Re: need a LOONG delay line

In article <ZF9Fg.22448$f71.22082@xxxxxxxxxxxxxxxxxxxx>,
colin <no.spam.for.me@xxxxxxxxxxxx> wrote:
"Phil Hobbs" <pcdh@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:44E516B5.20401@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Joerg wrote:
Hello Colin,


Im looking for a long delay line of about 10ms wich can handle a 10mhz
sinewave.
size is not too important as long as its able to be mobile,
a quick calculation reveals I would need about 2000km of cable,
wich means its probably far too expensive to do it this way, although
I only
need 1.
One idea I had was to re circulate the signal many times shifting it
up in
frequency each time,
im not sure if this could be done with just one mixer,
any ideas ?


Ponder John's suggestion of acoustic transfer. That's how they do the
64usec delay lines on PAL system color TV sets. Ok, you probably don't
want to rig 156 of those in series to get your 10msec but it still
sounds better than dealing with several flat-bed trucks full with huge
cable drums pulling up.

The mixer thing sounds too esoteric. At the end you'd be looking with a
magnifier for your signal.


Ten milliseconds is a long time for acoustics at 10 MHz. That's a
time-bandwidth product of 10**5, which is a factor of 10 higher than you
can usually get, at least in my experience. Digitize the signal and
use a big long FIFO buffer--at a 40 MHz sampling rate, 10 ms is only
400k samples, which is a piece of cake.

Cheers,

Phil Hobbs

I had thought of lots of TV delay lines as well lol, as for the cable idea I
was thinking more of the type that has lots of very fine wire wound round a
ceramic tube with ferrite/copper segments. A big reel of .1mm EC wire would
go a long way, I might ony need a few hundred of them ... maybe wind several
layers to save having 1000s of such tubes, maybe have to use twisted pair to
avoid crosstalk ...

The skin effect would kill you in a line that long, let alone its bulk.
Look, for example, at the attenuation at 10MHz in a 200ns long line of RG-174!

I vote for the digitize & shift register (Phil Hobbs' was the first to
suggest this IIRC).

-f
--
.