SDR - various uses including spectrum analyzer

[Electro Fan]

I'm starting to play with SDR in various forms.

This might have been posted elsewhere but I didn't see it when doing a (maybe too quick) search here:



Just curious to get comments on this, including whether anyone has seen similar apps for iPhones?

[SNGLinks]

Apple devices like the iPad and iPhone do not have USB interfaces!

[tggzzz]

I'm starting to play with SDR in various forms.

Not android, not tablets, definitely not iPhone, probably RPi but I haven't tried: you might be interested in https://entertaininghacks.wordpress.com/tag/sdr/

I've more results and will publish the scripts, but I've not yet had time to do it. With luck I'll have some time in the next few days.

[cdev]

In terms of using RTLSDRs as test equipment, science oriented users should learn about the "rtl_power" binary that comes with the driver -which can do quantitative measurement and write the results to a file for later analysis with the tool of your choice- or you can use the rtl_sdr binary and a pipe or fifo .. save the raw data to a file or pipe it to another tool in real time.

Also, the Linrad SDR program ( http://sm5bsz.com) is worth looking at because it has lots of test-related functionality and also supports a great deal of fine-grained configuration including the unique, as far as I know, ability to calibrate the dongle to parts per billion -assuming you can get really good stability out of it, that's an area where they vary a fair amount from model to model.

The calibrated noise figure device mentioned I think uses a modified library - which I think Linrad can also use if they are found. I have more info on that somewhere, I will have to dig it up.

I have two dongles - the ones I use the most, which both have very good frequency accuracy. One is under 1 ppm. It doesnt have a TCXO, it has not been modified in any way, it was super cheap, it just came that way. Its very stable. It runs quite cool, it never gets hot, maybe thats part of the reason why. Also it has a flat SMT crystal. (I think the can crystals are always way way off. Perhaps they are grade B from some other factory production line.)

One suggestion that seemed to work to make all dongles more stable- SM5BSZ found, was putting the bare dongle, removed from its case, in a closed container with a bunch of clean sand around it.

[Kalvin]

I have used an SDR-dongle for sniffing whether the external MCU oscillator is running or not, and whether the frequency is way out of normal range. Using an oscilloscope disturbed the circuit too much, so sniffing the oscillator with the SDR was a good choice. I took an oscilloscope probe and attached a small coil made of 10 turns to the probe. Hooked the probe to SDR using a BNC/SMA-adapter, placed the coil near the oscillator and the used the SDR-software to see the oscillator's frequency and status.

[cdev]

Actually, I want to revise my previous post. In trying to track down a problem, I am currently trying to use my RTLSDR as a spectrum analyzer, and bluntly, using non-specialized tools - (general purpose SDR receiver software) the RTL makes a lousy "spectrum analyzer", because spurs etc, can be anywhere and the spectrum is so large, drilling down to look at a specific spur and then trying to figure out whether its a spur or intended to be there or not is not an optimal way to do things.

[Electro Fan]

"a lousy "spectrum analyzer", because spurs etc, can be anywhere"

- this is regarding the RTLSDR, not necessarily all SDRs.... Yes?

[uncle_bob]

"a lousy "spectrum analyzer", because spurs etc, can be anywhere"

- this is regarding the RTLSDR, not necessarily all SDRs.... Yes?

Hi

True, but it certainly *is* the device a lot of people grab for when SDR comes up. There are (tiresome) ways to get it to dodge spurs, they are more useful for narrowband stuff than for wide range sweeps.

A more general limitation on an SDR is the lack of a built in input attenuator. You can add one. Many people don't think about that first and empirically determine the burn out performance of their SDR instead (ouch !!!).

Bob

[cdev]

I used a pickup loop and a x10 probe both connected to a CATV AB switch-  after the switch is an impromptu attenuator made out of two splitters with a CATV variable attenuator stuck between them.

[uncle_bob]

Hi

Another approach is to haunt eBay looking for any of the good old HP bench top dial attenuators. You may or may not get a good one on your first try.....There's also the time honored approach of pulling one out of a dead old spectrum analyzer.

Bob

[cdev]

Is there any place I can find the model numbers of such animals? I don't even know where to start. Yes, i would definitely love to have a precision attenuator, if it didn't cost an arm and a leg.

There are great deals on ebay sometimes of lesser known brands..

I am always of several minds on things like that, one part of me says, dont get it, you can make that yourself, but another part of me says "you'll never be able to do it right" and thats probably the righter of the two.

Ive been agonizing for a long time whether to get a signal generator too. I think I am just going to try to build one from a kit, using a DDS chip.

[uncle_bob]

Is there any place I can find the model numbers of such animals? I don't even know where to start. Yes, i would definitely love to have a precision attenuator, if it didn't cost an arm and a leg.

There are great deals on ebay sometimes of lesser known brands..

I am always of several minds on things like that, one part of me says, dont get it, you can make that yourself, but another part of me says "you'll never be able to do it right" and thats probably the righter of the two.

Ive been agonizing for a long time whether to get a signal generator too. I think I am just going to try to build one from a kit, using a DDS chip.

Hi

The one I was thinking about as I typed the message is an HP 355D. It has BNC's so it mates with a lot of bench stuff. A pretty good looking one shows up 6 items down on a quick eBay search for "HP attenuator". They only are rated to go to 1 GHz so they are not as expensive as some of the microwave versions The 8496B is the newer / higher frequency / better looking / more expensive version. It uses SMA's.  These are the wide range versions. There are also narrow range versions and binary units that are electrically driven.

Bob

[cdev]

I wonder, has anybody successfully modded an RTLSDR to extract the tunable local oscillator signal to use in something else?

Maybe another, "better" SDR?

[uncle_bob]

I wonder, has anybody successfully modded an RTLSDR to extract the tunable local oscillator signal to use in something else?

Maybe another, "better" SDR?

Hi

Does the oscillator even show up on a pin?

Bob

[cdev]

I am pretty sure that there is a sort of spectrum analyzer for the RTL that is implemented in python, which uses the binaries that come with the driver as its front end, and allows navigating around the spectrum, zooming, etc. Its very basic but it does let you do that. Basically its just an app that consists of a very few lines of code that links the command line rtl utilities with a Python data vis app that displays the result on the screen in realtime.

[uncle_bob]

Hi

As mentioned above, the RTL has some interesting spur and image issues when run with the normal spectrum analyzer code.

Bob

[cdev]

Quote from: uncle_bob on Today at 20:06:06>Quote from: cdev on Today at 20:01:58

I wonder, has anybody successfully modded an RTLSDR to extract the tunable local oscillator signal to use in something else?

Maybe another, "better" SDR?

Hi

Does the oscillator even show up on a pin?

Bob

Hmmm..

This looks promising..

http://www.steila.com/blog/index.php?controller=post&action=view&id_post=9 - description which links to

http://www.g8jnj.net/softwaredefinedradio.htm

[uncle_bob]

Hmmm..

This looks promising..

http://www.steila.com/blog/index.php?controller=post&action=view&id_post=9 - description which links to

http://www.g8jnj.net/softwaredefinedradio.htm

Hi

For even wider range outputs, there are a bunch of AD and TI (ex National) PLL chips with built in VCO's. They are not particularly expensive and you have a massive amount of documentation on them. The ADF 5355 came up in another thread here yesterday

http://www.analog.com/en/products/rf-microwave/pll-synth/adf5355.html#product-overview

Yes indeed AD is proud of their products. You could buy several RTL dongles for the price of one chip. The AD chips work. The National chips are less expensive, they may do what you need to do.

Bob

[cdev]

Checking out those AD chips is definitely on my "to do" list.