Thanks for the email, I'm not too bothered about the PIC/uProcessor side
of things, I know I can keep track of the pulse fairly easily, and with in
the power requirements. The aerial information is very handy though. The
main issue is how to ensure that all the radio's have the same latency
recieving the pulse through the circuitry, to ensure they are all in sync.

We've come across these
http://www.rfm.com/products/data/tr1100.pdf
they look pretty good, and the price isn't too bad either, does anyone
know what sort of range can be expected from them?

Mat

>> a minimum period of a year. Physical battery size is not
>> crucial but small is better :)
>
> A nW part (eg 12F675) with the 32kHz module running will
> consume around 20uA at 3.6V, => a lithium with more than
> 20x10-6 * 24 * 365 = 175200uAh capacity will last a year,
> excluding power needed for the receiver
>
>> Does anyone have any other suggestions how to achieve the
>> required synchronisation
>
> So, you keep the PIC running at 32kHz, which will be the
> rough time-base, with an instruction cycle time of 30.5-ish
> microseconds. Less than the accuracy you require from the
> synch clock pulse. At the required time, which you can now
> measure fairly accurately due to the crystal, turn the receiver
> on long enough to pick up a pulse
>
>> can anyone suggest any suitable radio IC's/circuits which
>> could be used as I am stuggling to find anything useful via
>> google (must be using the wrong keywords)
>
> I'm quite happy with the Keymark Rx-Tx pair, as mentioned
> in the recent thread [EE] Aerial for data link
>
> Transmitter, 212kB (NB, they say 3V supply but actually 2-5V)
>
> http://www.jaycar.co.nz/products_uploaded/ZW3100(mod).pdf
>
> Receiver, 779kB
>
> http://www.jaycar.co.nz/products_uploaded/ZW3102(mod).pdf
>
> At present it's what the datasheet suggests. I have a 173mm length
> of 22B&S (0.63mm) enamelled wire as a 1/4 wave at both ends.
> This works fine up to at least 100m line-of-sight
>
> Richard Prosser has made suggestions re aerials
>
> Wire Diameter:
> Will effect the Q of the antenna an also slightly effect the resonant
> length. As long as you are reasonably close to the datasheet, small
> changes in diameter won't really have a big effect. However, note that
> the rf energy is concentrated near to the surface of the antenna so if
> the diameter gets too small, the volume of conductor carrying the RF
> current will decrease and the losses will increase.
>
> Material
> You want it conductive. Copper is good - but heavy. Al is slightly
> less good but much lighter and may be easier to support. Magentic
> materials should be avoided in general. Watch out for corrosive
> problems if it is outdorrs - esp if exposed to salt spay etc.
>
> Configuration
> Basically the larger the antenna the bigger the gain possible. But
> dimensions and matching become more critical, and you experiance the
> law of decreasing returns. A 1/4 wave antenna on a ground plane
> radiates in all directions (horizontally) but fires a fair amount of
> energy up into the air. The radiation angle can be reduced by
> increasing the size of the driven element (e.g a 5/8) or matching into
> a 1/2 wave section etc. If you only want to send to/receive from one
> direction a reflector type will work well. Yagis can give very useful
> gain but may need a bit more care in setting up. There are a number of
> good designs available on the internet though. For single frequency
> operation you can get quite high gain if you are able to play around
> with the right equipment. Don't forget that gain antennas will assist
> both the transmitter and receiver - as opposed to increasing the
> output power which is a transmit only option.
>
> One type that may be worh looking at in the longer term is the
> J-pole.  Omnidirectional but has useful gain over a 1/4 wave, doesn't
> require a ground plane and has a reasonably low radiation angle. Can
> be made using old-style TV ribbon & placed inside PVC pipe for
> external protection if required (although the lengths need to modified
> slightly).
>
> http://en.wikipedia.org/wiki/J-pole
>
> http://www.hamuniverse.com/slimjim.html
>
> Dennis Crawley made these suggestions
>
> For directivity, use a yagui, with a parabolic plane as reflector,
> builded with 1,5mm bronze wire,(separation of elements < 1/16
> lamda),... mount the receptor near the antenna.
>
> For a omnidirectional:
> Choose rigid wire or little coper tube (1/4 lamda < 17cm).
> Mount the receiver in a sealed metal box and use a BNC to
> connect the anntena for the experiment.
>
> Then build a pi tank.
> Make the transmitter send a continous 0xAA at the desierd
> baudrate. Try to See the 0xAA with a scope on the RSSI pin,...
> or linear pin. Adjust the pi tank until the pulses have a good
> shape. Vary the cap values
> --
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> http://mailman.mit.edu/mailman/listinfo/piclist
>

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