HFU HF Underground
General Category => General Radio Discussion => Topic started by: ChrisSmolinski on June 03, 2017, 1610 UTC
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The operator of this transmission on 6880 the other day kindly sent me some information about the power levels he was using: https://www.hfunderground.com/board/index.php/topic,35242.0.html (https://www.hfunderground.com/board/index.php/topic,35242.0.html)
I took that info and put it on a plot of the signal strength of the station, along with the signal strength from a nearby frequency with no station, to use as a reference for the background noise level.
You can see a few interesting things here. First, the background noise level gradually went up over time, as the band opened to DX and we got more static from distant thunderstorms.
You can also see the changes in signal strength of the station with increases in transmitter power, a well as when the signal faded out while it was still at the higher power level of 50 watts. For reference, -73 dBm is considered an S9 signal. Every 6 dB down from that is an S unit, so -79 dBm is S8, etc. Looking at the difference between the two traces (making the assumption that the red trace is an approximation of the noise also present on the station's channel) may give a rough approximation of the signal to noise ratio. It's about 15 dB during the time the station used 50 watts and was best received.
I found a paper discussing required shortwave signal to noise ratios for different qualities of listener reception here, for those interested: http://onlinelibrary.wiley.com/doi/10.1029/97RS00843/epdf
Because this was an SSB transmission and not AM, we don't have a carrier, just the transmitted audio, so the signal strength is highly dependent on the audio/program content. Some of the variation is likely due to that, in addition to propagation and power level.
(http://i.imgur.com/Yu7WB9o.png)
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50 W? Not bad. I had a very faint and noisy copy out here where it was still broad daylight, nearly two hours before sunset. Below the noise floor and not really usable (confidential to eastern pirates - how about waiting just a little later to fire up the Tx and catch more listeners when you do? Just an idea to consider) but there.
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I am seeing another topic here beyond just propagation, too. SNR is the "real deal" as indicated, and from a technical standpoint, it could be beneficial to note signal and noise levels when logging a station. S7 over a S1 noise floor can be a dramatic listening difference from S7 over a S6 noise floor.
Chris, I suspect this is why IIRC you mostly log in SIO format, correct?
I used to do logging in SINPO, and I might go back to it or SIO as well.
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I am seeing another topic here beyond just propagation, too. SNR is the "real deal" as indicated, and from a technical standpoint, it could be beneficial to note signal and noise levels when logging a station. S7 over a S1 noise floor can be a dramatic listening difference from S7 over a S6 noise floor.
Chris, I suspect this is why IIRC you mostly log in SIO format, correct?
I used to do logging in SINPO, and I might go back to it or SIO as well.
Exactly, I feel that gives a better overall feel to the quality of reception. One exception is that for very strong signals, I'll note the signal strength, like S9+30, with the implied SIO 555.
That's an interesting idea, also mention the noise floor by measuring it on a nearby (empty) frequency.
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I can tell you from experiences why most Eastern SW pirates don't target the West, MDK, population densities. A pirate east of the Mississippi can string up a modest antenna using a moderate amount of power and cover 2/3's of the population of North America in the late afternoon with a decent signal.
West of say, Kansas City, the population is spread out over a large area and often very sparse except for the urban areas. You have to use more power to reach far fewer people, which costs more money to pull off.
What I've always wondered is why there aren't more SW pirates out West? That's always tended to be the stomping ground of what a friend once called "worm-warmers" , FM pirates who build costly studios and use transmitters that if they were using the same power on SW would get them across the country, instead of a 20 mile circle that by mode and nature make them dead easy to df.
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I've considered that, Pigmeat, but to me it makes more sense if they're trying to be heard in Europe. After all, it's already 11 pm daylight in the British Isles time at 2200 UTC. If they're concerned with just American listeners, they would only gain more by waiting. (Except for Skipmuck. He's the Ben Franklin of this group, early to bed and early to rise.)
I was mostly venting anyway. I'm not one to dictate to those who are already taking risks.
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Directional gain could be worth consideration if an East Coast pirate did want to try extending listener demographics further into the western states. Even a basic wire yagi with just a reflector (and maybe a director if possible) could get more of the signal into continental North America instead of the Atlantic Ocean. With only 2-3 elements, beamwidth still should be wide enough to cover the eastern states.
With my location in Florida, I have considered tossing up a ~40m inverted-v wire yagi pointing approximately NNW for pirate listening. Now if I actually felt like building and installing it....
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Now if someone in cali would just do some radio privateering, the folks out west would have stronger sigs. I note that at times west of Nebraska seems to be a radio hole of sorts for those to the east, I suppose it's the reverse for those west of Nebraska. Nebraska, much as I love it, is a hole.
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Now if someone in cali would just do some radio privateering, the folks out west would have stronger sigs. I note that at times west of Nebraska seems to be a radio hole of sorts for those to the east, I suppose it's the reverse for those west of Nebraska. Nebraska, much as I love it, is a hole.
As Guise Faux astutely noted several years ago, most HF pirate radio activity in the US occurs within 500 miles around Pittsburgh ;D
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Now if someone in cali would just do some radio privateering, the folks out west would have stronger sigs. I note that at times west of Nebraska seems to be a radio hole of sorts for those to the east, I suppose it's the reverse for those west of Nebraska. Nebraska, much as I love it, is a hole.
As Guise Faux astutely noted several years ago, most HF pirate radio activity in the US occurs within 500 miles around Pittsburgh ;D
Well that makes the field agents' job easy...
+-RH
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Nah, it just means all those "Grenades" are still working after 25 years.
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Seriously kali, why you no transmit? Surely there's enough audience in the LA/SF/SD regions?
https://www.youtube.com/watch?v=t5P6zdlPJ34