I would like to transmit trinary data (-1,0,+1) on 20-30m wave to be received 10,000km away. From Europe to US.

My first thought was this: https://www.researchgate.net/figure/Burst-modulation-mode-f-BM-280-Hz-duty-cycle-50-as-an-example_fig2_231130256 I am open to different suggestions

Desired performance here is:

  • max latency of signal processing (to increase SNR) is 4ms
  • data rate 2 tribit per second
  • as its not commercial i'd rather calibrate optimal missing reception etc per session (dependent on weather etc), so 20-80%..

What kind of power would I need on TX side for the above SNR?

Also note: I looked into known ham radio digital modes and signal processing algorithms - they seems to be too slow as they are designed to use minimal power for reasonable detection rates with pretty much infinite latency. My task is the other way around - to use maximal reasonable power to achieve low latency.

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    $\begingroup$ hey, what's a tribit? $\endgroup$ Jun 18 '20 at 22:22
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    $\begingroup$ Like a bit, but with 3 states instead of 2. In other words, about 1.58 bits. $\endgroup$ Jun 18 '20 at 22:28
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    $\begingroup$ I'm not really following there: 4bit/s is a rate of how much information you can put across in a fixed amount of time. So, if you define a data rate of 4 bit/s, then in 4ms you can transmit 4 ms · 4 bit/s = 16 millibit. A millibit is not really a useful thing? It's not even 1/30 of the information of "yes|no". So: where does the 4bit/s data rate requirement come from, what's the motivation to demand that data rate? $\endgroup$ Jun 22 '20 at 18:17
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    $\begingroup$ Boppity Bob, all your (many other) questions are related to the impulse response of a transatlantic data link. (Is your plan to get rich with high-frequency trading?). What you are asking in this forum is all that knowledge: latency, impulse response, spread in time, signal coherency versus bandwidth, reliability of the link, best frequency and so on. Hesitate to post this, but I do. Brightnoise, PA0FSB $\endgroup$
    – user16925
    Jun 24 '20 at 21:52
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    $\begingroup$ So, really, I know you don't like to hear this, we really need to know what you're trying to transmit for which purpose to help you any further, but really the data you're giving is still not explicit enough. How many bits (in information, not in symbols you need to send to get the information across) is a session in your question? What is "reasonable power"? What exactly is an acceptably low latency – your 4ms seem to be pretty strange, considering the time it takes your signal to propagate around earth is significantly longer than that. $\endgroup$ Jun 25 '20 at 19:09

What you're asking for is a link budget.

For HF, you can use software like VOACAP to estimate path loss. There are several ways you might use the software, but to start I'd suggest:

  1. Click the antennas button, and enter the kinds of antennas you have available for each band.
  2. Drag the location markers to the relevant places. Not all 10,000 km paths are the same. Things like water vs land make a difference, as well as alignment with the greyline, among other factors.
  3. Change the date in the lower-left to at least the month of interest. The sun influences HF propagation significantly, so the season is important. Over longer timescales, the sunspot cycle is also relevant.
  4. After editing these and other relevant parameters, click the "Prop Charts" button, and select the "SDBW Short-Path" chart. This shows the received power in dBW for each band and each hour of the day.
  5. Note the transmit power selected in the upper-right. It's in watts, but if you convert it to dBW then the difference between that and the "SDBW" chart is the path loss. It includes propagation loss and antenna gain.

Of note, HF propagation is highly variable. The number VOACAP gives for SDBW is a median value. Half the days will be better, half will be worse. Add or subtract some margin depending on how many days out of the month you are OK with communication not working. VOACAP can also generate 10th and 90th percentile values for this metric, but as far as I've found not in the online version.

Great, now you know how much power from the transmitter arrives at the receiver. Now how much power must arrive at the receiver to achieve your communication objectives?

The first part of this question is determining the noise at the receiver site. Perhaps you can measure it directly. If not, ITU-R P.372-13 is a good source of data on what noise can be expected generally.

Now you need to set a signal to noise ratio (SNR) objective. You could do this a couple ways:

  1. Use the Shannon-Haltley theorem to put a best-case lower-bound on the required SNR, or
  2. Find the bit error rate curve for a specific modulation you are considering. I have no idea what the thing you linked in the question is. BPSK might be a good starting point.

If this sounds complicated, it's because it is. There are a lot of variables required besides "how much power". But hopefully this gives you enough of an outline of the procedure that you can ask follow-up questions for additional detail as you need it.

  • $\begingroup$ 4ms meant - margin to error-proof the signal. not the whole latency.. Using your figure the total tolerable latency is ~35+4 $\endgroup$ Jun 18 '20 at 19:14
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    $\begingroup$ @BoppityBop Please edit the question to clarify. $\endgroup$ Jun 18 '20 at 22:27
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    $\begingroup$ For ssb, 100w is enough for most days. For digital modes using full modulation, 30w is similar. For narrow band slow digital modes (3bps is reasonable) 10w might be plenty. $\endgroup$
    – user10489
    Jun 19 '20 at 12:59
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    $\begingroup$ @BoppityBop Receiver ambient noise, solar weather, your definition of "most days", antenna gain, and your maximal permissible bit error rate can cause the required power to vary by several orders of magnitude. My gut feeling is you will require somewhere between 10W and 10,000W, depending on your particular parameters. $\endgroup$ Jun 22 '20 at 21:46
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    $\begingroup$ @BoppityBop please stop "simplifying" your question. You're honestly lacking the insight to understand what's important and what not. Instead, extend your question to explain what you want to do in the bigger picture, please. You're binding so much time through this. $\endgroup$ Jun 23 '20 at 22:39

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