clockworkpi

RTL-SDR module/mounting - general thread

The title says it all; I’m sure I’m not the only one that wants to be able to have their SDR handy in the field. This weekend I set about to do it, and I’ve learned a few lessons along the way. To put it bluntly: I don’t recommend anyone else try this without more forethought than I put in (none). I can somewhat pick up some of the stronger local FM stations when outside; granted, this is with the first collapsible antenna I had at hand, but I would still expect better reception. To put it bluntly, don’t forget to check your gain and bitrate settings like I did :upside_down_face:. Initially I had trouble picking up any signals, but once I tweaked my device settings in gqrx things started coming through decently (although practical testing still awaits)

(reception indoors of a broadcast FM tower a mile away, after my setting tweaks)

Since the RTL stick can draw a lot of power, I didn’t want to leave it connected when not in use, so I wired in a little switch on the VCC pin of the USB connection

I took a small plastic container, and hand-cut it to size with a razor blade; after enough trimming, it fits snugly over the mounting posts (I was also able to repurpose part of the side of the container, making that nice little lip to mount the SMA connector/switch on)

In order to make this relatively reversible, I used Dupont pins for all the connections; I originally had plans to fit a USB hub in as well, but couldn’t fit it. It did test without any loss of write speed to a USB stick though, so in the future it should make for a decent internal USB connection.

A note on fit: it’s snug. I had to compress the housing of the SDR with pliers (as seen below), and even then I had to trim some of the plastic away from the back half of the devterm case. I only kept the case on as a heatsink, and would recommend anyone else trying this either delid the stick, or trim off the upper rear portion of the metal case.

In any case, hopefully whoever attempts this next can learn from some of my mistakes. I’m going to do some more testing to see if I can improve the reception, and would love suggestions on how to do so

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Very nice! I hope to see some more updates on this, it’s definitely an interesting modification of the devterm. Do you think the antenna alone is responsible for the bad reception?

Thanks! It’s too early to tell, but I’m worried about a few things. I’m partially concerned with the amp draw; in the past, I’ve messed around with a few battery powered Pis and have gotten undervoltage warnings when plugging in a SDR. I used 18ga stranded Cat5e wire for the connections, and from what I read I’m juuuuust barely in spec for max amps.

I’m also wondering if the screen/rest of the unit might be causing some EMI, although the waterfall diagram in gqrx doesn’t seem to support that (to my untrained eye, at least). My dad pointed out that the ground plane might be the problem; the way i have it installed it’s entirely possible, i used a nut and lock washer to secure the SMA shaft to the mounting plate (along with a SMA crush washer I had laying around in between the SDR body and mounting lip). I’m thinking in this configuration there’s much less contact area with the metal body; I’m planning on installing a jumper wire from the SDR body to the SMA shaft (to test, at least).

The only thing I’m not concerned with is thermal drift. I used two tubes of artic silver thermal paste inside the SDR body, since I’ve had heat issues in the past.

Any pointers in this area would be graciously welcomed; I’m studying for my HAM technician license and am still having trouble grasping the finer points of antennas.

EDIT
played around in gqrx a bit, and increased the bitrate to 2.4mb/s and tweaked the gain; FM reception is much better now. It’s still not good enough for Stereo, but with Mono demodulation I can reliably pick up the FM tower a mile away, as well as the low-power NPR tower across town; editing my OP to reflect this

Instead of compressing the housing, how hard could it be to dehouse it? Actually I can check if I remember, as I have the same module and also can´t wait to get some signals on the go.

Hmm maybe those L shaped USB adapters would make it be outside the devterm but still snug enough

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It’s not hard at all to dehouse; I took the stick out several times for the cutting/mounting work (shot a self-tapping screw through the plastic plate and through the metal body, then filed off until it didn’t contact the board). If you do, the only thing to keep in mind is the thermal paste it comes from the factory with; when I took mine out a lot of the material came out along with it, so I’d recommend something to replace it with.

As far as the actual disassembly goes, there’s just two small Phillips screws on each face of the case; you just have to unscrew those, plus the retaining nut on the antenna shaft

This is a cool first attempt at this. I have the same SDR and am totally planning to shove it in my devterm. I got my technician license last summer, and bought the RTL-SDR radio on a whim but TBH I’ve barely played with it since.

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It looks like ground plane is a big part of the problem! I connected a piece of 14ga ground wire to a large crimp-on lug to the antenna shaft, then a smaller factory lug to one of the mounting screws of the SDR body (an imperfect process to say the least). Signal indoors is now good enough to use Stereo FM demod, and the waterfall looks cleaner to me.

I will say, I had to turn the bandwidth down to around 1.24mb/s, as much higher and the display would start to get laggy (I’m using the raspberry pi core)


Reception of my reference station in stereo. the stock speakers are way better than I thought they’d be, honestly quite listenable


Top view of the new addition, I didn’t plan very well so my nice model paint I/O markings are mostly covered

While working on this I realized everything would be infinitely easier if there was a 3d-printed bracket you could simply slide a stock SDR in and out of into a USB socket; I (currently) lack the skills to make it happen, but hope to make a much more reproducible v2 someday

I always use a Power Hat and feed the Power hat with close to 12 volts … I have a pi in the box that is in a Harbor Freight case - the 20 amp hour LipoFe is in a separate case… so it’s bulky but it won’t run the battery down…

Interesting, you then power the SDR through the PowerHat? I like your build, it reminds me of (a better version of) my cigar box Pi