UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions.

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In article ,
Scott wrote:
On Wed, 22 Jan 2020 10:58:43 +0000 (GMT), "Dave Plowman (News)"
wrote:


In article ,
Scott wrote:
It's not great, is it? I remember when it was first introduced with
'CD quality sound' and bitrate of 192 kbps. Listening to it now, it
sounds like medium wave without the fade or the static.


Comments like that just shows you've no real experience of either.


If you say so.


Could be you're simply deaf. And can't hear anything above 4.5 kHz.

--
*(over a sketch of the titanic) "The boat sank - get over it

Dave Plowman London SW
To e-mail, change noise into sound.
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In article l.net,
Dave Liquorice wrote:
On Wed, 22 Jan 2020 13:49:27 +0000 (GMT), Dave Plowman (News) wrote:


The car has DAB, the few times I've listened to it there is

something
about the quality/procesing that makes it very wearing to listen

to.
Can't take more than half an hour or so before having to switch to
something else, which can be the same station on FM that isn't
wearing...


Surely being a sound engineer you should be able to 'put a finger' on
what sounds different?


Some sort of higher frequency "edgeiness" and sounding if it's being
driven into a 5:1 compressor fairly hard.


It may well be hammering a compressor. Like a great deal of radio. And
could have different processing from the same station on FM.

--
*Puritanism: The haunting fear that someone, somewhere may be happy.

Dave Plowman London SW
To e-mail, change noise into sound.
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In message , mm0fmf writes
On 22/01/2020 12:46, Tim Lamb wrote:
am not clever enough to play with a raspberry pi.


Learn?

:-) I'm happy to let someone else do the donkey work!
ZX81 tested my limitations.
Internet *radio* on order.
I have some *must do* hedging before February 1st.


--
Tim Lamb
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In article ,
Dave Plowman (News) wrote:
In article ,
Scott wrote:
On Wed, 22 Jan 2020 10:58:43 +0000 (GMT), "Dave Plowman (News)"
wrote:


In article ,
Scott wrote:
It's not great, is it? I remember when it was first introduced with
'CD quality sound' and bitrate of 192 kbps. Listening to it now, it
sounds like medium wave without the fade or the static.

Comments like that just shows you've no real experience of either.


If you say so.


Could be you're simply deaf. And can't hear anything above 4.5 kHz.


I havea 60dB notch at 4.5kHz, but I can definitely hear above that
frequency/ My hearing aids pull it back about 40dB.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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On 23/01/2020 11:16, Dave Plowman (News) wrote:
In article ,
Martin Brown wrote:
DAB is dire when played back through a decent hifi even with good
signal. Internet, TDTV, Freesat and even FM leave all it for dust.
So how come it works in cars?


The engine noise masks most of its short comings. The only thing that
DAB does better than FM is the silent gaps inbetween programme material.


You have the only FM receiver that doesn't suffer from multi-path, then?


I don't spend a lot of time in big cities. Multipath is only a serious
problem when there are large reflecting structures about.

--
Regards,
Martin Brown


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In article ,
Martin Brown wrote:
On 23/01/2020 11:16, Dave Plowman (News) wrote:
In article ,
Martin Brown wrote:
DAB is dire when played back through a decent hifi even with good
signal. Internet, TDTV, Freesat and even FM leave all it for dust.
So how come it works in cars?


The engine noise masks most of its short comings. The only thing that
DAB does better than FM is the silent gaps inbetween programme
material.


You have the only FM receiver that doesn't suffer from multi-path,
then?


I don't spend a lot of time in big cities. Multipath is only a serious
problem when there are large reflecting structures about.


Then best to qualify your comments about any transmission system.

However, many portable radios will exhibit multi-path just with a person
moving about in the same room.

--
*Strip mining prevents forest fires.

Dave Plowman London SW
To e-mail, change noise into sound.
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In article , Martin Brown
wrote:
On 23/01/2020 11:16, Dave Plowman (News) wrote:
In article , Martin Brown
wrote:
DAB is dire when played back through a decent hifi even with good
signal. Internet, TDTV, Freesat and even FM leave all it for dust.
So how come it works in cars?


The engine noise masks most of its short comings. The only thing that
DAB does better than FM is the silent gaps inbetween programme
material.


You have the only FM receiver that doesn't suffer from multi-path, then?


I don't spend a lot of time in big cities. Multipath is only a serious
problem when there are large reflecting structures about.


Hills can also create multipath

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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On 23/01/2020 12:07, Tim Lamb wrote:
In message , mm0fmf writes
On 22/01/2020 12:46, Tim Lamb wrote:
am not clever enough to play with a raspberry pi.


Learn?

:-)* I'm happy to let someone else do the donkey work!
ZX81 tested my limitations.
*Internet *radio* on order.
I have some *must do* hedging before February 1st.


Ha! did mine last week!





--
If you tell a lie big enough and keep repeating it, people will
eventually come to believe it. The lie can be maintained only for such
time as the State can shield the people from the political, economic
and/or military consequences of the lie. It thus becomes vitally
important for the State to use all of its powers to repress dissent, for
the truth is the mortal enemy of the lie, and thus by extension, the
truth is the greatest enemy of the State.

Joseph Goebbels



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On 23/01/2020 14:38, charles wrote:
In article , Martin Brown
wrote:
On 23/01/2020 11:16, Dave Plowman (News) wrote:
In article , Martin Brown
wrote:
DAB is dire when played back through a decent hifi even with good
signal. Internet, TDTV, Freesat and even FM leave all it for dust.
So how come it works in cars?

The engine noise masks most of its short comings. The only thing that
DAB does better than FM is the silent gaps inbetween programme
material.

You have the only FM receiver that doesn't suffer from multi-path, then?


I don't spend a lot of time in big cities. Multipath is only a serious
problem when there are large reflecting structures about.


Hills can also create multipath

So can barbed wire fences
And trees


--
Socialism is the philosophy of failure, the creed of ignorance and the
gospel of envy.

Its inherent virtue is the equal sharing of misery.

Winston Churchill

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On Thu, 23 Jan 2020 11:17:54 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Scott wrote:
On Wed, 22 Jan 2020 10:58:43 +0000 (GMT), "Dave Plowman (News)"
wrote:


In article ,
Scott wrote:
It's not great, is it? I remember when it was first introduced with
'CD quality sound' and bitrate of 192 kbps. Listening to it now, it
sounds like medium wave without the fade or the static.

Comments like that just shows you've no real experience of either.


If you say so.


Could be you're simply deaf. And can't hear anything above 4.5 kHz.


I can assure you that upper-frequency cutoff is the least of my
concerns. Have you actually listened to any of the many stations now
broadcasting 80 kbps mono? On a scale with medium wave at one end and
CD at the other, DAB in my assessment lies to the left of the scale. I
accept that audio is subjective and you may believe that DAB sounds
like CD quality.


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In message , The Natural Philosopher
writes
On 23/01/2020 12:07, Tim Lamb wrote:
In message , mm0fmf writes
On 22/01/2020 12:46, Tim Lamb wrote:
am not clever enough to play with a raspberry pi.

Learn?

:-)* I'm happy to let someone else do the donkey work!
ZX81 tested my limitations.
*Internet *radio* on order.
I have some *must do* hedging before February 1st.


Ha! did mine last week!


Huh! In an effort to be nice to the RSPB farms are not allowed to trim
hedges after the end of January. The only allowed exception is necessary
roadside work.
I have had Sheep grazing for the last few weeks and am now running out
of suitable weather (no rain/drizzle as you then can't see out of the
cab) and preferably no bright Sun for the same reason.

--
Tim Lamb
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In article , F
news@nowhere.? scribeth thus
On 21/01/2020 20:03, tony sayer wrote:
In article , F
news@nowhere.? scribeth thus
We have a couple of DAB radio alarm clocks. One of them will find and
play radio channels, albeit with a low signal strength. The other can't
get a reliable signal despite being just the other side of the bed. Both
have lengths of thin wire for aerials.

Is there anything I can do to get reception? I've moved the wire on the
difficult one up, down, left and right but got nowhere.


Yes! Try FM


Not every station we listen to is on FM...


How sad


--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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On Thu, 23 Jan 2020 21:24:31 +0000, Tim Lamb wrote:

I have had Sheep grazing for the last few weeks and am now running out
of suitable weather (no rain/drizzle as you then can't see out of the
cab) and preferably no bright Sun for the same reason.


Get yer billhook out an' lay 'em properly. Stock proof, RSPB
friendly. Of course you can't lay 'em properly as there's nothing to
lay, having been flailed for the last few decades... B-(

--
Cheers
Dave.



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On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote:
However, many portable radios will exhibit multi-path just with a person
moving about in the same room.


That's really better described as the standing wave pattern in the room changing.

Bill


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On Thursday, 23 January 2020 14:42:55 UTC, charles wrote:
Hills can also create multipath


I've always thought (or assumed) that rounded hills don't so much reflect the signal as screen it, thus making reflections from other things more significant.

Having messed around with directional aerials in mountainous areas I've come to believe that rocky outcrops reflect signals more than other features. I've seen very striking examples of that.

Bill
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On Thursday, 23 January 2020 18:33:32 UTC, The Natural Philosopher wrote:
On 23/01/2020 14:38, charles wrote:
Hills can also create multipath

So can barbed wire fences
And trees


I've never been able to blame reflections on barbed wire, but I'm sure it's possible. Trees seem to cause more problems by simply screening the signal, or sometimes by passing it through and providing a secondary transmission path.

Bill
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On 23/01/2020 21:24, Tim Lamb wrote:
In message , The Natural Philosopher
writes
On 23/01/2020 12:07, Tim Lamb wrote:
In message , mm0fmf writes
On 22/01/2020 12:46, Tim Lamb wrote:
am not clever enough to play with a raspberry pi.

Learn?
:-)* I'm happy to let someone else do the donkey work!
ZX81 tested my limitations.
**Internet *radio* on order.
I have some *must do* hedging before February 1st.


Ha! did mine last week!


Huh! In an effort to be nice to the RSPB farms are not allowed to trim
hedges after the end of January. The only allowed exception is necessary
roadside work.


Trim? I was PLANTING

I have had Sheep grazing for the last few weeks and am now running out
of suitable weather (no rain/drizzle as you then can't see out of the
cab) and preferably no bright Sun for the same reason.


I thought the cut off was Mach 1st. Farmer here cut his last year on
March 2nd...

--
"If you dont read the news paper, you are un-informed. If you read the
news paper, you are mis-informed."

Mark Twain
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On 24/01/2020 02:19, Bill Wright wrote:
On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote:
However, many portable radios will exhibit multi-path just with a person
moving about in the same room.


That's really better described as the standing wave pattern in the room changing.

Bill

its exactly te same thing

Except with FM the wave doesnt stand does it?

--
"If you dont read the news paper, you are un-informed. If you read the
news paper, you are mis-informed."

Mark Twain
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On 24/01/2020 02:31, Bill Wright wrote:
On Thursday, 23 January 2020 18:33:32 UTC, The Natural Philosopher wrote:
On 23/01/2020 14:38, charles wrote:
Hills can also create multipath

So can barbed wire fences
And trees


I've never been able to blame reflections on barbed wire, but I'm sure it's possible. Trees seem to cause more problems by simply screening the signal, or sometimes by passing it through and providing a secondary transmission path.

Bill

YOU set up TV aerials.
I fly model planes. The barbed wire fence glitch is well known

Of course rusty fences have effective diodes in them. So you get
intermodulation of reflected signals as well.


--
The ultimate result of shielding men from the effects of folly is to
fill the world with fools.

Herbert Spencer


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"The Natural Philosopher" wrote in message
...
On 24/01/2020 02:31, Bill Wright wrote:
On Thursday, 23 January 2020 18:33:32 UTC, The Natural Philosopher
wrote:
On 23/01/2020 14:38, charles wrote:
Hills can also create multipath

So can barbed wire fences
And trees


I've never been able to blame reflections on barbed wire, but I'm sure
it's possible. Trees seem to cause more problems by simply screening the
signal, or sometimes by passing it through and providing a secondary
transmission path.

Bill

YOU set up TV aerials.
I fly model planes. The barbed wire fence glitch is well known


With low powered ground based transmitters, sure.
but I dont believe it is with FM or DAB transmitters.


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In message l.net,
Dave Liquorice writes
On Thu, 23 Jan 2020 21:24:31 +0000, Tim Lamb wrote:

I have had Sheep grazing for the last few weeks and am now running out
of suitable weather (no rain/drizzle as you then can't see out of the
cab) and preferably no bright Sun for the same reason.


Get yer billhook out an' lay 'em properly. Stock proof, RSPB
friendly. Of course you can't lay 'em properly as there's nothing to
lay, having been flailed for the last few decades... B-(


Hedge laying died out with WW2 on this farm. Food production took
priority and Land Army girls did not have the skills.
I took on linear spinneys!
A downside of laying a hedge is that it can only then be flailed *down
the grain* otherwise the machine picks up and eats whole limbs!
An upside here is that no hedges have been lost and birds do find enough
cover to nest.

Various permutations of CAP payments have encouraged a range of managed
hedges to cater for nesting preferences.


--
Tim Lamb
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In message , The Natural Philosopher
writes
On 23/01/2020 21:24, Tim Lamb wrote:
In message , The Natural Philosopher
writes
On 23/01/2020 12:07, Tim Lamb wrote:
In message , mm0fmf writes
On 22/01/2020 12:46, Tim Lamb wrote:
am not clever enough to play with a raspberry pi.

Learn?
:-)* I'm happy to let someone else do the donkey work!
ZX81 tested my limitations.
**Internet *radio* on order.
I have some *must do* hedging before February 1st.

Ha! did mine last week!

Huh! In an effort to be nice to the RSPB farms are not allowed to
trim hedges after the end of January. The only allowed exception is
necessary roadside work.


Trim? I was PLANTING


Watch out for Rabbits.

I have had Sheep grazing for the last few weeks and am now running
out of suitable weather (no rain/drizzle as you then can't see out of
the cab) and preferably no bright Sun for the same reason.


I thought the cut off was Mach 1st. Farmer here cut his last year on
March 2nd...

You are quite correct! I can relax:-)

--
Tim Lamb
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In article , Andrew
writes
On 22/01/2020 10:58, Dave Plowman (News) wrote:
In article ,
Scott wrote:
It's not great, is it? I remember when it was first introduced with
'CD quality sound' and bitrate of 192 kbps. Listening to it now, it
sounds like medium wave without the fade or the static.

Comments like that just shows you've no real experience of either.


You live in London though where DAB is fine while FM can be a
problem because of illegal transmitters, buildings etc.

Many parts of the country have better FM reception than DAB.

DAB is OK here. Use it in the house and car. More stations available,
Talksport 2 or 5Livex for continuous cricket commentary.
--
bert
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On 24/01/2020 09:51, Tim Lamb wrote:
In message , The Natural Philosopher
writes
On 23/01/2020 21:24, Tim Lamb wrote:
In message , The Natural Philosopher
writes
On 23/01/2020 12:07, Tim Lamb wrote:
In message , mm0fmf
writes
On 22/01/2020 12:46, Tim Lamb wrote:
am not clever enough to play with a raspberry pi.

Learn?
:-)* I'm happy to let someone else do the donkey work!
ZX81 tested my limitations.
**Internet *radio* on order.
I have some *must do* hedging before February 1st.

Ha! did mine last week!
*Huh! In an effort to be nice to the RSPB farms are not allowed to
trim* hedges after the end of January. The only allowed exception is
necessary* roadside work.


Trim? I was PLANTING


Watch out for Rabbits.

I have had Sheep grazing for the last few weeks and am now running
out* of suitable weather (no rain/drizzle as you then can't see out
of the* cab) and preferably no bright Sun for the same reason.


I thought the cut off was Mach 1st. Farmer here cut his last year on
March 2nd...

You are quite correct! I can relax:-)

Phew. So can I since he is off in the Caribbean now as the fields are
too wet and there is sod all else to do


--
The New Left are the people they warned you about.


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In article ,
Bill Wright wrote:
On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote:
However, many portable radios will exhibit multi-path just with a
person moving about in the same room.


That's really better described as the standing wave pattern in the room
changing.


Oh, indeed. But the audible results are similar. And the same sort of
problems with an inside aerial in VHF TV days.

Each transmission medium has its own individual problems.

--
*i souport publik edekashun.

Dave Plowman London SW
To e-mail, change noise into sound.
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On 23/01/2020 23:30, tony sayer wrote:
In article , F
news@nowhere.? scribeth thus
On 21/01/2020 20:03, tony sayer wrote:
In article , F
news@nowhere.? scribeth thus
We have a couple of DAB radio alarm clocks. One of them will find and
play radio channels, albeit with a low signal strength. The other can't
get a reliable signal despite being just the other side of the bed. Both
have lengths of thin wire for aerials.

Is there anything I can do to get reception? I've moved the wire on the
difficult one up, down, left and right but got nowhere.


Yes! Try FM


Not every station we listen to is on FM...


How sad


??

--
F


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On 22/01/2020 21:17, Brian Reay wrote:
Andrew wrote:
On 22/01/2020 11:19, The Natural Philosopher wrote:
On 22/01/2020 11:17, F wrote:
On 21/01/2020 20:03, tony sayer wrote:
In article , F
news@nowhere.? scribeth thus
We have a couple of DAB radio alarm clocks. One of them will find
and play radio channels, albeit with a low signal strength. The
other can't get a reliable signal despite being just the other side
of the bed. Both have lengths of thin wire for aerials.

Is there anything I can do to get reception? I've moved the wire on
the difficult one up, down, left and right but got nowhere.


Yes! Try FM

Not every station we listen to is on FM...

Use a raspberry pi or other computer to listen to them on the internet



Better still buy a Roberts Stream94 and avoid ALL the awful Linux
garbage.


The iStream94 is an excellent radio but I think you will find the software
is Linux based- I stumbled across some details of the software when
researching models.


So is my Humax HD FOXT2 PVR but I don't need to interact with it
directly.

For a bedroom radio you want something that is easy to use even
with the lights off !!

Unlike some of the cheaper Internet Radios, the user interface is very
straight forward and, above all, stable.

I use mine in DAB, Internet Radio, and Media mode - very occasionally in
FM.




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On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known


I haven't heard of this and I'm very interested. Please tell us more.

Bill

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On Friday, 24 January 2020 13:47:19 UTC, Dave Plowman (News) wrote:
In article ,
Bill Wright wrote:
On Thursday, 23 January 2020 14:19:49 UTC, Dave Plowman (News) wrote:
However, many portable radios will exhibit multi-path just with a
person moving about in the same room.


That's really better described as the standing wave pattern in the room
changing.


Oh, indeed. But the audible results are similar.


For VHF FM, a standing wave causing complete or near-complete signal cancellation obviously results in what is effectively weak or zero signal at the receiver. You'd expect degradation into noise pure and simple but there's usually another weak signal path from a reflection external to the room. With the direct path almost or completely cancelled out that signal becomes more significant so the audible result is often the high frequency audio distortion (lisping) that is also caused by simple signal reflections.
In the case of analogue TV, standing waves within the room (or loft)can, by the same mechanism, cause ghosting rather than simple weak signal.

Bill


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In article , Bill
Wright scribeth thus
On Thursday, 23 January 2020 14:42:55 UTC, charles wrote:
Hills can also create multipath


I've always thought (or assumed) that rounded hills don't so much reflect the
signal as screen it, thus making reflections from other things more significant.

Having messed around with directional aerials in mountainous areas I've come to
believe that rocky outcrops reflect signals more than other features. I've seen
very striking examples of that.

Bill


Edge diffraction there is a good article on it somewhere, can't think of
it right now tho..

--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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On 24/01/2020 20:34, Bill Wright wrote:
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known


I haven't heard of this and I'm very interested. Please tell us more.


back in the days of 35MHz NBFM it was well known that flying at
reasonable range over rusty fences would cause momentary loss of or
corruption of signal. Generally seen as a massive twitch on all flight
surfaces and a loss of throttle.

35MHz was never the best of mediums anyway but club fliers got to know
that certain places were prone to this effect.

Whether it was multipath, or diodic mixing causing intermodulation I
cannot say - or both.

For more information, the signal modulation on FM RC is/was a series of
frequency excursions marking the edges of a series of channel frames
about 1ms long with the lengh of a frame being the position of the
associated servo - in the range of 0.5ms to 1.5ms. A very long frame -
10ms or so - was used as a synchronisation frame.,

This form of modulation has only one benefit. A simple CMOS shift
regsiter could decode the pulse train to the servos.

But as an interference rejecting schema it was pants. Loss of a frame
edge meant one channel got two channels worth of info and the subsequent
channels got te wrong info.

Hence the massive glitch/twitch.


Bill



--
"It is an established fact to 97% confidence limits that left wing
conspirators see right wing conspiracies everywhere"
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In article , The Natural Philosopher
scribeth thus
On 24/01/2020 20:34, Bill Wright wrote:
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known


I haven't heard of this and I'm very interested. Please tell us more.


back in the days of 35MHz NBFM it was well known that flying at
reasonable range over rusty fences would cause momentary loss of or
corruption of signal. Generally seen as a massive twitch on all flight
surfaces and a loss of throttle.

35MHz was never the best of mediums anyway but club fliers got to know
that certain places were prone to this effect.

Whether it was multipath, or diodic mixing causing intermodulation I
cannot say - or both.

For more information, the signal modulation on FM RC is/was a series of
frequency excursions marking the edges of a series of channel frames
about 1ms long with the lengh of a frame being the position of the
associated servo - in the range of 0.5ms to 1.5ms. A very long frame -
10ms or so - was used as a synchronisation frame.,

This form of modulation has only one benefit. A simple CMOS shift
regsiter could decode the pulse train to the servos.

But as an interference rejecting schema it was pants. Loss of a frame
edge meant one channel got two channels worth of info and the subsequent
channels got te wrong info.

Hence the massive glitch/twitch.


Bill



Interesting!

Time for OFDM perhaps;?..
--
Tony Sayer


Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.


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On Saturday, 25 January 2020 00:02:48 UTC, tony sayer wrote:
In article , Bill
Wright scribeth thus
On Thursday, 23 January 2020 14:42:55 UTC, charles wrote:
Hills can also create multipath


I've always thought (or assumed) that rounded hills don't so much reflect the
signal as screen it, thus making reflections from other things more significant.

Having messed around with directional aerials in mountainous areas I've come to
believe that rocky outcrops reflect signals more than other features. I've seen
very striking examples of that.

Bill


Edge diffraction there is a good article on it somewhere, can't think of
it right now tho..


Edge diffraction! Six miles from a high powered TV tx. Rounded and bare heap of colliery waste in way. Move the rx aerial vertically up and down and there will be distinct peaks and nulls.
Bill
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On Saturday, 25 January 2020 10:28:47 UTC, The Natural Philosopher wrote:
On 24/01/2020 20:34, Bill Wright wrote:
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known


I haven't heard of this and I'm very interested. Please tell us more.


back in the days of 35MHz NBFM it was well known that flying at
reasonable range over rusty fences would cause momentary loss of or
corruption of signal. Generally seen as a massive twitch on all flight
surfaces and a loss of throttle.

35MHz was never the best of mediums anyway but club fliers got to know
that certain places were prone to this effect.

Whether it was multipath, or diodic mixing causing intermodulation I
cannot say - or both.

For more information, the signal modulation on FM RC is/was a series of
frequency excursions marking the edges of a series of channel frames
about 1ms long with the lengh of a frame being the position of the
associated servo - in the range of 0.5ms to 1.5ms. A very long frame -
10ms or so - was used as a synchronisation frame.,

This form of modulation has only one benefit. A simple CMOS shift
regsiter could decode the pulse train to the servos.

But as an interference rejecting schema it was pants. Loss of a frame
edge meant one channel got two channels worth of info and the subsequent
channels got te wrong info.

Hence the massive glitch/twitch.


Thank you.

Bill


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On 25/01/2020 13:37, tony sayer wrote:
In article , The Natural Philosopher
scribeth thus
On 24/01/2020 20:34, Bill Wright wrote:
On Friday, 24 January 2020 02:37:09 UTC, The Natural Philosopher wrote:
I fly model planes. The barbed wire fence glitch is well known

I haven't heard of this and I'm very interested. Please tell us more.


back in the days of 35MHz NBFM it was well known that flying at
reasonable range over rusty fences would cause momentary loss of or
corruption of signal. Generally seen as a massive twitch on all flight
surfaces and a loss of throttle.

35MHz was never the best of mediums anyway but club fliers got to know
that certain places were prone to this effect.

Whether it was multipath, or diodic mixing causing intermodulation I
cannot say - or both.

For more information, the signal modulation on FM RC is/was a series of
frequency excursions marking the edges of a series of channel frames
about 1ms long with the lengh of a frame being the position of the
associated servo - in the range of 0.5ms to 1.5ms. A very long frame -
10ms or so - was used as a synchronisation frame.,

This form of modulation has only one benefit. A simple CMOS shift
regsiter could decode the pulse train to the servos.

But as an interference rejecting schema it was pants. Loss of a frame
edge meant one channel got two channels worth of info and the subsequent
channels got te wrong info.

Hence the massive glitch/twitch.


Bill



Interesting!

Time for OFDM perhaps;?..

we have now gone 2.4GHz. Essentailly the wifi band. This uses a
collision detection algorithm and spread spectrum. Also some frequency
hopping. Since the frame rate is low - a complete model only needs 64
bits every 20 ms - a massive data rate of 3200 bits per second - the way
the systems work is to transmit a frame with error correction and a
transmitter ID, and back off if there is collision. The comms is bi
directional so the receivers request retransmits if a frame is corrupt.

Loss of a frame simply means that the model carries on doing whatever it
was doing - the actual perception is that it's sluggish and
unresponsive. Ther is usally a watchdog tomer that will move the
controls to user configurable preset positions - usully cut throttle and
mild level turn - in the event of total signal loss.

Since every transitter has a unique MAC code, operation of dozens of
models simultaneously is possible - all too many transmitters does, is
slow the data rate down a bit. Its like having a shared wifi network.

I used to get some issues flying through a tight beam from the local
radio mast that you know of all too well. Lets hope te 2.4GHz stuff is
more resilient


--
"Strange as it seems, no amount of learning can cure stupidity, and
higher education positively fortifies it."

- Stephen Vizinczey

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