Wanting to play with SDR

[james_s]

$329 *is* cheap for SDR, or it was until the insanely cheap RTL dongles appeared. Before those showed up on the scene $1k was considered cheap SDR, hence I never got into it until then. The reason the dongles are so cheap is that they're mass produced TV tuners intended for the consumer market. The SDR market is far more of a specialized niche.

Being able to transmit would be lots of fun, haven't needed it badly enough yet to justify the price though.

[Lord of nothing]

Sadly i found no software who would allow me to send something on a win pc.

[james_s]

Yeah a lot of that stuff seems to be Linux based. You can dual boot Linux on a Windows PC easily enough though.

[Lord of nothing]

I will try with an Virtual pc.
Paybe someone know how i can connect my Soundmodem to my CB?
https://www.eevblog.com/forum/rf-microwave/connect-a-soundmodem-with-my-cb-radio/

[Red Squirrel]

I finally got around to playing with this, I had the hardware and just kind of forgot about it.    For now I'm not using the upconverter, figured I'd play with it as is first.  Just using a basic antenna that came with an ADS-B receiver, I will experiment with different antennas over time.  Long wire is probably the easiest I would imagine.

I setup OpenWebRX.  One question though, and sounds stupid but can't find anything, how do I set the frequency range?  It defaults to about 143-145 Mhz.  I imagine there's a setting somewhere to set the range to something wider?

[Lord of nothing]

the most hardware support 2Mhz max.

[Red Squirrel]

Hmmm arn't some of these used for ADS-B?  That is 1090Mhz.

I found a setting center_freq which lets me change the frequency, but not sure how to change the range.  Some web SDRs go from 0-30Mhz for example. 

I'm not sure if it's my antenna or something else but when I set it to my local radio station I see it on the waterfall, but I don't hear anything. Just static.

[james_s]

The common USB tuner dongles cover from around 50MHz up to 2GHz. What software are you using? The entire FM broadcast band should be easily covered.

[stj]

Hmmm arn't some of these used for ADS-B?  That is 1090Mhz.

I found a setting center_freq which lets me change the frequency, but not sure how to change the range.  Some web SDRs go from 0-30Mhz for example. 

I'm not sure if it's my antenna or something else but when I set it to my local radio station I see it on the waterfall, but I don't hear anything. Just static.

i dont know what software your using,
but the one i played with you have buttons to select the decoding.
so you have to manually select AM,FM,FM-narrow,SSB etc.

[Red Squirrel]

Oh sorry thought I mentioned but didn't.  It's OpenWebRX.  In the config file I can set the centre frequency, but it then only displays like maybe 0.1Mhz on both sides.  I imagine there must be a setting somewhere to specify a larger range but can't find it.  I thought maybe the sample rate would affect it but it seems anything but default makes it really choppy.  Either lower or higher. 

Looks like a nice piece of software though, once I figure out how to use properly.


 
I'm not really picking up anything at this point, like that large area where I'm set to should be the local FM station but I only get static and the oddball slight sound of a voice or music, but that might just have to do with my antenna which is just a ballun with two pieces of wire sticking out hanging behind my server rack, not tuned or anything.  The server stuff probably generates lot of EMI.

Half the fun is going to be experimenting with different antenna types.   What I'll probably do is see if I can run coax to a location that's more convenient than my hot aisle then play with antennas there. 

 

[stj]

yes, when i got mine i learned real fast that i should have also got a BNC adapter at the same time!!
i think an outdoor wideband "scanner" antenna is probably a good investment.

[Red Squirrel]

Actually would Cable TV Coax work? I don't really know that much about impedance and all that but from what I understand you can only use certain impedance cable in certain applications.   I don't have cable TV anymore but I have coax running right to my server room from outside. I could put some BNC ends and a SMA to BNC adapter and then just buy a couple premade antennas to play with.  Probably easier and later on I can experiment with DIY once I understand more about the theory.  I do want to look at getting into ham radio and get licensed at some point, lots of reading to do though!   Figure playing with this is going to at least make me able to listen on some stuff and get started with the basics.

[james_s]

An outdoor antenna is not a bad idea, but I can easily pick up dozens of stations all across the FM broadcast band, as well as police, fire, business band, FRS radios, ADS-B, etc using just the crummy little antenna that comes with the dongles.

[Red Squirrel]

Yeah probably will experiment with indoor antenna first, just need to either buy a premade one or google some designs that are better than me sticking random pieces of wire in it.     What I find odd though is how the waterfall display has a very clear indication of something yet I only hear static.  Is that to be expected with a bad antenna?    If I unplug the antenna then I get no waterfall, so it's doing something.  I guess it's just picking up so much noise on top of the signal which is probably why I can't hear much.    I'm working now so I'll play with this again after Christmas time.   I also need to figure out why I get such a narrow range of frequencies, I presume that's a setting somewhere. 

[james_s]

You should be able to get a bunch of local FM broadcast stations with nothing more than a paperclip if the hardware and software is working correctly. A reasonably strong station will come in with nothing at all connected to the antenna socket. Focus on getting things working first, then look at antennas.

Did you try setting the tuner gain?

[Red Squirrel]

Hmmm I kind of thought so.  I built a rudimentary crystal radio using a sheet of foil and paper as the tuning capacitor and picked up the local FM station so not like it takes much.  Maybe there definitely is a problem then.  I set the gain to 0 which lets the tuner adjust itself.  I may have to play with different values.

Anything else worth looking at as well?


This is interesting:




Notice that anomaly in the middle, when it did that, I was able to hear the radio for a sec.    When I get around to it (at work now) I may move the entire setup upstairs away from the server rack just to rule out any kind of interference.  It is sitting on a shelf above the two network switches and wonder if it's picking up noise from all the ethernet cables or something.  Might be worth getting a small USB extension so I can put the dongle a bit away from the PI too just to try to eliminate possible issues.

[stj]

one thing worth pointing out is on Linux atleast, the hardware driver has variable gain.
i thought my setup was shit and hardly working till i found the gain control existed and was at about 10%!! jacked it to max and now find loads of stuff.

[Red Squirrel]

Yeah I played around with the gain.  I'm thinking I have a source of high noise though so I will need to play with the physical setup and move it completely once I'm done work just to rule out the server rack equipment being a source of noise. 

[Lord of nothing]

depend on the country its could be illegal to receive police and other. 

[rhb]

I bought an SDRplay RSP2.  It's quite remarkable for the price and at 12 bits has 24 dB greater dynamic range than the RTL-SDR.  Be aware that the design   of the front end means it will be crushed by a nearby transmitter in band.  This is true of all the cheap SDRs. The RSP2 improved the input preselection filters over the set in the RSP1, but a notch filter or other external preselection may be needed.  With the addition of a BG7TBL noise generator you can use the RSP2 to test filters.  Having a 10 MHz BW is a big help for that.

I chose the RSP2 because it covered HF without needing an external convertor.  Another advantage to the RSP2 is the external reference clock input and output.  This will let you do interesting things by phase locking multiple units which makes diversity reception, direction finding and other neat things possible.  At least if you're prepared to do some programming.

If you are at all curious, you will learn a lot playing with an SDR no matter what make.  You really can't go wrong.  I think the RSP2 hit the sweet spot and SDRplay  have been very responsive when I ran into issues.  A Windows update borked the software, but I got a fix in the form of a link to an MS patch very quickly.

Have Fun!
Reg

BTW You can certainly use 75 ohm coax.  Ideally you should have a 75-50 ohm transformer at the radio.  However, the impedance of a dipole at the feedpoint of the antenna varies with the height above ground so the impedance is not necessarily 50 ohms. Many years ago as a grad student  I ran a 6L6 and a rock using an inverted Vee dipole and scavenged TV coax.  The apex of the Vee was not very high, so based on a graph in the ARRL handbook  I estimated it was about 75 ohms.  You *should* have a balun, but I did not as I could barely afford to eat.  It worked and I made some QSOs using a Panasonic RF-2200 as the station receiver.  I quickly learned not to touch the dial after starting a QSO as I could never set it back correctly if I did.

[stj]

depend on the country its could be illegal to receive police and other. 

who cares, they listen to us.

[Lord of nothing]

especially in UK the Law about Drive Encryption is very restrictive.
So if the search your house and see that you maybe do some illegal stuff and the take your hardware with you.

[Red Squirrel]

depend on the country its could be illegal to receive police and other. 

who cares, they listen to us.

Yep and it's a beauty about radio, there is no way for them to track what we listen to.  Unlike internet.   

Well I guess technically when you are capturing radio waves you are "using" the energy so there may be a way to track that but I think it would be extremely hard, because everything is capturing it passively too.

I feel sad for the UK though they are really insane when it comes to mass surveillance and all that stuff, they might even be worse than the states.

I did not get a chance to play with my SDR further, can't figure out why I can't hear anything but did not get a chance to physically do anything.  I will need to move it just to rule out the server rack or anything physical going on.

Also not sure how to increase the frequency range that I can view, there's got to be a setting somewhere but can't find any info.  Only found a setting to change the centre frequency but not the range on both sides. 

[rhb]

As I understood it, you bought an RTL-SDR.  So far as I know that has a fixed frequency span of  96 or 192 KHz.  That was a major reason for my picking an RSP2.

FWIW It took me a while to get sound out of the RSP2.  The software is "interesting".

[james_s]

depend on the country its could be illegal to receive police and other. 

If someone doesn't want me to listen to their transmissions, they need to keep their radio waves off my property. I'll listen to anything I damn well please, they can't search my house without probable cause and they'd have to catch me in the act. Perfectly legal to listen to the police in the US anyway.

It was illegal to listen to analog cellular phones back when those were in use but it was completely un-enforcable. Every Pro-2004 to Pro-2006 scanner I've ever seen had the cellular band unlock hack done.