[time-nuts] Light Squared
hardy
hardyhansen at mail.tele.dk
Wed Jun 22 03:59:24 UTC 2011
http://www.technewsworld.com/story/72712.html
Hardy
----- Original Message -----
From: <time-nuts-request at febo.com>
To: <time-nuts at febo.com>
Sent: Tuesday, June 21, 2011 10:09 PM
Subject: time-nuts Digest, Vol 83, Issue 72
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> Today's Topics:
>
> 1. Re: DDS - Cosine v. Sine LUT (KD0GLS)
> 2. Re: DDS - Cosine v. Sine LUT (lists at lazygranch.com)
> 3. Re: DDS - Cosine v. Sine LUT (Luis Cupido)
> 4. Re: DDS - Cosine v. Sine LUT (Magnus Danielson)
> 5. Re: DDS - Cosine v. Sine LUT (Robert LaJeunesse)
> 6. Re: Replacing electrolytics - any disadvantages of high temp
> ones? (Poul-Henning Kamp)
> 7. Re: Light Squared, etc. (Robert LaJeunesse)
> 8. Re: Light Squared, etc. (Russell Rezaian)
> 9. Re: DDS - Cosine v. Sine LUT (KD0GLS)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 21 Jun 2011 14:03:49 -0500 (CDT)
> From: KD0GLS <kd0gls at mninter.net>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
> Message-ID: <F72D67E5-5F4B-4D22-ABD5-66930D060B8A at mninter.net>
> Content-Type: text/plain; charset=us-ascii
>
>
>> On Jun 21, 2011, at 13:39, Chris Albertson wrote:
>>
>> I used only 90 degrees of the table.
>>
>
>
> Yes, as did I and most implementations, but why a cosine quarter-table
> instead of the more common sine? A quick look at the data sheets (and the
> waveforms in the theory-of-op sections) for the two devices suggests they
> are clearly calling out one or the other, but without rationale regarding
> the choice.
>
> .73,
> Brent, KD0GLS, Minneapolis
>
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 21 Jun 2011 19:11:18 +0000
> From: lists at lazygranch.com
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
> Message-ID:
> <948099068-1308683479-cardhu_decombobulator_blackberry.rim.net-1357307805- at b12.c1.bise6.blackberry>
>
> Content-Type: text/plain
>
> The cordic needs to compute both sin and cos. You are right that you just
> need one or the other if you have one DAC.
>
> -----Original Message-----
> From: Chris Albertson <albertson.chris at gmail.com>
> Sender: time-nuts-bounces at febo.com
> Date: Tue, 21 Jun 2011 11:38:30
> To: Discussion of precise time and frequency
> measurement<time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
>
> On Tue, Jun 21, 2011 at 10:44 AM, KD0GLS <kd0gls at mninter.net> wrote:
>
>> Given a complete DDS chip with a single output channel (e.g. AD9834,
>> AD9835), why would one device favor a cosine LUT versus a sine LUT?
>
> Are the LUTs really different? Ages ago when I made something like
> this I used only 90 degrees of the table. That is all you need. The
> other 270 degrees can be made by flipping or inverting. I assume that
> what's stored is neither. It is data that needs to be interpeted
> based on the current quadrant. But the author might choose to call it
> which ever makes the most sense.
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
> _______________________________________________
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> To unsubscribe, go to
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>
> ------------------------------
>
> Message: 3
> Date: Tue, 21 Jun 2011 20:18:19 +0100
> From: Luis Cupido <cupido at mail.ua.pt>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
> Message-ID: <4E00EE7B.4020803 at mail.ua.pt>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hi Brent,
>
> A quarter table cos is exactly the same as a quarter table sin.
> Only backwards, and not telling which quarter it is makes it a
> quarter of either sin or cos. For one single output becomes irrelevant
> as you only need one.
> So I think it is just a matter of taste the name to call it.
>
> Luis Cupido.
> ct1dmk.
>
>
> On 6/21/2011 8:03 PM, KD0GLS wrote:
>>
>>> On Jun 21, 2011, at 13:39, Chris Albertson wrote:
>>>
>>> I used only 90 degrees of the table.
>>>
>>
>>
>> Yes, as did I and most implementations, but why a cosine quarter-table
>> instead of the more common sine? A quick look at the data sheets (and
>> the waveforms in the theory-of-op sections) for the two devices suggests
>> they are clearly calling out one or the other, but without rationale
>> regarding the choice.
>>
>> .73,
>> Brent, KD0GLS, Minneapolis
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Tue, 21 Jun 2011 21:26:01 +0200
> From: Magnus Danielson <magnus at rubidium.dyndns.org>
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
> Message-ID: <4E00F049.6060603 at rubidium.dyndns.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> On 06/21/2011 09:03 PM, KD0GLS wrote:
>>
>>> On Jun 21, 2011, at 13:39, Chris Albertson wrote:
>>>
>>> I used only 90 degrees of the table.
>>>
>>
>>
>> Yes, as did I and most implementations, but why a cosine quarter-table
>> instead of the more common sine? A quick look at the data sheets (and
>> the waveforms in the theory-of-op sections) for the two devices suggests
>> they are clearly calling out one or the other, but without rationale
>> regarding the choice.
>>
>
> By the way, you can save two bits of the LUT table width by only storing
> the difference of the binary phase and the sine. Add the phase
> (90-degree wrapped) to the output of the LUT to get the sine. In effect
> the LUT can be allowed to be shifted two bits down for improved precision.
>
> Cheers,
> Magnus
>
>
>
> ------------------------------
>
> Message: 5
> Date: Tue, 21 Jun 2011 12:31:42 -0700 (PDT)
> From: Robert LaJeunesse <rlajeunesse at sbcglobal.net>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>, kd0gls at mninter.net
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
> Message-ID: <649767.46970.qm at web83008.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Brent,
>
> For the specific case?of generating a?synchronous FSK signal with a fairly
> wide
> shift there may be a reason. Such an application presumes a high enough
> ratio
> between clock and output frequencies such that the DDS accumulator?landing
> adequately near zero is a certainty. If the FSK frequency is changed
> synchronously?- just after?the point of DDS accumulator rollover?- a sine
> LUT
> would potentially show an abrupt?change in dv/dt (slew rate) with the
> frequency
> change. By using a cosine LUT the signal would be at its peak, and dv/dt
> would
> be virtually zero both before and after the frequency change.
>
> Bob LaJeunesse
> Ann Arbor, MI
>
>
>
> ________________________________
> From: KD0GLS <kd0gls at mninter.net>
> To: Time-Nuts <time-nuts at febo.com>
> Sent: Tue, June 21, 2011 1:44:26 PM
> Subject: [time-nuts] DDS - Cosine v. Sine LUT
>
> With all the discussion lately regarding DDS and CORDIC, I'm reminded of a
> question that came up some time ago for which I've never found an answer.?
> Perhaps you enlightened people can enlighten me.
>
> Given a complete DDS chip with a single output channel (e.g. AD9834,
> AD9835),
> why would one device favor a cosine LUT versus a sine LUT?? On the
> surface,
> starting the roller coaster ride at the top of the hill (assuming the
> phase
> accumulator starts from zero) seems odd.
>
> .73,
> Brent, KD0GLS, Minneapolis
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
> ------------------------------
>
> Message: 6
> Date: Tue, 21 Jun 2011 19:39:54 +0000
> From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] Replacing electrolytics - any disadvantages
> of high temp ones?
> Message-ID: <2922.1308685194 at critter.freebsd.dk>
> Content-Type: text/plain; charset=ISO-8859-1
>
> In message <4E008A73.50701 at erols.com>, Chuck Harris writes:
>
>>and yet, I find that some electrolytic
>>capacitors that have been run at lower than normal voltage improve
>>markedly
>>when "reformed" by applying rated voltage through a 10K resistor for a
>>couple of hours.
>
> I noticed in a datasheet at one point, that the capacity only was
> warranted above a certain percentage of rated voltage. No explanation
> was given.
>
> --
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG | TCP/IP since RFC 956
> FreeBSD committer | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by
> incompetence.
>
>
>
> ------------------------------
>
> Message: 7
> Date: Tue, 21 Jun 2011 12:43:59 -0700 (PDT)
> From: Robert LaJeunesse <rlajeunesse at sbcglobal.net>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] Light Squared, etc.
> Message-ID: <191303.45693.qm at web83008.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> Light Squared backing off?
>
> http://spectrum.ieee.org/riskfactor/telecom/wireless/lightsquared-tacks-hard-in-the-face-of-opposition-says-it-has-solutions-to-gps-interference
>
> ------------------------------
>
> Message: 8
> Date: Tue, 21 Jun 2011 15:00:10 -0500
> From: Russell Rezaian <rrezaian at motorola.com>
> To: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] Light Squared, etc.
> Message-ID: <p06240813ca26a6bb0a52@[10.44.7.91]>
> Content-Type: text/plain; charset="us-ascii" ; format="flowed"
>
> There appears to be a lot of news coverage about this.
>
> There was this article in the Register earlier today.
>
> http://www.theregister.co.uk/2011/06/21/lightsquared_gps/
>
> All sorts of interesting information. The suggestion is that
> LiughtSquared will move to a lot of the Inmarsat spectrum, and go
> back to the original lower power levels for the L band spectrum.
>
> Not a huge set of actual technical detail, mostly an overview for
> those who are not radio experts in a more general technology/IT news
> site.
> --
> Russell
>
> At 12:43 PM -0700 2011/06/21, Robert LaJeunesse wrote:
>>Light Squared backing off?
>>
>>http://spectrum.ieee.org/riskfactor/telecom/wireless/lightsquared-tacks-hard-in-the-face-of-opposition-says-it-has-solutions-to-gps-interference
>>_______________________________________________
>>time-nuts mailing list -- time-nuts at febo.com
>>To unsubscribe, go to
>>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>and follow the instructions there.
>
>
>
>
> ------------------------------
>
> Message: 9
> Date: Tue, 21 Jun 2011 15:09:43 -0500 (CDT)
> From: KD0GLS <kd0gls at mninter.net>
> To: Robert LaJeunesse <rlajeunesse at sbcglobal.net>
> Cc: Discussion of precise time and frequency measurement
> <time-nuts at febo.com>
> Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
> Message-ID: <6D262144-D3CD-4D1D-BFF6-09EAC79189D2 at mninter.net>
> Content-Type: text/plain; charset=us-ascii
>
> That's an interesting thought. The diagram of the 9835 (the one labeled
> as having the cosine ROM) also shows some sync logic associated with the
> select lines steering the FSK and PSK registers. If that logic syncs the
> select lines to the phase accumulator rollover, as you said, the slope of
> the signal would be near zero at that point, as opposed to at the
> zero-crossing with a sine-based device. An interesting theory at least.
>
> On Jun 21, 2011, at 14:31, Robert LaJeunesse wrote:
>
>> Brent,
>>
>> For the specific case of generating a synchronous FSK signal with a
>> fairly wide shift there may be a reason. Such an application presumes a
>> high enough ratio between clock and output frequencies such that the DDS
>> accumulator landing adequately near zero is a certainty. If the FSK
>> frequency is changed synchronously - just after the point of DDS
>> accumulator rollover - a sine LUT would potentially show an abrupt change
>> in dv/dt (slew rate) with the frequency change. By using a cosine LUT the
>> signal would be at its peak, and dv/dt would be virtually zero both
>> before and after the frequency change.
>>
>> Bob LaJeunesse
>> Ann Arbor, MI
>>
>> From: KD0GLS <kd0gls at mninter.net>
>> To: Time-Nuts <time-nuts at febo.com>
>> Sent: Tue, June 21, 2011 1:44:26 PM
>> Subject: [time-nuts] DDS - Cosine v. Sine LUT
>>
>> With all the discussion lately regarding DDS and CORDIC, I'm reminded of
>> a question that came up some time ago for which I've never found an
>> answer. Perhaps you enlightened people can enlighten me.
>>
>> Given a complete DDS chip with a single output channel (e.g. AD9834,
>> AD9835), why would one device favor a cosine LUT versus a sine LUT? On
>> the surface, starting the roller coaster ride at the top of the hill
>> (assuming the phase accumulator starts from zero) seems odd.
>>
>> .73,
>> Brent, KD0GLS, Minneapolis
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> .73,
> Brent, KD0GLS, Minneapolis
>
>
>
> ------------------------------
>
> _______________________________________________
> time-nuts mailing list
> time-nuts at febo.com
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>
> End of time-nuts Digest, Vol 83, Issue 72
> *****************************************
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