Архив за 27.09.2019

Help needed troubleshooting my setup for Meteor M2/NOAA reception

Help needed troubleshooting my setup for Meteor M2/NOAA reception

Hi,

I have recently started capturing images from NOAA satellites using the V-dipole antenna supplied by RTLSDR Blog. This worked great for the most part, I was able to receive some nice pictures. After some time I decided to build a QFH antenna for Meteor M2 reception and better NOAA reception. I build the antenna according to the schematics at jcoppens.

I placed the antenna in mostly open air, about 5 meters from the ground on a roof. There are a few large buidings around me, but nothing taller than 12 meters and nothing closeby. The antenna can be seen here:

https://i.redd.it/xf4pjk6qm6p31.jpg

I build it using the following materials:

  • PVC tubes for the body
  • 3D printed parts to hold the conductors in place
  • 2.5mm2 solid copper installation wire (3 arms, see picture). This is the standard type of wire used in home electrical installations, I bought it at the hardware store. I did not cut these to the size specified by jcoppens because I expected if I cut the PVC accurately enough I could guide the copper into the right length. This may be part of the problem?
  • About 7 meters of RG58 50-ohm coax (1 arm and feed wire)

Installation wire used in three of the arms

The arms and coax are soldered according to the following diagram, which can be found at www.rish.kyoto-u.ac.jp:

https://i.redd.it/oogxfctht6p31.png

As seen in the above picture, this design uses the coax for one of the arms. Another interesting thing is that S1T and B1T (Small 1 Top, Big 1 Top) connect to the central conductor but at the bottom also connect to the braid, resulting in a short circuit. I don't know if this happens often in designs since I know very little about antenna's, but it feels strange to me. I could find very little information on this online, it would be helpful if anyone could clarify this for me. Note that this design results at the feeding point being at the bottom of the antenna. As recommended by the design I also made a balun directly under the antenna, this can be observed in the first picture.

Reception is done using an RTL-SDR Blog V3 dongle. I also have a knockoff HackRF One which I use every now and then. I'm very happy with the construction, it's solid and the 3D printed parts make it easy to guide the conductors. Here are some of the images I captured from NOAA satellites:

https://i.redd.it/20zkn44lo6p31.png

https://i.redd.it/52wqhhnmo6p31.png

I have not been able to sucessfully aquire pictures from longer passes than the image above shows. When using SDR# I can see the SNR is about ~15dB at the best point on a good pass, which is kind of dissapointing. Using an LNA completely distorts the NOAA picture resulting in no picture at all most of the time, I have tried two different LNA's both with similar results. Powering them from the Bias tee, an external powersupply or a raspberry pi seems to make no difference.

Now it's great I can receive something from NOAA but the real goal was to receive pictures from Meteor M2, which should be harder and requires a better antenna. Using the QFH, I get no signal from Meteor M2 at all. I've tested for a couple of days, with some really good passes but the signal is never there.

I recently purchased a NanoVNA to do some testing. While the antenna was on my roof I made the following chart:

https://i.redd.it/otdiol7uv6p31.png

The diagram shows almost no sensitivity around 137 MHz. This leads me to believe there is an issue with my antenna, but I don't know what. I also noticed I have quite a number of strong FM radio stations around my location, which may distort my reception:

Image captured while using the LNA

It would therefore be helpful if anyone has advice on what to do. Modifying the antenna should not be difficult.

I hope this is enough information, but feel free to ask anything.

submitted by /u/langestefan
[link] [comments]

Troubleshooting Help • Re: Rtl-sdr 1090mhz LNA

Thanks.

Statistics: Posted by snackerl — Fri Sep 27, 2019 10:43 pm


LNA with very simple variable gain control?

This is an idea that's been knocking around in my head for a bit, if you put a variable resistor between an LNA and it's power supply, could you use that resistor to change the power going to the LNA to control the LNA gain and get exactly as much amplification as you want, or do LNAs not work that way?

submitted by /u/DuckEsquire
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KerberosSDR • Re: direction finding of short pulses

On most computers the system samples about every half second. 20mS pulses are too short for the system to pick up. With some optimizations to the code and a really fast computer, it can sample faster. Apparently a problem with sampling too fast is that it will lose sync, then the bearings become garbage.

Statistics: Posted by ckoval7 — Fri Sep 27, 2019 8:57 pm


KerberosSDR • Re: Direction finding for intermittent signal

I already posted a related question before noticing this thread.

I'm a wildlife biologist, and this could be a game changer for tracking radio collared wildlife. The signals are very short duration pulses (20ms) at regular intervals (once every second or two).
If the system could be told the pulse interval and pulse width, and somehow pick the pulses out of the noise, that would allow automated radio tracking without using directional antennas.
Right now the only way to locate collared animals is using directional antennas. some researchers have set up arrays of multiple directional antennas for direction finding, but they were just using relative signal strength, rather than phase differences. The systems were huge and expensive.

to really be useful for locating a moving signal, you would need multiple stations that could each get simultaneous direction bearings on each pulse.

If I had a wish list of features:
the system could log the direction of each pulse, and multiple arrays could be used to triangulate the animal's location.
It might even be possible to incorporate some kind of mesh network to allow the receiving stations to relay their data to a base station where the data logging and triangulation could happen. If each station had a GPS and compass built in, you could just deploy several stations in a semi-random pattern across the landscape and they could each automatically determine their own location and orientation. The location/orientation could be included in the data being sent to the base station, and used in the triangulation calculations.

Statistics: Posted by mousedude — Fri Sep 27, 2019 7:51 pm


This peace of garbage got my group a award on science fair.

This peace of garbage got my group a award on science fair. submitted by /u/Gui_OiMeuChapa
[link] [comments]

KerberosSDR • direction finding of short pulses

What is the minimum duration of a radio signal required to obtain a direction bearing?

I've seen demonstrations of direction finding for continuous radio signals, but can this be used for short pulses? The reason I'm asking is because this system might be useful for tracking wildlife radio collars. These collars usually transmit short (20ms) pulses, about once per second. Is it possible to locate a signal of such short duration?

and on a related note, Could multiple stationary Kerberossdr antenna arrays be used to triangulate the position of a moving transmitter in real time?

Statistics: Posted by mousedude — Fri Sep 27, 2019 7:20 pm


Comment on Electrosense: RTL-SDR Based Crowd Sourced Spectrum Monitoring with a DC to 6 GHz Up/Downconverter by Laurin Cavender

How little you realize! This has been done for over 50 years, with predetection recording. When I was but a young and adventurous RF Explorer I built just such a Rube Goldberg device in the late 1960’s. I became aware that video recorders put out signals in the 80 meter ham band. Realizing that when I played back a taped prerecorded session it caused the same signals to be present at the same exact frequencies I studied the service manual for the video recorder that I was working on. Upon studying them very closely that these video signals were in the 3 to 4 megacycle (now called MegaHertz) range both on record and playback. I then tried first hooking an antenna into the video input ( with very little but noticeable results!) I then added an Ameco tunable recieve preamp in line between the antenna and the BNC video input. After tuning it to the 80 meter range I recorded and then played it back listening with my old National NC109 reciever. Over and over I heard the same signals. I did a deeper dive into the service manual and found points closer to the record and playback heads that served my purpose better. I soon acquired a similar recorder from a local cable tv station that they were nolonger using due to upgrade. I got the required service manual on that unit after confirming that it functioned the same as the first unit had, I proceeded to modify it to my purposes. I found the best point to apply my preamped antenna input signals, then found the cleanest strongest output signals from the tape head and fed them to new BNC connectors mounted on the rear of the unit. I then realized that I needed a way around the tuned input. I found some preamps made by HP at a Radio. Swapmeet. No one much at that time knew what good they were, so they were cheap for a while. Once it was discovered that were for use in the input section of extremely expensive HP Frequency counter that covered up above 1000 Megacycles, not only were they literally Gold but Gold in the eyes of experimenters because 2 meters was all the rage and 450 was coming on, so everybody but everybody wanted preamps to improve their receiving equipment. This drove the price high on these items (as it is still today, when they are available. ). These are wideband preamps, VERY wide band, covering way more than the recorder was capable of, I even used these on the 6 meter band, but I digress. Meanwhile back at the ranch, I built an addition to my setup by enclosing one of these HP preamps in a metal RF sealed enclosure and putting the wideband preamp in place of the frequency tuned one. Now I could run my recorder come back later and play it back and tune up and down the bands with my reciever and listen to various signals on various frequencies over and over. I discovered that on the bottom end my limit was my receivers capabilities which was around 500 Kilocycles. The top end was a little over 10 Megacycles. The receiver was hot enough here, I knew that from frequently listening to traffic in the 11 Megacycle range. But the recorder or the playback section was almost nonfunctional above 10 Megacycles. Sure I could hear WWV and the Strongest of stations on 11.175 Mhz but not much else up there. However down at 2.5, & 5.0 WWV was excellent, conditions permitting. 160, 80, 40 Meters were really functional. I added an old Pan-Adapter that came from an old WWII Radar and Surveillance set up so that I could see either side of the frequency that I was tuned to. This all predated Spectrum Analyzers as we know them today, and long before that I could afford one. With my setup I could record when I had to leave, then when I got back, rewind tune to the desired frequency and listen. Once I heard something of interest (i.e. an interfering signal) I could then tune WWV and know the exact time of the incident. That is the way that the FCC finds offending signals. A report is made of interference on a certain frequency, they pull up the time frame in question, go to the frequency in question and document the interference as evidence of the occurrence. This is the way predetection recording works in principle, while there have been enormous advances in technology, the premise remains the same today. The FCC has shuttered many of their field offices, and the monitoring stations are all but unmanned. Routine maintenance and other scheduled events are still manned but most of the time they are simply remote stations for antennas and remotely operated SDRs. Those stations are mostly remotely monitored by other machines recording wide swaths of frequencies that can be pulled back up and investigated at any future time. Those records are stored in a giant server farm somewhere for those who need access to have at their disposal at some future time. Laurin WB4IVG

Comment on Building An Open Source SDR Based Hydrogen Line Radio Telescope by Jose Rodriguez

I checked their document: the antenna has 18 db of gain and 20 deg aperture, so couldn’t a Yagi antenna be designed to these specs? I am thinking a smaller mount.

Comment on Building An Open Source SDR Based Hydrogen Line Radio Telescope by Jose Rodriguez

I checked their document: the antenna has 18 db of gain and 20 deg aperture, so couldn’t a Yagi antenna be designed to these specs? I am thinking a smaller mount.

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