Another SDRTrunk update

So, I posted a while ago about my SDRTrunk setup using a USB hub and a couple RTL-SDR sticks. This setup worked, but I wanted it to be more capable, so I bought 4 new RTL-SDR sticks to set up something more permanent.

Since I was planning ahead, I picked up four 8″ MCX to type F cables (ebay is great for wierd stuff like this) because I had planned on using a cable TV splitter to connect a single antenna to all four USB sticks.

Once the waiting game was over, and I had all the parts, I plugged the new USB Sticks into the hub I had been using – annnnd…. no luck. A USB1.1 or USB2.0 hub just can’t handle the throughput of 4 receivers simultaneously. Crap.

I went shopping online to see what I could find locally. I wanted something to sit flat on the table and hold the USB sticks – and it had to be USB 3.0. Best Buy had one for ~$30 that fit the bill. Great – I just doubled the cost of the scanner.

On the plus side – this setup worked well, as long as I set the gain on each stick up a bit to overcome a crummy antenna and the 6-12 dB of loss to each port. The down side is that that gain generated a lot of heat in each USB Stick – I’m not sure if it would damage them, but I didn’t want to find out.

I had 2 options…. I could find a way to cool the sticks, or decrease the tuner gain, and boost antenna performance ahead of the splitter. The solution seemed to be a preamp ahead of the splitter – by decreasing gain on the sticks, and keeping them cooler without external cooling, I would increase reliability. Ebay to the rescue again – they have a whole host 5V high gain (40 dB) wideband (2 MHZ – 4 GHz) preamps.

One example of an LNA

The cool part about it being a 5V device is that I could power it from an extra USB port on the hub. No need for external power. I did end up with an 8 port USB hub, so I had a few extra ports for power or expansion. Maybe a low profile USB stick in the future to store software.

With the gain on each of the USB Sticks around 10 – 20%, the control channel for the local trunked system was MUCH more stabile.

I still have an enclosure in mind for the system, but as it stands, I have 4 independent receivers, a single antenna, and no issues with heat…. and the whole system is easily powered from a standard USB port. Now… if only the local trunked system didn’t encrypt all the interesting stuff…

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