RTL-SDR Stock Whip Antenna

[eastons]

Hi,

I was just wondering if anyone's using the stock RTL-SDR dongle whip antenna for their ADS-B reception. If so, what kind of range are you getting? I get reception consistently out to about 300 km with my trimmed (69 mm) stock antenna in directions that aren't blocked by nearby buildings (the antenna is next to the window in my house and not particularly high up).

I've also been reading about quarter wavelength antennas needing to have ground planes - for the dongle's whip antenna, is it enough simply to place its magnetic base on a piece of metal? Or does the metal ground need to be connected to the antenna somehow?

I've also read of others trimming their whip antennas down to 65 mm, but I calculated the quarter wavelength for 1090 MHz to be 69 mm, so I'm not sure if I should be trimming it down further.

I've also tried building collinear antennas from RG6 coax based on designs I've seen online, but so far, the dongle's whip seems to be performing the best for me somehow.

Thanks in advance for any responses =).

[peterhr]

It always helps to get the antenna higher than nearby obstructions - the usual obstructions you need to get past are the building roof and chimneys. Big bags of water (AKA trees in leaf) will also cut the signal, but often you cant do much about those.

The main problem with the little whip antenna is the 1m cable, that's what makes most people want to use something better.

The problem with the coco is you cant easily be sure of the segment length you need without special equipment so it's easy to make a de-tuned antenna and adding more sections just makes it worse

Have a look at http://forum.flightradar24.com/threa...plified-dipole - this experimental antenna gives me 400-450km and I've not tried trimming it.

[DroidNine]

What sort of whip is it you are using? If its the generic wide band ones that come with the cheaper USB cards be careful trimming it as I dont believe they are straight out quarter wave vertical element, as there is a loading coil at the base of it. I am happy to sacrifice mine when I get home to check for sure if you like.

If there is a loading coil or some sort of impedance matching trimming for quarter wave will not give the desired results.

[eastons]

Thanks for the reply, Peterhr. I've made a simpler version of the dipole antenna you linked to (i.e. without amplifier) and it's getting me 400 km range in some directions (I have nearby buildings/terrain obstructing my line-of-sight).

Thanks for your reply also, DroidNine. It is indeed the cheaper whip aerial that comes with the USB dongles. I have six dongles and thus, six of those antennas so I've been experimenting with them. From observation, the range does seem to improve with it trimmed, though it's just through casual observation. In any case, I'm no longer using the bundled whip antenna.

[DroidNine]

No worries, I might take it apart anyway just to have a look. What sort of antenna did you end up going with, and have you compared it against the trimmed whip?

[eastons]

At the moment, I'm using a simple unamplified dipole made out of coax. This gives me around 400 km maximum range, compared to about 350 km for the whip. However, I've now bought another antenna from eBay, which I'm waiting for to arrive.

[DroidNine]

Did you make a coax dipole/bazooka? I'm actually making one as we speak from CNT-400. It'd be up in the air now if it wasn't for a slight hiccup after finishing it this afternoon when I realised I'd done the calcs for RG-213 not the CNT-400 I was using (VF 0.85 vs 0.66). Oh dear!

[peterhr]

If it's a plain dipole - each of the arms is 1/4 wavelength of signal in free air isn't it - VF doesn't enter the calcs?

[DroidNine]

It's a coax dipole so different to a normal half wave dipole. You can also make them end fed with a coax choke too so that will be the next test.

[eastons]

Hi,

I've attached a picture of my range (rings are 50 km apart) and the dipole that I've built.

It was only meant to be a temporary antenna, so it's not waterproofed or sturdy. It's constructed with RG6 cable and quarter-wavelength elements (68 mm, one pointing up and the other pointing down) made from the centre conductor of the RG6 cable.

It's not standing entirely vertically, as you can see in the picture, but it still seems to work fine – it's hard for me to adjust/fix it since it's up on the roof. My maximum range is showing as 221.7 nautical miles (about 400 km) with the dipole. I'm in a bit of a valley and have high rises around me, so I don't get 400 km in all directions. Nevertheless, I'm surprised it performs so well given its compact size and simplicity.

I also tried using an amplifier, but it seems to just make all the signals disappear – when the antenna is up on the roof. When the antenna is lower, it seems to boost the signal values. Perhaps a strong local signal is causing overloading and images.

[peterhr]

Hi,

I've attached a picture of my range (rings are 50 km apart) and the dipole that I've built.

It was only meant to be a temporary antenna, so it's not waterproofed or sturdy. It's constructed with RG6 cable and quarter-wavelength elements (68 mm, one pointing up and the other pointing down) made from the centre conductor of the RG6 cable.

It's not standing entirely vertically, as you can see in the picture, but it still seems to work fine – it's hard for me to adjust/fix it since it's up on the roof. My maximum range is showing as 221.7 nautical miles (about 400 km) with the dipole. I'm in a bit of a valley and have high rises around me, so I don't get 400 km in all directions. Nevertheless, I'm surprised it performs so well given its compact size and simplicity.

I also tried using an amplifier, but it seems to just make all the signals disappear – when the antenna is up on the roof. When the antenna is lower, it seems to boost the signal values. Perhaps a strong local signal is causing overloading and images.

That's about the range I would expect from the dipole, it might be a trick of the angles on the picture that make it look entangled with the TV aerial ... it clear of the TV reflector if it is behind it.

Adding an amplifier doesn't add much range but it does seem to bring in 10-15% more flights from within the range.