November 6, 2014 at 12:26Extend the range of Oregon Scientific weather station sensors
Some time ago, I finally unified weather stations in my apartment - I installed Oregon Scientific BAR800 and BAR801 in all the right places, which I dearly love not only for the design that allows them to be hung on the wall, but also for an external sensor that receives accurate time signals. The trick is that I basically catch the signals (DCF-77 from Frankfurt) at home, but only at the window or outside the window - that's why ordinary weather stations, in which the antenna is built into the station itself, standing in the back of the apartment, there's really nothing about time don't know. Of course, the use of the same type of stations means that you can get by with one sensor for everyone, rather than hanging the zoo through the windows.
Further, however, a problem was discovered, also related to the depth of the apartment - the station farthest from the external weather sensor regularly lost it, although it would seem that there was only a couple of walls between them. Especially this problem got out at subzero temperatures, despite the lithium battery standing in the sensor.
Choosing the right window for hanging a sensor or installing a second sensor is not our option, for a person must command the equipment, and not vice versa. Our option is to change the antenna in the sensor to increase its range.
Of course, the technique is suitable for any weather sensors, since the design of them all is about the same.
Unscrew:
There are already three antennas in this sensor (usually you will find one, maximum two). The ferrite core, however, does not interest us - it is a receiver of accurate time signals at 77 kHz, but two wire spirals are what we need.
They form the so-called half-wave dipole - an antenna consisting of two symmetrical parts with a total length of 1/2 wavelength. Dipoles are used when the antenna does not have a normal “ground” - one of the halves of the dipole actually plays the role of this “ground”, let me forgive the radio engineers for a somewhat simplified description. Each half has, accordingly, a length of 1/4 wave.
The sensor operates at a frequency of 433.92 MHz, respectively, half of the wavelength for it is 34.5 cm. In order not to make an antenna of such dimensions, it is made in the form of not a pin, but a spiral - the latter has one interesting property: if the diameter of the turns Since the helix is much shorter than the wavelength, it works like an ordinary whip antenna, radiating in a plane perpendicular to its axis, but it turns out to be several times shorter. Spiral antennas became widespread long before the appearance of weather stations - first of all, in portable radios, for which the length of the 1/4-wave pin in the 27 MHz range is almost 3 meters. A three-meter pin makes the walkie-talkie significantly less wearable than it could be.
Alas, all magic comes with a price: a spiral antenna has worse characteristics than a simple pin. Therefore, a spiral is always a compromise between dimensions and efficiency.
So, in order to slightly increase the range of the sensor, we need to change the helical antenna to the pin antenna - since the dimensions of the antennas are of concern to the logistics department of the manufacturer, but we, consumers, are of little concern - there is a lot of space on the balcony, the 17-cm antenna will somehow fit.
To accomplish this, you will need a piece of copper single-core wire in insulation 16.5 cm long (one core from any copper power cable with a cross section of 1.5-2.5 square mm is suitable), a soldering iron, sealant, minimally straight arms.
NB: since the wave propagation speed in copper is less than in vacuum, the actual length of the copper antenna should be less than 1/4 of the wavelength in vacuum; for copper, the correction factor is 0.95. Accordingly, 1/4 * (0.95 * 3 * 10 ^ 10 cm / s) / 433.92 MHz just gives us about 16.5 cm.
If you look at the transmitter board, you can see that one part of the dipole is connected to ground, the other - to the track, leaving under the screen of the transmitting part. We will change one half of the dipole - the one to the transmitting part. We solder it:
We put the board in place and through the hole into which the antenna was soldered (having cleaned it of solder), with a needle we mark a point on the sensor body through which a new antenna will go inside. Drill a hole nearbywith this point, we clean the last 5 mm of the new antenna from insulation, bend it with the letter “G” and insert it into the hole in the case.
Since the hole in the board in diameter is much smaller than the wire taken as an antenna, we cut off 5 mm of some thin wire (the output of the 0.125 W resistor will do) and solder to the end of the antenna (drill a hole near the desired point, and not directly in it , it was necessary just to get this soldering exactly on the board):
It is necessary to solder quickly so as not to melt the plastic case. In principle, it was possible to make the antenna out of a thin wire, but this is inconvenient - it easily wrinkles and bends.
We put the transmitter board on top, getting the board hole into our antenna, solder it to the board, close the transmitter. The final touch is to fix the antenna on its body and seal the input; I used a glue gun, but, firstly, I have a gun with a very thin sting, and secondly, the sensor hangs under the roof, the rain does not water it. If your situation is different, use any sealant or thick glue. It is also advisable to cover the top end of the antenna with a drop of glue so that water does not enter the copper core.
Actually, that's all. It is actually done faster than this text is written. It is suitable for any weather stations, and indeed any household radio transmitters, up to the “smart home” systems, since spiral antennas are used almost everywhere where you need cheap and cheerful. Pay only attention to the operating frequency: the transmitters are also at 866 MHz, and the new ones at 2.4 GHz (in these, however, the antenna is most often already made a track on the board). The whip antenna should be 1/4 wavelength.
PS Sense of beauty also reports that the best way to determine the ideal length of an antenna is to make it a little longer than 1/4 of the wave and then cut it by millimeter, checking the effectiveness. Reason answers that for a banal weather station this is already too much.
Further, however, a problem was discovered, also related to the depth of the apartment - the station farthest from the external weather sensor regularly lost it, although it would seem that there was only a couple of walls between them. Especially this problem got out at subzero temperatures, despite the lithium battery standing in the sensor.
Choosing the right window for hanging a sensor or installing a second sensor is not our option, for a person must command the equipment, and not vice versa. Our option is to change the antenna in the sensor to increase its range.
Of course, the technique is suitable for any weather sensors, since the design of them all is about the same.
Unscrew:
There are already three antennas in this sensor (usually you will find one, maximum two). The ferrite core, however, does not interest us - it is a receiver of accurate time signals at 77 kHz, but two wire spirals are what we need.
They form the so-called half-wave dipole - an antenna consisting of two symmetrical parts with a total length of 1/2 wavelength. Dipoles are used when the antenna does not have a normal “ground” - one of the halves of the dipole actually plays the role of this “ground”, let me forgive the radio engineers for a somewhat simplified description. Each half has, accordingly, a length of 1/4 wave.
The sensor operates at a frequency of 433.92 MHz, respectively, half of the wavelength for it is 34.5 cm. In order not to make an antenna of such dimensions, it is made in the form of not a pin, but a spiral - the latter has one interesting property: if the diameter of the turns Since the helix is much shorter than the wavelength, it works like an ordinary whip antenna, radiating in a plane perpendicular to its axis, but it turns out to be several times shorter. Spiral antennas became widespread long before the appearance of weather stations - first of all, in portable radios, for which the length of the 1/4-wave pin in the 27 MHz range is almost 3 meters. A three-meter pin makes the walkie-talkie significantly less wearable than it could be.
Alas, all magic comes with a price: a spiral antenna has worse characteristics than a simple pin. Therefore, a spiral is always a compromise between dimensions and efficiency.
So, in order to slightly increase the range of the sensor, we need to change the helical antenna to the pin antenna - since the dimensions of the antennas are of concern to the logistics department of the manufacturer, but we, consumers, are of little concern - there is a lot of space on the balcony, the 17-cm antenna will somehow fit.
To accomplish this, you will need a piece of copper single-core wire in insulation 16.5 cm long (one core from any copper power cable with a cross section of 1.5-2.5 square mm is suitable), a soldering iron, sealant, minimally straight arms.
NB: since the wave propagation speed in copper is less than in vacuum, the actual length of the copper antenna should be less than 1/4 of the wavelength in vacuum; for copper, the correction factor is 0.95. Accordingly, 1/4 * (0.95 * 3 * 10 ^ 10 cm / s) / 433.92 MHz just gives us about 16.5 cm.
If you look at the transmitter board, you can see that one part of the dipole is connected to ground, the other - to the track, leaving under the screen of the transmitting part. We will change one half of the dipole - the one to the transmitting part. We solder it:
We put the board in place and through the hole into which the antenna was soldered (having cleaned it of solder), with a needle we mark a point on the sensor body through which a new antenna will go inside. Drill a hole nearbywith this point, we clean the last 5 mm of the new antenna from insulation, bend it with the letter “G” and insert it into the hole in the case.
Since the hole in the board in diameter is much smaller than the wire taken as an antenna, we cut off 5 mm of some thin wire (the output of the 0.125 W resistor will do) and solder to the end of the antenna (drill a hole near the desired point, and not directly in it , it was necessary just to get this soldering exactly on the board):
It is necessary to solder quickly so as not to melt the plastic case. In principle, it was possible to make the antenna out of a thin wire, but this is inconvenient - it easily wrinkles and bends.
We put the transmitter board on top, getting the board hole into our antenna, solder it to the board, close the transmitter. The final touch is to fix the antenna on its body and seal the input; I used a glue gun, but, firstly, I have a gun with a very thin sting, and secondly, the sensor hangs under the roof, the rain does not water it. If your situation is different, use any sealant or thick glue. It is also advisable to cover the top end of the antenna with a drop of glue so that water does not enter the copper core.
Actually, that's all. It is actually done faster than this text is written. It is suitable for any weather stations, and indeed any household radio transmitters, up to the “smart home” systems, since spiral antennas are used almost everywhere where you need cheap and cheerful. Pay only attention to the operating frequency: the transmitters are also at 866 MHz, and the new ones at 2.4 GHz (in these, however, the antenna is most often already made a track on the board). The whip antenna should be 1/4 wavelength.
PS Sense of beauty also reports that the best way to determine the ideal length of an antenna is to make it a little longer than 1/4 of the wave and then cut it by millimeter, checking the effectiveness. Reason answers that for a banal weather station this is already too much.