[time-nuts] question for expert time guys (Hal Murray)
johncroos at aol.com
johncroos at aol.com
Fri Feb 1 12:16:27 EST 2013
Hello Hal -
I spent a lot of my RF engineering career in related areas, including radar, EW, and spread spectrum timing
systems. Since the distance is short and the cost is an issue you may wish to consider an analog
system solution.
Specifically your master station transmits a RF signal that is FM modulated with a high frequency tone.
The remote unit is a transponder. It receives the tone and re-transmits back on another frequency. Almost no parts required.
At the master station the phases of the outgoing and returning tones are compared. The distance is directly
proportional to the phase shift between the outgoing and incoming tones. For instance if the tone is 10 MHz
the 360 degrees of phase is 100 nS which is about 100 ft round trip.
The phase may be measured either analog and A/D converted or digitally and in either case is then easily converted to range by your processor.
By adjusting the tone frequency you can set the full scale range. To increase resolution higher frequency tones may be used. To overcome ambiguity when the range goes beyond 360 degrees of phase, add a lower frequency tone to resolve the ambiguity.
This scheme has been used in surveying instruments (the Teleurometer) and even an ill fated German bombing system in WWI. The latter proved delightfully easy to jam since the Brits had a spare TV
transmitter in the correct band.
Look up something like "tone ranging".
-john c roos k6iql
-----Original Message-----
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To: time-nuts <time-nuts at febo.com>
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Subject: time-nuts Digest, Vol 103, Issue 2
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Today's Topics:
1. Re: Loran again (Stan, W1LE)
2. question for expert time guys (Rick Harold)
3. Re: Low noise power supplies? (gary)
4. Re: Low noise power supplies? (John Miles)
5. Re: question for expert time guys (Hal Murray)
6. Re: question for expert time guys (Azelio Boriani)
----------------------------------------------------------------------
Message: 1
Date: Fri, 01 Feb 2013 00:30:40 -0500
From: "Stan, W1LE" <stanw1le at verizon.net>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Loran again
Message-ID: <510B5300.8000407 at verizon.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Fired up the SRS FS700 and auto found the GRI 89700 microsecond stations
in Dana Il (master)
and Seneca NY, (slave) both with equal signal strength of 63 db. Other
slaves were not to be found.
Noise margin of 32 dB and Rx gain of 72dB. So the Rx is all locked up.
Tomorrow I will have more data comparing the 10 MHz from the T'Bolt.
Right now they are comparing to within 10EE10.
Stan, W1LE Cape Cod
On 1/31/2013 10:44 PM, Stan, W1LE wrote:
> What GRI should we be listening for ?
>
> Stan, W1LE Cape Cod FN41sr
>
>
>
> On 1/31/2013 9:56 PM, paul swed wrote:
>> Rich indeed its on the air. Warming up the FS700 to see if it will lock.
>> Have a pattern ram thats getting flakey and takes about 30 minutes to
>> warm
>> up along with the oven.
>>
>>
>
> _______________________________________________
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Message: 2
Date: Thu, 31 Jan 2013 22:37:00 -0600
From: Rick Harold <rickharold at gmail.com>
To: time-nuts at febo.com
Subject: [time-nuts] question for expert time guys
Message-ID:
<CAODR2TDuMSpOr8JYvjMm-QRnRhM8sxYGkY=VrN6YttK5T3t2FA at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
To time experts/EE's.
I would like to triangulate a position of a device which moves using 3
fixed positions devices of known location.
The idea is to have these operate on 915mhz or 434mhz or 2.4ghz or
appropriate frequency.
These two type of devices (fixed and mobile) are all under my control and
thus customized as needed.
The mobile device (not a phone, custom device) would be the least expensive
item. I'd like a range of 150 feet or better and accuracy of 3 feet or
better.
When manufactured these items they can be calibrated in order to adjust for
any variation in IC's, discrete components etc...
We can assume for now the temperature is constant 70 degree temperature.
Cost is the key design factor.
The general flow is:
1. base station 1 indicates we are determining position of device A.
2. Each base station 1, 2, 3 take turns pinging the device to determine
distance.
3. A ping consists of (something like, e.g. frequencies as examples)
-send 915mhz signal from base station to device
-device response ASAP on different frequency
-station waits and counts 'time' for return
-this is repeated N? times to get best avg/accuracy.
-The mobile device does not move very fast
4. Since delays of the process on each unit is calibrated the device and
base station would subtrack that time out from the results.
5. obviously with 3 distances we can determine the 2D position of the
mobile device
I know the time accuracy is the key to count time = feet, 1ns. This
overall project is not new concept. How to make it "inexpensive" is key.
how inexpensive, very ;-) no OCXO or expensive components like that.
That's my goal, and I'm looking for help on the design/thought process of
getting there.
I am open to a consulting arrangement for a fee, please email if you like.
I've worked with 'regular' EE's (I'm a software guy) but this time
accuracy is too much for them.
Esp. finding a way to do it inexpensively.
Thanks for any thoughts.
------------------------------
Message: 3
Date: Thu, 31 Jan 2013 23:03:14 -0800
From: gary <lists at lazygranch.com>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] Low noise power supplies?
Message-ID: <510B68B2.40703 at lazygranch.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Are 4 and 5 regulated? Or is the zener picked to compensate for the VBE
drops?
Any of these circuits where the output transistor is in an emitter
follower configuration will have its noise effected by the load current,
since that current directly effects the output transistor transconductance.
On 1/31/2013 10:03 PM, John Miles wrote:
> Awhile back I ran some baseband plots of various supplies with an HP 3048A
> (image attached). In my experience measuring actual OCXOs, an LM317T or
> LM338K is quiet enough to avoid influencing oscillator PN. With these
> variable-voltage parts, you can bypass the reference pin for some additional
> improvement, but I don't believe I did that for these plots.
>
> It's easy to spot the difference between a 7812/7815 and an LM317T (see red
> versus green/white traces). As a lazy approach, try measuring the
> oscillator with both a 78XX and an LM317T. Because the 78XX is about 10 dB
> noisier across most of the spectrum, If you don't see a difference, you can
> assume that further optimization is pointless. Near 1 Hz this call may be
> questionable.
>
> If you don't need an LDO, don't use one. If you do, use the quietest part
> you can find. The best LDOs seem to be about as quiet as an ordinary
> LM317T.
>
> I've mentioned before that you need to be careful with large LC filters
> downstream of the regulator. A good power source will exhibit a low
> impedance at ALL offsets of interest.
>
> You sometimes see NIST circuits where the power is conditioned by a
> Darlington emitter follower whose base is fed with an RC-filtered Zener
> diode. The purple and orange traces are pretty informative with regard to
> that approach. On the orange trace, where the only filtering is the RC
> network between the Zener and the base, notice how the noise becomes worse
> than all of the other sources below 10 Hz. Here, the RC filter on the Zener
> becomes less effective and the Darlington pair obligingly amplifies the
> diode noise.
>
> An additional LC filter after the regulator may have the effect of herding
> the entire noise spectrum into a high-Q peak, even though the LC corner
> frequency is much higher than the RC filter in the base circuit (violet
> trace). Depending on your OCXO's supply rejection characteristics this
> could be a good thing or a bad thing.
>
> Finally, make sure the OCXO has good RF bypassing where its power supply pin
> enters the case. If in doubt, solder a 0.1 uF ceramic right at the point of
> entry. I've seen $2000 Wenzels that didn't bother doing this. I'm sure
> they looked good in a screen room.
>
> -- john
> Miles Design LLC
>
>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-
>> bounces at febo.com] On Behalf Of Richard (Rick) Karlquist
>> Sent: Wednesday, January 30, 2013 6:17 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] Low noise power supplies?
>>
>>
>> I know this topic has been discussed in the past on the list, but
>> a colleague is asking if there are any off the shelf low
>> noise power supplies for testing oscillators. Something
>> a cut above an HP "brick" lab power supply etc. They are hoping
>> to avoid having to homebrew a power conditioning circuit.
>> Did we ever arrive at a concensus as to the state of the art
>> in homebrew power conditioning circuits?
>>
>> Any help would be appreciated.
>>
>> Rick Karlquist N6RK
>> _______________________________________________
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------------------------------
Message: 4
Date: Fri, 1 Feb 2013 01:30:24 -0800
From: "John Miles" <jmiles at pop.net>
To: "'Discussion of precise time and frequency measurement'"
<time-nuts at febo.com>
Subject: Re: [time-nuts] Low noise power supplies?
Message-ID: <0e9101ce005e$c3d2eff0$4b78cfd0$@pop.net>
Content-Type: text/plain; charset="us-ascii"
> Are 4 and 5 regulated? Or is the zener picked to compensate for the VBE
> drops?
>
> Any of these circuits where the output transistor is in an emitter
> follower configuration will have its noise effected by the load current,
> since that current directly effects the output transistor
transconductance.
The load in all cases was a couple hundred mA worth of resistance at the
voltage in question, as I recall. It's been a few years since I captured
these plots.
The Zeners were just whatever parts came to hand, 1N474x parts basically. I
didn't care about the 1.4V drop across the Darlington, just the resulting
noise.
-- john
Miles Design LLC
------------------------------
Message: 5
Date: Fri, 01 Feb 2013 01:45:37 -0800
From: Hal Murray <hmurray at megapathdsl.net>
To: Rick Harold <rickharold at gmail.com>
Cc: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] question for expert time guys
Message-ID:
<20130201094537.35813800037 at ip-64-139-1-69.sjc.megapath.net>
Content-Type: text/plain; charset=us-ascii
rickharold at gmail.com said:
> I would like to triangulate a position of a device which moves using 3 fixed
> positions devices of known location. The idea is to have these operate on
> 915mhz or 434mhz or 2.4ghz or appropriate frequency.
> I'd like a range of 150 feet or better and accuracy of 3 feet or better.
> I know the time accuracy is the key to count time = feet, 1ns.
> How to make it "inexpensive" is key. how inexpensive, very ;-)
I think it's going to be tough to do it at low cost.
The low cost transmit/receive chip sets you can get for 915 MHz are low
bandwidth. That will turn into noise on the on/off transition that you need
for timing.
I'd suggest getting a pair of demo boards and running some experiments.
The first simple sanity check would be to wire them up to a couple of uProcs
and send messages and see if they work at your required range. Play around
to learn the error rate vs baud rate.
> -device response ASAP on different frequency
Not with low cost. But you don't need to use a second frequency.
My straw man would be something like this:
Only one station transmits at a time.
Wire up the transmit and receive lines to counter/timers.
On both the transmit and recv side, grab the time on each data-level change
and average them to figure out when the packet started.
Look at the NTP protocol. It collects 4 time stamps. From that, you can
compute the time of flight. The time at the remote server drops out.
The sequence would be something like this:
fixed->remote: long timing packet.
(with lots of 1/0 transitions to feed data to the timer hardware)
remote->fixed: long timing packet.
remote-> fixed: packet with 2 time stamps
first from the receive side, second from the transmit side
I'd put a CRC on the packets as a sanity check.
Handwave time:
Assume the counter/timers run at 100 MHz. That's 10 ns.
So you'll have to do lots of averaging to get below 3 ns.
But that's assuming the RF units work well and that the averaging works.
You could build a (much) faster counter/timer in a FPGA.
I'm not sure that will help.
Get a pair (or 2 pairs) of units and see how well they work.
I'd expect FSK to work slightly better than ASK (on/off), but
I'm not enough of an RF geek to turn than into numbers.
I'll say more if that will help. We should probably take it off list.
------------
One probably crazy idea...
Setup a directional antenna with a motor to aim it. Scan for the best signal.
--
These are my opinions. I hate spam.
------------------------------
Message: 6
Date: Fri, 1 Feb 2013 10:59:35 +0100
From: Azelio Boriani <azelio.boriani at screen.it>
To: Discussion of precise time and frequency measurement
<time-nuts at febo.com>
Subject: Re: [time-nuts] question for expert time guys
Message-ID:
<CAL8XPmMYuzsyNZ7_MCjTVfARP+ees7CPU=oFHxpN4N4DZjcC7Q at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
and even a more crazy idea: use a phasing array for the directional antenna.
On Fri, Feb 1, 2013 at 10:45 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
> rickharold at gmail.com said:
> > I would like to triangulate a position of a device which moves using 3
> fixed
> > positions devices of known location. The idea is to have these operate on
> > 915mhz or 434mhz or 2.4ghz or appropriate frequency.
>
> > I'd like a range of 150 feet or better and accuracy of 3 feet or better.
>
> > I know the time accuracy is the key to count time = feet, 1ns.
>
> > How to make it "inexpensive" is key. how inexpensive, very ;-)
>
> I think it's going to be tough to do it at low cost.
>
> The low cost transmit/receive chip sets you can get for 915 MHz are low
> bandwidth. That will turn into noise on the on/off transition that you
> need
> for timing.
>
> I'd suggest getting a pair of demo boards and running some experiments.
>
> The first simple sanity check would be to wire them up to a couple of
> uProcs
> and send messages and see if they work at your required range. Play around
> to learn the error rate vs baud rate.
>
>
> > -device response ASAP on different frequency
>
> Not with low cost. But you don't need to use a second frequency.
>
> My straw man would be something like this:
>
> Only one station transmits at a time.
> Wire up the transmit and receive lines to counter/timers.
> On both the transmit and recv side, grab the time on each data-level change
> and average them to figure out when the packet started.
>
> Look at the NTP protocol. It collects 4 time stamps. From that, you can
> compute the time of flight. The time at the remote server drops out.
>
> The sequence would be something like this:
>
> fixed->remote: long timing packet.
> (with lots of 1/0 transitions to feed data to the timer hardware)
> remote->fixed: long timing packet.
> remote-> fixed: packet with 2 time stamps
> first from the receive side, second from the transmit side
>
> I'd put a CRC on the packets as a sanity check.
>
> Handwave time:
> Assume the counter/timers run at 100 MHz. That's 10 ns.
> So you'll have to do lots of averaging to get below 3 ns.
> But that's assuming the RF units work well and that the averaging works.
> You could build a (much) faster counter/timer in a FPGA.
> I'm not sure that will help.
>
> Get a pair (or 2 pairs) of units and see how well they work.
>
> I'd expect FSK to work slightly better than ASK (on/off), but
> I'm not enough of an RF geek to turn than into numbers.
>
> I'll say more if that will help. We should probably take it off list.
>
> ------------
>
> One probably crazy idea...
>
> Setup a directional antenna with a motor to aim it. Scan for the best
> signal.
>
>
> --
> These are my opinions. I hate spam.
>
>
>
> _______________________________________________
> 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.
>
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