New rtlsdr Plugin

[rgleason]

My login has admin privledges.
When I started opencpn got messaage rtl_fm would not run. Copied the zidag drivers into the bin. No longer does that, but test for calib still get no ais messages.

Still working on this. May get bew dongle

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[rgleason]

Gerhard thanks for the link, will look into it. They have GPS + AIS which might be useful.

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[hsi88]

dAISy AIS receiver. Tried it out yesterday. I needed an adapter for my VHF antenna, but it works like a champ. It feeds directly to my laptop (OpenCPN) via a mini-USB cable and it receives both AIS channels.

At only $55, I wish I would have seen this before messing with SD radios. I bought 3 SD radios with antenna adapters, spent countless hours working with SD# and AISMON and this little box replaces all of the above.

https://www.tindie.com/products/astu...-ais-receiver/

Although I must say I learned a lot by working with the SD radios.

[rgleason]

I have downloaded rtlsdr scanner and installed. The install requires and internet connection to download python etc. I have read tbe manual and run some calibration tests on one of the dongles. These tests were largely using the small antenna that comes with the dongle, but some of them which were done earlier (noted in the notes) were done with the VHF antenna connected. Delete the doc please and unzip.

[rgleason]

Here is the earlier batch of rfs. Can someone look and advise what I should be setting for the calibration? -48db/hz?

[rgleason]

Several other questions...
1. Does this rtldsr dongle look good enough to get AIS signals on Opencpn?
2. I do not seem to get any signals when I try -48db calibration, so is there something I should be turning on or setting in Opencpn?
3. I have tried several connection types:
Net 127.0.0.1 Port 10110 UDP Input In:noner out none
Net 0.0.0.0 Port 10110 UDP Input In:none out:none

4. Is there some other setting I need to tickle with the rtlsdr plugin or Opencpn for AIS to show? (I have entered -48 into the Calibration field in the rtlsdr plugin.

[sbfreddie]

Originally Posted by rgleason

Several other questions...
1. Does this rtldsr dongle look good enough to get AIS signals on Opencpn?
2. I do not seem to get any signals when I try -48db calibration, so is there something I should be turning on or setting in Opencpn?
3. I have tried several connection types:
Net 127.0.0.1 Port 10110 UDP Input In:noner out none
Net 0.0.0.0 Port 10110 UDP Input In:none out:none

4. Is there some other setting I need to tickle with the rtlsdr plugin or Opencpn for AIS to show? (I have entered -48 into the Calibration field in the rtlsdr plugin.

Rick:
I reviewed your attachments, and in my opinion you are not getting a reliable signal long enough to get a good calibration.
Here's what I did to get a very reliable, repeatable offset (Offset is measured in ppm {parts per million} not db {decibels}). First I used one of the many working versions of rtlsdr receiver software. I use gqrx as it works on both Mac and Linux (you will probably use HDSDR or something similar). Then look for a constantly broadcasting radio signal. Then once you have found a good strong signal look at the difference between the peak signal level and the noise floor, make a note of the difference (its in db) then manually adjust the input gain of the rtlsdr dongle until you get the largest difference (This is called the signal to noise ratio or S/N ratio). This is the optimum gain setting for the dongle in rtl_ais (the setting is -g xxx).

For calibrating the offset in ppm I used the program "RTLSDR-Scanner". It has a very good auto calibration routine built in. But for calibrating the offset I have noticed and I recommend you find a constantly broadcasting station in the AM band. If you are in US waters there should be a marine weather broadcasting station somewhere in range of your current location (the reason for these stations is they broadcast 24-7 and they are narrow band AM broadcasts in the marine band, the one I use is at 162.425 MHz, point Reyes, California).

I have three of the cheap dongles and no matter how many times I check their calibration they are always the same (31.3 ppm).
I live 100 miles from the closest ocean and there is a 5,000 ft mountain range between me and the ocean, and am getting signals from as far away as 400 miles! I am using one of my homemake Discone antennas. At night as many as 50 sources show up because of atmospheric skip or bouncing.
If I can get that many signals from over 100 miles from the closest ocean your should have no trouble receiving many signals from a boat on the ocean.

If you have any questions, just ask.

Thanks for listening,
Freddie

[rgleason]

Freddie your description and procedure is very very helpful. I have been usind HDSR, sdr# and RTLSDR-scanner. I am getting pretty familiar with HDSR and RTLSR-scanner. Most of the readings and rsl charts are from rhat program.
1. I now understand that I should use a stable marine weather station in the VHF band with the VHF antenna not the little one provided to do the calibration. I had read a stable broadcast frequency should be used and Rtlsdr-scanner provided a default example in the 87 to 89 mhz range. The value I got was something like -48 (I have to check it again). Would that be the value needed?

I am a little confused about the use of db/hz term in RTLSDR-scanner that seems to be the ppm result of auto calibration over a certain range.
Also there is a drop down selection for db before you ask for the auto scan with lots of selections from 0 on up. What is this for?

I like your clear description of 1."look for a strong constantly broadcasting signal".
2. We are trying to maximize the difference between the peak signal level and the noise floor make note of the difference (in db) then manualy adjust the input gain of the dongle until you get the largest difference (in db) between peak and floor.

How do you adjust the input gain in HDSR? What value is it?

I suppose auto calibrate does that. It seems to do scans up to 19 or so and then will give the average, min, max setting for frequency and db/hz or ppm. So what one of those values should I use?

I am going to try to follow you guide using rtlsdr-scanner with the vhf antenna connected and the frequency for marine weather WX3 or WX1.

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[rgleason]

Also how do you manually adjust the input gain in rtlsdr-scanner?

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[rgleason]

NOAA Weather Radio Frequencies
162.400 MHz (WX2)
162.425 MHz (WX4)
162.450 MHz (WX5)
162.475 MHz (WX3)
162.500 MHz (WX6)
162.525 MHz (WX7)
162.550 MHz (WX1)

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[rgleason]

I have tried using rtlsdr-scanner in the 162 to 163 range. Scanning 17 times. Then when do auto scan with one of the peak freq, around 162.400 I do not get the same ppm result each time. In fact they vary widely with neg and large positive ppm. I tried the other dongle with the same result.

Then I tried the test frequency range of 86 to 87 then hit start after 17 sweeps got a single big spike at about 86.400391 with -27.71 db/hz at a gain selected of 1.4db, 1sec dwell , fft size 1024. Then ran auto calibrate with freq 86.400 and got -4,521 ppm multiple times. It never changes. The plot has a good base and a single peak.

I cannot seem to achieve this clarity or consistency in the 162 to 163 mhz range even though i am connected to VHF antenna.

Our vhf works fine when connected.

So does that mean these dongles are garbage for AIS frequencies?

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[rgleason]

Tried setting db to .9 for 162 to 163 mhz finding a peak at 162.159 mhz using that to auto calibrate and I and still hetting different pom. You say your dongles always have the same ppm. Something is not working I guess.

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[piluso]

So does that mean these dongles are garbage for AIS frequencies?

I just did a 2 day passage and the AIS signals received using one of these dongles with OpenCPN was a very valuable aid when crossing merchant routes.

However, the initial accuracy error (aka ppm) can be frustrating at first. Did you try my instructions here?: http://www.cruisersforum.com/forums/...ml#post1844966

You can do the same with _any_ other known signal, not just AIS. The problem is to find the deviation between the frequency selected with the tuner, and the real tuned frequency (in parts per million).

Tried setting db to .9 for 162 to 163 mhz finding a peak at 162.159 mhz using that to auto calibrate and I and still hetting different pom

If you can use HDSDR or SDR#, look at that range using the graphical tool, and probably you'll see EM noises due to broadcasting FM, or other spurious radio sources. Try to get a strong, stable,known frequency signal, and look in the spectrum graph for the difference between the number in the tuner and the reference frequency mentioned before.

Hope this helps,
David

[rgleason]

I am dubious about the quality of these particular dongles at the necessary frequencies for AIS. If all of these dongles are this picky about settings, it may not be for me as I am tired of screwing around with things that don't work. If it is a matter of purchasing a better dongle and auto calibrating fine. As I said I am getting widely ranging ppm using the best peak frequency available and this with the engine off and with vhf antenna attached.

I will try one more time using HDSDR with your instructions to make sure I am doing this correctly. Thanks so much for all the help and patience with my problems.

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[rgleason]

Originally Posted by piluso

This is a great plugin I use a lot too, but there are a couple of details to take care to get it working. Besides a good antenna, we need the calibration factor error , and is not trivial to know. Once you have it, you don't need to change it anymore, and is the same for any platform.

Here my way to find the ppm:

First, you need a working sdr radio environment, I use HDSDR software. The instructions for get it working are here:http://hdsdr.de/RTLSDR_with_HDSDR.pdf

You'll need some AIS traffic too.

Tune the AIS channel A at 161.975 Mhz. Choose a bandwidth of 12khz, and zoom in the spectrum waterfall as shown:


The AIS traffic is encircled in yellow.

As you see, the traffic is _outside_ of the tuning window, and that is because the dongle cristal errror. To correct this, you need to enter the ppm error value. Click the "ExtIO" blue button, and change the value until the signal enters the tuning window:


You can also calculate the value using the first screen, using the tuning freq and the center of the AIS signal:

1000000* (161975000-161963000)/161975000 =74 ppm

Then use that value for the plugin.

Before doing anything, you can try with a value of 73, that is typical for a lot of these dongles ;-)

Aside this, my previuos reply was for sharing a working two channels AIS receiver for this dongle, I hope Sean could go ahead with his plugin.

Regards, David

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