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Today's Topics:
1. Re: DDS - Cosine v. Sine LUT (KD0GLS)
2. Re: DDS - Cosine v. Sine LUT ([email protected])
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 <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
Message-ID: <[email protected]>
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: [email protected]
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
Message-ID:
<948099068-1308683479-cardhu_decombobulator_blackberry.rim.net-1357307805-@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 <[email protected]>
Sender: [email protected]
Date: Tue, 21 Jun 2011 11:38:30
To: Discussion of precise time and frequency
measurement<[email protected]>
Reply-To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
On Tue, Jun 21, 2011 at 10:44 AM, KD0GLS <[email protected]> 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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------------------------------
Message: 3
Date: Tue, 21 Jun 2011 20:18:19 +0100
From: Luis Cupido <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
Message-ID: <[email protected]>
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
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To unsubscribe, go to
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and follow the instructions there.
------------------------------
Message: 4
Date: Tue, 21 Jun 2011 21:26:01 +0200
From: Magnus Danielson <[email protected]>
To: [email protected]
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
Message-ID: <[email protected]>
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 <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>, [email protected]
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
Message-ID: <[email protected]>
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 <[email protected]>
To: Time-Nuts <[email protected]>
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
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------------------------------
Message: 6
Date: Tue, 21 Jun 2011 19:39:54 +0000
From: "Poul-Henning Kamp" <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] Replacing electrolytics - any disadvantages
of high temp ones?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
In message <[email protected]>, 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
[email protected] | 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 <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] Light Squared, etc.
Message-ID: <[email protected]>
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 <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
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
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------------------------------
Message: 9
Date: Tue, 21 Jun 2011 15:09:43 -0500 (CDT)
From: KD0GLS <[email protected]>
To: Robert LaJeunesse <[email protected]>
Cc: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] DDS - Cosine v. Sine LUT
Message-ID: <[email protected]>
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 <[email protected]>
To: Time-Nuts <[email protected]>
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 -- [email protected]
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
.73,
Brent, KD0GLS, Minneapolis
------------------------------
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End of time-nuts Digest, Vol 83, Issue 72
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