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

Attached is my antenna. It was added to the set with the 1985 Otake color TV set that is still operating today. Unfortunately, only in a few days I will be able to test its cooperation with the dongl, because only then will I have the MCX-> RF adapter. The telescopes are adjustable in length from 24.5 cm to 112 cm. Unfortunately, for example, in the case of receiving digital TV in Warsaw, this antenna works poorly - it only allows the reception of MUX3 and with cuts. And planes on 1090 MHz I managed to pick up even on this "stick" attached to the dongle - and without exposing it to the outside.



However, I repeat the question from my post # 963 - maybe someone has already successfully decoded their own calls and SMSs using the SDR dongle and airprobe software?

I will not tell you anything about intercepting your conversations or SMS, because it is beyond the scope of my interests. So I just raise your question from the post above.



As for the dipole from telescopes, I just wanted to add that when using it, you should spread its arms to the full width so that they are in line.
The second thing is whether you will put it, for example, behind a balcony or window, vertically or horizontally. As for the display, make the boom a meter or two away from the wall. Forget about receiving something from the antenna at home.

and the most important thing is to tune this antenna to the range you want to receive.
And it looks like this: -7300- you divide the frequency in -MHz- and you get the length of one arm of your antenna in -centimeters-

So you want to receive 172MHz is 7300: 172 = 42.4cm each arm.

The dipole is quite broadband, so 1-3cm accuracy is enough.
The antenna tuned in this way will have better efficiency, even if it turns out that the arms must be 10cm each. Longer is not better
the antenna is to be in resonance at a given frequency and matched with impedance to the "cable" and the receiver.

Good luck

Hello.
You can read about tampering with a simple open dipole, e.g. HERE - generally, in this project, a reflector and something for the 70cm band would be useful.
Maybe someone will indicate a description of a proven structure at 2m / 70cm.
Regards.

Here you go.

Entry No. 47 and entry No. 50 in this thread:

Link

I don't think you would find a better dual band antenna with an equally simple design.

Works very well on amateur bands and hears widely beyond them.
I will just say that since I put it on the roof, I quickly fired the DISCON standing there. He was losing at every frequency in terms of signal strength.

A similar construction, but with a greater gain due to the connection of two antennas, is the construction described here:

Link

best regards
SP5MET

Thanks for the link!
And the posts you refer to: 47 and 50 - from this thread? hmmm ...
Greetings

I have already corrected in the previous post. I went to bed at 4:00. it is just the presence of the mind that comes out.

mrqpa wrote:

... maybe someone has successfully decoded their own calls and SMSes ...

I just came across such an article: http://www.dobreprogramy.pl/Sieci-4GLTE-tez-p...ie-usunie-pnecna-jest-sluzbom,News,77025.html

In the case of GSM, this was also used some time ago.
There is, however, a small but. Both in the case of GSM and LTE (UMTS also probably the rest), the substitution of such a fictitious BTS involves costs of at least several thousand zlotys.
In the case of airprobe and SDR dongle, capturing data from the GSM band is less effective, but also much easier and cheaper.

The transmission I received today is attached.
In my opinion, this is the US military, but it would be nice if some experienced ham radio confirmed it. I keep saying "thank you", "one, five", "delta". Transmission takes place (continuously) at a frequency of approx. 7.19132 MHz in the LSB.
The joy of receiving this transmission is so great that I did not have to use any dedicated antennas or upconverters. The tuner itself with the R820T2 head and the antenna from post # 991 was enough (the length of the telescopes was selected experimentally, I did not even have to put it outside, it stood in the middle of the room in my apartment on the outskirts of Warsaw).

It's not an army
The range 7 to 7,200 MHz is the range of the amateur shortwave band, 40 meters to be precise.

The amateur radio competition is currently underway and will last until midnight today.
When working on this and other bands, English abbreviations are used.

It's crowded there today. Station next to the station.
If you had a piece of longer wire as an antenna and a HF converter, you would see what is going on there. I will take a screenshot in a moment and you will see how many stations are there.

This can be heard very poorly in your recording. It should thunder.





A screenshot from before ...

Regards, SP5MET

My suggestion was that the US military uses 8.992 MHz in the LSB as the emergency frequency.
But I am happy with this reception anyway, because it is my first transmission in LSB.

methyl wrote:

Here you go.

Entry No. 47 and entry No. 50 in this thread:

Link

I don't think you would find a better dual band antenna with an equally simple design.
... CUT ...
best regards
SP5MET

Thanks!

i.e. synthetically (antenna with # 47 and # 50, in this case only for listening):
- Al / Cu tube 6-8 mm
- lengths and separation of elements as shown in the drawing
- a waveguide with an impedance of 50? and a length of = 50k? ?

best regards

All dimensions of the antenna are to be as shown in the picture.
Changing the diameter of the pipes or changing other dimensions cause a smaller or larger "detune" of the antenna.

Each symmetrical antenna, i.e. each straight dipole, requires a balun, i.e. BAL-UN, if it is powered by a coaxial cable, i.e. an asymmetrical line.

The balun can be with impedance transformation, e.g. 4: 1 and such is used, for example, for loop dipoles with an impedance of 200-300 ohms, or it can be a balun with a 1: 1 ratio. This applies to straight dipole antennas where the impedance is about 70-75 ohms.

There are many types of baluns. One of the methods of symmetrization is to use a choke in the place where the asymmetrical line connects with a symmetrical antenna. These beads are ferrite sleeves. Instead, you can make a few turns of the coaxial cable and fasten it with bands. Such a coil will be created from the "concetric" that will act as a reactor-balun. It is about suppressing HF asymmetry currents. which we block in this way.

After using a balun, it theoretically does not matter which arm of the dipole is powered by the cable shield and which is powered by the "hot" wire.

The spacing between the legs should not be larger than the element diameter.
In this case, 6mm. I have about 3mm.

The short elements are not electrically connected to anything.

best regards
SP5MET

Excellent!

OK, I will look for a 6mm tube.

As for the balun 1: 1 - I have 4 ferrite cores "up my sleeve" EMI JMLF-75 .
They are for a 75mm cable, I want to use a classic 50? Tri-lan 240 with a diameter of 61mm to the antenna - will they be OK? How many should I wear?

One more thing - should the energized dipole arms be short-circuited directly with some high resistance (2W, 50-100 k? ?

Best wishes.

Even without the balun, the antenna will work, but it will work better with symmetrization. The lack of symmetrization, e.g. with directional antennas, where the active element is a simple dipole, is particularly noticeable. Such an antenna without a balun often has "squint" In addition, without symmetrization, the antenna cable braid is part of the antenna, which results in the collection of interference, and with transmitting antennas, it causes the emission of unnecessary radiation not where it is needed.

You can short-circuit the arms of the dipole with a large resistor.
This will not worsen the reception and may reduce static noise and partially protect the receiver.

... you asked about these cores. They will probably be ok. If the inside diameter allows 2 turns of the cable through such a core, one core will suffice.
It is difficult to say without measurements, but it is better to use even when it will work in 50% than not to give at all. Worsen will not worsen.

Thanks a lot! It generally has no questions.
The ferrites mentioned above ( Link ) is a closed model like you in the picture of the antenna. I will give these with ~ 2 at the antenna.
Thanks for the time and best regards.

Are there any Polish stations broadcasting in 2m? So far I haven't found a single one, probably not counting the French at 133 MHz and 17 MHz

My colleague seems to have got the scopes and concepts wrong.

The 2-meter band is the band with a frequency range of 144 - 146 MHz.
This is an amateur band, generally exclusive to amateurs, i.e. radio amateurs with the appropriate licenses-permits.

133 MHz is the airborne range and 17 MHz is the shortwave radio range.

It's time to read a bit about the basics of radio communication.

Can I use BFR91A instead of the BFY90 transistor, is there a 12k or 1.2k resistor at + power supply, I ask because the suspiciously large gap is between 1 and 2? :)

Arek_v1 wrote:

Can I use BFR91A instead of the BFY90 transistor

You can give BFR91 but you have to change the resistance values of the resistors. Instead of 4.7K give 120K and in the collector give two serial 1.2K.

Anyway, see how the first stage of the amplifier is built on this page.

https://www.elektroda.pl/rtvforum/topic734043.html

Additionally, you can limit the frequency response with L / C elements, depending on what band you will use this amplifier in.

Today, on the 434.687MHz frequency in WFM, I received a transmission from some plane or modelers from the conversation, you can deduce that they are trying to fly over the clouds but one of them is afraid of icing I looked on the internet but I can't find what purpose this section of the band is for / who is transmitting, can someone help me ??

https://pl.wikipedia.org/wiki/Pasmo_70_cm

If it is WFM, I would bet more on leaks from UHF cable than the 70 cm band.

mrqpa wrote:

If it is WFM, I would bet more on leaks from UHF cable than the 70 cm band.

It wasn't 100% leaks from the cable.

I think it could have been Narrow FM and only the show was set to WFM

And how can you minimize interference from cable networks?
There are 4 cable operators in my estate and they "sow" as much electromagnetic smog as they can.
This is especially noticeable in the VHF band and the bands below 80 MHz (CB, some amateur). Analogue TV audio, reverse channels and wired internet significantly deteriorate the reception quality on these bands.

Shielding your receiver may help, so it's worth a try.

mrqpa wrote:

And how can you minimize interference from cable networks?

Pressing them down to seal the net.
M.

Is it possible to decode the EP code? I've been playing with DSD recently and some transmissions are encrypted.

No, because the key value does not fly by radio. This only is the ID of the key you see in DSD.

The key value consists of the following characters: A, B, C, D, E, F and 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

The key value can be up to 10 characters long.