SDR Newbie

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truckdrivermn

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Hey all. I've been lurking for some time now so here goes my first post.

Since I've retired from trucking I've been looking for a little hobby to do with my boy (he's 6) I've known about SDR for some time now so I figured I'd drop the ball on a $25 dongle off Ebay. No brand name, DVB-T+DAB+FM. It came with a junky telescoping antenna.

Now, I'm no computer wiz or radio wiz. I'm a CB guy, from a lifelong spell in the trucking industry. I work on a few here and there on the side (I have the proper equipment and knowledge) as well as my ever changing "radio room" Its also been a life-long passion to get my Ham lic. Thats this weeks goal.

Anyway, my half brained CB knowledge set aside, This SDR setup kinda wants to make me pull my hair out. About all I can get on the antenna that came with the dongle is FM broadcast. And my WX stations closest to me are weak but audible. I made up a discone antenna it brought in the WX stronger.

But as far as what my son and I were really interested in IE: Air traffic (were 4 miles from a airport) the police/fire freq that are still analog around here and some Ham bands (from what I understood anyway) we get nothing but steady tones and static. We can clearly see the signals are there and what not but can't tune anything in.

Were using SDR # and HDSDR. Also SDR Touch on my Android (No luck as well)

Now remember Im about as dumb and one can get with this stuff. I'm learning, or trying to. Restoring a CB seems easy when it comes to this so far. And I didn't narrow things down very good but that's about all I got. I thought I'd ask on one of my "CB" forums that I know a few guys got into SDR and got laughed out. I didn't know I was supposed to be born with all the smarts to get this right.

Any pointers?
Thanks much!

Jared
 

AKJohnny

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Hey all. I've been lurking for some time now so here goes my first post.



Since I've retired from trucking I've been looking for a little hobby to do with my boy (he's 6) I've known about SDR for some time now so I figured I'd drop the ball on a $25 dongle off Ebay. No brand name, DVB-T+DAB+FM. It came with a junky telescoping antenna.



Now, I'm no computer wiz or radio wiz. I'm a CB guy, from a lifelong spell in the trucking industry. I work on a few here and there on the side (I have the proper equipment and knowledge) as well as my ever changing "radio room" Its also been a life-long passion to get my Ham lic. Thats this weeks goal.



Anyway, my half brained CB knowledge set aside, This SDR setup kinda wants to make me pull my hair out. About all I can get on the antenna that came with the dongle is FM broadcast. And my WX stations closest to me are weak but audible. I made up a discone antenna it brought in the WX stronger.



But as far as what my son and I were really interested in IE: Air traffic (were 4 miles from a airport) the police/fire freq that are still analog around here and some Ham bands (from what I understood anyway) we get nothing but steady tones and static. We can clearly see the signals are there and what not but can't tune anything in.



Were using SDR # and HDSDR. Also SDR Touch on my Android (No luck as well)



Now remember Im about as dumb and one can get with this stuff. I'm learning, or trying to. Restoring a CB seems easy when it comes to this so far. And I didn't narrow things down very good but that's about all I got. I thought I'd ask on one of my "CB" forums that I know a few guys got into SDR and got laughed out. I didn't know I was supposed to be born with all the smarts to get this right.



Any pointers?

Thanks much!



Jared


I'm pretty new at this too. But have you turned up the RF Gain for for your device? You can find it by clicking the cog/gear looking icon at top in SDR#. Just a thought.
 

br0adband

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Springfield MO
My first thought was the RF Gain could be set improperly but it of course could be a bunch of things. It's not nearly as difficult as it seems but that statement is coming from someone that's been at this for quite some time now so for a "Newbie" as you call yourself it can be daunting but it's just steps like anything else, one in front of the other, then the next one, and so on.

I recommend using SDR# as your basis since it is the most popular and most widespread software used and most anyone out there knows how to use it almost by default. Here are the basic steps:

- install the Zadig drivers so any SDR related software will be able to access and make use of the RTL stick which is what you bought meaning it's based on the RTL2832U chip which handles the USB communication with the computer/tablet/etc - the actual tuner chip is a Rafael Microelectronics R820T or R820T2, the T2 model is the newer improved one so hopefully that's what you got as most of the R820T2 based sticks also have the TCXO which is a temperature controlled oscillator, laymen's terms it's a better one than the original R820T sticks had which would change their frequency when the device warmed up or got hot. The R820T2 devices that do have the TCXO are the preferred ones obviously since they don't suffer nearly as much drift off-frequency as those original ones do.

I'm going to assume you did get the drivers installed since you've been able to get FM broadcast but that's easy for most people since FM broadcast signals are rather "booming" in terms of power of the signal. The concern again is that the RF Gain on the stick isn't enabled or turned up from the 0 dB default so that would basically keep you from tuning much of anything that's not right there beside you transmitting or extremely powerful. Because you got this far that means you already install the necessary DLL files using the install-rtlsdr.bat batch file when you extracted the SDR# archive so I don't need to cover that either.

- plug in the RTL stick, then fire up SDR# and make sure it's seeing the stick and functional (you appear to have done this before so you're just doing it again)

- click the Gear icon near the top left corner and make sure it shows "Generic RTL2832U OEM (0)" or something similar meaning it sees the stick that's plugged in (because you can have multiple sticks, of course)

- Sample Rate should be set at 2.048 - I know some folks say just use 2.4 MSPS but I recommend using 2.048 MSPS to get you situated and then later you can experiment if you want

- Sampling Mode should be left at Quadrature sampling

- No check in the Offset Tuning (disabled)

- No check in the RTL AGC (there are times when it can be useful but this isn't one of them so disabled)

- No check in the Tuner AGC (again, at some future point you can experiment but leave it disabled for now)

- RF Gain - set the slider to 32.8 dB for starters, you can adjust it more or less later on but that's a good solid starting point for most any signal activity

- the Frequency correction (ppm) needs to be set depending on the stick you have and this is another post all by itself. If the stick you bought says someplace on it or on the packaging/case "TCXO" that means it has the temperature controlled oscillator and you can set it for 1 or 2 for the moment - if it's an older non-TCXO device then you're going to have to figure out what the ppm (parts per million) offset for that specific stick happens to be and that won't be possible until it's been on for about 15-20 minutes and gets to operating temperature - will cover this more later in this post but for now we move on

- if it is a TCXO stick set it to 1 or 2 (you can adjust things again later as required) and then click Close

- on the main SDR# window click the Play button next to the Gear icon and you should get some activity on the spectrum and waterfall - by default SDR# uses some pretty horrid settings so we're going to adjust it to make things look better and more visually informative - right now you're probably staring at a big wall of yellow and red, like fire on the waterfall because it's set to be too sensitive. I'm going to do a screenshot of a totally clean first-time use SDR# and it looks like this without changing anything but what I just discussed above:



Now that we can see things more clearly, I'll leave the Contrast there at the default setting because we've "cleaned up" the waterfall so it ignores most of the noise and we can now see the signals. I'm going to tune to 162.550 MHz which is the NOAA weather broadcast here in Las Vegas. Note that on the pics just shown the mode is WFM or wideband FM for broadcast FM pickup. Since we know the NOAA broadcast is using traditional NFM or narrowband FM then I select that on the upper left side then tune to that frequency - I've also adjusted a few other things for my particular listening habits - I adjusted the Squelch to 70, and I altered the Step size to 5 kHz because frequencies in the 150-170 MHz range typically use 5 kHz stepping as a general rule. I also adjusted the spectrum pane to be a bit short since most info is on the waterfall that I find relevant, you can do that just grabbing the separator bar and drag it up or down as you wish.



If at this point you can follow those instructions and use your own local NOAA weather frequency, you should note the signal is much more readable at that point because if my suspicions were correct the RF Gain was just basically keeping you from receiving most anything. It's entirely possible that the antennas that came with the stick you got are just crap, unfortunately, but that's somewhat rare these days, they usually prove to be at least useful for bare reception purposes but not fantastic for it.

That should be enough to get you farther than you've been but if you need more help just ask, somebody will get to it if I don't. :)

Have fun, always...
 

br0adband

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Springfield MO
Second post related to the tuning with a ppm that's not within 1-2 ppm aka using a TCXO based stick.

To do this correctly you typically need to find a frequency that's pretty stable (for the most part) and while a lot of people use the NOAA signals that's fine but I prefer to use the ATSC digital TV pilot signal myself and the specific one is at 470.310 MHz - you may find that in your area is a strong signal but there are others so find one of them from this list (they're 6 MHz apart):

470.310 MHz
476.310 MHz
482.310 MHz
488.310 MHz

I use the 470.310 one because it's the first one in the UHF band and the others here in my area have interference around 'em whereas the 470.310 stands clear as shown and note that I used the Zoom slider on the upper right side to bring it into clearer/larger view.



And then the fixed more accurate tuning:



Note there is nothing demanding you to use the method or the frequency that I do, use whatever frequency you want but realize that with some RTL-based sticks there can be a difference between what the ppm is in the lower frequencies (VHF) and the higher ones (UHF) and it can be several ppm between those bands so when I say make sure it's set proper I say that because some hardware does need to be kicked into accuracy on occasion (not literally of course).

Once you know the ppm of a given stick, maybe put a piece of masking tape on it and label it so you know at a glance what it is. Even TCXO based sticks can be 1-2 or sometimes but rarely more off the theoretical "0 tuning" point meaning it's always perfectly on frequency when tuned. My two old RTL sticks are 55 and 49 and labeled clearly for such reasons. ;)

Hope this helps...

ps
Remember to adjust your Zoom back to full scale so things don't get funky, made that mistake myself a few times till I realized what I missed. :D
 

truckdrivermn

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Jul 1, 2011
Messages
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Location
Minnesota
Thanks for the awesome reply br0adband! I had it set up pretty close to how yo mentioned. And yes the stick I got has the TCXO I did notice it was off freq and readjusted.
Can I ask what antenna you're using? I "Jerry Rigged" A antenna last night and was actually able to pick up some weak air traffic from our airport at last.

And if I'm understanding it right from what I have read, these dongles typically cover 26 mhz and up from there? I have seen a few different sticks state different ranges along with software use. Im defiantly not to the point I want to be to utilize it yet..
 

KC5AKB

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Aug 8, 2010
Messages
285
Location
North Texas
With a few more posts you will be able to send and Rec. PM's
Radio is a good hobby to get into there are so many modes
Like Psk 31 , SSB ect and all the thinks you can build .with your
Son. Take time and enjoy .
 

br0adband

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Messages
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Location
Springfield MO
Ack, didn't see the question posted on 11-22, sorry about that.

I use 3 antennas basically and swap from time to time. For the past oh, 10 years I haven't even had an actual physical scanner, the last one I owned was the Uniden BC246T and I miss it these days but I just got a Radio Shack Pro-107 at a pawn shop recently and also put a Pro-668 on layaway and will get it at some point. On the monitoring front for the past few years (I took a break from the hobby for many years but got back into it around 2012-ish to some degrees) I've been using the "cheap USB TV tuners" aka RTL sticks like many others have because it's a big change in how things have been done for so long, a paradigm shift in my opinion, almost as big as going from conventional to trunked systems and then from analog to now digital.

The first antenna is the venerable Radio Shack 800 duckie that so many of us have come to love for its outstanding 800 MHz performance (actually 700-800-900 is remarkable) but also the fact that for some magical reason it works amazingly well down into the VHF range as well. I use mine for monitoring CivAir from 118-136 MHz, the 2m band at 144-148, into the VHF-Hi band from 150-174 and into the MilAir range at 225-380 MHz too and of course UHF from 406 to 470 MHz (there's nothing here in the Las Vegas area from 470 to 512 MHz like in some parts of the US, oddly). Suffice to say the price I paid for the RS800 over a decade ago was a wise investment for me and I'm sure others feel exactly the same way. If you go looking for one and can't find one for whatever reason there's a company called Remtronix which manufacturers almost a near-perfect clone of the RS800 these days in both BNC and SMA connector models.

Next up is the classic Diamond RH77CA dual bander that offers exceptional wideband receive performance and does a bit better on the VHF and UHF bands from 118 to 470 MHz since that's what it's designed for (it's a 2m/70cm Ham antenna for transmitting purposes) but it does receive into the 700-800-900 MHz ranges just fine in my experience. I get the same or similar signal bars using the RH77CA that I do with the RS800 in those ranges, but the RS800 does tend to get less scratchy reception if that makes any sense, just a tad better since the length of the RH77CA (it's about 15" tall) will cause it to not be a nice match on the wavelengths involved that high.

As for the "big one" that I use most of the time for general purpose monitoring mainly with the RTL sticks (I have 4 now, 2 original R820T tuner models and 2 of the newer improved R820T2 tuner models, they work basically the same but the improved ones have the TCXO support and use the SMA connectors along with being better shielded in their aluminum enclosures) I have a Homebrew OCFD aka an Off-Center Fed Dipole which you can read more about here:

Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

and in the long thread with a lot more info and people's experience with building and using them here:

http://forums.radioreference.com/build-your-own-antenna/259567-my-homemade-off-center-dipole-antenna.html

Made one a few years ago and was disappointed with it overall, disassembled it and put it in a closet but I put it back together last year at one point and damned if it didn't work better for whatever reason, it's weird but entirely true and I changed nothing with the cabling or the RTL sticks (that was before I got the newer R820T2 models a few months ago). Pulls in stuff across a wide bandwidth as it should be design, I've been extremely happy with it and all together I spent about $15 on the parts to build it and I'm very happy I did and then gave it a second chance. :)

I also have a few tuned 1/4 wave ground plane antennas made from coat hangers, spade lugs, screws and nuts, and SO-239 chassis mounts and that's it, not even soldered and they work great. The simple plan for making one can be found here:

2 meter 1/4 wave Ground Plane

While it says 2m that's for that specific one, if you adjust the length of the ground elements and the main one based on the 1/4 wavelength calculator you can find here:

Amateur Quarter Wave Ground Plane Antenna Calculator

it's easy to create one that's tuned to a specific frequency (roughly) for use with that particular band/range. I have one for CivAir/VHF (tuned to 150 MHz) and that one single antenna also works great for reception in the 450 MHz range and also the 900 MHz area including 800 MHz and even the upper 700 MHz public safety range as well because of harmonics and the length of the elements.

Anyway, since what you're working on is akin to a "Father/Son" type project the homebrew antennas are very simple to put together, dirt cheap or damned close to it in terms of actual cost, and will provide outstanding performance for your purposes. Make sure to use decent cabling to connect whatever you might create to your receiving hardware with connectors as required and you're good to go.

Hope this helps, and happy holidays. :D
 
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