Архив за 04.11.2017

lowering noise floor at 137Mhz for weather sat reception

I've spent the last week or so tracking down some of the noise sources affecting my weather sat reception at 137 MHz. I've been using rtl_power and heatmap to measure the differences between adjustments. Last night I managed to get some data from a METEOR pass (5% of packets, up from 0.1%, woohoo!). I've found some improvements and I thought I'd share.

My setup is an orangepizero with a usb extension to a rtl dongle. The rtl dongle is attached a airband filter, LNA, and turnstile antenna. The oPiZ is connected back to the local network with a 50 foot cat5 cable which carries signal and power. To power the unit I has a AC to DC PSU set to 18 VDC and at the oPiZ I have a DC/DC block to drop the DC back down to 5 volts for the oPiZ and the LNA. I'm running some scripts to record and process both NOAA and METEOR 2 passes.

  1. power supply noise
  2. Surprisingly the ebay DC/DC block i'm using as a POE adapter is not the culprit.
  3. I spend about a day trying various chokes, filters, and changing grounds point with little to no change.

  4. Ethernet noise - definitely the culprit.

  5. after messing about with the PSU filtering I tried dropping the ETH0 speed to 10 Mbps. There was an immediate change in amount of noise on the waterfall. It turns out the ethernet connection is the source of most of my noise.

right now I've got the following adjustments made * filtering the cat5 cable with clamp on ferrites. I've got two clamp on type ferrites on the ethernet cable to my oPiZ now. one at the switch and one at the oPiZ. there is noticeable decrease in strength of vertical bands on survey. however operating at 100Mbps doesn't work well any more.

  • drop the eth0 speed down to 10Mbps "sudo ethtool -s eth0 speed 10 duplex full"

  • disabling the local interface "sudo ifconfig eth0 down" before recording the pass or survey. Don't forget to turn it back on after for upload.

  • right now I'm running another survey with the cat5 cable connected to my routers 100Mbps port instead of my switches 1Gbps port. I'll post the outcome.

submitted by /u/machsFuel
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Вечерний пролет Метеор. Уже что то. Его можно красивей сделать?…


Вечерний пролет Метеор. Уже что то. Его можно красивей сделать?

Off-Topic • Re: serial over RF monitor

The baud rate is 34.8k 8 1 n
Frequency is 869.5Mhz

Statistics: Posted by I_Need_help — Sat Nov 04, 2017 9:03 pm


Off-Topic • Re: Pinnacle Miro PCTV

To get an answer you have to provide more information.

Which services/signals do you mean by "hear planes"?
SW, VHF/UHF, L-Band or higher?
Which product designation has your card?
Is it for terrestrial or satellite TV use?

While the other reply is correct, that RTL-SDR based software is not supported, the turner itself seems to be a hyperband capable European terrestrial TV turner, intended for reception of analogue TV channels , including all CATV channels defined for Europe up to around 800 MHz, and can be usefull for DIY projects.

Statistics: Posted by snn47 — Sat Nov 04, 2017 8:50 pm


Signal Identification Help • Re: 171MHz signal

Except for airborne and satellite operated transmitter, VHF is limite to Radio Line of sight. Since only you know which ITU-region, country and location you are located it, it will be hard to deduct the source. Are you shure it is a real signal and not some intermodulation product of other strong signals. Using a wide resolution for a narrow band signal also doesn't help.Check ITU-RR, which services have been awarded a primary and secondary status. Furthermore states can, based uppon ITU-RR 4.4, allow other uses/signals to operate in a band, if the signals do not interfere with use in adjacent countries.

If it is a notified service this should allow you to find more information on this signal.

Statistics: Posted by snn47 — Sat Nov 04, 2017 8:30 pm


Antennas • Re: Antenna for SW CHU time. 3.33, 7.850 & 14.67 Mhz

If you live in Europe there is e.g. DCF 77(.5 kHz), which is used by self synchonizing clocks. I assume that other regions have similar low frequency references and equipment that uses them, that you can use as basis for your trials.

Statistics: Posted by snn47 — Sat Nov 04, 2017 8:20 pm


Antennas • Re: Antenna for SW CHU time. 3.33, 7.850 & 14.67 Mhz

Rather than adding filter, for your purposes the antenna should tuneable to provide the selectivity instead in order to relieve the Rx from strong unwanted signals. While coils on ferrites, like the ones found in AM-Rx, would be smaller they most likely won't work above 2 MHz.

That leaves Magnetic (Loop) Antennas using coils of one or more turns. The thick tubing of 1 turn Magnetic Loop Antennas you find in many HAM radio designs are intended for use with transmitters.

A lot of information can be found e.g. here https://translate.google.com/translate? ... edit-text=
http://www.fading.de/rahmenantenne.php

Rahmenantenne means frame antenna, which again is another designation for multi turn Magnetic (Loop) Antenna.

Statistics: Posted by snn47 — Sat Nov 04, 2017 8:16 pm


Troubleshooting Help • Re: Running 2 Dongles on a Pi

tim_rtd wrote:
Sat Nov 04, 2017 6:18 pm
Hi Izzy, I edited my reply to you...hope it helps a little more
Thx, I will see what I can do tomorrow, thank you!

Statistics: Posted by Izze — Sat Nov 04, 2017 6:33 pm


Troubleshooting Help • Re: Running 2 Dongles on a Pi

Hi Izzy, I edited my reply to you...hope it helps a little more

Statistics: Posted by tim_rtd — Sat Nov 04, 2017 6:18 pm


Troubleshooting Help • Re: Running 2 Dongles on a Pi

tim_rtd wrote:
Sat Nov 04, 2017 5:48 pm
Start 2nd server rtl_tcp -d 0 -a 192.168.1.100 ... you differentiate dongles by -d 0 or -d 1 ...-d 2... and different port #
Thats what I do. See first code window, there are errors at the end and it wont start.

Statistics: Posted by Izze — Sat Nov 04, 2017 5:57 pm


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