Tagged: TCXO

GNSS-SDRLIB: Real Time GPS Positioning with RTL-SDR

Over on YouTube user taroz1461 has posted a video showing an RTL-SDR getting a real time GPS location fix using his GNSS-SDRLIB software package. Taroz1461 used an RTL-SDR modified with a temperature controlled oscillator (TCXO) to improve the frequency stability of the dongle.

In the video description he writes that GNSS-SDRLIB will soon have RTL-SDR support in the next update.

GNSS-SDRLIB: Real-time positioning with RTL-SDR (DVB-T Dongle)

TCXO RTL-SDR Soon Available Internationally

Andy, programmer of the RTL1090 ADSB decoder software, and owner of the 1090Mhz webstore has notified us that he will soon be selling to international buyers the TCXO RTL-SDR dongle modified by Nobu Saitou. We recently featured a story about the TCXO RTL-SDR and also gave it a review on this blog. From the review we concluded that the TCXO RTL-SDR is a good product and will be useful for applications that need good frequency accuracy and stability.

Interested buyers can look for the contact us link on the 1090MHz shop TCXO page description to contact Andy for a reservation and notification on when the TCXO RTL-SDR becomes available for sale. Andy expects the first batch of TCXO RTL-SDRs to arrive in January.

Review of the TCXO Modified RTL-SDR Dongle

A few days ago we had a post about a modified RTL-SDR dongle for sale which has the low quality 28.8 MHz oscillator replaced with a high quality 28.8 MHz temperature controlled oscillator.

Nobu Saitou, the creator of these dongles has sent us a sample to review. On the inside of the dongle the 28.8 MHz crystal has been removed, and replaced with a 28.8 MHz temperature controlled oscillator. The desoldering of the old oscillator and soldering of the new TCXO appears to be neatly and professionally done.

TCXO Photo
TCXO RTL-SDR Dongle Photo

After plugging in the dongle and firing up SDR#, we tuned to a known trunking control channel at 152.850 MHz and measured the frequency offset. It turns out that with the TCXO no frequency correction was required at all. I believe that from Nobu’s blog post, this oscillator can have a max deviation of +-2 PPM, which is incredibly small.

TCXO Dongle with Zero PPM correction required
TCXO Dongle with Zero PPM correction required

We compared this result to a standard dongle with the original oscillator and found the frequency offset required to be 44 PPM.

Standard Dongle Frequency Offset
Standard Dongle Frequency Offset

As the dongle heats up from use, the oscillator will experience thermal drift, causing the frequency offset to change. The TCXO should be immune to this problem due to it’s temperature compensation circuitry. To test the temperature compensation, we cooled both a TCXO dongle and a standard dongle down in a refrigerator first to simulate cool climate conditions. We then measured the change in PPM offset after 30 minutes of dongle operation. As expected, the TCXO had almost zero drift after 30 minutes (<<1 PPM), whereas the standard dongle had a drift of about 6-7 PPM (approx. 1 KHz drift).

TCXO Oscillator: Frequency drift after 30 minutes
TCXO Oscillator: Frequency drift after 30 minutes
Standard Oscillator: Frequency drift after 30 minutes
Standard Oscillator: Frequency drift after 30 minutes

The results of this simple test show that the TCXO used in these modified dongles is an accurate and stable frequency source as was expected. If you want one of these dongles they are for sale at the creators Amazon Store (direct link to TCXO product here). Currently it seems that Saitou’s products cannot be sent abroad outside of Japan, but he recommends this agent service for ordering internationally.

Edit: The TCXO can now be bought internationally from 1090mhz.com

Modified RTL-SDR with Temperature Controlled Oscillator (TCXO)

Nobu Saito, a Japanese RTL-SDR hardware developer has come out with a modified RTL-SDR which has a +-2PPM 28.8MHz Temperature Controller Oscillator (TCXO) instead of the standard 28.8 MHz stock oscillator. (Note this link is machine translated to English from Japanese).

Normally 28.8 MHz TCXO’s are difficult to find, but Nobu was able to find a source in Japan, and he is now selling on his Amazon Store (with international shipping) modified dongles.

The oscillator on the RTL-SDR is prone to thermal drift, which means that as the dongle heats up from use, the frequency you are tuned to may change over time. A TCXO compensates for differences in temperature, and thus keeps the frequency stable as the temperature changes. This is extremely useful for applications such as receiving GPS, Beacons, APT, HFDL, and for radio astronomy.

Nobu sells the modified dongle with TCXO on this page. We expect to receive a sample of his product soon and will write a review when we receive it.

Edit: Now available at the 1090 MHz webstore.