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Old 19-04-2019, 11:07   #1
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Improving Wefax reception

Not wanting to derail the recent thread on SSB noise I thought I'd start another.

Occasionally I can get nice clear images (usually from Point Reyes, but sometimes Kodiak, sometimes on 4 Mhz an sometimes on 8 Mhz), but generally the signal is very poor, often unusable, or comes and goes giving very poor images.

So I'm looking for suggestions for simple suggestions I can try to improve the signal.

Antenna ...
This is often the first place to start. I currently have a short length of coax coming out of the receiver to a black-box, that has an SO239 connector and two terminals labelled "+" and "-". I have a wire attached to the "+" that I haul the other end of up to the spreader on the flag halyard. I have nothing attached to the "-" connection. The black box is sealed, so I don't know what (if anything) is inside.

- Should I attach a "ground"? how? The boat has a bronze plate on the hull at the bottom of the mast that I could connect to.
- Would rigging it so that I can pull the antenna all the way up to the masthead help?

Receiver ...
Since I am using the laptop to run the fax decoding software, I thought I might as well use it as the radio too ... so I am using an SDR dongle with an upconverter ... but I can't believe this is a particularly great system.

- Would I see a significant improvement if I bought a dedicated reciever like the Tecsun 880? and fed the audio from that into the laptop.

RFI ...
I get the same kind of results whether I'm in port or out in the styx, so any RFI problems probably come from my own boat ... I noticed that I get better results if I power the upconverter directly from the laptop rather than a separate USB power supply ... I've tried turning everything else on the boat off, and it makes little difference, so the only significant potential source of RFI is the laptop itself, but without a separate receiver it is a little hard to know how serious it is.

- Would ferrites anywhere help?
- If I did get a separate receiver would it be worth recording the transmission with the laptop off, then running the fax software afterwards so that the laptop can't interfere? ... that obviously takes twice as long.
- Would a phone be quieter than a laptop?

Software ...
I don't imagine that the fax decoding software will make a difference, JVComm is doing a fine job (once I'm properly set up, I will upgrade from "demo" version) ... but if I stick with the SDR maybe there is something better than SDR#?

any suggestions? as you can see it is currently a bit hit and miss whether I get useable images ... or am I just located in a bad part of the world (Vancouver Island) to get reliable transmissions?
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Old 19-04-2019, 11:15   #2
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Re: Improving Wefax reception

Are you using a signal strength predictor to select a good time of day? There's one in the free Airmail app.
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Old 19-04-2019, 11:47   #3
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Re: Improving Wefax reception

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Originally Posted by Paul L View Post
Are you using a signal strength predictor to select a good time of day? There's one in the free Airmail app.
I've not been using one ... just empirically finding the better times of day ... just looked at this one ...VOACAP Online HF Predictions ... and it seems to suggest that either 4Mhz or 8Mhz should be good most of the day.


But these are the results I get during good times ... I get nothing if it's bad.
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Old 19-04-2019, 21:31   #4
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Re: Improving Wefax reception

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Originally Posted by Kelkara View Post
I've not been using one ... just empirically finding the better times of day ... just looked at this one ...VOACAP Online HF Predictions ... and it seems to suggest that either 4Mhz or 8Mhz should be good most of the day.


But these are the results I get during good times ... I get nothing if it's bad.
Its not my experience that 4 and 8mhz bands are strong all day. Not sure what the coloring means on the VOA graph you posted. Here is one from Airmail between Vancouver and central Cal. Green large number is good, red is bad.
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Old 19-04-2019, 23:04   #5
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Re: Improving Wefax reception

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Its not my experience that 4 and 8mhz bands are strong all day. Not sure what the coloring means on the VOA graph you posted. Here is one from Airmail between Vancouver and central Cal. Green large number is good, red is bad.
OK there is a slight dip at lunchtime ... but 8MHz does look pretty good doesn't it? with 19 hours a day over 75% and 10 hours over 99% ... I should be seeing more good than bad.

Which matches my experience ... Point Reyes repeats transmissions four times a day, and none of them on 8MHz seem to be consistently better or worse ... but 4Mhz isn't always there.

but thanks for pointing out these tools HF propagation has always been a bit of a mystery to me.
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Old 20-04-2019, 08:06   #6
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Re: Improving Wefax reception

It is odd that you are seeing the same propogation in a marina as out. Marinas are usually terrible places to use HF.
The propogation tables are just predictions. There are plenty of times when I've seen 75% predicted and not been able to connect to a station. In my case I am usually connecting to a Sailmail station, so tx comes into play. You are just receiving from a very strong transmitter.
Maybe you could find someone in your marina with a solid HF setup and see how well it receives wefax vs your SDR setup.
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Old 20-04-2019, 08:45   #7
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Re: Improving Wefax reception

Quote:
Originally Posted by Kelkara View Post
Occasionally I can get nice clear images (usually from Point Reyes, but sometimes Kodiak, sometimes on 4 Mhz an sometimes on 8 Mhz), but generally the signal is very poor, often unusable, or comes and goes giving very poor images.
That noise on the bad-reception wfax chart looks like it could be local QRM rather than atmospheric noise during poor propagation conditions (I see horizontal lines rather than random "snow"). Perhaps not, but if so you should try a different location out of the marina. Remember that the propagation forecast tools will know nothing about the habits of local noise sources.

Since you don't seem to be getting interference from on-your-boat sources, I doubt that a better antenna or ground will make much difference.
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Old 20-04-2019, 11:01   #8
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Re: Improving Wefax reception

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Since you don't seem to be getting interference from on-your-boat sources, I doubt that a better antenna or ground will make much difference.
The one potential on-boat source of noise that I haven't been able to turn off is the laptop itself, and that will follow me out of the marina. As Paul L suggested, it would be good to find a neighbour with a working set-up, but I don't know anyone here who uses HF, and haven't even seen a boat in the marina sporting an obvious HF antenna.

I'm only looking for the simplest RX set-up, but it is starting to sound like either the SDR receiver itself is not that good, or the presence of the laptop is killing it ... it would be kind of nice to hear someone say either "my SDR receiver is great" or "you're wasting your time trying with that arrangement".

I'm getting ready to head out beyond cell-phone (and VHF?) range in a couple of days, so I'll keep practising in quiet anchorages ... maybe when I'm using it in anger I'll get better results ... or maybe next time I'll try something different.

thanks.
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Old 20-04-2019, 20:26   #9
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Re: Improving Wefax reception

I've used The "Funcube Dongle Pro +" and two SDRPlays (the first and second versions of the single-port receiver) SDRs for receiving HF WFAX and they have worked fine. Which SDR do you have?

The fact that you have been able to receive a clean WFAX tells me that it's not your receiving setup or laptop, but external noise that comes and goes. I suppose it's possible that you are seeing the difference between a faint WX signal and a strong one, with the interference remaining constant, but your clean WFAX looks so good that I doubt this is the case.
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