rtl-sdr and similar rf devices (1 Viewer)

[Tekamthi]

I've recently swapped out my cheapo baofeng 2-way (i bought for $30 off CL) for an rtl-sdr dongle (i also bought for $30 off CL) that connects to my phone while travelling... i find having an RF device useful primarily for listening to the rail channels and figuring out wtf the train i'm on is stopping, alleviating my anxiety somewhat when this occurs. Sometimes it helps me decide which one to get on, too. As a bonus, its something interesting to listen to in strange towns i've never been to, without hitting wifi or data charges etc.

Its all still a little fresh, and I'm not sure I love the change, as this new setup is a little more fragile and less instant than just grabbing the old drop-proof/water-proof radio i used, but on the upside, it cuts weight and bulk of adapters and charging cables etc, and seems to open up some additional capabilities, albeit non-essential.

On my wishlist, i'd love to grab something with a wider frequency range (hackrf one?), but imagine this would be a little silly to travel with, and is beyond my budget anyway ($30 vs $300). Have any of my fellow tech nerd travellers tried anything similar? Have any pros/cons to share? Or can recommend specific RF devices that are better suited than others for travel?

 

[ali]

What antenna are you using, or can you use the dongle without an antenna?

 

[Tekamthi]

I've been using the chrome-finished telescopic antenna mast that came with the bundle... its about 20cm when collapsed and close to a meter fully extended... like a single ear off the old tv rabbit-ears from a few decades ago. Its very light and easily packed.. maybe 0.5cm in diameter. The antenna base is a bit of a nuisance, but altogether still easier to carry around the full radio handset i was using for these things previously, and I've threaded the cable strategically through my pack, just connecting the dongle and extending the antenna when i need it... setup this way its reminiscent of a WW2 backpack radio operator, though my pack is mostly filled with other non-radio stuff.

I didn't order it from this vendor directly, but it is very similar to the package listed here: Nooelec - Nooelec NESDR SMArt v4 Bundle - Premium RTL-SDR w/ Aluminum Enclosure, 0.5PPM TCXO, SMA Input & 3 Antennas. RTL2832U & R820T2-Based - https://www.nooelec.com/store/nesdr-smart.html

I haven't had a lot of time to look into what's best, and though I had become reasonably proficient with my baofeng, I am still a bit of an RF noob. This antenna was just the most convenient to get started, and as I understand things, the variable length is better-suited to multiple frequencies, whereas the fixed-length options are best for specific frequencies. The signal on some channels is less than stellar, but works okay for getting an idea of what's going on around me anyway. The baofeng i had with its default antenna seemed to work a little better tbh, but just barely.

For anyone else considering doing the same, note that my phone specifically required a usb 3.0 otg adapter (another CL purchase, $10) in order to recognize the dongle -- the more common usb 2.0 otg adapters just didn't work at all, but that may just be my phone, ymmv. Also should note there is no transmit, compared to a 2-way radio, but i never transmit when travelling anyway.

 

[ali]

Thanks for posting all this info. I don't have much useful to add, but i have been pondering picking up a scanner so it's cool to find there is a more "open source" solution than going with a Baofeng or Uniden.

The size of the dongle is really great, as is being able to multi-purpose your existing smartphone. Having used some other USB dongles on my phone before, i think the challenge might be using it when your battery is low. Is there some kind of splitter cable you can use to plug your phone into a power pack and also leave the OTG adapter for the radio?

Putting the antenna on your pack seems like a good idea, since those things can get huge. I don't know much about radio either. From what I've gathered online the whip antenna formula is something like 300/x where x is the MHz. So picking up 160MHz means 300/160 =~ 1.8m antenna. Apparently you can quarter it to still get decent reception, so 45cm might work. Still pretty long, eh.

On waterproofing: i've noticed a lot of bike/moped couriers using a special waterproof bag for their phone. Most of them could fit a dongle as well (although you would still have the antenna cable coming out). One of those is on my list to buy before the next time i'm out traveling.

 

[Tekamthi]

yeah your knowledge is roughly where I'm at, from the sounds of it. I can't really learn about these things just by sitting and reading though, so now that I have one to experiment with I'll probably increase my skills via trial and error.

When I next settle in an apartment or room of some kind for an extended period with a laptop, i'll experiment a bunch, and hopefully by next summer have this setup well refined. From what i've heard even just a flexible cable of the right type and length could serve as an antenna when extended out straight... possibly a small array of these improvised together just right might be able to pick up a lot of signals. I'm thinking i could keep a coil of whatever antenna cable and then mount my antenna(s) in a tree or on a handheld branch for good effect.. maybe I'm dreaming though

As for waterproof, I'm gonna try a 3 ft usb extender cable that runs into my pack, and keeping the dongle tucked in there permanently (it does get a little warm after being on for a while, mind you). That just leaves the phone with the cable connected to worry about.

Battery consumption certainly is higher with this thing running, but it hasn't had drastic effect as I mostly use it in brief stints. I've heard that some otg adapters have an extra port built-in for power, but I could not find any of the usb 3.0 variety that i needed. There were a few usb 2.0 options with this feature built-in. I imagine a powered usb hub could do the job too, but now we're talking about adding a lot of extras...