may only be site cleared for the higher end of the LTE
downlink allocation.


Failing such things being restricted by the agreements with OfCom I assume
each company will decide on the basis of what suits them best. Which - if
4G is the major crowd-puller they desire - will mean all channels and bases
going full tilt, and free sweeties... erm cheap filters for the masses who
otherwise will be told "eat cake"... erm sky.

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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #19  
Old March 10th 13, 11:18 AM posted to uk.tech.digital-tv,uk.tech.broadcast
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,326
Default 4G filter measurement

In article , SpamTrapSeeSig
wrote:
In article , Jim Lesurf
writes

[snip]

ch60 loss = 10 dB ; 4g adjacent channel rejection = 20 dB, then people
can know it will be useful for those who *don't* need to pick up
ch59/60. So OK for some areas but not others.


I assume if you cascade filters, the basic loss (insertion loss) is too
high, so that you don't gain anything.


It would increase the rejection ratio. But may mean more amplifiers in some
cases to boost a wanted TV signal... which means another amp to protect in
the chain!

And what about phase shifts beow the nominal cut-off - do they cause
issues?


It will depend on the details. An RX will be expected to cope with some
phase shifts due to the effects of multipath. But there's bound to be a
limit to the kinds of shifts, etc, it can handle without problems.

The DTTV mux has a set of carriers and symbols designed to aid the RX
remove phase and amplitude variations across the mux at the FFT/demod
stages. But there will be a point beyond which this won't correct the
problems.

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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #20  
Old March 10th 13, 11:23 AM posted to uk.tech.digital-tv,uk.tech.broadcast
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,326
Default 4G filter measurement

In article ,
wrote:
On Sun, 10 Mar 2013 10:24:04 +0000 (GMT), Jim Lesurf
wrote:



Not a very effective filter but nonetheless there will be many
marginal locations where it will be adequate.


I'd suspect about as many people will have their problem fixed by a 6dB
pad!

Possibly, but not necessarily the exact same locations. An intelligent
installer would have both options (and others) available.


Yes. This is part of the problem.

The situation isn't likely to be solved by a single kind of 'free sweetie'.
(Unless a very expensive sweetie!) So viewers and riggers and shops will
have to have a bag full of assorted sweeties and try various ones to see
which might do the trick.

Given the range of prices, think of the scope for mis-selling of needlessly
expensive items...

....and for something to be fitted, only later on to not be good enough as
the situation evolves, etc.

Nightmare for all concerned. And expensive for many.

If they'd ensured a wider guard band (e.g. 10 MHz) the whole situation
would be better defined and we'd have a much higher chance that a single
reference filter design would handle almost all cases. The 'polluter pays'
principle would mean that the 10 MHz gap would be on the telco side of the
fence, and they'd be paying for the reference-design filters. But guess
what, this isn't happening... :-/

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
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

 




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