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'[EE:] 2km UHF transponder ideas'
2004\01\10@175245 by Rob Stockley

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I'm building a unit that needs to head away from its point of origin
until it gets to a preset distance. At the moment the distance calc is
based on time elapsed. This doesn't work very well because speed varies.

I like the idea of building a UHF transponder/beacon set. The unit sends
a unique pulse train then listens for a reply. The beacon receives and
decodes the pulse train, waits a preset time, then replys. The unit
receives the reply and calculates distance from the signal's time of
flight. Jittering the PRF and range gating would improve signal to
noise.

Max distance is around 1500m so a 2km range would be desireable. I'd
like transmit status information in the pulse. Basically what I'm after
is a low power UHF (~400MHz) version of the air traffic secondary
surveilance radar.

Trouble is I don't know where to start :(

I'm comfortable making my own PCBs and programming PICs but don't know
much at all about RF circuits. Would someone care to point me to a good
starting point? A website or a readily available book would be nice. A
similar project I could examine would be even nicer :)

TIA
Rob

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2004\01\10@182049 by Hopkins

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Check out
http://www.telelink.com.au/
http://www.radiomodules.net/

As advertised on the back page of Silicon Chip Magazine.

We use selcom radio's at work - will need to find the address - Christchurch
I think.

ps I see u are in NZ

*************************************************

Roy Hopkins

.....rdhopkinsKILLspamspam@spam@ihug.co.nz

*************************************************
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2004\01\10@185505 by Rob Stockley

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On Mon, 2004-01-12 at 01:18, Hopkins wrote:
> Check out
> http://www.telelink.com.au/
> http://www.radiomodules.net/
>
> As advertised on the back page of Silicon Chip Magazine.
>
> We use selcom radio's at work - will need to find the address - Christchurch
> I think.
>
> ps I see u are in NZ

The second link times out. The first link has some real possibilities
although I imagine they are on the pricey side. I'll have to wait for
their reply.

I was actually more interested in learning about RF circuits and
building my own. I have some old "Electronics Notebooks" by Colin
Mitchell which have a bit about RF circuits, however, they are all based
on tank circuits and I want more stability than that.

Still if the Telelink modules are cheap enough I might not bother
building.

Rob

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2004\01\10@185713 by John J. McDonough

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You may want to check with the New Zeland equivalent of the FCC.  Here in
the U.S., unlicensed 435 MHz operation is limited to very low power and very
small antennas.  Under those conditions, 2 km may be unrealistic.  Since all
nations coordinate their spectrum use, it is very likely that NZ rules are
similar.

72/73 de WB8RCR    http://www.qsl.net/wb8rcr
didileydadidah     QRP-L #1446 Code Warriors #35

----- Original Message -----
From: "Rob Stockley"
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Saturday, January 10, 2004 5:52 PM
Subject: [EE:] 2km UHF transponder ideas

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2004\01\10@190332 by Josh Koffman

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I don't know that much about making your own RF stuff. If you have the
budget, I'd suggest using premade modules, unless you have a particular
need for space or tight integration. In either case, a good book might
be the ARRL handbook. I believe their website is http://www.arrl.org.
It's a pretty good reference on many things RF.

Hope that helps.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

Rob Stockley wrote:
> Trouble is I don't know where to start :(
>
> I'm comfortable making my own PCBs and programming PICs but don't know
> much at all about RF circuits. Would someone care to point me to a good
> starting point? A website or a readily available book would be nice. A
> similar project I could examine would be even nicer :)

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2004\01\10@190749 by John J. McDonough

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----- Original Message -----
From: "Rob Stockley"

> I was actually more interested in learning about RF circuits and
> building my own. I have some old "Electronics Notebooks" by Colin
> Mitchell which have a bit about RF circuits, however, they are all based
> on tank circuits and I want more stability than that.

70 cm stuff isn't easy to build, but it's not impossible, either.  This is a
popular amateur radio band, so you can find a lot of construction
information looking at amateur publications.  There are plenty of DDS parts
capable of generating stable 435 MHz and many include fsk capability on
chip.  Amplifier parts are quite widely available, as well as mixers.  The
challenge is that capacitances and inductances at this frequency are quite
small, so construction techniques are a bigger deal than the actual
circuits.

72/73 de WB8RCR    http://www.qsl.net/wb8rcr
didileydadidah     QRP-L #1446 Code Warriors #35

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2004\01\10@195639 by Rob Stockley

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On Sun, 2004-01-11 at 12:56, John J. McDonough wrote:
> You may want to check with the New Zeland equivalent of the FCC.  Here in
> the U.S., unlicensed 435 MHz operation is limited to very low power and very
> small antennas.  Under those conditions, 2 km may be unrealistic.  Since all
> nations coordinate their spectrum use, it is very likely that NZ rules are
> similar.

Excellent advice. In NZ the information is available from
http://www.med.govt.nz/rsm/.

The amateur window at just over 400MHz is small. There are others at
approx (read from chart) 30MHz, 51-54MHz and 144-148MHz. From comments
and web reading so far it seems UHF may not be a beginner's best option.
I'm still searching for the national regs on tx power, antenna length
and sideband attenuation.

Thanks for the steer on the ARRL. I remembered I have a copy (1997)
tucked away and have just laid my hand back on it.

Since the unit will always be heading away from the base the antennae
could be highly directional perhaps mitigating the range vs power issue.
I'll look into special function ic's once I am more familiar with the RF
concepts.

Rob

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2004\01\10@210901 by Roy J. Gromlich

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The simple answer - unless you are very experienced in analog RF design -
is BUY IT.  It is one thing to build a small short-range
transmitter-receiver
for experimental  work around your lab, but the approval process you
would need to go through to be able to SELL the product would be
prohibitive in the extreme. With spectrum space as scarce as it is these
days the international governing bodies are very strict about what is
allowed to  broadcast.  There are a few blocks in the microwave area
which can be used by individuals (garage door/car door openers and
the like) but even they must be type approved by the FCC.  Anything
which could work over a 2 km range would use more than the allowed
output power and or have a very state-of-the-art receiver.

Roy J. Gromlich (once WA2CMB, and an analog circuit designer)

{Original Message removed}

2004\01\10@211109 by Dave Tweed

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Rob Stockley <spamBeGonerobstockleyspamBeGonespamMOWGLI.NET.NZ> wrote:
> I like the idea of building a UHF transponder/beacon set. The unit sends
> a unique pulse train then listens for a reply. The beacon receives and
> decodes the pulse train, waits a preset time, then replys. The unit
> receives the reply and calculates distance from the signal's time of
> flight. Jittering the PRF and range gating would improve signal to
> noise.

You've just described DME (distance-measuring equipment) as used on
aircraft almost exactly. See
  http://www.acay.com.au/~willt/yssy/enthus/whatis/vordme.html

You might be able to pick up some used equipment and modify its frequencies
and power levels to suit your project.

To address a point that another responder brought up, there are ways to
achieve high precision in time while still using narrowband signals.
For example, look up "chirp radar" on Google.

-- Dave Tweed

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2004\01\11@045045 by Robert Rolf

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And a $80 GPS puck giving meter position accuracy is too expensive for him??

What is your time worth? Do you have the deep pockets needed to pay for
certification of your system since it is unlikely they would work
out to 2km in any license free band/power? FRS radios are probably close, but
they are not licensed for use with any antenna other than
the one they come with. But you are not prevented from strapping one to
a tower to increase it's range. Some even have subaudible tones to open
the squelch, and which might be usable for phase measurement to get distance
if hacked up to a high, inaudible frequency (as suggested in an earlier post).

See also 'radio altimeter' for ranging methods using frequency chirps.

There are also a couple of patents on using existing radio stations
to navigate by looking at multiple carrier phase relationships, and
comparing them to a 'reference' station log (which you would send
to your rover).

Do let us know what you finally work out.

Robert

Dave Tweed wrote:
{Quote hidden}

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2004\01\11@122246 by Hopkins

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Where can you get this GPS puck - web address?
*************************************************

Roy Hopkins

EraseMErdhopkinsspamihug.co.nz

*************************************************

> And a $80 GPS puck giving meter position accuracy is too expensive for
him??
>



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2004\01\11@124815 by Hopkins

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Another thought is passive such as a gyro system or electronic compass
http://www.robot-electronics.com/

Are you using a model plane?

Do you want to know its distance from you or are is the model? trying to do
it's own calculation internally?

*************************************************

Roy Hopkins

RemoveMErdhopkinsspam_OUTspamKILLspamihug.co.nz

*************************************************

> > And a $80 GPS puck giving meter position accuracy is too expensive for



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2004\01\11@130031 by Hopkins

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Yet another thought - how are you controlling this object?

If you have a radio control system why can't you send data over the same
link i.e. when the model senses there are no radio control commands been
sent to it's receiver it can send data back to you - PWM etc.

*************************************************

Roy Hopkins

EraseMErdhopkinsspamspamspamBeGoneihug.co.nz

*************************************************



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2004\01\11@132802 by Rob Stockley

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On Sun, 2004-01-11 at 22:49, Robert Rolf wrote:
> And a $80 GPS puck giving meter position accuracy is too expensive for him??
>

No this is not too expensive. Where would I find one? What are they like
to integrate? The vehicle is autonomous so this would be a great
solution.
Rob

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2004\01\11@135917 by Paul Tustin

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www.globalsat.com.tw/web/A3-1.php?serial=41

-----Original Message-----
From: pic microcontroller discussion list
[spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU]On Behalf Of Rob Stockley
Sent: 11 January 2004 18:28
To: KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU
Subject: Re: [EE:] 2km UHF transponder ideas
Importance: High


On Sun, 2004-01-11 at 22:49, Robert Rolf wrote:
> And a $80 GPS puck giving meter position accuracy is too expensive for
him??
>

No this is not too expensive. Where would I find one? What are they like
to integrate? The vehicle is autonomous so this would be a great
solution.
Rob

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2004\01\11@154624 by p.cousens

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Bear in mind you will also need the radio link between the unit to the
base
Which depending on terrain may be a lot harder than you think

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[spamBeGonePICLISTspamKILLspamMITVMA.MIT.EDU] On Behalf Of Paul Tustin
Sent: 11 January 2004 18:48
To: .....PICLISTspam_OUTspamMITVMA.MIT.EDU
Subject: Re: [EE:] 2km UHF transponder ideas


http://www.globalsat.com.tw/web/A3-1.php?serial=41

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2004\01\11@171435 by Russell McMahon

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> > And a $80 GPS puck giving meter position accuracy is too expensive ?

> No this is not too expensive. Where would I find one? What are they like
> to integrate? The vehicle is autonomous so this would be a great
> solution.

What is being referred to is the use of ANY GPS receiver to give you
positional accuracy of from 1m to 10m without reference to the base station.
(They access the GPS satellite constellation instead).
GPS receivers are available in NZ form eg DSE from about $NZ300 up BUT
almost any GPS module or receiver with an output would do. Many receivers
have a 4800 baud serial output which is very easily read by a
microcontroller to determine (amongst other things) speed, position in 3
dimensions and time of day.

If you want to use a UHF link - you can buy a pair of UHF transceivers from
eg DSE for about $NZ120. These will probably achieve a range of 2 to 3 km if
placed on a pole with a clear line of sight. Range is much less if hand held
and with obstructed sight lines. NZ max allowed power output is
substantially greater than that allowed in some other countries.



       RM

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2004\01\12@114434 by Mike DeMetz

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www.codereward.org/

> Where can you get this GPS puck - web address?
> *************************************************
>
> Roy Hopkins
>
> .....rdhopkinsspamRemoveMEihug.co.nz
>
> *************************************************

Mike DeMetz
N9GEZ
RemoveMEn9gezspamspamBeGoneqsl.net

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2004\01\12@115300 by Amaury Jacquot

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Mike DeMetz wrote:
> http://www.codereward.org/
>
>
>>Where can you get this GPS puck - web address?
>>*************************************************
>>
>>Roy Hopkins
>>
>>spamBeGonerdhopkins@spam@spamspam_OUTihug.co.nz
>>
>>*************************************************
>
>
> Mike DeMetz
> N9GEZ
> TakeThisOuTn9gezspamspamqsl.net

Thanks mike, I was also looking for something like this :D

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