EMRFD Message Archive 4821

4821 2010-07-25 14:45:31 thomas Delay lines Message Date From Subject 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. 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. Regards David GI8FNR ________________________________ Micro-Coax, who make delay lines, give these equations; http://www.micro-coax.com/pages/technicalinfo/equations-3.html 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. Kerry. 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! - farhan On 7/26/10, Kerry wrote: > Micro-Coax, who make delay lines, give these equations; > > http://www.micro-coax.com/pages/technicalinfo/equations-3.html > > 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. > > Kerry. > > -- Sent from my mobile device 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. Many comm 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 Mark AD5SS 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. :-) ========================================================== Mike Mayer mwmayer@tds.net -----Original Message----- 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.