You cannot just join it electrically, the impedance must be maintained. You
could fit connectors and then seal it all with self-amalgamating tape.
Unless it is a very long run the best solution is to replace the cable. If
it is more than five years old it is probable that it will have deteriorated
enough to reduce the signal significantly.

--

"Chris" ] wrote in message
]...
Joining co-axial cable outdoors - what's the best way to do it?
I've got an aerial cable running along the outside of the house wall
and I want to splice in an extra length.
Would soldering be best?
And how would it be done neatly?
--
Chris

Chris ] wrote in ]:

Joining co-axial cable outdoors - what's the best way to do it?
I've got an aerial cable running along the outside of the house wall
and I want to splice in an extra length.
Would soldering be best?
And how would it be done neatly?

I agree with Peter, unless, there are compelling reasons against, replace
the whole lead with quality coax -it's the second most important bit of
your telly - the aerial is the first. You will lose about half the signal
in two joints to fit plugs, needed to introduce a coupler.

Having said that, I would try neatly soldering it, keeping the shape as
much as possible, as I think it would be lees worse than 2 joints + a
coupler.

I would do it in a small diecast box, waterproofed by all available means,
grommets, etc.

mike r

Dave Plowman wrote in
:


I had fox damage ;-) to my TV cable,

Flying foxes?

and I jointed it with normal Belling
Lee connectors then used glue shrink wrap followed by self amalgamating
tape. It worked fine, and has for several years, but then I'm in a strong
signal area and wouldn't notice a slight attenuation of the level.

Lucky od sod, I used to live in a wet string area, but now I need something
like Goonhilly, but I'm still defeated by cochannel from across the channel
on fine summer evenings

And now ***** Sky is taking away channels 3, 4, and 5 unless I subscribe, I
didn't think that was legal, and freeview piillates and locks solid,
usually in the middle of a recording.

BTW, are the modern boxes any better than my Philips Ondigital? Apart from
the locking up it produces LF audio which is annoying through my audio
system (but inaudible on the telly speakers

mike r

The problem with joining cables is not signal loss but signal reflection at
the joint. This can be a disaster for digital signals.

See http://www.satcure.co.uk/accs/page8.htm

Martin

mike ring wrote:
Dave Plowman wrote in
:


I had fox damage ;-) to my TV cable,

Flying foxes?

and I jointed it with normal Belling
Lee connectors then used glue shrink wrap followed by self
amalgamating tape. It worked fine, and has for several years, but
then I'm in a strong signal area and wouldn't notice a slight
attenuation of the level.

Lucky od sod, I used to live in a wet string area, but now I need
something like Goonhilly, but I'm still defeated by cochannel from
across the channel on fine summer evenings

And now ***** Sky is taking away channels 3, 4, and 5 unless I
subscribe, I didn't think that was legal, and freeview piillates and
locks solid, usually in the middle of a recording.

BTW, are the modern boxes any better than my Philips Ondigital? Apart
from the locking up it produces LF audio which is annoying through my
audio system (but inaudible on the telly speakers

The newer boxes are a world apart from the older ondigital ones. I've got
both an old Philips which is now only used for radio and a newer Daewoo,
which is rock solid. The Setpal tuner in the Daewoo can be found in several
others as well, usually around £70 upwards.

--
James...
http://www.jameshart.co.uk/

In article 0,
mike ring wrote:
I had fox damage ;-) to my TV cable,

Flying foxes?

No - the aerial cables come down the side wall and into the cellar via an
air brick. And a dying fox decided to chew them as a final act before
popping his clogs.

snip

And now ***** Sky is taking away channels 3, 4, and 5 unless I
subscribe, I didn't think that was legal, and freeview piillates and
locks solid, usually in the middle of a recording.

BTW, are the modern boxes any better than my Philips Ondigital?

Yes.

Apart from the locking up it produces LF audio which is annoying through
my audio system (but inaudible on the telly speakers

I've not had this trouble with mine, and have in fact relegated it to an
audio only device. It used to cause the most amazing splats on TV audio
when it locked up, though, but doesn't lock up on sound only stuff. At the
moment, the bitrates off Freeview are rather better for radio than DAB.
But I'm sure they'll find a way of worsening them soon.

--
*You are validating my inherent mistrust of strangers

Dave Plowman London SW 12
RIP Acorn

In article ,
Martin Pickering {UK} wrote:
The problem with joining cables is not signal loss but signal reflection
at the joint. This can be a disaster for digital signals.

Hence the need for a properly made joint.

--
*There's no place like www.home.com *

Dave Plowman London SW 12
RIP Acorn

Dave Plowman wrote in
:


BTW, are the modern boxes any better than my Philips Ondigital?

Yes.

It used to cause the most amazing splats on TV
audio when it locked up, though, but doesn't lock up on sound only
stuff. At the moment, the bitrates off Freeview are rather better for
radio than DAB. But I'm sure they'll find a way of worsening them
soon.

That's a point, the sound never locks

Any suggestions as to boxes - Argos have a nice selection, but they are not
covered by the return guarantee, which makes me think it's still a big
gamble

mike r

"mike ring" wrote
| Any suggestions as to boxes - Argos have a nice selection, but they
| are not covered by the return guarantee, which makes me think it's
| still a big gamble

QVC home shopping often have DTT boxes and they have a 30 day no quibble
money back guarantee, which gives you plenty of time for fiddling with the
aerial. Okay, so you can't get QVC without a box, but try www.qvcuk.com
occasionally or phone 0800 50 40 30

Richer Sounds have a Thomson box for twenty quid with any plasma screen :-)
Or a Goodmans at £70 or Thomson at £80

Owain

In article 0, mike
ring writes
Chris ] wrote in ]:

Joining co-axial cable outdoors - what's the best way to do it?
I've got an aerial cable running along the outside of the house wall
and I want to splice in an extra length.
Would soldering be best?
And how would it be done neatly?

I agree with Peter, unless, there are compelling reasons against, replace
the whole lead with quality coax -it's the second most important bit of
your telly - the aerial is the first. You will lose about half the signal
in two joints to fit plugs, needed to introduce a coupler.
Having said that, I would try neatly soldering it, keeping the shape as
much as possible, as I think it would be lees worse than 2 joints + a
coupler.
I would do it in a small diecast box, waterproofed by all available means,
grommets, etc.

One thing that may help - it's a radio FM aerial - not a telly.
I can' t easily get to the aerial to replace the whole wire - it's very
high - and I'm frightened of high ladder work.
Haven't heard of "self-amalgamating tape", which sounds interesting.
--
Chris

Peter Crosland wrote:

You cannot just join it electrically, the impedance must be maintained. You
could fit connectors and then seal it all with self-amalgamating tape.
Unless it is a very long run the best solution is to replace the cable. If
it is more than five years old it is probable that it will have deteriorated
enough to reduce the signal significantly.


True if pedantically interpreted, but untrue in practice.

To join coax the procvess is as fillows.

First of all stribp backl the outer insulation, then fold back the
braiding and get it out of the way to expoose the inner isnulation.

Strip about half an inch of that on each cable.

Now slip some BIG heatshrink tubin over one of the cables outers, and
another smaller diameter bit over the inner insulators.

Solder the inner conductors together by laying them parallel and
flooding with solder.

Pull the heatshrink over the inner and seal down with ahirdryer/heta gun
etc.

Thats teh conductor done, and insulated

Now pull the braids together and just solder em someohow to make a
connection. needent't be perfect.

Now get some aluminium foil and wrap teh lot with a thin layer of that.
Don't try and solder it. It won't.

Silde the big heatshrink tubing over he joint, slap some silicone sealer
or epoxy resin inside and seal with heatgun.

If you are really worried about corrosion, wrap the whole thing in a few
layes of cloth soaked in silicone

VSWR won't be exactly 1, but will be better than most plugs and sockets :-)

Martin Pickering {UK} wrote:

The problem with joining cables is not signal loss but signal reflection at
the joint. This can be a disaster for digital signals.

See http://www.satcure.co.uk/accs/page8.htm

Martin





A well made joint will be less than a couple of connectors.

On Mon, 08 Sep 2003 11:54:30 +0100, The Natural Philosopher
wrote:

Utter bolocks.

Could you qualify your response please?

When I studied for my HNC Electronics at college we specifically
looked at this issue, and RFI signal degradation was certainly a
result - trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection -
otherwise known as distortion - into the signal because you had an
improperly terminated circuit. Now whether or not this might impact
the TV or radio you are feeding is another matter, but the degradation
was very real.

Naturally I will bow to your higher level of intelligence if you can
provide some alternative suggestions which are backed by fact.

PoP

In article , PoP
writes
trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection

All I'm trying to do is to make the aerial longer,
without high ladder work.
I'm not splitting it.
I just want it to go to a room further away from the aerial on the roof.
And - it's FM radio - if that makes a difference.
--
Chris

On Mon, 8 Sep 2003 13:19:08 +0100, Chris ] wrote:

All I'm trying to do is to make the aerial longer,
I'm not splitting it.
I just want it to go to a room further away from the aerial on the roof.

That wouldn't be a problem - I misread the word "splice" to mean that
you wanted to create a tee junction to split the signal.

And - it's FM radio - if that makes a difference.

Not really.

Easiest way is probably to get an inline plug/socket for the aerial
lead, do the join, then wrap it thoroughly with self-amalgamating tape
as others have suggested.

If you attempt to solder the lengths together you might (and most
likely will) create a source of interference. Aerial cables carrying
RF signals are co-axial, and to perform the solder work you'd have to
break thru the outer circuit to get at the central core. This would
disturb the impedance of the cable.

But possibly not enough to be noticable.

PoP

"mike ring" wrote in message
52.50...
Dave Plowman wrote in
:


BTW, are the modern boxes any better than my Philips Ondigital?

Yes.

It used to cause the most amazing splats on TV
audio when it locked up, though, but doesn't lock up on sound only
stuff. At the moment, the bitrates off Freeview are rather better for
radio than DAB. But I'm sure they'll find a way of worsening them
soon.

That's a point, the sound never locks

Any suggestions as to boxes - Argos have a nice selection, but they are
not
covered by the return guarantee, which makes me think it's still a big
gamble

mike r

So just order it from argos via the net or by phone then your still get 7
days to return it

In article ,
PoP wrote:
When I studied for my HNC Electronics at college we specifically
looked at this issue, and RFI signal degradation was certainly a
result - trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection -
otherwise known as distortion - into the signal because you had an
improperly terminated circuit. Now whether or not this might impact
the TV or radio you are feeding is another matter, but the degradation
was very real.

Teeing off is a rather different matter than jointing a cable. For a
start, if you're feeding two destinations, you'll get a double termination
unless it's done correctly.

--
*Growing old is inevitable, growing up is optional

Dave Plowman London SW 12
RIP Acorn

PoP wrote:

On Mon, 08 Sep 2003 11:54:30 +0100, The Natural Philosopher
wrote:


Utter bolocks.


Could you qualify your response please?

When I studied for my HNC Electronics at college we specifically
looked at this issue, and RFI signal degradation was certainly a
result - trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection -
otherwise known as distortion - into the signal because you had an
improperly terminated circuit. Now whether or not this might impact
the TV or radio you are feeding is another matter, but the degradation
was very real.


We are not I believe talking about splitting it or tapping into it. we
are talking about joining it. A solder joint as I described is usually
better than a plug and socket.





Naturally I will bow to your higher level of intelligence if you can
provide some alternative suggestions which are backed by fact.



Only a dozen years as a prtacticisng electronic engineer and an MA in
the subject I am afraid.


PoP

Chris wrote:

In article , PoP
writes

trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection


All I'm trying to do is to make the aerial longer,
without high ladder work.
I'm not splitting it.
I just want it to go to a room further away from the aerial on the roof.
And - it's FM radio - if that makes a difference.


Not much difference.

The issue is, as has been pedantically stated, one of reflection. This
may set up resonances in teh stubs to each side of teh joint, so that
some stations arer stronger, othgers weaker, depending on frequency.

However we used to join cables a lot in test situations, and the VSWR
was never high enough to be a significant problem.

Do it, and if its seriously ****e you can blame me and do the job
'properly'. But you won't need to.

On Mon, 08 Sep 2003 19:51:37 +0100, The Natural Philosopher
wrote:

Notice the retreat.

???

If I was wrong in what I said previously then I'm always happy to
concede. However, as it happens I stand 100% behind what I said
previously, and await with some patience you revealing what your facts
are based upon.

If you do it like wot I said, and presevre the
phsyical dimensions of teh cable, and restoire teh screen with foil, its
a lot BETTER than all bar the most expensive connectors. Try butting a
belling lee - or even a BNC plug and socket on a VSWR meter and
see...and if you really want to gasp with amazement, take the back off
your hifi receiver and see how THEY terminate onto the socket

Very helpful. There's clearly distance between our methods. One is to
do the job properly, the other is to bodge it. Must be bodge-a-job
week I guess

PoP

On Mon, 08 Sep 2003 19:47:02 +0100, The Natural Philosopher
wrote:

Only a dozen years as a prtacticisng electronic engineer and an MA in
the subject I am afraid.

Bugger. Trust me to pick an argument with an MA

prtacticisng

??? Tsk.

I spent 15 years as an EE.

PoP

In uk.d-i-y, The Natural Philosopher wrote:

We are not I believe talking about splitting it or tapping into it. we
are talking about joining it. A solder joint as I described is usually
better than a plug and socket.

Agreed. (The wording of the original post did suggest a 3-way "tap"
rather than a simple join, but I think that was an oopsie of phrasing).
A *neat* solder joint, as taught to radio hammer-chewers, is indeed more
likely to perform well at RF than introducing a plug-n-socket; although
a crappy soldered joint would be worse than competently-attached plug and
socket.

So, to repeat in Stefek-speak the "how to solder coax" instructions: the
goal is to create as neat and just-like-the-rest-of-the-cable join as possible,
definetely including using the same inner insulation ('dielectric' if you
like the fancy words) and resulting cable dimensions, not great gobs of
insulating tape, stupidly sharp turns, wierd lumps, odd transition
materials, or whatever. So you strip back both ends, carefully: strip
outer insulation for say 2 cm, slitting it neatly up to the stripping point
and not chucking it away. Push back the outer braiding into a nice bell
shape. Cut off the inner insulation/dielectric for say 1cm on both cables;
slit one of those slugs down its length. Now lay the inner 1cms side by
side, and holding in place using your third and fourth hands solder
quickly together (don't melt the insulation higher up) - practice this
step on scrap bits. If you don't have a third and fourth hand, you can
wrap the two inners firmly together with some thin wire before you solder.

Now put the slit slug of dielectric back over the soldered-together inners;
a single turn of thin insulating tape can help hold it in place, but don't
overdo it with lots of turns. Now it's time to join the outer braids together.
As others have written, if it's copper it's eminently solderable: tease
the end of the braid apart a bit, weave the two ends together to create
a nice not-noticeably-thicker interlacing of the two braids, spot-solder
(don't overdo the soldering - again, the idea is not to melt the inner
dielectric). If aliminium or copper foil, soldering won't work: smooth
into place, maybe add the bit of ali foil another poster suggested.
Cover with the previously slit slug, or a scrap bit of the outer
insulation, holding down with insulating tape or the previously-
mentioned heatshrink (which you didn't forget to slip on first ;-). For
a joint to be subjected to sun and rain, it's worth hunting down the
adhesive-lined heatshrink, which will make a much more waterproof joint.

If you think you're too cackhanded to do this neatly, then a plug-n-socket
might give better results. BUT how are you going to attach those? If
soldering, it's somewhat easier than a cable join, but still susceptible
to oopsies; if you get crimp-on fittings, you'd better know someone who
will lend you the 100-quid-plus proper crimping tool - you're unlikely to
get a quality joint with your second-best pair of slipjoint plumber's
pliers ;-) If you really want to louse up the RF properties of the coax,
separate out the inner and outer conductors for a good few inches, join
inner-to-inner, outer-to-outer in a bit of oversize (30 amp) choccie block,
wrap with gobs of self-amalgamating tape, bang a masonry nail through
it all to 'secure' it to the wall, and call yourself a registered $ky
installer ;-)

HTH, Stefek

In article ,
The Natural Philosopher wrote:
The issue is, as has been pedantically stated, one of reflection. This
may set up resonances in teh stubs to each side of teh joint, so that
some stations arer stronger, othgers weaker, depending on frequency.

Makes you wonder how the fairly standard:-

aerial - cable - plug - DA - plug - cable - outlet - plug - cable - plug
- inlet ever works at all...

--
*Why don't sheep shrink when it rains?

Dave Plowman London SW 12
RIP Acorn

In article ,
The Natural Philosopher wrote:
Teeing off is a rather different matter than jointing a cable. For a
start, if you're feeding two destinations, you'll get a double
termination unless it's done correctly.


Yep. You have to use a resistive pad to get it right, and you lose 3db
in the process.

Better, surely, to use a low loss inductive type?

--
*Women like silent men; they think they're listening.

Dave Plowman London SW 12
RIP Acorn

In message , Dave Plowman
writes
In article ,
The Natural Philosopher wrote:
The issue is, as has been pedantically stated, one of reflection. This
may set up resonances in teh stubs to each side of teh joint, so that
some stations arer stronger, othgers weaker, depending on frequency.

Makes you wonder how the fairly standard:-

aerial - cable - plug - DA - plug - cable - outlet - plug - cable - plug
- inlet ever works at all...

The phasors won't take it cap'n
--
geoff

In article , writes
In uk.d-i-y, The Natural Philosopher wrote:

We are not I believe talking about splitting it or tapping into it. we
are talking about joining it. A solder joint as I described is usually
better than a plug and socket.

Agreed. (The wording of the original post did suggest a 3-way "tap"
rather than a simple join, but I think that was an oopsie of phrasing).
A *neat* solder joint, as taught to radio hammer-chewers, is indeed more
likely to perform well at RF than introducing a plug-n-socket; although
a crappy soldered joint would be worse than competently-attached plug and
socket.

So, to repeat in Stefek-speak the "how to solder coax" instructions: the
goal is to create as neat and just-like-the-rest-of-the-cable join as possible,
definetely including using the same inner insulation ('dielectric' if you
like the fancy words) and resulting cable dimensions, not great gobs of
insulating tape, stupidly sharp turns, wierd lumps, odd transition
materials, or whatever. So you strip back both ends, carefully: strip
outer insulation for say 2 cm, slitting it neatly up to the stripping point
and not chucking it away. Push back the outer braiding into a nice bell
shape. Cut off the inner insulation/dielectric for say 1cm on both cables;
slit one of those slugs down its length. Now lay the inner 1cms side by
side, and holding in place using your third and fourth hands solder
quickly together (don't melt the insulation higher up) - practice this
step on scrap bits. If you don't have a third and fourth hand, you can
wrap the two inners firmly together with some thin wire before you solder.

Now put the slit slug of dielectric back over the soldered-together inners;
a single turn of thin insulating tape can help hold it in place, but don't
overdo it with lots of turns. Now it's time to join the outer braids together.
As others have written, if it's copper it's eminently solderable: tease
the end of the braid apart a bit, weave the two ends together to create
a nice not-noticeably-thicker interlacing of the two braids, spot-solder
(don't overdo the soldering - again, the idea is not to melt the inner
dielectric). If aliminium or copper foil, soldering won't work: smooth
into place, maybe add the bit of ali foil another poster suggested.
Cover with the previously slit slug, or a scrap bit of the outer
insulation, holding down with insulating tape or the previously-
mentioned heatshrink (which you didn't forget to slip on first ;-). For
a joint to be subjected to sun and rain, it's worth hunting down the
adhesive-lined heatshrink, which will make a much more waterproof joint.

If you think you're too cackhanded to do this neatly, then a plug-n-socket
might give better results. BUT how are you going to attach those? If
soldering, it's somewhat easier than a cable join, but still susceptible
to oopsies; if you get crimp-on fittings, you'd better know someone who
will lend you the 100-quid-plus proper crimping tool - you're unlikely to
get a quality joint with your second-best pair of slipjoint plumber's
pliers ;-) If you really want to louse up the RF properties of the coax,
separate out the inner and outer conductors for a good few inches, join
inner-to-inner, outer-to-outer in a bit of oversize (30 amp) choccie block,
wrap with gobs of self-amalgamating tape, bang a masonry nail through
it all to 'secure' it to the wall, and call yourself a registered $ky
installer ;-)
HTH, Stefek

That does indeed help. What a wonderfully clear and helpful
description!
I am truly grateful. I shall do it today, with a very long extension
cable for my soldering iron.

--
Chris

Dave Plowman wrote:

In article ,
The Natural Philosopher wrote:

The issue is, as has been pedantically stated, one of reflection. This
may set up resonances in teh stubs to each side of teh joint, so that
some stations arer stronger, othgers weaker, depending on frequency.


Makes you wonder how the fairly standard:-

aerial - cable - plug - DA - plug - cable - outlet - plug - cable - plug
- inlet ever works at all...



Exactly. As Pop said, it shouldn't work at all.

But it does.

We ****ed around in the lab once with bits of cable and a VSWR and a
scope and a pulse generator as young graduates in our first job.

Plugs aren't as percfect as cable, and solder is very little different -
even if not 'done correctly'. - i.e. bringing the tails out side by
side, making the joint and insulating with tape.

Splitting is immediately noticeable tho.

Nearly all connections in the equipment were not done onto circuit board
with a coaxial connection: Normally you have a solder tag to the chassis
by the socket, and wire to that with a tail from a bit of coax. and the
barid then goes to a pin on teh ground plane. Hardly ideal, but in
practice very little different from 'ideal'.

The difference between a theoretical and a practical engineer is the
theoretician knows what makkes a difference, the practical knows how
much difference. And ignores if less than a dB.

Dave Plowman wrote:

In article ,
The Natural Philosopher wrote:

Teeing off is a rather different matter than jointing a cable. For a
start, if you're feeding two destinations, you'll get a double
termination unless it's done correctly.



Yep. You have to use a resistive pad to get it right, and you lose 3db
in the process.


Better, surely, to use a low loss inductive type?


Yes. but you still lose the 3db Sctually it must be more with
resistors mustn't it?

In uk.d-i-y, Chris ] wrote:
........... If you really want to louse up the RF properties of the coax,
separate out the inner and outer conductors for a good few inches, join
inner-to-inner, outer-to-outer in a bit of oversize (30 amp) choccie block,
wrap with gobs of self-amalgamating tape, bang a masonry nail through
it all to 'secure' it to the wall, and call yourself a registered $ky
installer ;-)
Oh, I forgot one more crucial tip for the budding install monkey: wrap up
the joint in self-am tape, *but* make sure you leave the braid exposed futher
away from the joint itself, so rain can make its way up the cable by
capillary action ;-)


That does indeed help. What a wonderfully clear and helpful
description!
I am truly grateful. I shall do it today, with a very long extension
cable for my soldering iron.

Thank you for your words of appreciation. Do have a practise in a more
comfortable place on some scraps of coax first - and be warned that
soldering with the wind blowing can be a pain in the bum, as you lose heat
quite a lot faster than indoors. Fine if you have a 40W temp-controlled
iron, as it'll simply keep up with the added loss; less fine if you are
waving that 15W little yellow Antex about ;-)

Cheers, Stefek

In article , writes
Thank you for your words of appreciation. Do have a practise in a more
comfortable place on some scraps of coax first - and be warned that
soldering with the wind blowing can be a pain in the bum, as you lose
heat quite a lot faster than indoors. Fine if you have a 40W
temp-controlled iron, as it'll simply keep up with the added loss; less
fine if you are waving that 15W little yellow Antex about ;-)

It's done. And it works. Radio 3 reception is wonderful.
But I made one stupid mistake which made me burst out laughing.
I joined the cable neatly - and tested it - and then started fixing it
to the wall - and found I hadn't taken the cable behind drain pipes
etc.!
So maybe I'll do it again - but not today!
--
Chris

On Tue, 9 Sep 2003 15:39:07 +0100, Chris ] wrote:

It's done. And it works. Radio 3 reception is wonderful.
But I made one stupid mistake which made me burst out laughing.
I joined the cable neatly - and tested it - and then started fixing it
to the wall - and found I hadn't taken the cable behind drain pipes
etc.!

But you didn't ask us for advice about putting it in front of or
behind the drainpipes, so how can it be a mistake?

PoP

On Mon, 08 Sep 2003 12:26:19 +0100, PoP
wrote:

On Mon, 08 Sep 2003 11:54:30 +0100, The Natural Philosopher
wrote:

Utter bolocks.

Could you qualify your response please?

When I studied for my HNC Electronics at college we specifically
looked at this issue, and RFI signal degradation was certainly a
result - trying to tap into a wire (or split it to go in two different
directions) would invariably introduce harmonics and reflection -
otherwise known as distortion - into the signal because you had an
improperly terminated circuit. Now whether or not this might impact
the TV or radio you are feeding is another matter, but the degradation
was very real.

Naturally I will bow to your higher level of intelligence if you can
provide some alternative suggestions which are backed by fact.

PoP


Did you actually pass your HNC because you seem to be talking cobblers
?

As a former BBC transmitter engineer with 25 years experience of RF
issues I offer the following advice.....

The aim of the exercise is not to introduce discontinuities of
impedance along the cable. You can get pretty close to this using the
method someone suggested earlier with exposing the inner, soldering
it, covering the joint with a slit piece of the insulator (same
dielectric constant you see), then covering the now insulated middle
bit with the two bits of braid that should be dangling etc etc.

It's a load of arsing about. Get two connectors and a back to back
socket and wrap in in self amalgamating tape.

Couple of points...its unlikely the terminations an either end of the
cable are very close to the characterisitc impedance of the cable
anyway cos TVs are built on the cheap and so are aerials. Secondly,
most TV wall sockets are appalling from a design point of view but
work OK.

Finally, if your TV signal is weak enough that using connectors and a
piece of tape makes a difference then your picture is probable
borderline to ****e anyway.

n

On Tue, 09 Sep 2003 21:56:06 +0100, norm wrote:

Did you actually pass your HNC because you seem to be talking cobblers

I certainly did. However, admittedly I went the digital electronics
route rather than the analogue

The aim of the exercise is not to introduce discontinuities of
impedance along the cable. You can get pretty close to this using the
method someone suggested earlier with exposing the inner, soldering
it, covering the joint with a slit piece of the insulator (same
dielectric constant you see), then covering the now insulated middle
bit with the two bits of braid that should be dangling etc etc.

It's a load of arsing about. Get two connectors and a back to back
socket and wrap in in self amalgamating tape.

Which is exactly what I have been suggesting all along. The
suggestions relating to soldering etc weren't mine - are you sure you
aren't confusing me with someone else?

Finally, if your TV signal is weak enough that using connectors and a
piece of tape makes a difference then your picture is probable
borderline to ****e anyway.

As I commented earlier, the acid test is to make the modification and
feed the signal into the back of the TV (or radio). If it works then
great, if it doesn't then maybe the signal was not helped with the
modifications to the aerial feed.

PoP

norm wrote:
...
As a former BBC transmitter engineer with 25 years experience of RF
issues I offer the following advice.....
[...advice snipped...]
Finally, if your TV signal is weak enough that using connectors and a
piece of tape makes a difference then your picture is probable
borderline to ****e anyway.

That'd be a technical term, then?

Edwin.

I have just done some measurements, and it hardly makes a gnat's cock of
difference!

Aim
Compare signal losses due to various types of join in coax cable.

Apparatus
Coax cable (unknown type, about 2-ft length, 50 Ohm, terminated in SMA
connectors)
Network analyser (HP 8753E)

Method
1. Measure insertion loss and return loss (or VSWR) of unbroken cable. Use these
results as reference.
2. Cut cable near the middle.
3. Re-connect the ends as crudely as possible (inner soldered, braid just
twisted) and re-measure IL and RL at 650MHz and 750MHz.
4. Re-connect ends as well as possible and re-measure.

Results
Original return loss: 27dB (Very good)
Original insertion loss 0dB (relative, not absolute)
Crude join: IL = 0.3dB at 650MHz, 0.31dB at 750MHz.
Better join: IL = 0.1dB over 650 to 750MHz.

Note: Yes, this is high-quality 50-Ohm coax, not 75-Ohm TV stuff, but the
principal's the same.

Conclusion: Yes, there's a measurable difference, but it's damn small. As
someone else said, you'd have a very marginal reception to notice any
difference.

Regards

Edwin
Bath.

Edwin Spector wrote:

I have just done some measurements, and it hardly makes a gnat's cock of
difference!

Aim
Compare signal losses due to various types of join in coax cable.

Apparatus
Coax cable (unknown type, about 2-ft length, 50 Ohm, terminated in SMA
connectors)
Network analyser (HP 8753E)

Method
1. Measure insertion loss and return loss (or VSWR) of unbroken cable. Use these
results as reference.
2. Cut cable near the middle.
3. Re-connect the ends as crudely as possible (inner soldered, braid just
twisted) and re-measure IL and RL at 650MHz and 750MHz.
4. Re-connect ends as well as possible and re-measure.

Results
Original return loss: 27dB (Very good)
Original insertion loss 0dB (relative, not absolute)
Crude join: IL = 0.3dB at 650MHz, 0.31dB at 750MHz.
Better join: IL = 0.1dB over 650 to 750MHz.

Note: Yes, this is high-quality 50-Ohm coax, not 75-Ohm TV stuff, but the
principal's the same.

Conclusion: Yes, there's a measurable difference, but it's damn small. As
someone else said, you'd have a very marginal reception to notice any
difference.

Regards

Edwin
Bath.


What was teh VSWR?

In uk.d-i-y, Edwin Spector wrote:
I have just done some measurements, and it hardly makes a gnat's cock of
difference!


[ ... ]

Conclusion: Yes, there's a measurable difference, but it's damn small. As
someone else said, you'd have a very marginal reception to notice any
difference.

Ah yes, but think of the pride in workmanship ;-) But thanks for injecting
real data into the speculation. RF folklore doesn't travel all that well
from its original context; so for radio-hams and wannabes pushing 100W of
ERP up coax, and needing to be sure it's going only where it's supposed to, a
degree of paranoia about cable/joint integrity creeps in which isn't
necessarily relevant to broadcast signal reception in non-marginal areas.

Cheers, Stefek

The Natural Philosopher wrote:

Edwin Spector wrote:

I have just done some measurements, and it hardly makes a gnat's cock of
difference!
...snippetty...
What was teh VSWR?

Return loss of better than 20dB over 650 to 750 MHz, which is equivalent to a
VSWR of 1.22:1. Theoretical loss due to this mismatch is 0.043dB (I looked it
up).

Edwin.

In article , Edwin Spector
writes
I have just done some measurements, and it hardly makes a gnat's cock of
difference!

Aim
Compare signal losses due to various types of join in coax cable.

Apparatus
Coax cable (unknown type, about 2-ft length, 50 Ohm, terminated in SMA
connectors)
Network analyser (HP 8753E)

Method
1. Measure insertion loss and return loss (or VSWR) of unbroken cable.
Use these
results as reference.
2. Cut cable near the middle.
3. Re-connect the ends as crudely as possible (inner soldered, braid just
twisted) and re-measure IL and RL at 650MHz and 750MHz.
4. Re-connect ends as well as possible and re-measure.

Results
Original return loss: 27dB (Very good)
Original insertion loss 0dB (relative, not absolute)
Crude join: IL = 0.3dB at 650MHz, 0.31dB at 750MHz.
Better join: IL = 0.1dB over 650 to 750MHz.

Note: Yes, this is high-quality 50-Ohm coax, not 75-Ohm TV stuff, but the
principal's the same.

Conclusion: Yes, there's a measurable difference, but it's damn small. As
someone else said, you'd have a very marginal reception to notice any
difference.

Regards

Edwin
Bath.

I am very impressed by someone who actually finds out something!
Thankyou.
--
Chris

Edwin Spector wrote:

I have just done some measurements,...snippetty...
Results
Original return loss: 27dB (Very good)
Original insertion loss 0dB (relative, not absolute)
Crude join: IL = 0.3dB at 650MHz, 0.31dB at 750MHz.
Better join: IL = 0.1dB over 650 to 750MHz.

Footnote:
It's probably worth spending a couple of minutes making the joint as 'nice' as
possible. A discontinuity in a TV feed could produce a reflection which could
give a ghost on the telly image.

Edwin.