Over on our store we now sell our dongles with a receive only dipole antenna kit that replaces the older magnetic whip style antennas from the previous kit. This was done for a few reasons
mide contains other products and information you need, so please check it out.
While the magnetic whip still works perfectly fine, the dipole kit should make it easier to get the antenna outside or in a better position away from noisy computers/electronics, and it also allows for a simple v-dipole configuration for satellite reception.
The units are currently in stock at our Chinese warehouse either bundled with an RTL-SDR or as an individual antenna set.
www.rtl-sdr.com/store
This post is a guide on how to use the dipole antenna set in various configurations. First we'll show and explain about what's included in the set:
Signals are normally transmitted with either horizontal, vertical or right hand/left hand circular polarization (RHCP/LHCP). This is essentially the 'orientation' of a signal, and an antenna with the same polarization should be used too for best performance. A dipole can be used in either vertical or horizontal polarization, just by orienting it either vertically or horizontally.
If you mismatch vertical and horizontal polarization or RHCP and LHCP you'll get an instant 20dB loss. If you mismatch vertical/RHCP, vertical/LHCP, horizontal/RHCP, horizontal/LHCP you'll only get a 3dB loss.
For vertical polarization, in theory it does not matter which way around you orient the antenna as long as it's vertical. However in practice, you may get slightly better results by having the element connected to the center coax conductor pointing UP. You can confirm which element is connected to the center conductor by temporarily removing the black lid on the dipole base (it can be easily pried off with a nail or flat head screwdriver).
There are also ways to optimize the radiation pattern with dipoles. For example for LEO VHF satellites you can use a V-dipole configuration. You can also make a somewhat directional antenna by using a bent dipole configuration. Some more examples of dipole configurations can be found on KK4OBI's page on bent dipoles.
Most signals broadcast terrestrially (on Earth) are vertically polarized.
To use the dipole for vertically polarized signals, all that you need to do is orient the elements vertically (up and down).
In theory there is no up and down for the dipole when used in the vertical orientation. However in practice you may find slightly better performance when the 'active' element points up. The active element is the one connected to the center conductor. You can check which element is connected to the center conductor by removing the top cap on the dipole base. This will let you look inside at the connections.
The dipole can be used in a V-Dipole configuration for polar orbiting satellite reception. See Adam 9A4QV's post where he wrote about how he discovered that it was possible to use dipoles in this configuration for excellent satellite reception. The idea is to use the dipole in horizontal polarization. This gives 3dB loss on the RHCP satellite signals, but also nicely gives 20dB loss on terrestrial signals which could be overloading your RTL-SDR.
For 137 MHz satellites like NOAA and Meteor M2 extend the larger antenna elements out to about 53.4 cm each (about 2.5 sections). Angle the dipole so it is horizontal and in a 'Vee' shape, at about 120 degrees. Place the dipole in the North-Source direction.
With an appropriate L-band LNA like the Outernet LNA the dipole can also somewhat work to receive L-band satellites. Using the smallest antenna collapsed, use a V-dipole configuration and point it towards the L-band satellite. Ideally use a reflector too. In the image below we used a simple cookie tin as a reflector. A hole was drilled into the center and the mount used to clamp in the antenna. This together with the Outernet LNA was enough to receive AERO and STD-C.
Like with the whip you can use an online calculator to calculate the optimal length for your frequency of interest. We recommend this dipole calculator. The exact length does not matter too much, but try to get the lengths as close to what the calculator says as you can. With the dipole you want both elements to be the same length.
In reality extending the antenna to almost any random length will work just fine for most strong signals. But if you're really trying to optimize those weak signals you'll want to fine tune the lengths.
Basically the longer the antenna, the lower it's resonant frequency. The shorter the antenna, the higher the resonant frequency. You want to be close to the resonant frequency. Remember that there is about 2cm of metal inside the antenna itself which needs to be added on. Below is a cheat sheet for various lengths and frequencies. Note that the length refers to the length of one side of the dipole only (e.g. the length that you need to extend each element out to).
See the SWR plots at the end for a more accurate reading of the resonance points. But in most cases no matter what you extend the length to the SWR should be below 5 at most frequencies which results in 2.5 dB loss or less. More accurate info on VSWR loss graphs can be found in this document from the ARRL "Understanding SWR by Example" (pdf).
The suction cup mount allows you to easily place the antenna on a window, or any smooth surface. To use it first clean the surface thoroughly with isopropyl alcohol or glass cleaner. Then apply the suction cup and close the lever to lock it in place. The lever requires some force to push down, and this ensures a strong grip. You can then angle the antenna in the orientation that you need using the ball socket. Once in place close the ring to lock the ball socket in place.
The flexible tripod mount is useful to mounting the dipole to almost everything else. Including tables, doors, poles, trees etc. The legs of the tripod have a flexible metal wire inside and rubber sheath so they can be bent into a position to grip almost anything.
Note that the mounts and RG174 extension allow you to more easily use the dipole antennas outside or in a better indoors position (e.g. on a Window). But please note that like our older magnetic whip we do not recommend permanently mounting this antenna outdoors. This antenna is designed to be a portable antenna that you put up and take down at the end of the day - not for permanent outdoor mounting. It is not protected against water, not grounded so cannot handle a lightning strike and could be damaged with dirt and grime build up. For permanent outdoor mounting you could conceivably fill the inside and hinges of the dipole with silicon putty or maybe even hot glue and ground the antenna yourself, but we have not tested this. The stainless steel antennas won't rust, but dirt and grime could gum up the collapsing mechanism.
Once you've got the orientation of the dipoles the way you want, you might want to tighten the hinge so the elements don't move so easily anymore. To do this simply take a small screwdriver and tighten the screw on the hinge.
Note that our older antennas had a 100kOhm ESD bleed resistor between the two elements. This is no longer the case on newer models. The purpose of the resistor was to slowly bleed any ESD buildup to ground.
We decided to improve ESD protection on the dongle instead, so the ESD bleed resistor is not longer required and is now omitted on newer productions.
Note that this is NOT an antenna designed for TXing. It is an RX antenna only. So please do not TX with it unless you really know what you are doing as you could damage your TX radio.
Over on our store we now sell our dongles with a receive only dipole antenna kit that replaces the older magnetic whip style antennas from the previous kit. This was done for a few reasons
While the magnetic whip still works perfectly fine, the dipole kit should make it easier to get the antenna outside or in a better position away from noisy computers/electronics, and it also allows for a simple v-dipole configuration for satellite reception.
The units are currently in stock at our Chinese warehouse either bundled with an RTL-SDR or as an individual antenna set.
www.rtl-sdr.com/store
This post is a guide on how to use the dipole antenna set in various configurations. First we'll show and explain about what's included in the set:
Signals are normally transmitted with either horizontal, vertical or right hand/left hand circular polarization (RHCP/LHCP). This is essentially the 'orientation' of a signal, and an antenna with the same polarization should be used too for best performance. A dipole can be used in either vertical or horizontal polarization, just by orienting it either vertically or horizontally.
If you mismatch vertical and horizontal polarization or RHCP and LHCP you'll get an instant 20dB loss. If you mismatch vertical/RHCP, vertical/LHCP, horizontal/RHCP, horizontal/LHCP you'll only get a 3dB loss.
For vertical polarization, in theory it does not matter which way around you orient the antenna as long as it's vertical. However in practice, you may get slightly better results by having the element connected to the center coax conductor pointing UP. You can confirm which element is connected to the center conductor by temporarily removing the black lid on the dipole base (it can be easily pried off with a nail or flat head screwdriver).
There are also ways to optimize the radiation pattern with dipoles. For example for LEO VHF satellites you can use a V-dipole configuration. You can also make a somewhat directional antenna by using a bent dipole configuration. Some more examples of dipole configurations can be found on KK4OBI's page on bent dipoles.
Most signals broadcast terrestrially (on Earth) are vertically polarized.
To use the dipole for vertically polarized signals, all that you need to do is orient the elements vertically (up and down).
In theory there is no up and down for the dipole when used in the vertical orientation. However in practice you may find slightly better performance when the 'active' element points up. The active element is the one connected to the center conductor. You can check which element is connected to the center conductor by removing the top cap on the dipole base. This will let you look inside at the connections.
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The dipole can be used in a V-Dipole configuration for polar orbiting satellite reception. See Adam 9A4QV's post where he wrote about how he discovered that it was possible to use dipoles in this configuration for excellent satellite reception. The idea is to use the dipole in horizontal polarization. This gives 3dB loss on the RHCP satellite signals, but also nicely gives 20dB loss on terrestrial signals which could be overloading your RTL-SDR.
For 137 MHz satellites like NOAA and Meteor M2 extend the larger antenna elements out to about 53.4 cm each (about 2.5 sections). Angle the dipole so it is horizontal and in a 'Vee' shape, at about 120 degrees. Place the dipole in the North-Source direction.
With an appropriate L-band LNA like the Outernet LNA the dipole can also somewhat work to receive L-band satellites. Using the smallest antenna collapsed, use a V-dipole configuration and point it towards the L-band satellite. Ideally use a reflector too. In the image below we used a simple cookie tin as a reflector. A hole was drilled into the center and the mount used to clamp in the antenna. This together with the Outernet LNA was enough to receive AERO and STD-C.
Like with the whip you can use an online calculator to calculate the optimal length for your frequency of interest. We recommend this dipole calculator. The exact length does not matter too much, but try to get the lengths as close to what the calculator says as you can. With the dipole you want both elements to be the same length.
In reality extending the antenna to almost any random length will work just fine for most strong signals. But if you're really trying to optimize those weak signals you'll want to fine tune the lengths.
Basically the longer the antenna, the lower it's resonant frequency. The shorter the antenna, the higher the resonant frequency. You want to be close to the resonant frequency. Remember that there is about 2cm of metal inside the antenna itself which needs to be added on. Below is a cheat sheet for various lengths and frequencies. Note that the length refers to the length of one side of the dipole only (e.g. the length that you need to extend each element out to).
See the SWR plots at the end for a more accurate reading of the resonance points. But in most cases no matter what you extend the length to the SWR should be below 5 at most frequencies which results in 2.5 dB loss or less. More accurate info on VSWR loss graphs can be found in this document from the ARRL "Understanding SWR by Example" (pdf).
The suction cup mount allows you to easily place the antenna on a window, or any smooth surface. To use it first clean the surface thoroughly with isopropyl alcohol or glass cleaner. Then apply the suction cup and close the lever to lock it in place. The lever requires some force to push down, and this ensures a strong grip. You can then angle the antenna in the orientation that you need using the ball socket. Once in place close the ring to lock the ball socket in place.
The flexible tripod mount is useful to mounting the dipole to almost everything else. Including tables, doors, poles, trees etc. The legs of the tripod have a flexible metal wire inside and rubber sheath so they can be bent into a position to grip almost anything.
Note that the mounts and RG174 extension allow you to more easily use the dipole antennas outside or in a better indoors position (e.g. on a Window). But please note that like our older magnetic whip we do not recommend permanently mounting this antenna outdoors. This antenna is designed to be a portable antenna that you put up and take down at the end of the day - not for permanent outdoor mounting. It is not protected against water, not grounded so cannot handle a lightning strike and could be damaged with dirt and grime build up. For permanent outdoor mounting you could conceivably fill the inside and hinges of the dipole with silicon putty or maybe even hot glue and ground the antenna yourself, but we have not tested this. The stainless steel antennas won't rust, but dirt and grime could gum up the collapsing mechanism.
Once you've got the orientation of the dipoles the way you want, you might want to tighten the hinge so the elements don't move so easily anymore. To do this simply take a small screwdriver and tighten the screw on the hinge.
Note that our older antennas had a 100kOhm ESD bleed resistor between the two elements. This is no longer the case on newer models. The purpose of the resistor was to slowly bleed any ESD buildup to ground.
We decided to improve ESD protection on the dongle instead, so the ESD bleed resistor is not longer required and is now omitted on newer productions.
Note that this is NOT an antenna designed for TXing. It is an RX antenna only. So please do not TX with it unless you really know what you are doing as you could damage your TX radio.
The RTL-SDR Blog V3 is back in stock in Amazon USA (Dongle + Antenna) (Dongle Only). International buyers can continue to purchase units from our store at www.rtl-sdr.com/store.
Apologies for the long out of stock period, we sold out of our remaining Amazon US stock almost immediately a few weeks ago due to a large Reddit thread which popularized the Reddit /r/rtlsdr forums (a big welcome to any new RTL-SDR users!). Amazon is currently processing the new stock and it should be ready to ship out in a few days.
We also have a new antenna set in the works which should be ready for purchase in a few weeks. This antenna set is essentially a custom modified TV dipole with mounting kit. The kit will contain:
The telescopic antennas mount onto the antenna base via a screw, so they can easily be removed and interchanged between the large and small ones, or packed away for storage.
The dipole antenna base attaches to the suction cup or bendy tripod mounts using a 1/4″ camera screw. So any cheap camera mounting accessories like clamps, tripods etc can be used to mount the dipole as well.
The coax cable on the base also has a ferrite core choke on it to help decouple the feedline from the antenna, and there is a 100kOhm bleed resistor added to reduce static discharge.
The included suction cup mount allows you to mount the dipole on a window (ideally outside) and orient it into a vertical, horizontal or V-Dipole position. The bendy tripod allows you to use the antenna on your desk, folded over a door, on a tree branch, pole, or anywhere that the tripod legs can be wrapped around.
The biggest problem that new RTL-SDR users face is the antenna. Most are starting off with a mag mount whip, and have no way to mount them outside where they should be for better reception. Keeping them inside can cause poor reception and increased pickup of local interference from electronics. Our dipole with the mounts aims to solve this problem.
Using a dipole generally results in better reception than with a mag mount whip, and also allows for easier outdoor mounting. The 3M coax extension cable allows you to get the antenna at least to a window in your room.
Note that although we recommend using the antenna outside, please remember to take the antenna back inside when not in use to avoid lightning/ESD/weathering problems. It is not designed for permanent outdoor mounting and please remember that any permanently mounted outdoor antenna should have good grounding to protect your radio against ESD and lightning.
For general use we recommend using the dipole in the vertical orientation as most signals are vertically polarized. The dipole can also be used in a V-Dipole configuration for excellent VHF satellite reception, such as for NOAA/Meteor weather satellites. Just extend the telescopic dipoles to be as close as possible to resonant at the frequency of interest using this calculator. Getting the length perfect is not critical, and actually using any length will still receive something.
Apart from NOAA we’ve also tested the dipole with L-band satellites. Together with an LNA and the smaller telescopic antennas it’s possible to receive Iridium and Inmarsat signals. Reception is not as good as a patch antenna, but you can still get the stronger AERO and Iridium signals quite easily. If you add a reflector made out of a small cookie tin the signals can be boosted further, and this is enough to receive the weaker STD-C and Outernet signals.
Eventually this dipole set will replace the mag mount antenna bundled with the dongles currently. Target price is between $9.95 – $14.95 for the antenna set by itself, and $25.95 for the dongle + antenna set. We expect the antenna set to be ready for shipping in 2-3 weeks, and about 3-4 weeks for the dongle + antenna set. More details and usage examples will be shown nearer to the release.
In this post we will review the FlightAware ADS-B Antenna and their MHz band pass filter. The FlightAware ADS-B antenna is claimed to have 5.5 dBi of gain, a rugged weatherproof radome and N-type female connector. It costs $44.95 USD on Amazon for US customers and $54.95 USD on eBay for international customers (plus shipping). They write that they are selling this antenna at cost in order to improve FlightAware coverage.
The FlightAware ADS-B filter is a bandpass filter with a pass range of 980MHz - MHz, ~1.5dB insertion loss and more than 40dB attenuation of unwanted frequencies. It costs $19.95 USD on Amazon for US customers and $24.99 USD on eBay for international customers (plus shipping). Generally it is much cheaper than other ADS-B filter options on the market.
FlightAware.com is a company that specializes in aggregating ADS-B data from contributors around the world. People can contribute by using the FlightAware official hardware, or with a simple SDR, like an RTL-SDR dongle. They display the data on their website as it can be used to help track flight arrival times. A similar company is flightradar24.com.
If you are interested in getting started with ADS-B reception with your RTL-SDR then we have a tutorial here.
The FlightAware antenna is about 64cm in length and about 2cm in diameter. It uses an N female connector and comes included with mounting brackets and U-bolts. It is painted olive green.
In the photo below we compare the size of the antenna against a reference monopole antenna, an RTL-SDR dongle and the FlightAware ADS-B filter. The antenna appears to be very solidly built and of a high quality finish. The antenna is wareproofed with some silicon caulking used around the seams of the endcaps.
The FlightAware ADS-B antenna is a collinear type antenna. Collinear antennas are omnidirectional (receives equally from all directions) and have a higher gain compared to most other omnidirectional antennas, but their radiation pattern is flattened and directed more towards the horizon. This is a good thing for receiving planes that are far away as they will be at lower elevations, but aircraft at higher elevations relative to your antenna may be received poorer. Although, it is likely that any aircraft at high elevations to your position will be closer to you anyway, and thus have a stronger signal making the reduced gain at higher elevations less important. Judging by it's ~60cm length and it's specified gain of 5.5dBi, the FlightAware antenna is likely to be a 4 element collinear.
A 4 element collinear generally has positive gain from 0 - 20 degrees of elevation, whereas a simple dipole or ground plane may have positive gain from between 0 - 40 degrees of elevation. A typical commercial jet flys at about 10km. At a distance of 100km this jet would be at a 5.7 degree elevation, and at 10km 45 degrees. Smaller aircraft fly at about 3km maximum, and at 100km would have an elevation of 1.7 degrees, and at 10km 16.7 degrees, so the collinear covers most cases.
A reader wrote in to us to let us know that the internals of the FlightAware antenna had actually previously been posted in an old thread on their forums. From the image it looks like the antenna may be a sleeved dipole + whip + impedance matching design, or something similar. This design is somewhat of a collinear design thanks to the additional whip which also gives a flatter radiation pattern with more gain direction out towards the horizon. These antennas are omnidirectional (they receive equally from all directions) and have a higher gain compared to most other omnidirectional antennas, but their radiation pattern is flattened and directed more towards the horizon. This is a good thing for receiving planes that are far away as they will be at lower elevations, but aircraft at higher elevations relative to your antenna may be received poorer. Although, it is likely that any aircraft at high elevations to your position will be closer to you anyway, and thus have a stronger signal making the reduced gain at higher elevations less important.
If you live in a valley, or have multiple obstacles such as trees or buildings blocking your view of the horizon then the higher gain design may work worse than a dipole/quarter wave ground plane/folded monopole type antenna. In this situation you'd mainly only be able to receive ADS-B signals from higher elevations, so an antenna with a less flat radiation pattern would work better. See the end of this post for some example radiation pattern diagrams.
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