Software Defined Radio (SDR)

[MarkInTampa]

If you haven't played around with it yet, I've been kinda addicted to the websdr.org website. Listen to all sorts of HF, VHF and UHF in real time from receivers all around the world over the web. It's a bit of a learning curve but it's fun.

So I picked up a USB SDR dongle for around $50 a few days ago and hooked it up to my spare GMRS antenna. The antenna doesn't do HF at all but does seem to work ok on the VHF and UHF bands for the most part. It has also been a bit of a learning curve but getting I'm getting there, it's only been a few days. It takes a bit to figure out what kind of signals you are looking at on the waterfall. At the moment I'm just looking for normal FM repeaters but with software plugins you can decode DMR, Packet and all sorts of other signal types. I can also have it set to record audio only when the squelch is broke. Cool for recording your local GMRS repeater 24hrs a day if you want.

Anybody else play with SDR?

 

[SteveShannon]

50 minutes ago, markskjerve said:

If you haven't played around with it yet, I've been kinda addicted to the websdr.org website. Listen to all sorts of HF, VHF and UHF in real time from receivers all around the world over the web. It's a bit of a learning curve but it's fun.

So I picked up a USB SDR dongle for around $50 a few days ago and hooked it up to my spare GMRS antenna. The antenna doesn't do HF at all but does seem to work ok on the VHF and UHF bands for the most part. It has also been a bit of a learning curve but getting I'm getting there, it's only been a few days. It takes a bit to figure out what kind of signals you are looking at on the waterfall. At the moment I'm just looking for normal FM repeaters but with software plugins you can decode DMR, Packet and all sorts of other signal types. I can also have it set to record audio only when the squelch is broke. Cool for recording your local GMRS repeater 24hrs a day if you want.

Anybody else play with SDR?

 

I’ve scratched the surface, but that’s all. I bought one of the dongles also. I’m sure it isn’t the quality of my Yaesu transceiver, but for something the size of my index finger it’s amazing!

[gortex2]

Have a dozen of them. Monitor multiple P25 trunked systems with mine as well as ADSB Recevier and APRS IGate. I prefer Airspy but the cheap ones on amazon seem to work well for APRS and ADS. I use quality antenna systems on all of them and not the packages stuff that comes. On my APRS I actually run a pass filter to keep the other VHF stuff at home out of the receiver. 

[MichaelLAX]

There are also Web-SDRs just waiting for you to listen to them online.

[MarkInTampa]

On 11/30/2022 at 7:34 AM, gortex2 said:

Have a dozen of them. Monitor multiple P25 trunked systems with mine as well as ADSB Recevier and APRS IGate. I prefer Airspy but the cheap ones on amazon seem to work well for APRS and ADS. I use quality antenna systems on all of them and not the packages stuff that comes. On my APRS I actually run a pass filter to keep the other VHF stuff at home out of the receiver. 

Do you have any experience with the Airspy HF+? I know the Realtek based dongle I have currently is ok for VHF and UHF but sucks at HF. Right now if I try and listen to HF off my dongle (DX-Patrol) off a 35ft long wire for the most part all I get are harmonics from a AM broadcast station playing Glen Beck shows on all bands.  I'm getting ready to put up a 35ft mast for my GMRS antenna and something like a EndFedz SWL end fed half wave while I'm at it and want a decent HF SDR receiver to go along with it. Use would be 50/50 between shortwave listening and ham band listening.

If you have any advice on another dilemma... My new mast is 35ft and want to run the HF end fed dipole from my mast to my shed, a distance available of 85ft. The EndFedz antenna is 45ft so it would be no problem. Also thinking of a EndFedz 40 meter that is 74ft would work as well. If I run it this way I'll be paralleling power lines that are 30ft away (see picture). I'm in central Florida and the house and antenna would be positioned from north to south. My biggest concern is if I'll be picking up a ton of noise because of the proximity to the power lines. I can run the antenna east/west but that would probably rule out a 74ft antenna. Any thoughts?

 

[gortex2]

I personally do not listen to any HF on an SDR. With the limited filtering I can't imagine they are that good. 

 

[kidphc]

Actually, with my crappy antennas the sdr hears better then my ft991a. Plus displays more on the waterfall. Since atleast with the sdr (using adr console). I can zoom in faster and more then the radio.

You can hear on the sdr and transmit on the radio. Doesn't mean they will ever hear me, again crappy antennas.

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[WRWR489]

Use DSD plus fastlane with your dongle for the best public service you can get, 35 Bucks for lifetime and it handles simulcast better than any of my scanners. 10 Bucks for a year if you want to try it.

[kidphc]

Use DSD plus fastlane with your dongle for the best public service you can get, 35 Bucks for lifetime and it handles simulcast better than any of my scanners. 10 Bucks for a year if you want to try it.

Awesome. Will look into it.

Using an unification g5 pager, lent from a friend on long term renta.

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[MarkInTampa]

On 4/8/2023 at 5:24 PM, WRWR489 said:

Use DSD plus fastlane with your dongle for the best public service you can get, 35 Bucks for lifetime and it handles simulcast better than any of my scanners. 10 Bucks for a year if you want to try it.

Since I've started this thread I've switched over to SDR# with Simple APCO (P25) and Simple DMR free plugins. Doesn't do simulcast but works great for monitoring un-encrypted business and ham DMR and P25 with a simple point and click on the signal. Keep meaning to try out Fastlane, just haven't had a chance.

[WSAA635]

I've played around with SDR using a RTL2832U dongle that I got from the Hak5 shop years ago and Gqrx on my Linux Box. I think my main drawback is not having a very good antenna. Other than that they are a lot of fun to play around with.  In fact, pulling out the SDR and trying to listen to stuff got me thinking about Amateur Radio which lead to GMRS a couple weeks ago and here I am now, LOL.

[WSAQ406]

I do good hearing Fire&EMS, but I can't seem to get GMRS. I got in to this to look at the traffic going throw my club repeater. But when I go to our frequency both on in put and out put I do not see anything. I tried NFM and WFM. I currently using SDR++. SDR-Sharp performed the same. I can only think I'm over looking a setting some where. 

Any suggestions?

[WSAA254]

I am currently using a SDR play with there SDR connect software.  I also have a gmrs setup with a switch between the two "radios".  It works well.  If I am working with the SDR I always go the the freq that the repeater is transmitting (462.***).  I have notice between the gmrs receiver and the sdr, that the quality of the reception of the gmrs is better.  This makes sense since its a superhet receiver.  The big difference if voice quality, and the gmrs radio has less static.  On your sdr make sure that the squelch is reasonable, you should see some activity on the waterfall.  Also try to play with the sampling rate, this may provide a better resolution.  Best of luck, the SDR stuff can be like drinking from a fire hydrant.   A lot of time the gmrs is kind of quiet, so see if there is  a known network traffic at somepoint.  All info is good info...  regards

[ssugarek1956]

I tried a random wire antenna connected through an UNUN to the SDR, and was blown away by the amount of increased stations it picked up. They only minus is a heavy 60Hz  to 120Hz  noise floor on the AM frequencies. The higher frequencies work great!

[WSAA254]

I should have mentioned antennas, my apologys.   I use the compactenna scan-III that is only about 10ft in the air.   The response is fairly good from 100mhz and up,  HF is not that great, although I can get better response at night.  I am sure there are much better antenna setups for HF stuff, but for my purpose this works ok..  I also use the same antenna for GMRS, with very good results.  Having an outside antenna makes all the difference in the world, anything you do outside will beat any little antenna they give you for inside application.  Best of luck..   all info is good info...   regards

[PACNWComms]

Have been using SDR's for a long while now, as well as software defined military radios. Wat made me break into the amateur side was finding out that Icom was supplying the first few "black box" receivers for the Predator (RQ-1, surveillance only, no Hellfire missiles back then) fleet. The civilian versions of the PCR-1000 had some issues, like being able to be opened up like those purchased for military/export use.

Now, like others have mentioned, I monitor my own networks with SDR receivers, and the HackRF is better than the cheaper USB versions, but it is so easy to just carry along a small USB/antenna and listen to what is nearby. For portability, I used a re-purposed Hinge Health Amazon Fire tablet and SDR# with USB dongle. For the money, great combination and makes the tablet useful again. My newest "scanner" would be a Uniden BCT-15X (possibly a handheld Uniden floating around somewhere), as the SDR USB sticks are on every older computer now, doing something at some point. 

[PACNWComms]

Monitoring analog UHF near my work right now. Always busy on UHF, and a lot of DTR series Motorola radios in use on default TalkGroups as well (they were sold to many on the local river to get away from the UHF users that proliferate the area). Lots of vessel crews, barge workers, construction and flaggers on DTR, and those that did not get that memo, still using cheap UHF blister pack radios. 

[aj22185]

On 11/30/2022 at 7:34 AM, gortex2 said:

Have a dozen of them. Monitor multiple P25 trunked systems with mine as well as ADSB Recevier and APRS IGate. I prefer Airspy but the cheap ones on amazon seem to work well for APRS and ADS. I use quality antenna systems on all of them and not the packages stuff that comes. On my APRS I actually run a pass filter to keep the other VHF stuff at home out of the receiver. 

Do you have individual antennas for each, or some kind of splitter? I can think of multiple applications for just one antenna and multiple receivers. It just seems like there would be too much signal loss.

[gortex2]

I use a multicoupler on soime but the basic ones just use a T. If you have really good signal  that works ok. The ones with marginal coverage go thru the splitters.

 

[GMRSJohn]

The websites and all this are fascinating. But I have no idea what this is or what the purpose is… if any of yall would like to educate a new guy. 

[SteveShannon]

21 minutes ago, GMRSJohn said:

The websites and all this are fascinating. But I have no idea what this is or what the purpose is… if any of yall would like to educate a new guy. 

It’s a radio receiver that’s controlled by your computer.  It’s extremely flexible, allowing you to listen in on almost any mode over an extremely wide range of frequencies. Because it’s controlled by your computer you can manipulate the received signal and view it however you’d like.

[GMRSJohn]

5 minutes ago, SteveShannon said:

It’s a radio receiver that’s controlled by your computer.  It’s extremely flexible, allowing you to listen in on almost any mode over an extremely wide range of frequencies. Because it’s controlled by your computer you can manipulate the received signal and view it however you’d like.

Awesome! I enjoy tinkering around with stuff. Sounds like something to try.

[kidphc]

As well as people like me whom are more visual then auditory. I find it easier to identify signals and their types visually than listening to the signals.

Doesn't hurt that the entry cost for it are as minumum as you want. So it is worth a try. Usually, a cheap RTSLDR dongle is under $80. The software for basic usage is free or minimal in cost. Tons of articles on setting up antennas. There is very little that is as cheap with the same flexibility and versatility in the radio world.

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[WRYS709]

Living in an area that has high QRM, I find it helpful to listen on a WebSDR, such as the Half Moon Bay, CA WebSDR or even the Northern Utah WebSDR.

Of course, these are focused mostly on the Ham Bands and in some cases the International Shortwave Bands and not on GMRS so much.

There is even a Windows program, CATSync, that will actually control a transceiver such as to allow more easily listening on the WebSDR, while transmitting on the transceiver (and again, of course this is for Ham Radio).

[dosw]

On 12/2/2024 at 7:46 AM, GMRSJohn said:

The websites and all this are fascinating. But I have no idea what this is or what the purpose is… if any of yall would like to educate a new guy. 

This is a great question (except it wasn't asked as a question), and great topic. SDRs are somewhat game-changing for amateur radio, even for GMRS.

Start with a traditional scanner. In a traditional scanner such as a Uniden or old Radio Shack scanner, the scanner walks step by step through a frequency range (at a predetermined step size), or through a bank of channels. A good scanner will run through 20-50 steps or channels per second. This is pretty fast, though it means a scanner will hit all GMRS channels in about 1/3rd to 1 second.

Now consider a 2-way radio like a Baofeng. Such a radio does have both a VFO and channelized scan mode, where you can scan frequency steps, or channels. In either mode, it will run through 2.5-5 steps or channels per second. I think Baofeng states the RM series (UV-5G Plus, for example) will step through 3 per second. Very slow. It would take four to five seconds to get through all GMRS channels.

Scanners and 2-way radios can be good at filtering in only those frequencies they're looking at (good selectivity) and can have pretty good sensitivity for those frequencies they're receiving.

An SDR works differently. You select a band, about 2.4MHz wide for the RTL-SDRv4 ($40) or wider for some more expensive models, and the SDR will take 44k samples per second of that entire band's RF spectrum. An SDR doesn't have particularly good sensitivity -- often you need linear amplifiers or band amplifiers, and they don't have great selectivity because they're designed to "hear everything." Band reject filters are commonly added to reject FM Broadcast, AM Broadcast, or band-pass filters to only allow through specific bands. But an SDR allows you to do a lot of neat things. And its view of a swath of bandwidth is instantaneous. No stepping through channels. It's an instant, continuous snapshot in realtime of a 2.4MHz wide swath of bandwidth.

• As a scanner, an SDR (or a few of them) can work to follow trunked systems, to scan frequency bands at any step (or really any frequency, not only by step), instantly.
  • SDRTrunk is good software for this.
  • SDR-based scanning, the scanner picks the strongest signal, not the first signal in sequence
  • Scanning bands larger than 2.4MHz requires more than one SDR
• As a spectrum analyzer
  • You get to watch the spectrum, watch the waterfall
  • Record the raw spectrum in realtime
  • Adjust gain / attenuation
  • Add attenuators in front of the SDR so that you can direct-connect a radio to it and observe its spurious emissions and its power output (calculations required)
  • Verify your radios are centered on the frequency they're supposed to be transmitting on.
• As a radio for listening
  • It's really easy to watch the waterfall, and soon you'll start recognizing FM, USB, LSB, AM, WFM, CW, even digital mode transmissions in the waterfall. This makes it REALLY easy to point an SDR at a swath of 20m amateur, and then at just a click or two you're listening to someone in another country DXing.
  • It's really easy to focus on the repeater swath of 2m and start clicking and listening.
  • It's easy to use an SDR to verify you're receiving a new radio, or to set it to VOX record mode so that you can drive around and let the SDR record your signal. Great way for checking propagation.
• Lots of other hobbies
  • Following the ISS repeater and ISS amateur signal is really cool. You can SEE the doppler shift in effect as you listen. You can see the repeater on ISS coming in a few kHz high, and then as it passes overhead and begins to depart, you see the signal coming a few kHz low. And you can easily listen to it just by clicking through the Doppler shift. With a 2-way you sort of have to program it in and step down through the shift blindly.
  • You can use an SDR to pull in signals from digital (transmitting) thermometers and weather stations, with a down-verter (or an SDR that handles 2.4GHz range) pick up digital modes like wireless keyboards and mice, Bluetooth, Wifi.... these are pretty advanced projects. I haven't dabbled in them at all.

You can get into it pretty inexpensively; you need an SDR ($40 for an RTL-SDRv4 which handles 500kHz to 1.76GHz), an antenna for the bands you wish to listen to, and later on you can add accessories such as more SDRs, or a HamItUp (up-verter for improved HF listening), HamItDown (down-verter for 1.9GHz and above), band reject filters, linear amplifiers, and so on. Software is free. I mostly use SDRTrunk, and SDR++.

You can also get your feet wet by tinkering with other peoples' SDRs by visiting http://www.websdr.org/ . That's mostly useful for HF.