Gaius wrote in
:

Lostgallifreyan wrote:

Conversely, I found some nice coax in a skip once that had two heavy
braids amounting to almost complete coverage around a single fine
stranded core. (Found outside a telephone exchange, but I don't know
what frequency they were intended for, though I used some for an
outdoor VHF receiving quarter wave dipole with good results, and I
suspect it will do for a SW longwire once I get a matching transformer
for it).

If it was a UK (BT) telephone exchange, then it probably was "Cable
coaxial 2003".
Used for critical video and general HF use. I don't know what it's
officially spec'd to, but it would work well up to several hundred MHz.
Characteristic impedance of 75ohms, and easily capable of 100W into a
decent match.



Sounds like the same stuff, though I have 2002 on mine (which in absence of
other markings was cryptic enough that I was unsure of it, though I think it
might have been earlier than 2002 when I found it. I thought it might be
75 ohm but I had no idea it might efficiently carry high power. But I knew it
was well over-spec'd for the uses I put it to. I was lucky to find it. The
staff there were happy enough for me to raid the skip, too... Should try it
again sometime. That stuff seems to last forever even outside in strong daily
temperature changes and direct sunlight.

Lostgallifreyan wrote in
:

Gaius wrote in
:

Lostgallifreyan wrote:

Conversely, I found some nice coax in a skip once that had two heavy
braids amounting to almost complete coverage around a single fine
stranded core. (Found outside a telephone exchange, but I don't know
what frequency they were intended for, though I used some for an
outdoor VHF receiving quarter wave dipole with good results, and I
suspect it will do for a SW longwire once I get a matching transformer
for it).

If it was a UK (BT) telephone exchange, then it probably was "Cable
coaxial 2003".
Used for critical video and general HF use. I don't know what it's
officially spec'd to, but it would work well up to several hundred MHz.
Characteristic impedance of 75ohms, and easily capable of 100W into a
decent match.



Sounds like the same stuff, though I have 2002 on mine (which in absence
of other markings was cryptic enough that I was unsure of it, though I
think it might have been earlier than 2002 when I found it. I thought
it might be 75 ohm but I had no idea it might efficiently carry high
power. But I knew it was well over-spec'd for the uses I put it to. I
was lucky to find it. The staff there were happy enough for me to raid
the skip, too... Should try it again sometime. That stuff seems to last
forever even outside in strong daily temperature changes and direct
sunlight.


I forgot to mention that I also used some for a pair of DIY scope leads for a
100 MHz scope, and they worked right even without the little capacitative
adjuster usually supplied on properly made probes. A bit clumsy, but a nice
find all the same.

Lostgallifreyan wrote:
Sounds like the same stuff, though I have 2002 on mine (which in absence of
other markings was cryptic enough that I was unsure of it, though I think it
might have been earlier than 2002 when I found it. I thought it might be
75 ohm but I had no idea it might efficiently carry high power. But I knew it
was well over-spec'd for the uses I put it to. I was lucky to find it. The
staff there were happy enough for me to raid the skip, too... Should try it
again sometime. That stuff seems to last forever even outside in strong daily
temperature changes and direct sunlight.

If it has 2002 printed on it, that means it's "Cable coaxial 2002",
which is one down the scale in loss terms from 2003. 2002 (nothing to do
with the date!) is as good quality as 2003 (which is thicker), but the
loss is a bit higher. The three usual types were AFAIR -

2001 - single screened, foam dielectric. Quite thin - used for short
runs and jumpers.
2002 - General purpose, high quality. Solid dielectric.
2003 - Top quality (in loss terms). Solid dielectric.

All are 75ohms - like pretty well all telecom coax. (50 ohm is usually
only found in antenna feeders and traditional ethernet). The normal PVC
jacket colour was "Light straw" (yellowish cream), but other colours
were occasionally used for special purposes.

Gaius wrote in
:

Lostgallifreyan wrote:
Sounds like the same stuff, though I have 2002 on mine (which in
absence of other markings was cryptic enough that I was unsure of it,
though I think it might have been earlier than 2002 when I found it.
I thought it might be 75 ohm but I had no idea it might efficiently
carry high power. But I knew it was well over-spec'd for the uses I put
it to. I was lucky to find it. The staff there were happy enough for me
to raid the skip, too... Should try it again sometime. That stuff seems
to last forever even outside in strong daily temperature changes and
direct sunlight.

If it has 2002 printed on it, that means it's "Cable coaxial 2002",
which is one down the scale in loss terms from 2003. 2002 (nothing to do
with the date!) is as good quality as 2003 (which is thicker), but the
loss is a bit higher. The three usual types were AFAIR -

2001 - single screened, foam dielectric. Quite thin - used for short
runs and jumpers.
2002 - General purpose, high quality. Solid dielectric.
2003 - Top quality (in loss terms). Solid dielectric.

All are 75ohms - like pretty well all telecom coax. (50 ohm is usually
only found in antenna feeders and traditional ethernet). The normal PVC
jacket colour was "Light straw" (yellowish cream), but other colours
were occasionally used for special purposes.



Thanks. That matches closely except the dielectric, which I think is foam (is
certainly foamy or foamish). Colour is same too, though closer to white than
yellow. As far as I know the impedance is purely based on the scale and
geometry of the cross-section, and if so, I guess the central conductor of
2003 is also thicker. I think there were seven strands of very thin copper.
If you or anyone reading this really wants to know I'll get a vernier gauge
and find a bare cable end somewhere... External diameter is approx 5mm on the
2002 type.

Do you know if it's only BT internal use? If I can buy it economically, I'd
consider it. I like working with it, when I'm in the mood for picking apart
cable braids.

Lostgallifreyan wrote:

Thanks. That matches closely except the dielectric, which I think is foam (is
certainly foamy or foamish). Colour is same too, though closer to white than
yellow. As far as I know the impedance is purely based on the scale and
geometry of the cross-section, and if so, I guess the central conductor of
2003 is also thicker. I think there were seven strands of very thin copper.
If you or anyone reading this really wants to know I'll get a vernier gauge
and find a bare cable end somewhere... External diameter is approx 5mm on the
2002 type.

Do you know if it's only BT internal use? If I can buy it economically, I'd
consider it. I like working with it, when I'm in the mood for picking apart
cable braids.


You're right - my memory must be porous. 2002 has a FOAM dielectric.
Also, 2003 has a single strand inner conductor (spec must have changed -
used to be stranded). You can buy 2002 from RS - it's a BT spec, but
available for anyone. Have a look at :

http://uk.rs-online.com/web/search/s...ct&R=520306 8

It's only £58 for 100m, and the loss is reasonable at 3.61dB/100m @
4MHz. (2003 cable is 2.33dB/100m @ 4MHz)

Gaius wrote in
:

Lostgallifreyan wrote:

Thanks. That matches closely except the dielectric, which I think is
foam (is certainly foamy or foamish). Colour is same too, though closer
to white than yellow. As far as I know the impedance is purely based on
the scale and geometry of the cross-section, and if so, I guess the
central conductor of 2003 is also thicker. I think there were seven
strands of very thin copper. If you or anyone reading this really wants
to know I'll get a vernier gauge and find a bare cable end somewhere...
External diameter is approx 5mm on the 2002 type.

Do you know if it's only BT internal use? If I can buy it economically,
I'd consider it. I like working with it, when I'm in the mood for
picking apart cable braids.


You're right - my memory must be porous. 2002 has a FOAM dielectric.
Also, 2003 has a single strand inner conductor (spec must have changed -
used to be stranded). You can buy 2002 from RS - it's a BT spec, but
available for anyone. Have a look at :

http://uk.rs-online.com/web/search/s...method=getProd
uct&R=5203068

It's only £58 for 100m, and the loss is reasonable at 3.61dB/100m @
4MHz. (2003 cable is 2.33dB/100m @ 4MHz)


Nice. Given what RS are charging for RG59 with a double braid that appears
similar, it looks very good. I don't know enough to choose between them
though, especially given the huge variety of cables RS show for RG59 with
costs varying more than tenfold per metre. From what I've seen of it I'd go
for that BT cable at their price. (They add VAT though..) I guess BT's
economies of large scale help this stuff to be cheaper than it otherwise
would be.