Inside my remote-sensor thermometer

Mar 22, 2007 4 Replies
A

I have got a thermometer with a remore temperature sensor that sends radio signals to update the base unit's display. The base unit also has its own temperature sensor to let it display the indoors temperature as well as the sensor's temperature.



The sender unit's antenna is a coil of wire which is about 1/4-inch diameter and a couple of inches long. See these pics:


2_sender_B
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3_sender_(underside)
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The base unit's antenna is just a short length of wire. See these pics:


4_thermo_(extra_panel)
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5_thermo_A (circuit only)
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TWO QUESTIONS: What is the best orientation for each of these units so their antennas are postioned optimally? For simplicity I am assuming no obstructions.


TWO MORE QUESTIONS: which component in the sender is the temperature sensor? The sender's case seems sealed with no air vent! Similarly, which component in the base unit is the sensor for the indoors temperature? You can see the air vents in the base unit in picture #4 but which component seen in close-up in #5 is the temp sensor?
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B

With the one I have (similar thing) it doesn't really matter, the coil would suggest circular polarity

I believe it's the round metal? component on the underside

Again a guess at the white rectangular thinhie stood away form the board by the ribbon cable.

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G

Run that past me again?

A helical antenna has circular polarisation? I don't mean a helical directional antenna for UHF, that one in the picture is just a helically loaded antenna like you would get on a handheld radio so its either going to be horizontal or vertical.

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A

I am the OP and I must say that I guess Brian's reply is accurate in that it doesn't matter on which part one stands with respect to the

360 degrees of the curved part of the coil.

But even with your extra info about being similar to a handheld device, I am still too much of a radio noobie to understand properly! Sorry

I don't know if the ERP is at its max along the coil's axis or at right angles to it. If it is maximal on-axis then is there anything in radio theory which says one end of the coil's axis (eg. the free end) in my device is better than the opposite end (ie. the attached end)?

And don't forget my other queries about the base unit's reception! See above.

Alex

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