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

I made a few NE602 or 612 converters in a symmetrical configuration, because it has a gain by 3db greater than in a non-symmetrical system. Symmetrical has 3K input and output resistance. I made the adjustment to 50ohm on transformers with a ratio of 7.75: 1. Two-hole cores obtained from baluns of television antennas. Of course, you can use other cores that will work in the range of up to 80MHz, for that at the input of the low-pass filter and the output of the high-pass. Both filters designed in RFSim99 to suck from the net for free. For this 50MHz generator. I recommend it works great. The whole structure complies with all the rules in this field. It is about matching the resistance, which is important because hardly anyone matches the impedance of the mixer to the impedance of the filters. Here you can see what the correct fit of the NE602 cube looks like in various configurations. If anyone wants, I can draw a diagram, but just download the application of this cube and everything will be clear.


http://www.electronics-tutorials.com/devices/602.htm

If you can find some time, please outline your converter circuit with input and output circuits.
I would like to do and compare how it works. I have some problems here due to possible lack of matching to the mixer. Maybe this will be the golden mean
And the program, or actually filter design programs, is currently testing but instead of getting clearer, a lot of question marks appear ;)


Best regards!!

Here is a diagram of my project. For the filter coils, I only gave inductances, but this can be easily converted with a calculator for converting inductance to turns, winding length and coil diameter.

Filters designed for 50? I / O resistance. The high-pass filter has been calculated for the cut-off frequency of 47MHz. At this point it has -3db attenuation, and the input or low pass filter has a cutoff frequency of 31MHz, here it has -3db attenuation.

Thanks for the diagram. I will put it together for sure, maybe even today and let you know about the effects here.
While the impedance of the mixer and tuner is clear and it is easy to transform it with a suitable circuit, what should be done with an active antenna of the "Mini Whip" type

Do you think that when designing the low-pass input filter, its impedance other than 50R should be taken into account? And how much of this antenna actually has this resistance seen from the side of the system?

I am asking because while playing with the filter simulations, you can clearly see that by connecting a different "load" to the input than the 50R for a given filter which had a nice flat characteristic, it becomes uninteresting and according to what is shown on the chart, the filter should be recalculated for this other antenna. This also applies to most of the antennas used by users here, i.e. a piece of wire with an impedance not closer to each other. How to consider it whether to take it into account at all or simply agree to losses by mismatch.

It is also possible that I am thinking wrong, maybe someone will explain to me?

Each antenna is connected via a cable, usually 50?, so the TRX is not converted to other input resistances, but you only need to adjust the cable and the antenna to the TRX. So I am trying to do TRX to the standard resistance. What if someone did not have a suitable antenna and used a cable other than 50? And dismantled the radio to adapt it to the existing antenna system . The radio is to have 50 ?, and the antenna system needs to be adjusted, although when it comes to the reception itself, some major mismatch will still pass. If you want to send on a random wire, buy yourself a kilogram of tips, because you will burn them, and as they say, you will fly from the window to the yard . In the case of these converters, you will listen to a lot with about 10m of wire, but such wire should be connected via the antenna cable anyway, because the antenna must be away from the computer, TV, etc. Otherwise there is terrible "shot" and it is difficult to catch distant stations, especially at 1.8 and 3.5MHz. It is also worth powering the converter from a transformer power supply, not from USB or, for example, a 5-volt phone charger, because it is very humming.

I made this layout of the converter with a symmetrical input, but for the moment I did not compare with the previous layout because I took my block off the roof, MINI WHIPA and hooked up to the "Long Wire" which I have hung up here and annoying the building maintenance man. I am testing the antenna preselector as part of the fight against QRMs ;)

I know that TRXs have a standard 50? input as well as antenna cables for this equipment. What ends broadcasting on the antenna with high WFS, I know because about 15 years ago, when CB was more popular, I "exchanged" 2sc2078 2sc2075 and similar, sometimes with a driver, on radio which people broadcast from a curtain rod or bicycle rim, praising it on 11m airwaves ;)

Maybe I did not express myself well in the question or I was not fully understood, but it is not very important, I already understand the topic myself. I had a bad understanding of how the filter transfer characteristic looks depending on the impedance of the loads.

I have been supplying the laptop with a transformer power supply for a long time, because I have a "noise-phono" on the original one, I have already mentioned it and I advise others to do so.

And it is possible to transmit from a random piece of wire quite effectively, without burning silicon, of course through the appropriate ant box. :D

Coming back to MINI WHIP those who do not have the possibility or want to have washing hangers over 20 m long, go ahead and fold them and look for a pole.
Antenna properly placed above the roof works very well.
There are a few modified antennas of this type and I want to test them before I leave the "pole" permanently.

Sorry with the post, but today I put on a MINI WHIPA on the roof after a slight tuning in the form of changing the transistors to j310 / 2n4427 and the former BF245 / KFW17, plus a change of ceramic capacitors, which apparently work badly on MKP here.

It is connected to the NE612 converter and the effect is interesting.
Earlier I had good reception of KF, but going down the frequency, the last thing that could be heard nicely was the PR1 225kHz and a little LORAN at 100kHz.

Now the PR1 has a signal until it goes out of scale and reception actually starts from scratch.
Transmissions from ALFA at 10-14kHz can be seen very well, despite the disturbances and crackles from lightning. These are the short vertical lines next to each other


I think that it will be possible to receive SAQ transmissions on VLF 17.2kHz, it will be the best test.

It would be nice to see a movie with bandscans and some interesting dxs on commercial stations and ham radio bands. Such a set rtl-sdr + downconverter + mini-whip is an interesting set for a beginner, which is inexpensive for a lot of possibilities and the antenna has a lot of possibilities, small dimensions, it is easy to mask when our neighbors for some reason do not want antennas on a common roof. In case of strong interference to which the mini-whip antenna is sensitive, x-phase is very helpful, which I have recently had and use with mini-whip and de1103. With the help of such a set, it is possible to monitor even in a block where the aether is very cluttered and there are no conditions for a "normal" antenna.

@methyl and tell me how this antenna behaves, as if I put it on the windowsill on the ground floor of the building, because unfortunately I have no other option I just wanted to get one on BF245 eno I am still looking for a rather overwhelmed scheme

The question is not directed to me, but let me answer it. The mini-whip antenna needs space and placing it in the eye is a bad idea as it will have a very weak signal. You could hook this antenna on a tree if it grows near your window. The thin conductor will not be noticeable, and certainly the signal from the antenna placed on the tree, preferably at the top of the tree, but as far as possible from the walls of the buildings, will give a much better effect than placing the antenna on the window.

@ Ganjor86 the problem is that there is no tree near my window, and I can not put the antenna on the roof because the conservator of monuments does not agree ... But I will try something with this antenna as I will have a diagram

Jezzman - To see how Mini-whip works, you do not need to watch the movie, you can organoleptically test its operation on the website WebSDR . As the previous speakers say, this active antenna does not like the presence of metal elements that suppress / bend electromagnetic radiation.
http://wwwhome.ewi.utwente.nl/~ptdeboer/ham/tn/

Maybe on the ground floor, in your conditions, however, magnetic loop would have been better. The mini-whip is a great little antenna, but it needs to be in the right conditions.

Only that magnetic-loop, as far as I know, is an extremely band antenna, unlike Whip, but it can be transmitted from it.

Jezzman, I live on the ground floor myself and sometimes tested the Mini Whip "outside the window".
If you equip yourself with a 2-3 meter long pipe / fishing rod and after attaching the "Mini Whip" to it, you put it out of the window, eg at night, so as not to scare people, you will hear something accompanied by disturbances and noise. Unfortunately, in order for the antenna to work properly, it must be the highest point within a radius of at least a few dozen meters.
The antenna reacts to the electric component of radio waves, so the perfect place for it is a tin roof where it will have something to breathe ;)

I have tested many antennas and if you really want to hear something more from the ground floor, it is just "magnetic loop". Its advantage is that it works even while standing in a room, less efficient but it works. Its narrowband nature is both an advantage and a disadvantage.
This makes it difficult to search the band but eliminates a lot of interference from strong stations.

Some people suggest active loop antennas and other inventions, but for me it did not work at all in ground level tests.

Additionally, magnetic loop is bi-directional, not omnidirectional, and its manufacture is simple and its components are cheap.

Ganjor86 wrote:

Additionally, magnetic loop is bi-directional, not omnidirectional ...

Are you sure?
What is the polarity of this antenna when it is placed horizontally above the ground?

Then it is ocular but gives a weaker signal.

As a curiosity, it gives a screenshot of the "tracking" frequency of the heterodyne / oscillator of the Philips mini-tower tuned every 50KHz . I believe that there was no antenna in the antenna socket and the sensitivity of the SDR was at a minimum ... After all, I know which radio stations the neighbors are listening to ...

It's nice to see how the heterodyne is retuning. I recently saw a signal from a wireless mouse by accident. It turned out that it works at 27MHz and draws nice signals on the waterfall when it is working.

Why do you have such a strange SHIFT set in SDR # ??

General curiosity
I recently installed Ubuntu 14.04 and
pros
- there is a packet rtl-sdr
https://launchpad.net/ubuntu/trusty/+package/rtl-sdr

- Gnu radio is now in the repositories
https://launchpad.net/ubuntu/trusty/+source/gnuradio

- GQRX is in the repositories.
https://launchpad.net/ubuntu/trusty/+source/gqrx-sdr

minuses
You have to turn off the standard driver either permanently or before using the dongle in sdr mode.
sudo rmmod dvb_usb_rtl28xxu rtl2832

There is no native support for SDR going from kernel 3.15
http://www.rtl-sdr.com/rtl-sdr-native-support-coming-linux/

Hello....
I would like to try to hear what squeaks on low frequencies as an amateur
below FM, therefore planning to buy a receiver to receive RTL-SDR, first however
I want to ask about the antenna, I have this antenna http://www.dipol.com.pl/antena_radiowa_dipol_1ruz_pm_b_A0221.htm in the passive version, will it be suitable for
beginning to receive SDR?

jarekm27
Two wires, a piece of concentrate, possibly a broomstick to eject from the balcony and the plug and you have the antenna. The length of these wires is adjusted to the frequency.

The second question is how low do you want to go down because you may need an upconverter.
There is also a lot to listen to above

http://www.rtlsdr.com/2013/07/fractal-antenna-for-use-with-rtl-sdr-or-your-hdtv/ " target="_blank" rel="nofollow noopener ugc" class="postlink inline" title="" > http://www.rtlsdr.com/2013/07/fractal-antenna-for-use-with-rtl-sdr-or-your-hdtv/ Anyone tried this before? Apparently it is supposed to work from 50MHz to 1GHz or at higher frequencies.

All in all, I would like to test the whole band as much as the receiver would allow ...
I live in a single-family house, I would have no problems with this stick
screwed to the mast, maybe you have some schematics for these antennas,
what would you do yourself ...

The easiest way to start is an open dipole. Of course, it is matched to the frequency.

SDR with the r820t tuner allows you to listen to frequencies from 24MHz to 1850MHz so there is plenty to listen to and using the upconverter you can listen from really low frequencies, i.e. 10KHz (and maybe even lower using the appropriate parts) to 1850MHz. There is something to listen to. And so, out of curiosity, what is interesting to listen to from 500MHz to 1850MHz and whether it is possible to build a downconverter with e.g. 1800MHz and then it would be possible to receive frequencies up to 3600MHz but something feels that it is impossible because someone would have already figured it out.

There was something mentioned somewhere with the down-converter, probably even on this subject. There was also a link I think.

ASDB works on 1030 interrogators and 1090 replies from planes.
As for the downconverter, the sat converter is a down converter.

jarekm27 -As you can on the mast, the J-pole antenna is a two-band 144 / 433MHz
or even a single stranded one, it can be scraped from the copper pipes and elbows of the CO installation, or from the old 300 Ohm symmetrical cable.