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iridium:antennas [2015/01/25 22:33] – schneider | iridium:antennas [2019/01/21 13:34] – [Commercial] ::1 | ||
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Iridium transmits around 1.626 GHz and uses right-hand circular polarization (RHCP). | Iridium transmits around 1.626 GHz and uses right-hand circular polarization (RHCP). | ||
- | To receive Iridium signals you need an antenna which is able to receive at this frequency ideally also uses RHCP. | + | To receive Iridium signals you need an antenna which is able to receive at this frequency |
- | If the antenna uses liner polarization, | + | If the antenna uses liner polarization, |
- | All following antennas | + | All following antennas |
===== Active vs. Passive ===== | ===== Active vs. Passive ===== | ||
- | An active antenna is a passive antenna immediately followed by an active circuit. Most of the time, this circuit is an amplifier which amplifies the received signals. | + | An active antenna is a passive antenna immediately followed by an active circuit. Most of the time this circuit is an amplifier which amplifies the received signals. |
This is done to counter effects of long cables or noisy amplifiers at the input of the receiver. | This is done to counter effects of long cables or noisy amplifiers at the input of the receiver. | ||
Just as every other circuit, these amplifiers also add noise to the system. They are not a magical way to improve the signal quality which is available at the antenna. | Just as every other circuit, these amplifiers also add noise to the system. They are not a magical way to improve the signal quality which is available at the antenna. | ||
- | They are still very useful though. If you don't want to (or can) place your SDR right next to the antenna, you can use them to counter the losses of the cable. See http:// | + | They are still very useful though. If you don't want to (or can't) place your SDR right next to the antenna, you can use active antennas |
Another use for these amplifiers arises if the first amplifier of the receiver has a large noise figure. This is usually not a problem with higher end devices like an USRP or a HackRF, but can help a little with RTL-SDR based receivers. The reason for this is that the total noise figure of the system is basically determined by the noise figure of the first amplifier. See http:// | Another use for these amplifiers arises if the first amplifier of the receiver has a large noise figure. This is usually not a problem with higher end devices like an USRP or a HackRF, but can help a little with RTL-SDR based receivers. The reason for this is that the total noise figure of the system is basically determined by the noise figure of the first amplifier. See http:// | ||
- | Active antennas have one small and one major drawback | + | Active antennas have two general drawbacks |
- | * They need some from of power supply to perform the amplification. | + | * They need some form of power supply to perform the amplification. |
* Without additional circuitry, a simple active antenna can not be used to transmit a signal. | * Without additional circuitry, a simple active antenna can not be used to transmit a signal. | ||
- | The power to operate | + | The power to operate |
The major drawback of not being able to transmit might or might not be a problem for your particular use. Just be aware of this fact. | The major drawback of not being able to transmit might or might not be a problem for your particular use. Just be aware of this fact. | ||
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The easiest way to get a working Iridium antenna is to just buy a commercial one. | The easiest way to get a working Iridium antenna is to just buy a commercial one. | ||
- | These are usually passive antennas as they are intended for bidirectional communication with the satellite. This means that, depending on your setup you might have to add some kind of amplifier right next to the antenna. | + | These are usually passive antennas as they are intended for bidirectional communication with the satellite. This means that, depending on your setup, you might have to add some kind of amplifier right next to the antenna. |
Here is a list of easily available antennas: | Here is a list of easily available antennas: | ||
^ | ^ | ||
- | | 33-2600-00-0500 | + | | 33-2600-00-0500 |
| 33-3600-01-11 | | 33-3600-01-11 | ||
| IAA.01.121111 | | IAA.01.121111 | ||
|ADA-A1621-S | |ADA-A1621-S | ||
+ | |TW2600A | ||
+ | |TW2643A | ||
- | Most of these have a magnetic mount. They need some kind of metal plane bellow | + | Most of these have a magnetic mount. They need some kind of metal plane below them to work properly. A small metal patch of about 20 cm in diameter (round or square) is more than adequate. |
===== Modified Active GPS Antennas===== | ===== Modified Active GPS Antennas===== | ||
As the GPS band is very close to the Iridium band, active GPS antennas can be used as a basis for an active Iridium antenna. | As the GPS band is very close to the Iridium band, active GPS antennas can be used as a basis for an active Iridium antenna. | ||
- | This is probably the cheapest option to get an active Iridium antenna. The process is pretty straight forward and can be adapter | + | This is probably the cheapest option to get an active Iridium antenna. The process is pretty straight forward and can be adapted |
- | Active GPS antennas contain a bandpass filter to block all signals which are not part of the GPS signal. This is done as the amplifiers will also amplify the signal of all other sources and forward this to the receiver. | + | Active GPS antennas contain a bandpass filter to block all signals which are not part of the GPS signal. This is done as the amplifiers will also amplify the signal of all other sources and forward this to the receiver. |
- | We found that after removing this filter, these antennas work quite OK as Iridium antennas. They work even better if you replace the standard patch antenna with a special Iridium patch antenna. | + | We found, that after removing this filter, these antennas work quite OK as Iridium antennas. They work even better if you replace the standard patch antenna with a special Iridium patch antenna. |
Cheap active GPS antennas cost around 10 USD (7 Eur). Try to get one with screws so you can access the inside without damaging the protective case. | Cheap active GPS antennas cost around 10 USD (7 Eur). Try to get one with screws so you can access the inside without damaging the protective case. | ||
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{{: | {{: | ||
- | To make it into an active Iridium the antenna needs to be modified: | + | To make it into an active Iridium |
==== Remove the Shielding ==== | ==== Remove the Shielding ==== | ||
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All active GPS antennas will have a filter in them. It might look different between the different models though. All antennas which we have opened yet follow the same design: | All active GPS antennas will have a filter in them. It might look different between the different models though. All antennas which we have opened yet follow the same design: | ||
- | - A first amplifier directly connected to the antenne | + | - A first amplifier directly connected to the patch antenna |
- A bandpass filter to filter out unwanted frequencies | - A bandpass filter to filter out unwanted frequencies | ||
- | - A second amplifier to amplify the signal | + | - A second amplifier to amplify the signal |
Here are two examples of different filters in active GPS antennas: | Here are two examples of different filters in active GPS antennas: | ||
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After the filter has been removed, the pads connecting to the input and output of the filer need to be connected together. Usually there are two or more pads connected to ground, one pad connected to the input and one pad connected to the output. Just connect the input and output via a very short piece of wire. You can use use some silver coated copper wire as it solders very easily. Just make sure that the wire is not longer than necessary as it will not be impedance controlled and can introduce a bit of mismatch inside the RF path. | After the filter has been removed, the pads connecting to the input and output of the filer need to be connected together. Usually there are two or more pads connected to ground, one pad connected to the input and one pad connected to the output. Just connect the input and output via a very short piece of wire. You can use use some silver coated copper wire as it solders very easily. Just make sure that the wire is not longer than necessary as it will not be impedance controlled and can introduce a bit of mismatch inside the RF path. | ||
- | After the modification, our antenna | + | After the modification our antenna looks like this: |
{{: | {{: | ||
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^ | ^ | ||
- | | IP.1621.25.4.A.02 | + | | IP.1621.25.4.A.02 |
Just remove the old patch antenna by desoldering the single pin with which it is connected to the PCB and fit the replacement patch antenna from Taoglas. Both antennas have an adhesive strip which glues them to the PCB. You will need a thin blade or knife to remove the original patch antenna while at the same time desoldering it. It is a bit tricky but you can use a bit of force to get it out. Use the adhesive strip of the new patch antenna to fix it to the PCB. Your antenna should look like this now: | Just remove the old patch antenna by desoldering the single pin with which it is connected to the PCB and fit the replacement patch antenna from Taoglas. Both antennas have an adhesive strip which glues them to the PCB. You will need a thin blade or knife to remove the original patch antenna while at the same time desoldering it. It is a bit tricky but you can use a bit of force to get it out. Use the adhesive strip of the new patch antenna to fix it to the PCB. Your antenna should look like this now: | ||
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===== Self Made ===== | ===== Self Made ===== | ||
+ | Exchanging a smaller package for something more sensitive like the following design will require more filters an LNAs. Amplifier noise can be reduced with better components when compared to an active GPS antenna. | ||
+ | |||
+ | |||
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+ | LNA4ALL: http:// | ||
+ | L-Band Filter: http:// | ||
+ | Patch Antenna Design: https:// |