Category: Linux

Jim’s experience with the Android tablet SDR was very similar to mine. But he used a “Ham It Up” up converter ahead of the RTL-SDR while I used an RTL-SDR modified for direct sampling of HF. I built a pre-amp/pre-selector stage for mine. On my Android Tablet (50 bucks via Amazon) I found the touch screen to be kind of clunky — it was hard to get the receive passband lined up with the incoming signal. The touch screen was not nearly as smooth as the one on my IPhone. A Bluetooth mouse solved that problem.

Like Jim, I am using SDRtouch from the GooglePlay. I’ll have to follow his lead and try Droid RTTY and PSK.

My reaction to the completed project was also similar to Jim’s: He writes that this is, “The first and last of my SDR adventures. This is just not the same as scratch building!” Indeed, it is not. But still, for very little money you end up with a pretty impressive receive capability, and you get some valuable insight into an intriguing method of receiving radio signals. And you don’t have to mess with Linux!

I have a question for the SDR gurus: With direct sampling, we are just running an ADC at RF. So we no longer need an I-Q front end to take care of the image problem we had when we were running soundcard-based SDRs, right? But I sometimes I hear that even with direct sampling systems, there is a digital generation of I and Q signals. Why would you need I and Q if you are just digitizing the incoming passband, multiplexing it, and sending it to the software?

Hi Guys

OK, so I am a little (A LOT) behind you guys in my bench work. Several unfinished projects are waiting in the wings. But I thought I would also dabble in Software Defines Radios. Thought I would go the Raspberry Pi route as Pete did. Then I woke up and sided with Bill. I don’t want to learn Linux!!

For about the same price as a Pi-3 and a 7” screen I bought one of Bills Android tablets and I found on eBay an estate sale that had a bag of NuElec parts. The RTL dongle, a Ham it Up vs. 3, and several cables, all unused. Last but not least I bought an Android ‘On the Go’ USB cable adapter.
I removed the LED and UV diode for the remote to drop the current some. Then tapped some power off the USB connector and ran it out to the Ham it Up. A few holes and some double sided carpet tape and ‘Bobs Your Uncle”. I added an enable switch to the up converter for the noise source but still waiting for the SMA connector to come in. Then I’ll see what that can do as a poor man’s spectrum analyzer for filter design.

I found several interesting apps on GooglePlay. Besides the SDRTouch program I downloaded Droid PSK and RTTY. Also the RFCorb client that allows you to connect to hundreds of remote stations around the world. That I may have to spend some time exploring but not really part of this build.
The Up Converter fired right up and after tuning around some I jumped to 14.070, the PSK hot spot. The tablet truly does multitask. I left SDRTouch running and opened Droid PSK. A waterfall full of signals jumped up and I was easily copying stations on the East coast and Canada.

All this running on the USB power from the tablet! How cool is that. After about 45 minutes or so the battery was about half. The only problem that I may have to address is that the tablet and/or the Ham it Up gets pretty warm and my carpet tape lets go and things fall apart. HA. Haven’t ran it long enough yet to see what else the heat might effect.

So that was fun and I will be playing with it some more. I have coffee on Mondays with some ham buddy’s. When I showed them the PopCorn radio they jibbed about it not being battery powered.

Well Monday is coming!! HA

Jim WA7HRG

Earlier this week I shocked Pete Juliano by telling him that I was taking a break from my normal analog, discrete component, no-chips mode of construction so that I could put together a Raspberry Pi-based SDR receiver. Even from 3000 miles away, his astonishment was clearly perceptible. He seemed briefly disoriented by it. I’m sure some of you may have a similar reaction.

I’d been lured in by that video of the Raspberry Pi RTL-SDR receiver with the very cool touch screen display. It has a waterfall! And a touch screen! How could I resist?

I went to Amazon, but there I discovered that that attractive display is not exactly cheap. And maybe I’d need a new Raspberry Pi. At this point, in search of economy and convenience, I began rummaging through my digital junk box. There I found a Rasp Pi Model B. And an old computer monitor. This will be easy, I thought. Just get some SDR code into that Pi, hook up the RTL-SDR dongle and Bob’s my uncle, right?

Not so fast. I quickly began to run into daunting digital obstacles. Sure, the Raspberry Pi fired right up and filled the computer display with lines of code. But it was all Linux. Yuck. Sorry Linux fans, but for some of us mere mortals, Linux is a weird opaque world in which every little thing is somehow a lot harder.

I also began to suspect that my 2013 Model B might be sort of a Model T in the Rasp Pi world. It might not be up to the computing task.

And finally, as I poked around the internet, I began to conclude that the Raspberry Pi software for SDR is not quite done yet. All the sites seemed to have the word “experimental” in there. And lots of “I’m pulling my hair out” comments Maybe I’m wrong, but maybe we just need to give this more time.

Let me ask the distinguished group some questions:

Is my Model B really useless for SDR purposes, even if I don’t need all the bells and whistles?

Is there an SDR program that can be easily placed in a Raspberry Pi by someone who has NOT mastered the mysteries of Linux?

For now, I have cleared the raspberries from the bench and am back to working on HDR stuff.