EMRFD Message Archive 4821
Message Date From Subject 4821 2010-07-25 14:45:31 thomas Delay lines Hello.
I'm in need for an delay line that works from 300KHz to 3GHz. I should only need around 10nS delay but it's important that the loss is even over the whole range, so an low-pass filter would not work.
I guess maybe an length of semi-rigid coax would work? Is there an formula to calculate the length of the coax?
73's de Thomas LA3PNA.
4822 2010-07-25 16:38:57 David Stone Re: Delay lines Thomas, a length of coax would be ideal, abiut 1.5 ns / foot (5 ns / m) so about
2m should be just fine. Loss would be pretty low. Length = 3x 10 exp8 /length
seconds * velocity factor (about 0.6 for solid dielectric cable). Use 0.5 for
solid dielectric cable, and 0.67 for foam ones for the velocity factor unless
you have the manufacturers data.
4823 2010-07-25 17:33:40 Kerry Re: Delay lines Micro-Coax, who make delay lines, give these equations;
There is a lot of other useful information on their website.
They caution against using solid-dielectric cable but I think that they work in an ultra-precise (and expensive) field (military, radar etc) as opposed to the work we amateurs do.
4824 2010-07-26 19:03:32 ajparent1 Re: Delay lines 4825 2010-07-26 20:48:50 Ashhar Farhan Re: Delay lines How much space do you have? A transmission based delay line can be as
long as 3 meters for a 10n delay. The bigger it gets, the lesser will
be the losses. For instance, you can suspend a silver wire in a copper
tubing with few teflon spacers.
What you should remember though is that the performance will depend
upon your ability maintain constant impedance on both sides.
Coax will tend to be lossy and susceptible to age.
More often than not, our compromise is for a more compact design.
Often, higher performance can be traded for miniaturization. I
remember turning a 144 MHz experimental duplexer cavity into an
extremely stable vfo. However, it was 19 inches long!
On 7/26/10, Kerry <firstname.lastname@example.org> wrote:
> Micro-Coax, who make delay lines, give these equations;
> There is a lot of other useful information on their website.
> They caution against using solid-dielectric cable but I think that they work
> in an ultra-precise (and expensive) field (military, radar etc) as opposed
> to the work we amateurs do.
Sent from my mobile device
4830 2010-07-27 11:04:14 Tim Re: Delay lines I spent a lot of time in physics labs where coax cables were hung
on the wall and labeled according to length. 1ns, 2ns, 3ns, 4ns.
In effect, the length in feet was not the measure, but the length in nanoseconds were the measure.
4831 2010-07-27 11:06:52 Mark Bayern Re: Delay lines fun typo alert!
> Many common coax cables (e.g. RG-8, RG-213) have a velocity factor of 0.67. That works out to about 0.66 feet per second.Two thirds of foot second ... really? Seems to be off by a few orders
of magnitude. hi hi
4832 2010-07-27 11:12:25 Mike Mayer Re: Delay lines It is actually quite useful, and makes a good fitness program. If you don't
have enough coax to reach to your antenna and you are transmitting CW, you
transmit one symbol, disconnect the coax from your transmitter, run to the
antenna and connect it. Then disconnect at the antenna and run back and
connect to the transmitter. Repeat for each symbol. If you can run fast
enough you can have your antenna quite far from the transmitter.
4833 2010-07-27 12:06:51 Tim Re: Delay lines Ha! Good catch!
It's astonishing that a scope can be used to measure time periods from sub-nanosecond to many seconds. It's like a yardstick that could be used to measure the distance to pluto just as easily as the thickness of a hair.