How does a weak receiving signal from a pirate broadcast be given an accurate reading? Say for instance, all things being equal in the household RFI department, and there is just the usual atmospheric noise, and your receiver has a steady S5 noise floor. Now then, you hear music, just above that level, doe one give the report as an S5 or S6? Obviously if your noise floor is S5 but the signal is an S8 with peaking at S10 and back down, well then that's fairly easy to report. Granted there are many variables involved here, antenna, type & height, receiver, a stingy S-meter, changes in propagation, direction of signal, etc. It's all pretty individual readings and signal strengths at that point, from different QTH's. I know my particular setup now is not nearly as sensitive or receives as well as the one I had in the 80's.
You report the signal you are hearing at the signal level reported by your radio. Unless there is something wrong with your radio, the design or calibration of how it measures S units, then you cannot really usably detect an S5 AM voice signal in an S5 noise floor. Because the audio of even a 100% modulation AM signal is at least 6 dB down from the carrier (and normally stations are a bit further down than that) then even if the audio is right at the noise floor, and so indistinguishable from the noise, the carrier should push the meter level up at least one S unit. Of course, with SSB there is no carrier to push up the meter and audio can be understood at S meter levels closer to the noise floor, and this also applies if you are using SSB to detect an AM signal that is very near the noise floor.
Regardless of what might or might not be possible, report what the meter is saying at the time you identify the station. You can only report what you see, you cannot “quantify” it for the station without a couple pages of detail
Naturally, if you want to add detail I see no issue there, example “you were S6 with an S5 noise floor, so audio was not well understood”.
Also, with regards to “peaking at S10”, there is no “S10”. The scale goes from S1 to S9, with S1 being equal to -121 dBm (50 Ohm, 30 MHz and below) and S9 being equal to -73 dBm, each S unit is a change of 6 dB. I suppose one could argue that there might be an S0, at 6 dB below S1, or at -127 dBm. Above S9 the expression is “dB above S9”, or S9+dB. So that a signal that is 10 dB above S9 (-63 dBm) would be S9+10, and a signal 20 dB above S9 (-53 dBm) would be S9+20. You can see from this that if there was an S10, and each S unit is defined as a 6 dB change, then S10 would be -63 dBm (S9) plus 6 dB, or -57 dBm, but S9+10 dB is equal to -53 dBm, so S10 and 10 over S9 (S9+10 dB) cannot be the same.
If your radios meter goes to S10, or S11, or some other higher “S” number than the meter is not an actual S meter, and you cannot tell the scale that it might be calibrated to. The meter in such a case is just a scale that has no recognized specification and even if every other aspect is the same, location, receiver sensitivity, antenna gain and performance, feedline loss, etc, then S3 on such a meter is NOT the same as S3 on an actual S meter, unless by chance they just happen to line up, but if they do then no other value should probably line up.
Many times I hear a signal at, or just slightly above the noise level. So if one hears music just above S5 noise the correct report would be S5 signal, and if the noise is S7 and you barely hear the music, your signal report would be S7. Sound right? If the incoming signal doesn't make it past the noise level of your radio - you're just not going to hear it. Right? Or do we go in reverse?
If you just barely hear a signal above a S5 noise floor, do we give our report as a S1 or S2 (above the noise floor?) or keep it as a S5 signal in the report? If I see someone (myself included) post a signal strength of S2 or S3, does that mean they have a S0 noise floor? Whew! Or...are listeners generous and bump up to the next dB for reports?
No, you should not report the “delta” between your noise floor and the signal as the “S” number. An S7 signal with an S4 noise floor is NOT an S3 signal. It is an S7 signal. As I said before, if you want to add data by saying it was an S7 signal and an S4 noise floor then that is your call, but giving a “wrong” S meter reading is just…wrong.
Things like SINPO tell a station how well it is being heard, in a relative way. An S meter reading is supposed to tell the station really how strong the station is being received at the antenna port. That is one of the reasons it was traditional to include data on your antenna, antenna height, and radio type in a QSL report. Knowing this data helped to give the station a real idea of how well it was getting into a specific area.
T!
Topic: Weak "S" signals / noise level / Nagging questions (Read 7799 times)