Search found 21 matches

by Github
Mon Feb 26, 2018 5:42 am
Forum: User Projects
Topic: Cooler for SDR-RTL
Replies: 2
Views: 5687

Re: Cooler for SDR-RTL

Can I ask if it is noisy or not?
by Github
Mon Feb 26, 2018 3:25 am
Forum: Antennas
Topic: Is it normal for an antenna not have lowest swr in its advertised band?
Replies: 7
Views: 4852

Re: Is it normal for an antenna not have lowest swr in its advertised band?

How are you doing the scans? Remember that VSWR measurements with a noise source, directional coupler and RTL-SDR are not terribly accurate. I do see a dip at 477 MHz though. It is possible that antennas will have multiple resonant points. Remember that just because an antenna is resonant doesn't n...
by Github
Mon Feb 26, 2018 3:23 am
Forum: Antennas
Topic: Is it normal for an antenna not have lowest swr in its advertised band?
Replies: 7
Views: 4852

Re: Is it normal for an antenna not have lowest swr in its advertised band?

The scale you are using is quite large. I guess the real question is, does it have the SWR that the manufacturer stated at the frequency of interest? If it does then you have what you bought. If not then you might have a case for misleading advertising and getting your money back (certainly here in...
by Github
Sun Feb 25, 2018 4:34 am
Forum: Antennas
Topic: Is it normal for an antenna not have lowest swr in its advertised band?
Replies: 7
Views: 4852

Is it normal for an antenna not have lowest swr in its advertised band?

I bought this small CB antenna, it is advertised to work at 477 MHz. But looks like the swr is not the lowest at 477 mhz. Is it normal?
by Github
Sat Feb 24, 2018 7:57 am
Forum: RTL-SDR Discussion
Topic: Do you need a high performance pc to play SDR?
Replies: 3
Views: 2556

Do you need a high performance pc to play SDR?

Do you need a high performance to decode digital voice and other stuff? I am currently using my ultrabook to play rtl-sdr but I notice the noise from cooling fan is so loud even when I am decoding analog voice. And sometimes my ultrabook is getting pretty hot and cpu is being throttled. So I am wond...
by Github
Sun Feb 04, 2018 6:21 am
Forum: Off-Topic
Topic: Any Radar that can trace the location of the radio transmitt
Replies: 3
Views: 12464

Re: Any Radar that can trace the location of the radio transmitt

Basic idea is pretty simple, you can find the direction according to signal strength or arrival time (phase difference). In actual operation, it‘s simpler to do according to the signal strength. You need to have two dongles equiped with yagi antenna and putted in different location, then rotate them...
by Github
Sat Feb 03, 2018 11:51 am
Forum: Off-Topic
Topic: What are we actually doing when increasing the gain?
Replies: 6
Views: 4555

Re: What are we actually doing when increasing the gain?

I have a new understanding to the RF gain, don't know if it is correct or not. A LNA amplify everything include thermal noise by 30 db, then decrease 1 db to the SNR. And the reason we need high gain low noise figure LNA is because ADC needs more power to work better as long as the signal doen't ove...
by Github
Mon Jan 29, 2018 8:26 pm
Forum: Off-Topic
Topic: What are we actually doing when increasing the gain?
Replies: 6
Views: 4555

Re: What are we actually doing when increasing the gain?

I did some calculations by myself, I realized when reciever has the same noise figure as an LNA, or antenna noise temperature is too high, add a LNA is meanless. So when a signal is really really weak at antenna end, it is equivalent to high antenna noise temperature, am I correct?
by Github
Mon Jan 29, 2018 8:02 pm
Forum: Off-Topic
Topic: What are we actually doing when increasing the gain?
Replies: 6
Views: 4555

Re: What are we actually doing when increasing the gain?

Ok know I understand. From my understanding, every receiver have a noise figure (rtl sdr is really high!), when an input signal enter receiver, it needs to be amplified to overcome noise figure, because noise figure doesn't change when gain changes. The guy in video used a differnt way to approach t...
by Github
Sun Jan 28, 2018 6:56 pm
Forum: Off-Topic
Topic: What are we actually doing when increasing the gain?
Replies: 6
Views: 4555

Re: What are we actually doing when increasing the gain?

One hypothesis I can come up with is that an amplifier only amplify natural/human noise (universe noise, sun noise, out of band noise etc.), it doesn't amplify thermal noise. So the signal strength after an amplifier should be input signal strength + amplifer gain - amplifier noise figure - all nois...