TV and radio clashing signals

On Jun 11, 11:40*am, "Gary" wrote:
"Roderick Stewart" wrote in
thisbit.myzen.co.uk...





In article , Scott wrote:
Following the North London and clashing signals thread I thought I
would recount an equally weird experience I encountered in my student
days in the 70s. *My FM radio used to pick up TV sound. *As VHF
television carried AM sound I assumed it must be something to do with
UHF television. *I thought about maybe harmonics of the TV signal or a
TV set within the building causing interference.

As I was not studying physics at the time I never got beyond thinking
and never got to the bottom if it. *Any ideas?

I remember that too, on a really cheap and nasty FM receiver. Difficult
to remember all the details after all this time, but I'm sure it must
have been receiving BBC2 because I came to the conclusion that the local
oscillator must have been full of harmonics, one of which was beating
with UHF TV.

Rod.
--
Virtual Access V6.3 free usenet/email software from
http://sourceforge.net/projects/virtual-access/

In the 80'S Practical Wireless (I would not swear to it ) but a hobby
electronics mag had a TV sound project where you got a TV tuner , did
something to a coil and fed the output to a FM tuner. *My dad and I did this
and the results were good , just a bit tricky to set up.

Gary- Hide quoted text -

- Show quoted text -

I did one of these. What you did was adjust the tuner so the IF output
was within 88-108. Mine worked really well. Another dodge with old
tuners was to disable the LO and feed the amplified RF out. The first
stage was tuned so you could combine the outputs of several tuners. It
was like having a really sharply tuned adjustable diplexing
arrangement.

Bill

On Jun 11, 2:25*pm, "Dave Plowman (News)"
wrote:
In article ,
* *Ian Jackson wrote:

In the 1980s, I made a simple 'TV-sound-taker-offer' for a works
colleague, so that he could put the sound through his hi-fi system. It
consisted of a sniff coil coupling to the 6MHz field of last IF
transformer, a crystal oscillator on around 90MHz, a 4-diode
double-balanced mixer, and a PP3 battery. There were no actual
connections to the TV set. Like many of my gizmos, it was built in a
tobacco tin, and it hung on the back of the set. The output at around
96MHz was added into the aerial feed to his FM tuner using a 10dB
directional coupler tap. It was yet another of my heroic successes, and
worked very well indeed.
--

Think the pro version was called a TeleFi.

I simply made a one transistor buffer amp fed across the volume control
driving a rep coil.

I think the point of the devices described was to avoid any direct
connection to the telly.

Bill

In article b1c6094a-10d2-4a43-b755-
, wrote:
Think the pro version was called a TeleFi.

I simply made a one transistor buffer amp fed across the volume control
driving a rep coil.

I think the point of the devices described was to avoid any direct
connection to the telly.

"Rep coil" = "repeater coil" = GPO/BBC techspeak for audio isolating
transformer.

Rod.
--
Virtual Access V6.3 free usenet/email software from
http://sourceforge.net/projects/virtual-access/

On Thu, 10 Jun 2010 21:10:06 +0100, Scott wrote:

Following the North London and clashing signals thread I thought I would
recount an equally weird experience I encountered in my student days in
the 70s. My FM radio used to pick up TV sound. As VHF television
carried AM sound I assumed it must be something to do with UHF
television. I thought about maybe harmonics of the TV signal or a TV
set within the building causing interference.

As I was not studying physics at the time I never got beyond thinking
and never got to the bottom if it. Any ideas?

Scott

I remember this too. It was always ITV and it happened on more than one
FM set in more than one location (including London and also before 625
line UHF started). The TV sound could be heard in the upper part of the
FM band. I've sometimes wondered about it - in particular whether the
transmitters were responsible but didn't need fixing since the unwanted
radiation was on an unused frequency.



--
Steve Hayes, South Wales, UK -- please remove colours from address

" wrote in message
...
On Jun 11, 1:05 am, "Dave Plowman (News)"
wrote:
In article ,
and never got to the bottom if it. Any ideas?

A poorly designed FM receiver will pick up AM if the signal is strong
enough.

It's called slope detection.
Bill


Other way around, FM on a AM RX

An FM receiver with poor limiting will receive AM quite well

I used to listen to BBC1 Crystal palace 405 sound on 41MHz
using an army WBFM 88set

Steve Terry
--
Welcome Sign-up Bonus of £1 when you signup free at:
http://www.topcashback.co.uk/ref/G4WWK

In article
,
wrote:
I simply made a one transistor buffer amp fed across the volume control
driving a rep coil.

I think the point of the devices described was to avoid any direct
connection to the telly.

With some sets, IIRC Sony, you had to take the back off and place the
sensor inside.

But if you're capable of building one what's the problem with soldering a
few wires to the TV?

--
*Gravity is a myth, the earth sucks *

Dave Plowman London SW
To e-mail, change noise into sound.

The message
from "Dave Plowman (News)" contains these words:

In article
,
wrote:
I simply made a one transistor buffer amp fed across the volume control
driving a rep coil.

I think the point of the devices described was to avoid any direct
connection to the telly.

With some sets, IIRC Sony, you had to take the back off and place the
sensor inside.

But if you're capable of building one what's the problem with soldering a
few wires to the TV?

The problem was the use of "Half Live" chassis were the expression half
live was really a reference to the 50:50 odds that the chassis would be
connected to the live wire from the mains socket.

"Dave Plowman (News)" wrote in message
...

But if you're capable of building one what's the problem with soldering a
few wires to the TV?

Floating chassis.

SteveT

"Dave Plowman (News)" wrote in message ...
In article
,
wrote:
I simply made a one transistor buffer amp fed across the volume control
driving a rep coil.

I think the point of the devices described was to avoid any direct
connection to the telly.

With some sets, IIRC Sony, you had to take the back off and place the
sensor inside.

But if you're capable of building one what's the problem with soldering a
few wires to the TV?

Because we are talking about past practices.
In the 70s and earlier, TV chassis were connected directly to one side of
the mains, hopefully the neutral, but you could get lucky and it would be the live.

Throughout the 70s (more or less) the design changed and now usually the
chassis would be connected to the -ve terminal of a bridge rectifier fed directly from the mains.
This put the chassis at half mains potential irrespective of which way round the plug was wired.
Both of the above designs could be lethal.

Even today there is a non-isolated section of a TV circuit upstream of the switch-mode
transformer, the difference is the that the metal chassis and the common rail of the rest
of the set is isolated from this part by the SM transformer itself and opto-isolators.

--
Graham.

%Profound_observation%

" wrote in message
...
On Jun 11, 11:40 am, "Gary" wrote:
"Roderick Stewart" wrote in
thisbit.myzen.co.uk...





In article , Scott wrote:
Following the North London and clashing signals thread I thought I
would recount an equally weird experience I encountered in my student
days in the 70s. My FM radio used to pick up TV sound. As VHF
television carried AM sound I assumed it must be something to do with
UHF television. I thought about maybe harmonics of the TV signal or a
TV set within the building causing interference.

As I was not studying physics at the time I never got beyond thinking
and never got to the bottom if it. Any ideas?

I remember that too, on a really cheap and nasty FM receiver. Difficult
to remember all the details after all this time, but I'm sure it must
have been receiving BBC2 because I came to the conclusion that the local
oscillator must have been full of harmonics, one of which was beating
with UHF TV.

Rod.
--
Virtual Access V6.3 free usenet/email software from
http://sourceforge.net/projects/virtual-access/

In the 80'S Practical Wireless (I would not swear to it ) but a hobby
electronics mag had a TV sound project where you got a TV tuner , did
something to a coil and fed the output to a FM tuner. My dad and I did this
and the results were good , just a bit tricky to set up.

Gary- Hide quoted text -

- Show quoted text -

I did one of these. What you did was adjust the tuner so the IF output
was within 88-108. Mine worked really well. Another dodge with old
tuners was to disable the LO and feed the amplified RF out. The first
stage was tuned so you could combine the outputs of several tuners. It
was like having a really sharply tuned adjustable diplexing
arrangement.

Bill

I once used a mechanical UHF tuner with the LO disabled as a channel filter
to combine HTV from M-y-P into my Winter Hill system.
Come to think of it I think its remains is on the flat roof above my head.

--
Graham.

%Profound_observation%