My apologies to the group for posting about Algeria on 153 kHz in a reply about Morocco on 171 kHz. I have reposted my message with a new/correct subject line.This evening I did a quick review of some LF recordings I made over the last month. Despite poor-to-fair (at best) propagation I have been bothered by the exceptionally strong carrier of Radio Algeria on 153 kHz yet unable to hear or listen to any modulation most of the time. On any given night their carrier is always the strongest here for me in the Midwest yet only rarely do I get to actually listen to any programming.
I noticed that there are abrupt changes in the modulation index on their carrier at different times. I.e., carrier always strong yet no or little modulation heard then all of a sudden they sound almost like a local. And it goes the other way around too. I will be listening to them fine and all of a sudden their modulation goes way down. I think, and this is just speculation, that when they change their audio feed from one source to another someone is not monitoring the VU meter close enough. I never see a change in the carrier level, only the amount of modulation on that carrier.
I could go back and review older recordings and get better examples but using the samples I collected over the last month I want to present a couple of examples of what I am talking about.
One thing I do need to point out is that we have had poor-to-fair (at best) propagation these last 2-3 months so even at best the audio in a few of these recordings will be so-so.
I made a crude video with some different recordings strung together one after the other. Some are from the same evening, some from different nights. The times are all local EST, not UTC. What you will see is that in all cases the carrier level is pretty strong but the modulation is all over the place, from not so horrible to just detectable. And what is a real shame is that if any other LWBC station had a carrier level as strong as 153 kHz I would be making recordings to keep as I am sure the quality would be very desirable. I took a stab at summarizing the video with the notes below.....I may have goofed on one or two of them but I think you will see what I am talking about.
At 22:01 is an example of weak audio even thought the carrier was moderately strong at a reported 45 dB S/N. The relative carrier amplitude was ~-97 dBm.
At 22:59 we hear modulation so-so then hear it drop down. The carrier S/N was about 50 dB and the relative strength was ~-90 dBm. Notice the time.
At 19:04 we hear an example of weak audio even thought the carrier was moderately strong at a reported 47 dB S/N. The relative amplitude was ~-97 dBm.
At 22:19 we hear an example of weak audio even though the carrier was moderately strong at a reported 58 dB S/N. The relative amplitude was ~-87 dBm.
At 19:57 we hear an example of so-so audio with the carrier at a reported 52 dB S/N. The relative amplitude was ~-92 dBm.
At 20:00 we hear an example of weak audio even thought the carrier was moderately strong at a reported 52 dB S/N. The relative amplitude was ~-95 dBm.
At 22:57 we hear an example of weak audio that under goes a change even though the carrier was moderately strong at a reported 47 dB S/N. The relative amplitude was ~-97 dBm. Again note the time.
At 20:32 we hear an example of weak audio even thought the carrier was moderately strong at a reported 48 dB S/N. The relative amplitude was ~-97 dBm.
At 20:11 we hear an example of weak audio even thought the carrier was moderately strong at a reported 43 dB S/N. The relative amplitude was ~-97 dBm.
At 21:56 we hear an example of weak audio even thought the carrier was moderately strong at a reported 48 dB S/N. The relative amplitude was ~-97 dBm.
At 22:16 we hear an example of poor audio even thought the carrier was pretty strong at a reported 57 dB S/N. The relative amplitude was ~-97 dBm.
Here is a URL to that MP4 video:
drive.google.com/file/d/1NqWhgIAZwK-oHqrL-NO_PDS5RDeRSb2c/view?usp=sharing
Gedas W8BYA Indiana