Weatherfax_pi Recievers: RtlSDR + SSB radios

[rgleason]

This topic is about inexpensive and effective ways of receiving weatherfaxes via EMR/SSB and use with weatherfax_pi.


There are some relevant posts starting with Maulrun's post going down, in the Weatherfax_pi thread. We are trying to move this discussion over to this thread as it is more relevant, and the weatherfax_pi thread is intended for the plugin itself!

[LeaseOnLife]

Great move Rick :-)

I am currently running an AirspyHF SDR with a dedicated PI4. The PI is tuning & converting to audio with GQRX, sending the audio to a virtual-sink (pulseaudio) to JWX as well as fldigi for decoding the audio to images.
I currently do frequency switching via a schedule in crontab.

My antenna is the same backstay antenna and ground system the SSB uses, I have an antenna switch for that : DAIWA CS-201. I did try to use shrouds, or a simple wire pulled up with a halyard, but on this boat nothing comes close to using the backstay antenna and ground plane thru the antenna-tuner.

I believe, the current implementation of the O-weatherfax plugin does not deal with the SDR directly, but only with the audio. So a decoder for the SDR is still needed (I use gqrx on the PI4 but prefer SDRPP on the linux laptop).

The issue of scheduling also needs to be discussed: Stations don't send on all frequencies for all 24h and propagation (and with that the preferred frequency) changes by location and the position of the sun (and sun spots etc).

I still have fond memories of my old Furunu paper weatherfax: Once I set it to a station (lets say RMC / Pt Reyes California), it will scan all frequencies for RMC until a working one is found. Once the signal is lost, it will start scanning again. A similar functionality would be awesome.

To date, the plugin can alarm the user with a reminder, then the crew has to tune the receiver/SDR.

Shorthanded ocean passages can be tiresome and I would like not to miss a weatherfax and hope for more automation in the scheduling.

Cheers


Dirk

[Franziska]

Regarding external antenna length for SSB weather fax reception, how long should it be ideally?

[sailorF54]

Classical antenna



l = c / (F*4)

where l is length in meters, c is speed of light in meters / F frequency of transmitter in Hz
If c is in kilometers, F should be in KHz, l is still in meters



example
US Coast Guard, Boston, USA

Frequencies:

• 4235.0 kHz: 0230-1015 UTC (tune radio to 4233.1 kHz)
• 6340.5 kHz: 0000-2400 UTC (tune radio to 6338.6 kHz)
• 9110.0 kHz: 0000-2400 UTC (tune radio to 9108.1 kHz)
• 12750.0 kHz: 1430-2215 UTC (tune radio to 12748.1 kHz)

AFAIK, the first two are widely used
so l is either 17,7 m or 11,8 m
Fortunately, the antenna length is not crucial for reception (as opposed to transmission), so 15 m is in the right ballpark

[Franziska]

Originally Posted by sailorF54

Classical antenna



l = c / (F*4)

where l is length in meters, c is speed of light in meters / F frequency of transmitter in Hz
If c is in kilometers, F should be in KHz, l is still in meters [emoji2]



example
US Coast Guard, Boston, USA

Frequencies:

• 4235.0 kHz: 0230-1015 UTC (tune radio to 4233.1 kHz)
• 6340.5 kHz: 0000-2400 UTC (tune radio to 6338.6 kHz)
• 9110.0 kHz: 0000-2400 UTC (tune radio to 9108.1 kHz)
• 12750.0 kHz: 1430-2215 UTC (tune radio to 12748.1 kHz)

AFAIK, the first two are widely used
so l is either 17,7 m or 11,8 m
Fortunately, the antenna length is not crucial for reception (as opposed to transmission), so 15 m is in the right ballpark

Thanks, very helpful.

Do you happen to know what would be best for European weather chart reception as well?

[sailorF54]

Everything you should know about weatherfaxes all over the world, including schedule /content of transmissions (up to date 02/2022)


The frequencies are pretty much in the same bands all over the world, so a 15 m long antenna is adequate...


For Europe, Hamburg (aka Pinneberg) and Northwood provide great coverage

[Franziska]

Originally Posted by sailorF54

Everything you should know about weatherfaxes all over the world, including schedule /content of transmissions (up to date 02/2022)


The frequencies are pretty much in the same bands all over the world, so a 15 m long antenna is adequate...

For Europe, Hamburg (aka Pinneberg) and Northwood provide great coverage

Awesome resource. Many thanks again.

I will run the anrenna cable up inside our Dyneema shroud.
Should that be coax?
Shall I terminate with a Dipole at the upper end? If yes, I'd just stick the "legs" out on opposing sides of the Dyneema weave.
How long should I make the Dipole legs then?

Regarding ground, would a stainless bolt below the waterline be enough?
I would then run a wire from there to the radio ground terminal.
We do not have other HF equipment.

Alternatively, in case we were to install a real grounding plate, could it be used in common with the ground terminal of our VHF and perhaps the radar or other equipment.

[sailorF54]

Let me be clear. I am assuming we are talking about a HF RECEIVER. An HF transmitter is a much more complex beast to set up.
Your antenna will be a simple copper wire in some kind of plastic sleeve (i.e. an ordinary wire). Do not use a coax. No need of what you call a dipole. You need a "ground " as long as your receiver requires one (i.e. has a dedicated socket for it), which is not the case for most basic portable radio sets. In case you need one, a thick copper wire to a keel bolt is adequate, provided there is some connection to the seawater through the keel. Use an ohmmeter to check (one wire touching the keel, the other to the bolt, the resistance should not be infinite) This "ground" can be shared with other équipements.

The key to a good signal reception is the lack of (HF) noise. You may have to turn off all power supplies (including the one for the computer) and leds. This is why a battery powered receiver is great. Try shutting down all electrical devices in turn (VHF, radar, echo sounder, chart plotter, gps etc...) to check whether it improves the signal to noise ratio. Reception in marinas is often (very) poor as the sources of noise are many and powerful. Try to run the antenna cable as far as possible from electric supply wires.

[Franziska]

Originally Posted by sailorF54

Let me be clear. I am assuming we are talking about a HF RECEIVER. An HF transmitter is a much more complex beast to set up.
Your antenna will be a simple copper wire in some kind of plastic sleeve (i.e. an ordinary wire). Do not use a coax. No need of what you call a dipole. You need a "ground " as long as your receiver requires one (i.e. has a dedicated socket for it), which is not the case for most basic portable radio sets. In case you need one, a thick copper wire to a keel bolt is adequate, provided there is some connection to the seawater through the keel. Use an ohmmeter to check (one wire touching the keel, the other to the bolt, the resistance should not be infinite) This "ground" can be shared with other équipements.

The key to a good signal reception is the lack of (HF) noise. You may have to turn off all power supplies (including the one for the computer) and leds. This is why a battery powered receiver is great. Try shutting down all electrical devices in turn (VHF, radar, echo sounder, chart plotter, gps etc...) to check whether it improves the signal to noise ratio. Reception in marinas is often (very) poor as the sources of noise are many and powerful. Try to run the antenna cable as far as possible from electric supply wires.

Great. Will follow this.
For the short run from the Tecsun PL-880 receiver to the shroud, should I use a shielded cable and/or run it through some suppressor ferrites?
I can not avoid to run parallel to a few electric cables there.
I could run it shielded up to the shroud and than strip the shield away for the 15m.

[Bill O]

Originally Posted by LeaseOnLife

Great move Rick :-)

I am currently running an AirspyHF SDR with a dedicated PI4. The PI is tuning & converting to audio with GQRX, sending the audio to a virtual-sink (pulseaudio) to JWX as well as fldigi for decoding the audio to images.
I currently do frequency switching via a schedule in crontab.

My antenna is the same backstay antenna and ground system the SSB uses, I have an antenna switch for that : DAIWA CS-201. I did try to use shrouds, or a simple wire pulled up with a halyard, but on this boat nothing comes close to using the backstay antenna and ground plane thru the antenna-tuner.

I believe, the current implementation of the O-weatherfax plugin does not deal with the SDR directly, but only with the audio. So a decoder for the SDR is still needed (I use gqrx on the PI4 but prefer SDRPP on the linux laptop).

The issue of scheduling also needs to be discussed: Stations don't send on all frequencies for all 24h and propagation (and with that the preferred frequency) changes by location and the position of the sun (and sun spots etc).

I still have fond memories of my old Furunu paper weatherfax: Once I set it to a station (lets say RMC / Pt Reyes California), it will scan all frequencies for RMC until a working one is found. Once the signal is lost, it will start scanning again. A similar functionality would be awesome.

To date, the plugin can alarm the user with a reminder, then the crew has to tune the receiver/SDR.

Shorthanded ocean passages can be tiresome and I would like not to miss a weatherfax and hope for more automation in the scheduling.

Cheers


Dirk

Dirk,
Which airspy product are you using (mini,HF+, etc.)? Tried to use a different RTL-SDR dongle on a Pi3 w/fan (before the Pi4 came out) and it didn't work well.
Always wanted the SDR backup to the SSB and also better programming w/the SDR.

[rgleason]

Thank you Dirk! A very pithy statement. I had to understand it better.

RTL-sdr

• AirspyHF SDR+
  
• AirspyHF SDR+Discovery
• RTL-sdr review of AirspyHF SDR+

RPI using GORX to Tune and Convert to Audio

• GORX
• Supported Hardware - AirspyHF SDR+

Sending the audio to a virtual-sink (pulseaudio)

• Freedesktop.org Pulseaudio
• Wikipedia PulseAudio
• Ubuntu PulseAudio

to JWX A Java short-wave weatherfax receiver/converter

• https://arachnoid.com/JWX/

as well as fidigi

• W1HKJ Software

for decoding the audio to images.


It appears to me that weatherfax_pi has much of this built-in, but having not used the sound decoder side, or the scheduling features, I certainly don't know much about it. I do think it could be improved significantly by incorporating some of these newer programs and updating the Weatherfax Radio schedules.


We need some willing volunteer programmers to do this.

Originally Posted by LeaseOnLife

Great move Rick :-)

I am currently running an AirspyHF SDR with a dedicated PI4. The PI is tuning & converting to audio with GQRX, sending the audio to a virtual-sink (pulseaudio) to JWX as well as fldigi for decoding the audio to images.
I currently do frequency switching via a schedule in crontab.

My antenna is the same backstay antenna and ground system the SSB uses, I have an antenna switch for that : DAIWA CS-201. I did try to use shrouds, or a simple wire pulled up with a halyard, but on this boat nothing comes close to using the backstay antenna and ground plane thru the antenna-tuner.

I believe, the current implementation of the O-weatherfax plugin does not deal with the SDR directly, but only with the audio. So a decoder for the SDR is still needed (I use gqrx on the PI4 but prefer SDRPP on the linux laptop).

The issue of scheduling also needs to be discussed: Stations don't send on all frequencies for all 24h and propagation (and with that the preferred frequency) changes by location and the position of the sun (and sun spots etc).

I still have fond memories of my old Furunu paper weatherfax: Once I set it to a station (lets say RMC / Pt Reyes California), it will scan all frequencies for RMC until a working one is found. Once the signal is lost, it will start scanning again. A similar functionality would be awesome.

To date, the plugin can alarm the user with a reminder, then the crew has to tune the receiver/SDR.

Shorthanded ocean passages can be tiresome and I would like not to miss a weatherfax and hope for more automation in the scheduling.

Cheers


Dirk

[LeaseOnLife]

Originally Posted by Bill O

Dirk,
Which airspy product are you using (mini,HF+, etc.)? Tried to use a different RTL-SDR dongle on a Pi3 w/fan (before the Pi4 came out) and it didn't work well.
Always wanted the SDR backup to the SSB and also better programming w/the SDR.

I got the airspyHF Discovery, with the single antenna connection.

[rgleason]

Comparison of AirSpy HF SDR+ to WinRadio WR-G33DDC 'EXCALIBUR Pro'
https://www.fenu-radio.ch/Airspy_HF-...scovery-en.htm
See Test Conditions at the bottom.

• https://www.winradio.com/home/g33ddc.htm
• https://www.winradio.com/ep/
• https://www.radiomasterlist.com/en/w...wr-g33ddc.html

[LeaseOnLife]

A bit more info on my setup to get others started:



Virtual sink in Pulseaudio for routing audio from the SDR/GQRX to FLDIGI (and JWX)


I added this to /etc/pulse/default.pa

load-module module-null-sink sink_name=Virtual_Sink-GQRX-to-FLDIGI sink_properties=device.description=Virtual_Sink-GQRX-to-FLDIGI

I tried using "pavucontrol" to route signals but couldn't make it 'stick' reliably. GQRX is pulseaudio-aware and the sink above can be selected as audio output.

JWX uses the first default alsa card and may need to be pointed to use above. I start JWX as follows:

export PULSE_SINK="Virtual_Sink-GQRX-to-FLDIGI"
export PULSE_SOURCE="Virtual_Sink-GQRX-to-FLDIGI.monitor"
/home/pi/JWX/JWX.sh

similar for fldigi:

export PULSE_SINK="Virtual_Sink-GQRX-to-FLDIGI"
export PULSE_SOURCE="Virtual_Sink-GQRX-to-FLDIGI.monitor"
fldigi

A word on latency / cpu load / interrupts:

I often had steps in the wefax picture. I tried many things to fix that, first was to build a dedicated PI4 for just that purpose. Then I fixed CPU speed to 1 GHZ to avoid CPU speed changes. MY PI4 runs with that speed without a fan happily. I played with process priorities. I made sure no timesync is changing the clock. And I tried much more I can't remember... Interestingly, when the CPU load was high, I had less steps. There is a thread on the gqrx group forum (https://groups.google.com/g/gqrx) with similar observations.
In the end I added latency of 3000ms (!) in pulseaudio to allow it to catch up when an under-run happens. That solved the stepping in the images to >95%.


I start gqrx this way to achieve the desired, constant latency:

env PULSE_LATENCY_MSEC=3000 gqrx

Obviously I would like to see the root cause fixed, but the next long passage is waiting and this system has been running well now for a month.

[sailorF54]

Originally Posted by Franziska

Great. Will follow this.
For the short run from the Tecsun PL-880 receiver to the shroud, should I use a shielded cable and/or run it through some suppressor ferrites?
I can not avoid to run parallel to a few electric cables there.
I could run it shielded up to the shroud and than strip the shield away for the 15m.

Yes, a shielded cable in the vicinity of electronic appliances is useful not necessarily up to the shroud. Note that the length of wire from the receiver to the shoud is part of the antenna length.
Sorry, no idea whether (clamp-on) ferrites are useful.