RTL-SDR - an SDR receiver from a cheap DVB-T tuner on a USB connector

Tomek... wrote:

Well, you can see what it is like. I took up the subject of SDR 2 weeks ago, I want to finally listen to the 80m band after 16 years of break. For now, 2m and the vicinity can be heard and it would be useful to go lower, and because I wanted to have something in one box, I'm looking for something interesting for reasonable money. For now I have LV5TDLX working with different antennas and it's pretty cool, we'll see what happens next.

However, I am in favor of not having everything in one box. I think then you have more control and possibilities over the equipment. Besides, I am of the opinion that if something is good for everything, it is usually good for nothing. If you buy a regular, cheapest tuner based on the above-mentioned chips and then buy a few different upconverters, then it will be enough to start with. You will see for yourself how different each structure works. In addition, you also deepen your knowledge then. That is why I think that when buying ready-made constructions, I think that we limit ourselves in some way. For example, when I bought one of the upconverters, I even got a schematic in case of modification Tunerek, on the other hand, is easy to understand. Scalaki and their derivations are widely available, for example here: http://www.datasheetspdf.com/PDF/R820T/792285/1 Nothing but to have fun and create

Direct sampling is better instead of converters. Then we have DC reception up to about 30Mhz. I have one decoder from musu so connected (after the storm the r820 tuner fell, RTL2832 survived). For this preselector. 40m, 20m, 15m, 11m bands, and KF broadcasting stations, and sometimes in good weather I receive something from the sea / ocean. Home Made GP antenna for 70cm band, on a 3 meter mast. 6 meters from the ground.

arturavs wrote:

Direct sampling is better instead of converters. Then we have DC reception up to about 30Mhz. I have one decoder from musu so connected (after the storm the r820 tuner fell, RTL2832 survived). For this preselector. 40m, 20m, 15m, 11m bands, and KF broadcasting stations, and sometimes in good weather I receive something from the sea / ocean. Home Made GP antenna for 70cm band, on a 3 meter mast. 6 meters from the ground.

I tried but I do not recommend it. From what I remember, you had to connect the antenna to another leg of the system. He had quite a weak sensitivity for me. After using the upconverter, more stations appeared immediately.

The issue of adequately accurate implementation of modifications for direct sampling. Simply plugging into inputs I and Q of RTL2832 does not guarantee the effect. You have to completely disconnect the tuner circuit from the converter, and use an appropriate wideband transformer at the input (desolder the DC component separating capacitors between the tuner (eg R820T and the RTL2832 converter). Otherwise the sensitivity will be poor. The tuner significantly attenuates the signal for the converter.

arturavs wrote:

The issue of adequately accurate implementation of modifications for direct sampling. Simply plugging into inputs I and Q of RTL2832 does not guarantee the effect. You have to completely disconnect the tuner circuit from the converter, and use an appropriate wideband transformer at the input (desolder the DC component separating capacitors between the tuner (eg R820T and the RTL2832 converter). Otherwise the sensitivity will be poor. The tuner significantly attenuates the signal for the converter.

Both capacitors have been desoldered and the antenna is connected experimentally to one of the two inputs. I even made a loop of about 300m of cable and connected between I and Q by shorting. Of course, something is always picked up there, but still, through the upconverter, I had much better performance. Fact, I did not try the broadband transformer. Do you think you would settle the matter?

I and Q are the differential inputs of the ADC of the RTL system. The next pins are: 1-I + (positiv), 2-I- (negativ), 3-GND, 4-Q + (positiv), 5-Q- (negativ) !! If you connected the antenna to I and the ground to Q, no wonder that it does not work ... Again, I repeat again: tuners based on R820T / T2 chips do not use the Q input !! Link

I had fun with this site:
http://www.rtl-sdr.com/rtl-sdr-direct-sampling-mode/

You can buy a version of the tuner with a generator instead of quartz and there is already a prepared output for the HF antenna. The description is on the page below.


http://www.rtl-sdr.com/modifying-an-rtl-sdr-by-adding-a-diplexer-to-receive-hf-and-vhfuhf/

The HF input can be put on a separate socket and both HF and VHF antennas can be connected, and we switch only in the dongle settings of the band we want to listen to, switching between Direct sampling Q and Quadrature sampling.

Hello, how to make a good sdr antenna? such as to receive CB, satellites, police services, etc. and some cheap or simple amplifier to be made

Well, you have a lot of spread when it comes to the bands you want to receive. One antenna cannot receive all frequencies with the same efficiency. Therefore, it is best to have a separate antenna tuned for a given frequency range for each band. It can be, for example, a simple dipole (omnidirectional antenna) or a Yagi (directional antenna). Calculators for calculating the dimensions of antennas are available on the Internet, but I suggest you first read and familiarize yourself with the subject of antenna construction. There are plenty of articles on the web on this subject, and there are also many specialized books.

I connected the antenna from cb and silence, maybe I live in the countryside, I can not hear anything, I have to go to the city somewhere and then I will see

Added after 1 [minutes]:

Xantix wrote:

Well, you have a lot of spread when it comes to the bands you want to receive. One antenna cannot receive all frequencies with the same efficiency. Therefore, it is best to have a separate antenna tuned for a given frequency range for each band. It can be, for example, a simple dipole (omnidirectional antenna) or a Yagi (directional antenna). Calculators for calculating the dimensions of antennas are available on the Internet, but I suggest you first read and familiarize yourself with the subject of antenna construction. There are plenty of articles on the web on this subject, and there are also many specialized books.

And a schematic of some amplifier?

grzesiu16lat wrote:

I connected the antenna from cb and silence, maybe I live in the countryside, I can not hear anything, I have to go to the city somewhere and then I will see

Normally my hands drop as I read this. After all, such an antenna is a short circuit for the bands you want to receive (it is about various services from the 2m and 70cm bands). You will only receive something when the station broadcasts very closely. Make a dipole as a colleague advises.

You have not written what tuner you have.

Thus, the subject of antennas appears in this thread from time to time. Look for.
One more thing. Maybe your sensitivity is twisted that you don't hear anything.

kriss51 wrote:

grzesiu16lat wrote:

I connected the antenna from cb and silence, maybe I live in the countryside, I can not hear anything, I have to go to the city somewhere and then I will see

Normally my hands drop as I read this. After all, such an antenna is a short circuit for the bands you want to receive. You will only receive something when the station broadcasts very closely. Make a dipole as a colleague advises.

There is no need to give up A lot of laymen and beginners here. Patience can be learned :P

As for the topic, you can try to convert the CB antenna by changing the coil in the first place.

It's just that it's a pity for the antenna, because they will probably barely pull it from the car .... Amplifier ?? the first better than a mesh antenna is enough to start with. In the town and in the vicinity of your profile, there are a lot of stations that you can pick up without an amplifier!

There is also something about amplifiers in this thread. Post 307.

@ kriss51 There is almost everything in this topic, links, etc etc ... but you have to read and be willing to understand. After all, 23 pages and 675 posts can't be about anything ....:]

For those who did not play direct sampling, the information that apart from the galvanic separation and impedance matching in the form of a properly wound ball-una hit, one should use bandpass filters, especially above 14 MHz. Due to the way this connection works, from 0 to 14.4 MHz is tolerable and above 14.4 MHz the eggs start because there are signals from above 14 and below 14 MHz mixed together.
I've seen this mess with my own eyes and I wouldn't recommend it without filters

Make a preselector like this:

http://sp-hm.pl/thread-1648.html

For such a simple system, it works great.

I recommend the preselector from the attached link and also say that it works great. It is very narrow and introduces attenuation, but on HF, if we have a long wire antenna, it is an advantage. A strong signal from the antenna introduced to a converter built on, for example, NE (SA) 612 (602) causes a total mess and you need to use an antenna attenuator. This is where the preselector takes care of it.

One note. This preselector must somehow be forced to work above 10 MHz.
It is good up to 80m, 40m, 30m but higher up you would have to reduce the coil, not only the number of turns. For the 160m band, I added additional capacitance to the variable capacitor and had an additional number of turns on a separate tap.

I recommend !

grzesiu16lat wrote:

Added after 1 [minutes]:

Xantix wrote:

Well, you have a lot of spread when it comes to the bands you want to receive. One antenna cannot receive all frequencies with the same efficiency. Therefore, it is best to have a separate antenna tuned for a given frequency range for each band. It can be, for example, a simple dipole (omnidirectional antenna) or a Yagi (directional antenna). Calculators for calculating the dimensions of antennas are available on the Internet, but I suggest you first read and familiarize yourself with the subject of antenna construction. There are plenty of articles on the web on this subject, and there are also many specialized books.

And a schematic of some amplifier?

What the hell should I give the amplifier right away? First, make a decent, well-tuned antenna, even this simple dipole, and you will see for yourself how much you can hear. The amplifier is not the "key to luck" when it comes to picking up weak signals. If that were the case, the producers of TV antennas would attach a nice box with a super-sensitive amplifier to the piece of nail and the reception would be excellent. And it is known that the construction of better TV antennas differs significantly from the construction of the nail. What's more, if you have a bad antenna, the amplifier will make things even worse. Because it will amplify both the useful signal and the "garbage" signal, i.e. the useless signals. So first make a good antenna, and how will you test it and see what and how to go about the amplifier.

Honestly speaking, the key concept in many receptions is "input resonant circuit". If we manage to "match" to the frequency of receiving the stations we are interested in on the primary stage, we are delighted without unnecessary "other enhancers" ...

Using an amplifier for the SDR USB dongle is asking for trouble.
It makes sense only when we want to listen to a specific frequency to which we have a specifically tuned antenna, a bandpass filter that cuts off the entire received unnecessary garbage and most importantly, we want to get a lower noise level than the one provided by the internal dongle amplifier. So in the donglu we set the gain to the minimum and connect the LNA hoping to improve the reception.

These USB SDR receivers are extremely easy to override which results in a huge amount of garbage being produced. For this to work properly, we turn off all AGC in the dongle settings and with the RG GAIN slider in the example SDR SHARP program, we set the maximum to "28". If we have a good antenna on the roof, setting a higher gain will jam the receiver with signals from strong sources.
Well, unless we are happy inhabitants of a "radio quiet" village, I am sincerely jealous ...

Then we cool our USB dongle with liquid nitrogen to reduce our own noise and set the gain to MAX, which results in receiving transmissions from a neighboring galaxy even without an antenna.
Of course a joke ...

T.

Hello. I also became the owner of a USB dongle with RTL, R820T systems and, like some of those who write and ask for help in radiocommunication matters, I am a layman. Of course, before writing this post, I read the whole topic here as well as on other recommended forums. The receiver is installed correctly on "SDR Sharp" and GQRX (the minimum frequency here is 27MHz)
I tried listening on my CB "President Missouri" antennas and "SV Total" radio antenna and yesterday I made a 2mm wire half-wave dipole with 51 cm arms (later trimmed to 43 and 41 cm).
The best reception of the FM radio band was on the dipole, also on the dipole, I heard the 172 MHz band for 1 minute and then I did not succeed, despite the fact that there was activity around the above-mentioned band.
I would have a few questions related to the topic:
- does it make sense to "play" in finding and selecting antennas or is it better to buy, for example, DISCONE (PLN 200 for me, the price is approx.)?
- is it possible to "create" something from the "SV Total" antenna and its amplifier. (I do not have a TV antenna, I have cable and radio, I also listen to the Internet)
- is there any sense in "playing" with a donkey or is it better to buy a handheld scanner, for example:
http://www.aliexpress.com/item/Baofeng-Walkie...-174MHz-400-520MHz/555726682.html?ws_ab_test= searchweb201556_7, searchweb201644_4_79_78_77_82_80_62, searchweb201560_3 ... some recommend a dongle amplifier, others not ..?
Bandwidth on which I "care" .. services .. also 172 .. and maybe CB ..

The Discone antenna is not a perfect antenna.
I have it and a few other "comparator" antennas on the roof, and I am slowly gathering this Christmas tree down.
The reason is that it actually collects everything but it has a low return, it is deaf.
Analyzing its radiation pattern, and thus the reception (reciprocity principle), it is easy to notice that at lower frequencies the antenna still works and hears "sideways". Unfortunately, the higher the frequency, the more the antenna listens to "space". There are also other problems with it.

If you live outside the city and want to listen to what is happening from a distance of more than 20 km, I suggest a Logoperiodic Antenna (LPDA) that you can scrape out yourself.

If you are listening in the city, I recommend a simple two-band antenna in the DIAMOND x-30 style or making a two-band dipole about which you can find info in my earlier post in another topic https://www.elektroda.pl/rtvforum/topic.html ? p = 15232423 # 15232423] Link " target="_blank" class="postlink inline" title="" > https://www.elektroda.pl/rtvforum/topic.html ? p = 15232423 # 15232423] Link

See entries 47 and 50

If you are only interested in VHF, say 120-170 MHz, then a vertical dipole made of aluminum tubing with as large a diameter as possible (increases broadband) will do the trick.
Converting the antennas to the CB band is pointless.
The SV Total antenna is in the radio range and only works properly there.
Buying a scanner is the convenience of having it with you. I have several scanners and most have worse sensitivity, selectivity and resistance to strong signals than a DVB-T USB dongle. What you have pasted is not a scanner but a portable radio, a duobander. It is not suitable as a scanner. Even the scanning of pre-programmed frequencies as channels is so slow that it makes you nervous. You want a scanner then look for AOR, better UNIDEN, ICOM, .....

The most important thing that I say very often is where the antenna is.
You want to hear, the antenna has to be high. It cannot be obstructed by buildings.
Better a random piece of wire on a roof mast connected with a good cable to the receiver than a super-tuned and sensitive antenna but at ground level.

T.

Thank you very much for help. She explained a lot to me. After the next reading, I invented something like this:
http://www.ebay.pl/itm/UNIDEN-BC72XLT-SCANNER...193064?hash=item21077780e8:g:sa0AAOSw3KFWedFo
I will assemble the antenna after Christmas, like the one from your post about antennas .. Write also how it is connected (or like "half-wave" .. hot to the top and braid to the bottom)

I advise against buying such equipment if it is to work under an antenna larger than the built-in or "housewarming" antenna. I had identical hardware and got rid of it quickly.
It is totally immune to strong signals. If you come across a radio transmitter nearby, the radio becomes a garbage can and loses sensitivity by clogging the input stages with a foreign signal.

If the scanner is decent with better electronics than toys like this.
Unfortunately, a "good scanner" is from 700-800 PLN for a used one.
At the moment, apart from various DVB-T dongs, I have AOR-2000, Albrecht AE-300, Icom IC-R10 and I have been reworking several other models. Of the ones above, only the Ic-r10 behaves quite decently.
A suggestion from my side, look around for the older UNIDEN scanners, the less miniature ones, or the Radioshack in this right size too. There is a lot of it on the Allegro. For PLN 200 you can have equipment that may not fit with the antenna in your pocket but has better parameters than these micro toys.

Or go crazy and for example ICOM IC-R20 or something of that class :)

You power the antenna like a dipole. Hot to top, screen to bottom.
Make a few turns of the coaxial cable near the antenna connection point and fasten it with bands. It will be a symmetrizator. The antenna should be as far away from metal elements and walls as possible. Preferably on an insulating piece of mast.

best regards
T.

I built such an antenna some time ago - Off Center Dipole Antenna .
with asymmetrical arms with a built-in symertizer.
My current scanner runs on such an antenna Link
except that the vertical arms of the antenna are hidden in PVC pipes (to protect against the vagaries of the weather) and additionally stabilized inside.

Ask colleagues if anyone tried to play with Edacs but on one SDR from this link
http://users.vline.pl/~pewusoft/sdr/how.html
I mean the SDR itself with two plugins
1. AUX VFO
2. SerialController
I tried to upload these plugins several times but I still have an error
If any of my colleagues has such an SDR, I will gladly take it.
Regards, Krzych

To decode EDACS tracking, you do not need to combine anything, you normally turn on sdrsharp and UNItrunker decodes. I added sound samples in the attachment, just turn them on and play them on Virtual Audio Cable. The first file is EDACS48 and the second is EDACS96. And I will add that I have sampling set to 48000 in VAC and in sdrsharp, not like in link 96000.