How does sdr work?

[reconrider8]

Since I got shot over here I figured I would go on band ask but someone said to use SDR for HF for utilities and such. Keep it in English please lol not to technical. Thanks

 

[corbintechboy]

It's just as it sounds, Software Defined Radio.

That means that the basic mechanics are there for the radio, but what the radio can do is defined by the software used. It doesn't really matter if the software comes in the form of a computer program or in the form of firmware loaded in the radio with software.

So as long as the hardware is capable, many choices of filters,AGC or really anything within the hardware limits can be added to the software.

 

[tomisius]

"...I got shot over here..."
Seek medical attention or dust off the CLS bag. lol

"Keep it in English please lol not to technical. Thanks"
Hard to pack into a nutshell. An analog signal is sampled -- converted to a digital representation of itself. The digital signal is usually fed to a computer for storage, analysis and/or further processing. The particulars are very complex but there are several manufacturers that offer SDR that's very plug-and-play - plenty that offer HF. They're pricey but you don't have to know all the ins and outs to enjoy the features if you don't care to know.

There are a ton of academic papers on the web that explain the general concept pretty well without diving into math hell. Again, a good consumer-friendly HF SDR rig only requires that you install a piece of software and plug in the USB cable, antenna, etc..

 

[reconrider8]

thats all i want lol plug and play for the most part... what antennas does it run? and kinda off topic but i see on the grundig or how ever you spell it they have a small antenna like the old antennas how good do they receive?

 

[tomisius]

thats all i want lol plug and play for the most part... what antennas does it run? and kinda off topic but i see on the grundig or how ever you spell it they have a small antenna like the old antennas how good do they receive?

I think you can use just about any antenna that you would use with a traditional radio so long as the impedance isn't horribly mismatched. Just be sure the radio doesn't use a hard-to-adapt or proprietary connector. You can adapt/convert virtually any standard connector type to another (that's what I do). Some form of isolation would be wise if the radio doesn't incorporate one in design.

Stick to time-tested and well-documented IMHO...

 

[popnokick]

Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 6_1_4 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10B350 Safari/8536.25)

I've used this with my SDR dongles. Works way better than the stick of wire they come with. You will need an MMCX to F connector adapter:
http://wiki.radioreference.com/index.php/Homebrewed_Off-Center_Fed_Dipole

 

[fourthhorseman]

thats all i want lol plug and play for the most part... what antennas does it run? and kinda off topic but i see on the grundig or how ever you spell it they have a small antenna like the old antennas how good do they receive?

Your not going to get plug n play..Youll need to load the unique drivers and DLLs to get the dongle to act as a wide band receiver..

as far as antenna..get it as high as you can and use the best coax you can afford..CATV coax will work or some rg58 from radio shack..that will keep your start up costs lower..

 

[Token]

Since I got shot over here I figured I would go on band ask but someone said to use SDR for HF for utilities and such. Keep it in English please lol not to technical. Thanks

If you are talking about a description of how SDR works then it will not be very complete without getting technical. Suffice to say a lot of the things that used to be done with discrete electronic components and blocks are now done in software.

Doing it in software has several advantages, including the ability to add modes and features. For example, if you buy a traditional radio and it only has AM mode of operation on it (talking AM demodulation, not the band) then it is difficult to add SSB or FM to that radio. To add a new mode of operation to an SDR you just add the ability to the software, a simple matter of coding

If you are asking “how it works” from an operational aspect, for utilities and such, I can say very, very, well.

With a traditional radio you have to be tuned to the right frequency at the right time to even detect that a transmission has occurred. Since utilities tend to be unscheduled, short duration, transient signals this can be a task. Most SDRs marketed to hobbyist include a waterfall or spectrum display. This display shows the frequency you are tuned to plus some spectrum above and below that point. A “window”, if you will, to many possible channels / frequencies. Yes, you still only listen to one or two conversations at a time (however many your mind can process, many SDRs allow multiple simultaneous demodulation channels, like multiple VFOs on a traditional radio), but you can potentially see many more.

Also, with an SDR you can record spectrum for later review. Not record a channel, as you can with audio and a traditional radio, but record entire chunks of spectrum with all transmissions within that chunk recorded for later review. With the right SDR a person who is into medium wave broadcast listening can record the entire AM broadcast band at the top of the hour, and potentially ID hundreds of stations in one recording.

In the following example I am looking at the bottom 80 kHz of the ham 15 meter band. Each of those vertical dotted lines is a ham transmission in CW (Morse Code). This image shows over 100 simultaneous conversations. To hear one all I have to do is click on it with the mouse, and the SDR tunes to that signal.

This image shows a frequency hopping OTHR (Over The Horizon Radar) invading the 20 meter ham band. I can easily see it is active and what frequencies it hits. However, if I had been tuned to a single conversation in the band with a traditional receiver I might not have known it was there at all.

Here is an image of 450 to 464 MHz. Each one of those little pips is a transmission. It makes it very easy to find new frequencies.

My YouTube channel has many examples of how an SDR can help in the world of shortwave utility listening.
FirstToken - YouTube


SDR literally brings to the average hobbyist abilities that just a few years ago only governments and professionals had.

Your not going to get plug n play..Youll need to load the unique drivers and DLLs to get the dongle to act as a wide band receiver..

as far as antenna..get it as high as you can and use the best coax you can afford..CATV coax will work or some rg58 from radio shack..that will keep your start up costs lower..

Was the OP just talking about the SDR Dongles like the R820T or E4000? I thought it was a more general question.

Yes, SDR can be a pain in the butt to set up for some people, depending on their computer savy. However, it tends to be a case of “you get what you pay for”. Lower cost stuff can be difficult, but higher cost tends to be very plug and play.

For example an SDR Dongle like the R820T and a Ham-it-up converter can be problematic. Remember, this is a hack, this SDR was not marketted for this application. I have seen many, many, users ask “what am I doing wrong?” trying to set it up. But hey, for less than $100 USD you can have a receiver that is good from below 1 MHz to almost 2 GHz, that is phenomenal value. Sure, it does not have the sensitivity, image rejection, ease of use, or several other performance factors of a more expensive radio, but never in history has a hobbyist gotten so much value for so little cost.

And the softrock series, like the Ensemble II, is a good performer at its cost point. Again, under $100 and you get a receiver that has SDR features and will outperform anything at its cost point.

On the other hand, once you spend a little more money, an SDR like the RFSpace SDR-IQ, the Microtelicom Perseus, or the WinRadio Excalibur series generally are really plug-and-play. Load the software with the click of a mouse, plug in the hardware, and away you go. And these types of SDRs do perform significantly better than their lower cost cousins.

T!

 

[fourthhorseman]

Interesting write up and comments sir Token...

Question as far as image rejection..what external filters coupld i apply to help with this.
is there a software alternative?

I was just answering in regards to the e4k/r820 devices..assuming the OP was looking
to get their feet wet rather than jump all in..Its an easy in for the cost(and SDR# is free..)

 

[prcguy]

If the OP is asking how SDR works technically I don't think that has been answered.

In a conventional HF or other modern radio there are hardware filters that may only allow the band of frequencies to be received to keep circuits downstream from being overloaded by out of band signals. Then the frequencies of interest are converted to an intermediate frequency where they can be filtered to a narrow bandwidth so only the single frequency you want with modulation is left and there may be multiple hardware filters depending on what bandwidth is required.

Then there are hardware demodulators that finally strip the audio information from the RF carrier and the hardware will be different for demodulating AM, FM, SSB and other modes. There will also be various stages of amplification and automatic gain circuits and so on.

In a DSP radio the RF spectrum is digitized into 1s and 0s at some point and the remaining functions of a receiver are emulated by software, The DSP designer manipulates the 1s and 0s to get the desired function and effect.

Simple DSP radios like the USB dongles do not have much if any preselection and their ultimate performance in a high level RF environment will be limited. Higher end DSP radios will have some hardware filtering and may resemble a conventional radio to some extent with hardware preselecters, high level hardware mixers and a conventional IF with hardware xtal or other filters before signals are sent to an A/D converter where the DSP magic can then do its work.

The very first DSP radios produced in the late 80s and early 90s were hybrid radios with some conventional receiver front end and IF circuits before the A/D and DSP. These were designed with military and cell phone base station use in mind and were finally produced for consumers with the WJ HF-1000 being an early one I remember.
prcguy

 

[tomisius]

@Token: Nice explanation and demonstration. That's a busy 15 meter band there!

@fourthhorseman: I assume your question pertains to a USB dongle-type receiver. GNUradio has a source block for this type of receiver. I do own one but have never attempted to use it in GR. Once your samples are piped in, you can do just about anything you want in the way of filtering, decimating, etc..

Good discussion in general. SDR is an extremely interesting field in spite of the steep learning curves one must climb.

p.s.: I was under the impression that the OP wanted something like the Perseus which would be plug-and-play. Still, a USB dongle would be a great starter since most of the 'hacking' has been done and one only needs to follow instructions to get it up and running. Adapting a Ham It Up (for < 25Mhz) is trivial and cost-effective.

 

[reconrider8]

what sdr program would you guys recommend for a starter? and what antenna setup would you use? i havnt got a tower up outside yet so i would have to stick to something inside for now but now i kinda want to get something rolling to learn more

 

[Token]

what sdr program would you guys recommend for a starter? and what antenna setup would you use? i havnt got a tower up outside yet so i would have to stick to something inside for now but now i kinda want to get something rolling to learn more

What program to use will be determined by what hardware you have. Remember, although several aspects of the effort are now done in software you still have to have hardware sampling the signal before the software has anything to work with. This can be something as low cost as the R820T / E4000 SDR Dongles to prices on the order of several thousand dollars for things like the WinRadio G35DDC Excalibur Ultra. The “heart” of the envelope, the point were performance becomes very good and prices not yet falling off the cliff, is probably the $500 to $1100 range. This is comparable in cost and generally superior in performance to an entry level or a little better desktop shortwave receiver.

As for antenna it is the same problem as any radio technology. The type of antenna you need is driven by your conditions and what you are trying to do. You have not said exactly what you want to listen to, are we talking VHF/UHF scanner type stuff? Or HF stuff?

The one thing you mentioned was utilities and Coast Guard, and you asked it in the HF/MW/LW General Discussion Forum, so I assume you mean HF utilities and Coast Guard.

Inside antennas for HF are generally very poor. You have many more noise sources to deal with on HF than on VHF/UHF, and many of those noise sources are right there in your home. Getting the antenna outside is key for a couple reasons, first it gets the antenna further form many common noise source, and second it allows for a larger antenna.

In general HF antennas are much larger than anything you might have used for scanners. Yes, there are small HF antennas, but they are a compromise. A good general rule for HF antennas is as much as you can get away with, for example a full sized half wave dipole for the 10 MHz region would be about 47 feet long. You don’t need a tower, but a nice elevated point for the feed point of a dipole or similar antenna is good. You most definitely can get away with a simple wire antenna, I would venture to say that probably most HF listeners use wire antennas. These wire antennas can be built or bought, you can generally build one for less than $30. Depending on the kind of antenna you can support (size and area) it might be one of several different types, random wires, long wires, dipoles, delta loops, sky loops, etc, etc. There are many different designs that work.

T!

 

[Yokoshibu]

No one even bothered to explain In-Phase and Quadrature.... sheesh a bunch of amateurs.. j/k Really good write up's everyone.

Token... excuse my ignorance... what software is that you took a screenshot of? it looks like something I should investigate. It isn't the flex software is it?

 

[Token]

Token... excuse my ignorance... what software is that you took a screenshot of? it looks like something I should investigate. It isn't the flex software is it?

No, that is the WinRadio GUI for the G33DDC, although the G31DDC GUI is essentially identical minus a few features. Also the G39DDC GUI is very similar.

T!

 

[majoco]

If you want to 'try before you buy' you can play with a remote SDR here...

http://websdr.ewi.utwente.nl:8901/

I can hear Radio Romania on the Netherlands SDR and at home here in NZ on my Debeg 7313 on 9645kHz at 0355z! The direct audio gets here first...

After 0400z he shifted to 9770kHz with a huge signal on the SDR and here too, S9+ on the JRC NRD 515 (the Debeg doesn't have a 'proper" "S" meter) - sounds like they're reading the news. I can get a handle on most European languages but Romanian has got me beat!

If I wanted to check on the WinRadio G303 I'd have to take the antenna off the Debeg - I'll have to make a switch box one day...:roll:

 

[Zaratsu]

Very cool Martin.

This is an addicting tuning method.

Thank you!