Improving a software defined radio with a few bits of wire

Impressed by the recent advances in the software defined radio scene, [Jason] picked up a $20 USB TV tuner dongle to check out his local airwaves. Unfortunately, the antenna included with the little USB dongle is terrible at receiving any signal other than broadcast TV. [Jason] wanted to improve his reception, so he got some wire and made his own discone antenna.

The discone antenna┬áis ideally suited for [Jason]‘s setup – properly constructed, it’s able to┬áreceive over the entire 64 to 1700 MHz band the RTL-SDR dongle is able to read. To construct his antenna, [Jason] checked out [VE3SQB]‘s list of antenna design programs, got the dimensions of his antenna, and set to work attaching wire to PVC pipe.

The antenna is a massive improvement over the stock antenna included with the TV tuner dongle. After mounting his discone at the far end of his back yard, [Jason] started picking up a few blips from the transponders of passing aircraft.

23 thoughts on “Improving a software defined radio with a few bits of wire

  1. That looks quite useful. The cheap-SDR movement is neat. And I love how antenna-design is black magic and art.

    1. Antenna design is not a black/magic art. It’s simply knowing the math. Get a copy of the ARRL handbook and learn to be an Antenna Wizard of the highest level.

      1. You need to use simulation/optimization software to make efficient antenna design. Especially small antenna’s. The ARRL handbook is quite outdated.

        1. It’s hard for physics to become outdated… antenna theory hasn’t changed. Perhaps people’s ability/willingness to slog through the maths has decreased (and software is faster, for sure), but the ARRL antenna handbook is certainly not outdated.

      1. I will still call it black magic because i have no idea what some service provider is using for me to match it remotely :-(

  2. Do note that a Discone like this is very prone to overloading the RTL2832U based dongles. Makes it harder to listen to signals in other bands when the antenna is also grabbing the 88-108MHz radio stations and overloading the tuner. It is a great idea to filter out the broadcast frequencies.

    Also, many of the dongles are missing the static protection diodes and building and attaching one of these can quite easily break your dongle.

  3. The site seems to be hackadaydotted and it’s down. Anyone has a cache copy?

    Maybe i’ll try tomorrow. I bought one of this dongles yesterday from china (dx SKU 92096). It’s just like the one in the youtube videos.

    Excelent work. For Amazed, can you explain how are this static diodes connected. I would like to build this antenna and try it.

    Here is another link that might be useful to those interested in trying to get the noaa satellites with this dongle:

    http://www.qsl.net/l/lu7did/docs/NOAA/Antena_QFH_LU2HAM.pdf

    1. The helical is a tough design (IMHO) to get right to use with NOAA birds. I never could get all the nulls out of the signal during a pass.

      I ended up doing just as well with a J-pole tuned to 137.5Mhz.

    2. I think Amazed meant an RF limiter when he says static protection diodes. RF limiters for wideband reception are usually implemented using PIN diodes. Small signal diodes like 1N914 (US) or 1N4148 (EU) are not useful because they have too much parasitic capacitance (<4pF) and they create unwanted inter-modulation products. The Avago website has several application notes pertaining limiters – look for AN1050, AN5438 and AN5443.

  4. Hadn’t thought about aircraft transponders (what software and freq do you use to translate the output, anyway?)… but I personally will be using mine to look for radiosondes on 1680MHz.

      1. As you can see in fig. 4 of the aforementioned document, the discone’s beam is ‘lifted’ (Brewster angle) in the elevation plane (same as other ground-plane verticals). I think it is for this reason, professional aerial makers like Agilent and EMCO, prefer to market the bi-conical variant.

  5. That antenna is vertically polarized. He may be better served building something with circular polarization. As well, something directional could be very useful.

    A good combination of the two would be a cross-yagi.

  6. this software defined radio, its like the police/radio scanner? could it listen to radio and tune in to the local trunking systems I get with my radio?

    1. Yes, the government trunking still uses narrow band FM in my area at about 160MHz. I can get the police, ambulance and other services loud and clear with the RTLSDR dongle and the HDSDR program in Windows.

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