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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.

childhood inventions



 
 
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  #101  
Old February 27th 18, 10:10 PM posted to uk.tech.digital-tv
tony sayer
external usenet poster
 
Posts: 5,001
Default childhood inventions

In article , Max
Demian scribeth thus
On 24/02/2018 08:57, Brian Gaff wrote:
Yes when I was young I did a similar thing. It actually worked point to
point using alantern torch, but the bias was through a class a run big power
transistor. Very wasteful of course. if you modulated it too much though you
ended up with some weird kind of contrast expansion distortion.

There was a project in Radio constructor back many years ago using mains
filament lamps mounted on a high post. that did use transformers but also
had to derive 200 volts of DC as well which was quite a mean feat and the
amp required for the audio had inverse distortion to compensate for the non
linearity of the bulbs.
The audio was receive in a similar way to described, however Ithink you
mean convex lenses. I used some plastic ells cheapo kids telescopes.


I did once try to send audio wirelessly with electrodes buried in the
ground, similar to the (telegraphic?) communication used in WW1. It only
reached a few feet and there was lots of mains hum:

+------ ------+
| |
| |
Transmitter Receiver
| |
| |
+------ ------+


Did just that when i was a nipper worked quite well over around a
hundred yards or so and no maims 'um;!...

Need to set the earth electrodes a decent distance apart..
--
Tony Sayer



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  #102  
Old March 1st 18, 12:33 AM posted to uk.tech.digital-tv
Johnny B Good[_2_]
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Posts: 513
Default childhood inventions

On Tue, 27 Feb 2018 23:10:19 +0000, tony sayer wrote:

In article , Max
Demian scribeth thus
On 24/02/2018 08:57, Brian Gaff wrote:
Yes when I was young I did a similar thing. It actually worked point
to point using alantern torch, but the bias was through a class a run
big power transistor. Very wasteful of course. if you modulated it too
much though you ended up with some weird kind of contrast expansion
distortion.

There was a project in Radio constructor back many years ago using
mains filament lamps mounted on a high post. that did use
transformers but also had to derive 200 volts of DC as well which was
quite a mean feat and the amp required for the audio had inverse
distortion to compensate for the non linearity of the bulbs.
The audio was receive in a similar way to described, however Ithink
you
mean convex lenses. I used some plastic ells cheapo kids telescopes.


I did once try to send audio wirelessly with electrodes buried in the
ground, similar to the (telegraphic?) communication used in WW1. It only
reached a few feet and there was lots of mains hum:

+------ ------+
| |
| |
Transmitter Receiver
| |
| |
+------ ------+


Did just that when i was a nipper worked quite well over around a
hundred yards or so and no maims 'um;!...

Need to set the earth electrodes a decent distance apart..


Unlike wireless communication, the attenuation rate (like wired and
fibred links) is a constant dB per unit distance similar to an analogue
fader in a sound studio mixing desk.

Assuming, for the chosen electrode separation, your "Earth-link" had a
loss of 100dB over that 100 yds range, each additional yard of range
would add another dB of attenuation. Doubling the range would add another
100dB (possibly even more) unlike the case of a wireless link where
doubling the range increases the attenuation by a mere 6dB for each
successive doubling.

Like the case of the "Light Phone", it's just another 'interesting
experiment' to prove the limitations of such novel means of
communication. That's not to say either technique is completely useless,
more a case of being rather limited in their application.

--
Johnny B Good
  #103  
Old March 1st 18, 12:09 PM posted to uk.tech.digital-tv
Terry Casey[_2_]
external usenet poster
 
Posts: 768
Default childhood inventions

In article
,
says...


I did once try to send audio wirelessly with electrodes buried in the
ground, similar to the (telegraphic?) communication used in WW1. It only
reached a few feet and there was lots of mains hum:


My brother and I tried this over 50 years ago and it worked
quite well, considering the rather crude set up.

The transmitter end was quite good - a Mullard 5-10 connected
to the water main which din't encounter the earth proper until
it got to the other end of the house and an old chassis buried
at the far end of the back garden, so a fair distance between
them.

The receiver was crude beyond belief - a pair of longish wires
connected across the volume control of a transistor radio with
crocodile clips on the ends!

The problem was finding suitable areas of earth to use as
reception sites - back alleys, mainly, but did work our way
down to a road that had grass verges each side - which made it
much easier to insert our probes - meat skewers! - than the
compacted earth of the alleyways.

However, whereas before our probes were in a parallel plane to
those of the transmitter, we were now going sideways and
reception started to drop off rather rapidly (and the hum
increased!). I can't honestly remember how far we got all that
time ago but it was several hundred yards. Of course, had the
water main gone straight down, it would have reduced the
distance between transmission probes to half, or possibly
less.

--

Terry

---
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  #104  
Old March 1st 18, 12:55 PM posted to uk.tech.digital-tv
Max Demian
external usenet poster
 
Posts: 3,970
Default childhood inventions

On 01/03/2018 13:09, Terry Casey wrote:
In article
,
says...


I did once try to send audio wirelessly with electrodes buried in the
ground, similar to the (telegraphic?) communication used in WW1. It only
reached a few feet and there was lots of mains hum:


My brother and I tried this over 50 years ago and it worked
quite well, considering the rather crude set up.

The transmitter end was quite good - a Mullard 5-10 connected
to the water main which din't encounter the earth proper until
it got to the other end of the house and an old chassis buried
at the far end of the back garden, so a fair distance between
them.

The receiver was crude beyond belief - a pair of longish wires
connected across the volume control of a transistor radio with
crocodile clips on the ends!

The problem was finding suitable areas of earth to use as
reception sites - back alleys, mainly, but did work our way
down to a road that had grass verges each side - which made it
much easier to insert our probes - meat skewers! - than the
compacted earth of the alleyways.

However, whereas before our probes were in a parallel plane to
those of the transmitter, we were now going sideways and
reception started to drop off rather rapidly (and the hum
increased!). I can't honestly remember how far we got all that
time ago but it was several hundred yards. Of course, had the
water main gone straight down, it would have reduced the
distance between transmission probes to half, or possibly
less.


Were these (and Tony Sayer's) experiments prompted by a
Practical/Wireless/World type article?

My idea came from a (first world) wartime magazine called Amateur
Mechanic (of which we had two (properly bound) volumes), covering
everything from how locks work to how to stuff (taxidermically) a cow).
DIY before the term was invented/popularised.

It was in an article about "wireless" communications, which made the
distinction between "wireless" and "radio", the latter illustrated by
instructions how to make a crystal set to receive ultra long wave Morse
communications from ships. This was before wireless telephony, whether
radio or ground.

--
Max Demian
 




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