need a LOONG delay line

10mhz

although

don't

huge

a

you

idea

maybe

use

with

digitise

up,

it

end

to

cool, so I'l only need 1000 handheld spools, thanks :)

Colin =^.^=

*Acoustically* you would only need around 10 feet ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

whats that in millimeters ?

Colin =^.^=

In message , dated Mon, 21 Aug

2006, colin writes

Your original question is too vague to be answered in the way you want. So I answered it as well as possible.

--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Well all you did realy was just log it. ;)

But anyway I have a rubidium reference wich when I compare with another similar unit and one is rotated it is affected by the earths magnetic field and there is a slight change in frequency, how much shielding would be required to reduce the effect of the magnetic field by a factor of 10 + I tried a catfood tin wich I just happened to have at hand (empty of course) wich just fitted over it but didnt make much of a noticable difference.

I assume Il need a mu metal sheild but how much 1mm, 10mm, ... 100mm thick ?

Its interesting the OCXO I have are not affected by magnetic field yet are to sensitive to change in acceleration from just being tilted a few degrees.

thanks Colin =^.^=

In message , dated Mon, 21 Aug 2006, colin writes

That's better! Now there is enough data to be more helpful. You may not need mu-metal; cat-food tin is very thin but mild steel **as a closed box** may well be sufficient for 20 dB reduction, maybe more. Try a box made of 1/16th sheet; this is usually not too heavy or cumbersome. But it MUST be a closed box; a five-faced box is no good. Obviously it has to be in two parts, and there are many ways of arranging that. Make them overlap generously; the width of overlap depends on how big the box is. Be generous with the number of screws holding the parts together.

--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Sorry I think you cannot shield against rotation . I believe that you are getting a Doppler modulation like in a rotating rate gyro,and that is rather fundamental. You could check by not rotating, but moving a small coil around the unit ,with a field strength comparable with the earth magnetic field, if that does not produce the same effect, I would bet on the Doppler explanation, in which case no shielding will work. The only remedy against that is a smaller unit, and a different layout(inside the reference unit).

is

magnetic

course)

thick

are

degrees.

Thats very interesting, however the unit is rotated 180' slowly and stopped, It is slighlty slower in one orientation than in 180'. This is due to the Zeeman effect I beleive.

Colin =^.^=

No, I'm talking about real components. Inductors and capacitors that you can pick up in your fingers.

in --+---UUUU---+---UUUU---+---UUUU---+---UUUU---+---UUUU---+-- out | | | | | | --- --- --- --- --- --- --- --- --- --- --- --- | | | | | | GND GND GND GND GND GND

It's called, I think, a "lumped-time-constant delay line" or something like that.

It has to be impedance-matched at both ends, of course. :-)

Cheers! Rich

In message , dated Tue, 22 Aug 2006, Rich Grise writes

Lumped-component delay line. There is a LOT in the mid-20th century books about them. Widely used in WWII radar.

Like any other LC filter.

--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

10mhz I

up

transmission

lossy,

stages,

500mmx500mm

well its damned hard to pick up those 0402 size SMD packaged inductors and capacitors with your fingers ! and when you use tweezers they always seem want to cling on to the tweezers somehow. (actualy if you have sticky fingers you can pick up quite a few with just one finger) but yes I think I knew what you meant, maybe the capacitance of a pcb pad is far too small to use as a single element after all at 10mhz. but still only maybe only 1M^2 of pcb space might be needed.

If you look at the inside of some delay lines they have a coil wound on a former with ferrite and copper strips running lengthways, wich basicaly forms lumped elements albeit rather small ones, maybe its worth taking one apart to measure the length of wire to see what the propagation velocity is.

of course. I remember (vaguely) we had a lumped delay line in class, if you left the end OC and got it to resonate you could generate a lot of volts. (maybe this could make up for losses.)

Im not sure about using a distributed amplifier over the whole length of the delay line, my understanding of distributed amplifiers was just to lose the effect of their input capacitance, my old tek 585a has a few of them inside.

otherwise a buffer every 100 stages or so should make up for losses.

thanks Colin =^.^=

although

it

Very

tweezers

is

only

is.

you

the

the

inside.

Colin, I don't think I've seen it mentioned, but you told us your signal is (very) low bandwidth, didn't you? How low is it?

Taking advantage of this, why don't you downconvert both signals (your ref and the other one), using the same LO, to a low enough frequency where generating a 10ms delay is way much easier: a 2KHz 1rst order APF will give you 1ms delay with a 0.003% error upto 10Hz, 0.26% upto 100Hz. You'll only need 10 of these to achieve your 10ms delay. Then you can process the signals in the baseband or upconvert them back to

10MHz, still using the same LO.

--
Thanks,
Fred.

I'd expect that it would take a seriously heavy and expensive structure of mu metal. Beyond that, fabricaton of a mu metal enclosure that works can be done but it is not a trivial matter.

But magnetoresistive sensors are available with resolution of 1 nanotesla.

Earth's field is about 50 microtesla, more than 90 dB higher. So, with a closed-loop system comprised of such sensors and pairs of Hemholtz coils, I would think that 40 dB (100:1) or more reduction by active cancellation in the region occupied by your mobile rubidium reference should be quite easy to achieve.

is

course)

thick

cool, I wonder what it uses. Im not sure what accuracy you can get from using a toroid with a few coils around it rather than through it, but its capabale of measuring the earths field. I only need a factor of 10-100 reduction. mumetal.com have a sheild for a magnetic device on their website (squid), it weighs 3 tons ! I have another rubidium device now wich is already in a mu metal sheild case, yet to measure its effetiveness.

Im also going to try and get some PAL TV delay lines, anyone know any surplus that might have some, or are they so old theyr unlikely to be any sigificant quantity about ?

Colin =^.^=

In message , dated Tue, 29 Aug

2006, colin writes

The best place to get old TV stuff is:

Sendz Components

01702338894 212 London Road , Southend On Sea , Essex SS1 1PJ

You may need to phone them, because last time I looked down there, I think they may have moved.

--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

are you sure you are not seeing the earth's rotation? We use it to test gyroscopes on satellites in ground testing. (You just need to know your latitude to get a predict on apparent angular rate).