Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
iridium:antennas [2015/01/25 22:34]
schneider
iridium:antennas [2021/04/18 12:35] (current)
Line 3: Line 3:
 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 and ideally also uses RHCP.
  
-If the antenna uses liner polarization, you can expect a loss of about 3 dB. If the antenna is left-hand circular polarized, you can expect a loss of about 30 dB. See http://sv1bsx.50webs.com/antenna-pol/polarization.html for details on this topic.+If the antenna uses liner polarization, you can expect a loss of about 3 dB. If the antenna is left-hand circular polarized, you can expect a loss of about 30 dB. See http://www.qsl.net/sv1bsx/antenna-pol/polarization.html for details on this topic.
  
-All following antennas used RHCP unless otherwise noted.+All following antennas use RHCP unless otherwise noted.
  
 ===== Active vs. Passive ===== ===== Active vs. Passive =====
-An active antenna is a passive antenna immediately followed by an active circuit. Most of the timethis 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://fabiobaltieri.com/2014/06/22/lna/ for some details on that.+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 to counter the losses of the cable. See http://fabiobaltieri.com/2014/06/22/lna/ for some details on that.
  
 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://www.microwaves101.com/encyclopedias/noise-figure for some details. 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://www.microwaves101.com/encyclopedias/noise-figure for some details.
  
-Active antennas have one small and one major drawback though: +Active antennas have two general drawbacks though: 
-  * 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 active antenna is usually supplied via the same coaxial cable which is used to receive the signal. Have a look at [TODO] for some details on this.+The power to operate an active antenna is usually supplied via the same coaxial cable which is used to receive the signal. Have a look at [TODO] for some details on this.
  
 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.
Line 34: Line 34:
 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 setupyou 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:
  
 ^       Name             Manufacturer     ^ Connector       ^ Approximate Cost ^ Distributors ^ ^       Name             Manufacturer     ^ Connector       ^ Approximate Cost ^ Distributors ^
-| 33-2600-00-0500  | Tallysman Wireless Inc | Short SMA cable | 70 USD           | [[http://www.digikey.com/product-detail/en/33-3600-01-11/1526-1018-ND|Digi-Key]] [[http://de.farnell.com/tallysman-wireless/32-2600-0/ant-iridium-sbd-sma-tw2600/dp/2056660|Farnell(DE)]] [[https://hbe-shop.de/Art-2056660-TALLYSMAN-WIRELESS-32-2600-0-ANT-IRIDIUM-SBD-SMA-TW2600|HBE(DE)]] |+| 33-2600-00-0500  | Tallysman Wireless Inc | Short SMA cable | 70 USD           | [[http://www.digikey.com/product-detail/en/33-3600-01-11/1526-1012-ND|Digi-Key]] [[http://de.farnell.com/tallysman-wireless/32-2600-0/ant-iridium-sbd-sma-tw2600/dp/2056660|Farnell(DE)]] [[https://hbe-shop.de/Art-2056660-TALLYSMAN-WIRELESS-32-2600-0-ANT-IRIDIUM-SBD-SMA-TW2600|HBE(DE)]] |
 | 33-3600-01-11    | Tallysman Wireless Inc | TNC             | 70 USD           | [[http://www.digikey.com/product-detail/en/33-3600-01-11/1526-1018-ND|Digi-Key]] | | 33-3600-01-11    | Tallysman Wireless Inc | TNC             | 70 USD           | [[http://www.digikey.com/product-detail/en/33-3600-01-11/1526-1018-ND|Digi-Key]] |
 | IAA.01.121111    | Taoglas                | 1 m SMA cable   | 25 USD           | [[http://www.mouser.com/ProductDetail/Taoglas/IAA01121111/?qs=sGAEpiMZZMt9rZLnhhqRz3ld4Fm2CGGq|Mouser]] | | IAA.01.121111    | Taoglas                | 1 m SMA cable   | 25 USD           | [[http://www.mouser.com/ProductDetail/Taoglas/IAA01121111/?qs=sGAEpiMZZMt9rZLnhhqRz3ld4Fm2CGGq|Mouser]] |
 |ADA-A1621-S       | ADACTUS                | 2 m SMA cable   | 50 USD           | [[http://www.newark.com/adactus/ada-a1621-s/antenna-iridium-sat-comms-mag/dp/55T5184|Farnell(US)]] [[http://de.farnell.com/adactus/ada-a1621-s/antenne-iridium-sat-comms-mag/dp/1899486|Farnell(DE)]] [[https://hbe-shop.de/Art-1899486-ADACTUS-ADA-A1621-S-ANTENNEIRIDIUM-SAT-COMMSMAG-MT|HBE(DE)]] | |ADA-A1621-S       | ADACTUS                | 2 m SMA cable   | 50 USD           | [[http://www.newark.com/adactus/ada-a1621-s/antenna-iridium-sat-comms-mag/dp/55T5184|Farnell(US)]] [[http://de.farnell.com/adactus/ada-a1621-s/antenne-iridium-sat-comms-mag/dp/1899486|Farnell(DE)]] [[https://hbe-shop.de/Art-1899486-ADACTUS-ADA-A1621-S-ANTENNEIRIDIUM-SAT-COMMSMAG-MT|HBE(DE)]] |
 +|TW2600A           | Tallysman Wireless Inc | ?               | ?                | [[https://www.tallysman.com/index.php/gnss/products/antennas-iridium/tw2600a/|Tallysman TW2600A]] |
 +|TW2643A           | Tallysman Wireless Inc | ?               | ?                | [[https://www.tallysman.com/index.php/gnss/products/antennas-gpsbeidougalileoglonass/tw2643a/|Tallysman TW2643A]] |
  
-Most of these have a magnetic mount. They need some kind of metal plane bellow them to work properly. A small metal patch of about 20 cm in diameter (round or square) is more than adequate. +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 to many different types of active GPS antennas.+This is probably the cheapest option to get an active Iridium antenna. The process is pretty straight forward and can be adapted to many different types of active GPS antennas.
  
-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. As the amplifiers are not perfect and the GPS signal very weak, this can have an impact on the quality of the GPS signal. For our purposes these filters are a problem though. They basically make an unmodified GPS antenna unusable to receive Iridium antennas.+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. The amplifiers are not perfect and the GPS signal very weak. This can have an impact on the quality of the GPS signal. For our purposes these filters are a problem though. They basically make an unmodified GPS antenna unusable to receive Iridium signals.
  
-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 foundthat 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.
Line 66: Line 67:
 {{:iridium:antennas:active-gps-antenna-7.jpg?direct&200|}} {{:iridium:antennas:active-gps-antenna-7.jpg?direct&200|}}
  
-To make it into an active Iridium the antenna needs to be modified:+To make it into an active Iridium antenna, the GPS antenna needs to be modified:
  
 ==== Remove the Shielding ==== ==== Remove the Shielding ====
Line 75: Line 76:
 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 time+  - A second amplifier to amplify the signal again
  
 Here are two examples of different filters in active GPS antennas: Here are two examples of different filters in active GPS antennas:
Line 88: Line 89:
 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 modificationour antenna now looks like this:+After the modification our antenna looks like this:
 {{:iridium:antennas:active-gps-antenna-filter-4.jpg?direct&200|}} {{:iridium:antennas:active-gps-antenna-filter-4.jpg?direct&200|}}
  
Line 104: Line 105:
 ===== 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.
 +
 + 
 +
 +LNA4ALL: http://lna4all.blogspot.com/2013/04/lna-for-all-low-noise-amplifier-for.html
  
 +L-Band Filter: http://adsbfilter.blogspot.com/2016/02/l-band-inmarsat-thuraya-iridium-gps.html
  
 +Patch Antenna Design: https://www.rtl-sdr.com/building-and-testing-an-l-band-patch-antenna-for-inmarsat-c-reception/
  • iridium/antennas.1422225287.txt.gz
  • Last modified: 2021/04/18 12:32
  • (external edit)