Re: [time-nuts] Building a DC Block Thingy....
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi Jason, The value of the capacitor is not critical in this case, anywhere from 47pF to 0.01uF. The series inductance and possible resonances are more important. I used a small axial leaded multi-layer ceramic but any type intended for high frequency de-coupling or RF applications should be OK. Generally smaller is better. Ideally you would use surface mount devices on a micro-stripline PCB, but its over-kill where we are only interested in one frequency. You can't do much better without access to a network analyser (or a lot of work with simpler equipment) or specialised RF components. Robert G8RPI. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jason Rabel Sent: 31 July 2007 01:31 To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Building a DC Block Thingy ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Robert, Thanks, that's kind of the method I was thinking. I was just unsure of the capacitor to use. I have also seen in schematics where an inductor is used in series with the resistor to block the RF from going to ground (and possibly causing screwy things I suppose). I'm still waiting for the unit to arrive, when it does then I can figure out how I'm going to do all the connections and everything. Jason Hi Jason, I had the same issue with a SatSync GPS. I got an old attenuator (burned out or unknown spec), N type in my case but whatever matches your splitter. I unscrewed it and removed the resistors. I placed a 0.001uF 63V ceramic capacitor between in and out and a load resistor (calculated to draw just above the antenna warning current) between out (Rx side) and ground. I did not feel this resistor would affect the signal too much, but slipped a ferrite bead over the ground end lead just for luck. It seems to work OK. Robert G8RPI. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. Genetix Limited - Queensway, New Milton, Hampshire, BH25 5NN Registered in England No. 2660050 www.genetix.com Any opinions expressed in this email are those of the individual and not necessarily Genetix Ltd (Genetix) or any company associated with it. This email and any files transmitted with it are confidential and solely for the use of the intended recipient. If you are not the intended recipient or the person responsible for delivering to the intended recipient, be advised that you have received this email in error and that any use is strictly prohibited. If you have received this email in error please notify Genetix by telephone on +44 (0)1425 624600. The unauthorised use, disclosure, copying or alteration of this message is strictly forbidden. This mail and any attachments have been scanned for viruses prior to leaving Genetix network. Genetix will not be liable for direct, special, indirect or consequential damages as a result of any virus being passed on, or arising from alteration of the contents of this message by a third party. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Software Sawtooth correction prerequisites?
); SAEximRunCond expanded to false
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On Jul 24, 2007, at 1:32, Dr Bruce Griffiths wrote:
Perhaps a software implementation of a 1 bit oversampled DAC the 1 bit
output of which is low pass filtered to control the EFC input is the
closest approach to this ideal.
With an appropriate algorithm the idle tone and inherent instability
problems (of high order modulators - 3rd or higher order) of the sigma
delta modulator will not occur.
It is easy to design stable sigma delta converters of orders higher
than two. I have calculated a 7th order ADC which is implemented on
silicon and stable of coarse. A 11th order sigma delta with
oversampling ratio 128 is stable in simulation and has 228dB snr.
{This is no typo two hundred and twenty eight dB)
Higher order sigma delta converter require higher order
reconstruction filters but it is easy to design for more bandwidth
than needed and so to relax the filter spec.
Henk
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Re: [time-nuts] Scope Clock
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY as ordered will these boards accept 1pps or was yours a special? Eric kg6kqt On 7/23/07, Mark Amos [EMAIL PROTECTED] wrote: ); SAEximRunCond expanded to false Errors-To: time-nuts-bounces+eric.fort= [EMAIL PROTECTED] Time Nuts, I built one of these clocks a couple of months ago. In earlier correspondence with Jan De Rie I asked him to allow for input of an external 1PPS clock (which he graciously did!) I drive the clock from a conditioned 1PPS signal out of a Shera GPSDO that I built. It's a great conversation piece, and it's very inexpensive (not including the scope...) Jan's a great guy and does nice work. Mark W8XR -Original Message- From: [EMAIL PROTECTED] [ mailto:[EMAIL PROTECTED] Behalf Of Maggie Leber Sent: Monday, July 23, 2007 8:07 AM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Sorry: meant to change the subject line: New o-scopeclock display project Maybe some of you haven't seen this oscilloscope clock display yet: http://www.makezine.com/blog/archive/2007/07/avr_oscilloscope_clock.html ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Scope Clock
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY In a message dated 31/07/2007 23:23:38 GMT Daylight Time, [EMAIL PROTECTED] writes: as ordered will these boards accept 1pps or was yours a special? Eric kg6kqt --- Hi Eric Take a look at. _http://www.dutchtronix.com/ScopeClock.htm_ (http://www.dutchtronix.com/ScopeClock.htm) It looks like the 1PPS is standard. I've got a 12 inch X-Y display doing nothing right now.. and I'm very tempted to have a play with one of these:-) regards Nigel GM8PZR ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Software Sawtooth correction prerequisites?
); SAEximRunCond expanded to false
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Henk ten Pierick wrote:
On Jul 24, 2007, at 1:32, Dr Bruce Griffiths wrote:
Perhaps a software implementation of a 1 bit oversampled DAC the 1 bit
output of which is low pass filtered to control the EFC input is the
closest approach to this ideal.
With an appropriate algorithm the idle tone and inherent instability
problems (of high order modulators - 3rd or higher order) of the sigma
delta modulator will not occur.
It is easy to design stable sigma delta converters of orders higher
than two. I have calculated a 7th order ADC which is implemented on
silicon and stable of coarse. A 11th order sigma delta with
oversampling ratio 128 is stable in simulation and has 228dB snr.
{This is no typo two hundred and twenty eight dB)
Higher order sigma delta converter require higher order
reconstruction filters but it is easy to design for more bandwidth
than needed and so to relax the filter spec.
Henk
Henk
There is no theory to show that sigma delta modulators of order higher
than 2 are actually unconditionally stable.
Merely simulating the device is not conclusive proof that the modulator
will never saturate, albeit infrequently.
Most implementations include saturation detection circuitry that resets
the modulator should this occur.
If saturation isn't too frequent then for most purposes this is only a
minor annoyance.
However cascaded first order modulators as employed in the MASH
technique are stable in theory and practice.
However if one adopts a non linear control theory approach, one can
actually design high order modulators that both stable in theory and in
practice.
The resulting circuit isn't a sigma delta modulator, however it has
similar noise shaping characteristics.
Bruce
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