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SDR Questions from a Novice

A pal of mine since the 4th grade -- we differ when we met -- bought an SDR unit.
Now, this was after *I'd* turned him on to the SDR site for DXing purposes! The nerve!
He says there were a few different ones available. With the unit he acquired, he now claims that by using a certain manner of external antennae and a few flips and tweaks of the site's workings, he can 'null' a closer AM station and hear a co-linear station PAST it. He has sent audio clips of this window of largesse.
PA big mouth me -- a few times an 'odd-person-out' in random think sessions of little distinction -- asked if, well, if you can vaporize ONE station like that, chuckle, would it be possible to cancel out the SECOND station as well?
Sample: Cancel out WBBR 1130 NYC and get 1130 Detroit. Being that those two stations are sort of co-linear, how about the possibilty of setting the steering wheel steady and muting Detroit and leaving an aqueduct for Madison to come in?
So, he's working on that now (probably as we speak here).
I haven't seen his setup on Cape Cod, and know little about it. But the premise seems to be (to my non-tech comprehension, anyway) a digital version of the setup used by the National Radio Club member Ron Schiller of Miami. He called it the LSCA -- Loop-Sense Cardioid Array.
I have just the basic 4-foot NRC loop and a vacant backyard where I recently moved in. A longwire is a piece of cake if needed.

Has anyone aboard here tinkered with these SDR units that way?
Are SDRs simply radios on a computer chip? Are there various prices of them for various explorers?
All I know is I see a screen of a dial and a stream of colored rows, on each of the 15 or so sites I have in favourites. It'd be real neat to discover other uses and warpings available on, say, the basic Milford PA site on the Delaware, or the CT-MA site near their border.
Any input welcome -- in as plain Primer English as possible, lol. EMail me or feel free to list some stuff here.
 
The magic is in the software where you can filter interference record the stations, tweak the radio, and waterfall settings tune in the stations. The SDR dongles receive the signals and convert them to a digital format that can be used by the computer. Among the software available is SDR Sharp for AirSpy and RTL-SDR devices, SDRUno and SDRConnect for SDRPlay devices and SDRConsole that can be used with both SDRPlay and AirSpy devices. SDR Sharp has Co-Channel Canceller that can be used for nulling out stations and SDRPlay has RSPduo with diversity mode that can also be used to null stations.
 
Has anyone aboard here tinkered with these SDR units that way?
Are SDRs simply radios on a computer chip? Are there various prices of them for various explorers?

The SDRs use a different method than a traditional tuner.

A traditional tuner uses electronic components, most commonly a variable capacitor, to select a channel and pass its RF to a mixer and a demodulation stage.

An SDR is a concept that does the steps in a different order. The SDR samples the entire spectrum (a process known as analog to digital conversion) and allows the tuning and demodulation to be done in software. This allows changing the bandwidth or doing a pop/click filter, or even more complicated analysis.

The advantage: software can be more complex than what is feasible in pure electronics components.
The drawback: that it is more expensive than a traditional tuner and consumes a little more electricity.
 
The drawback: that it is more expensive than a traditional tuner and consumes a little more electricity.
Analog to digital converters or the reverse are rather power hungry. That is why we never got usable HD Radio portables that actually worked. And, in addition to satellite reception requirements, it's why no portable satellite radio works, either (I know, I wasted about $200 on one back when I was programming some of the XM channels).
 
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