Over at RTL-SDR.com, I found out about a great new product that’s just come out for more precise SDR applications: a customized R820T-based stick with a high stability temperature compensated crystal oscillator (TCXO) in place of the stock crystal, giving an incredible 1ppm frequency accuracy.
A precision TCXO like this nearly eliminates frequency drift. The stock crystal on the dongles isn’t that accurate, which can cause your tuned frequency to migrate around a bit. That’s not good for reception, especially if you’re trying to receive digital data or precisely time align multiple dongles like in a trunking or diversity application. RTL-SDR.com made these great recordings of the stability to illustrate the point:
On the left with a stock crystal, the dongle’s tuning wobbles around the center frequency. On the right with the TCXO, it’s dead stable.
You can pick your own up on eBay for $65 with free shipping. It’s a little more than a basic dongle, but given the cost of the custom part and the very precise surface mount re-work needed to make the swap, it’s quite reasonable. It’d work well with an upconverter, too.