SDR = Software Defined Radio

 I don't I don't have a spectrum analyzer and this could be a cheap way for me to have one. Wonder how accurate it is?

You still need RF circuitry for SDR's.

However, a good deal of the functionality is implemented via microprocessors.  Either in one located on a board in the SDR, or your own computer.

This makes the SDR very flexible, as functionality can be added just be upgrading the firmware.

As an example, I used to own an SDR Cube, an amateur radio SDR QRP transceiver - it implemented its control circuitry through a separate board that was contained within the radio, so you didn't require a computer (that board was the computer).  When I first purchased it, it would support the SSB and CW modes.  They added AM reception and transmission via a firmware upgrade later on.

This flexibility comes at a price.  SDR's are not cheap.  Some of that is the limited production runs, but not all.  The SDR I had was just over $300 in kit form, and over $500 fully assembled - and to make it fully functional across all amateur bands you had to purchase various options, such as band modules, etc.  Fully outfitted, they can easily run over $1000.  One of the more popular SDR's is the Flex, and it can cost you a lot more than that.

Thanks I thought they were a simple USB dongle with an antenna jack and you could buy the converter if you wanted Shortwave.  I was going to use my computer with it to do a spectrum check on my FM Transmitter.

I bought an RTL-SDR USB dongle which will receive 54 MHz to 2.1 GHz with no extra hardware other than the PC to plug it into and an antenna.

There is a free download of the SDR software to operate the receiver.  And yes, this provides a spectrum display of the RF.  It supports several modes of modulation detection.

The dongle was sold along with a kit which will allow reception below 54 MHz, down to the VLF range.  I haven't assembled the kit portion yet as I'm having fun with the dongle itself.

To assemble the kit you must dismantle the dongle and mount the dongle PC board on a small (2"x2") mother board along with some additional surface mount components.  This provides the up-conversion to allow receiving the lower frequencies.

The one I purchased from Ebay was around $25.

Thanks Bob this can be handy for testing FM Transmitters for Harmonics and spurs.  May just get the dongle and Download the software.  At least I can use my Laptop and roam around outside and check for spurs while I do so.

I have my doubts as to how effective this can be for the price being paid.  Maybe for playing around.  There is a more expensive one that looks interesting, though.

A friend gave me a dongle.

He is going to help me with the software.

(Because I can't see well.)

 I am working on building up a good LF-HF

monitoring set-up (a long story in itself.)

I am  working on PSK-31 and JT-65 receive.

I actually have a receive antenna phasing unit
coming in the mail this week.  (Another long story.)

I am in an apartment with no outside antennas

(at this point.)  

I am enjoying the challenge of the thing.

I also have a ham license but transmitting

will come later.  I mght try some QRP transmitting

in the summertime.

Best Wishes,

Brooce, All kinds of Part 15 Experiments,

Hartford, CT

P.S.  This SDR stuff is really where it's at.

I still love my old vacuum tube radios, though  

So...  I guess the word "Dongle" came

from some kind of small unit that hangs

(or dangles) off the end of a USB port on

a computer.  I suppose there must be all

sorts of dongles that have different functions (??)

I don't want to be misleading in the fact that

the dongle I want to work with is only a small

experiment along with a bunch of other ones.

I guess that's what's I'm trying to say.

The dongle will not be receiving any digital modes.

The aim is to just to get it going with on local

signals at first, like maybe the local FM ham repeaters.

As far as I know, the dongle I have was never intended

as any kind of communications receiver.  This dongle

was made to receive European HDTV.  And the software

that is included in the package is for that purpose.

This dongle can receive ham radio and local comms

(AM, FM, SSB, whatever?) because experimenters

in ham radio and communications wrote the software

so the dongle could be used as a comm receiver - and

not for it's oriiginal intented purpose.  Are these 25 dollar

dongles really great receivers?  I don't think so.

I think they are sensitive, but they only have about 40 dB

dynamic range.  Personally, I don't care.  I just want to

learn about how they work.  There are software defined

transmitters and receivers (and transceivers) - many for

ham radio and SWL use - - that work really well - but cost

more money.

I have numerous experiments happening with different

transmitters and receivers here, including Part 15 AM and FM.

I intend to receive PSK31 and JT65 with regular conventional

analog receivers that i already have here.

I have several QRP transceivers that I hope to get

running one of these days.

So I have a lot of things happening, all at a snail's pace. 

Oh, yeah - -I think RTL is part of the designation for the

chip in the dongle.  The whole part number is RTL2832???

Is that right?

Brooce, Part 15 and other stuff, Hartford, CT 

I've only played with this USB RTL-SDR a bit. 

With a 14" wire stuck in the antenna jack I'm able to receive local Ham 2 meter repeaters and some simplex conversations.  Also, most any FM station I hear on my boom box I can receive with the dongle.  I've heard some aircraft around 121 MHz and public service/public safety radio. 

Yes, it will receive AM, WFM, NFM, USB, LSB, DSB and CW.

I don't know what the actual sensitivity is but considering the antenna situation, can't be too bad.

It is a resource hog.  Mine is an older AMD Athlon 64 dual core processor 4000 at 2.1 GHz with 2 gig ram.  If I run the scrolling spectrum display other than slow, the PC bogs a bit.

Here's a screen shot of the GUI interface:

That's a shot of my FM yardcaster at 93.5 FM.

Being able to see our Part 15 signals in that way is very useful, and I would think most Part 15 broadcasters would want something like that.

I have a spectrum analyzer, so I don't need that feature, but am always curious about what else there might be...

For example, can one of these SDRs be rigged to see modulation envelopes on either AM or FM?

Here is a shot of the dongle plugged into the USB bus.  It's the one with the RED clip-lead stuck in the end.

That's the setup which received the signals noted above.  The dongle was tuned to my FM yardcaster for the screen shot.  The FM receiver shown is tuned to my LPFM which is why the frequency is different than the screen shot.

Hi Guys

As a radio person who is very interested

in propagation, a hope the dongle will

be helpful.

I have spent hours and hours reading

about sporadic E propagation.  

I have not had equipment to receive the

6 meter (50 to 54 MHz) ham band for

years, but I hope the dongle will be able

to tell me when 6 meters starts cookin,

and the "E" season is almost here. Or..

Well.. I haven't checked, but it is probably

already occurring down in the southern

latitudes.  I'm in Hartford, CT.

I missed a rare winter opening on Dec 26,

the day after Christmas.   The Maximum 

Usable Frequency (MUF) was up into the 

FM BCB and one of my good friends heard

an FM station about 1000 miles to the south

of here litterally blasting in at almost local

strength for about 15 minutes until the

E cloud broke down and everything went

back to normal.

I want to hear 6 meters so I can keep a

better eye on that stuff.

Also, you can monitor, (but not decode)

the HDTV carriers.  They are 310 kHz (?)

above the bottom end of the TV channel

assignments for 2 through 6.  (And all

of the others too, although for E skip,

only TV channels 2 through 6 apply -

99.99 percent of the time anyway.)

RARELY

Maybe 5 or 10 times in the last 20 years,

E skip has gone higher.  An astonishing thing.

Hams listening to 220 MHz have made very

brief contacts in the past.  2 ways, I mean.

So for 10 or 20 seconds you get this rock

crushing mind blowing 60 over S9 signal.

And those guys that used to watch the

analog TV channels between 7 and 13

(174 to 216 MHz) would get TV there from

1000 miles away of so.   E skip on the high

band TV channels 7 through 13 used to be

strong, with very violent fading, ghosting,

phase shifting, and basically a wild ride

for a TV DXer in the past.  But back then,

a few intrepid guys saw and photographed

IDs way up to TV channel 13!!  Those days

of course are no longer with us.  We can only

look back and reminice. (sp) 

Even W1AW code practice on 147.555 MHz was

heard in Nebraska once.

Sorry, I know this is really another thread.

I just wanted you guys to know that the

dongle would be for E skip searching, mainly.

Here, anyway.

Brooce, Goofy Experiments Dept., Hartford, CT

Here's a link to a short video showing the RTL-SDR dongle doing it's thing:

The Dongle

Thank you for that, Bob!

We ALL should try this and 

compare notes.

Depending on the software - - there

are other things that can be decoded

with this dongle and others that are

similar.  A few people are decoding data

from communications satellites (weather fax,

I assume) and others are looking at text

from airplanes - - fuel consumption, etc.

Brooce, Goofy RF, Room 13, 14th Floor,

Just past the water fountain in the multi-

purpose hallway, watch out for the cleaning

lady...  more later