FM reception

[Mark Roberts]

What is soft muting and how is it different than blending?

Blending just reduces the difference component of the FM signal to reduce the noise introduced by the amplitude-modulated subcarrier that carries that information. In other words, it reduces stereo separation.

I think it may be easiest to understand muting in terms of how hi-fi equipment used to handle it: the tuner simply ignores signals whose strength falls below a certain level. The hiss that you would hear between stations was also blanked out. That kind of muting was an all-or-nothing proposition. Soft muting reduces the audio level of anything below a certain level, but doesn't eliminate it altogether. So you hear the hiss between stations, but at a lower volume. This seems to frustrate DXers in a couple of ways. First, because most radios with this feature don't let you turn it off. Then, when listening to a weak signal, instead of the volume being somewhat proportional to the signal strength on weak signals, the volume suddenly drops off.

Muting should be treated as a personal preference, and should be something that can be disabled. I always left muting turned off on hi-fi equipment that I had. That was back when the FM dial wasn't jammed full of low-power stuff the way it is now. The hi-fi tuners I use now don't have muting; my DSP-based radios do have soft muting, but the newer ones let you turn it off.

 

[wildthangjim]

Interesting observation. My own theory is that the infilling of the dial with low-power operators (LPFMs and translators) along with rimshots simply reduced the number of open slots available for tropo or E-skip to break through for listeners with ordinary receivers and simple antennas. At one time, the FCC wisely tried to control congestion on the FM dial. Those days are long gone. Whether the trade-off is worthwhile is a whole other question. My own opinion is that it's just replicated the mistakes made on the AM band, resulting in more interference and increased listener fatigue, thus hastening the exodus of listeners from the band to other audio sources. When everyone is shouting, no one can hear anything.

Certainly here in Houston, LPFM and translators are much of the problem. There are an insane number of them here, with ever changing formats. Radio Locator lists 93 signals audible here! However, there are certain frequencies that once had reliable tropo and are still free of local signals, but none or very infrequent tropo now.

 

[The New Chico]

Certainly here in Houston, LPFM and translators are much of the problem. There are an insane number of them here, with ever changing formats. Radio Locator lists 93 signals audible here! However, there are certain frequencies that once had reliable tropo and are still free of local signals, but none or very infrequent tropo now.

I think you have to look at what has changed, and what has not. Tropo is a natual condition and is not likely to change much or go away over time. So what has changed? Tuner architecture and open spaces on the dial. Most modern automotive tuners use DSP and that is mainly set up to help the average listener get the most out of their audio experience. It isn't really set up to honor the needs of the DXer. But if you are using the same equipment you were using years ago and still perceive a lack of tropo, then it likely has to do with the openings available. Here's an example in my own experience:

I live near Bellingham WA, close to the Canadian border. We have a local class C at 106.5 (KWPZ), which normally runs HD. There is a station N of the border (CJNY) at 106.3FM They are very high (600 meters HAAT) but only 9000 watts. When the HD was off for a few weeks this winter on the 106.5, I sudeenly had 106.3 in the clear and easily usable as I drove around my area. Soon as they got the HD on 106.5 up and running again, away went the 106.3 signal, entirely. Even though it seems like an empty spece on the dial...there is no perceived audio at 106.3 now, but clearly the HD signal is wiping out that space. I suspect this is happening to your tropo signals!

For that matter, there are a ton of RF emitters out there that may not sound like anything on FM, but they still exist and they still override weak signals. Think your LED lights, computer screens and what not.

 

[gar hi]

My experience from having lived in Florida for 31 years was that distant FM stations within the state generally came in better when I first moved there as opposed to right before I moved away.

I'm wondering if the RDS technology built into the newer radios had something to do with it.

 

[billy2047]

When the HD was off for a few weeks this winter on the 106.5, I sudeenly had 106.3 in the clear and easily usable as I drove around my area. Soon as they got the HD on 106.5 up and running again, away went the 106.3 signal, entirely. Even though it seems like an empty spece on the dial...there is no perceived audio at 106.3 now, but clearly the HD signal is wiping out that space. I suspect this is happening to your tropo signals!

That's exactly what I've been experiencing with DXing distant FM. It really doesn't matter how sensitive or selective your FM radio/tuner is, you just won't get anything until it's above certain signal strength threshold. It's very much like the picket fencing effect, but digitally rapidly flipping between pink noise (IBOC upper or lower sideband) back to station back to pink noise back to station rather than fading naturally.


I was able to get WPCV 97.5 in Lake City when WSKY on 97.3 turned off HD. That's a whopping 150+ miles away. I did lose some high end, but it was definitely listenable. Once WSKY turned HD back on, nothing but pink noise IBOC hash.

 

[billy2047]

My experience from having lived in Florida for 31 years was that distant FM stations within the state generally came in better

I remember listening to WFLZ from St. Pete to Daytona to Boca Raton to Naples and back before HD and low power were booming. Gotta miss those days!

 

[billy2047]

The hiss that you would hear between stations was also blanked out. That kind of muting was an all-or-nothing proposition. Soft muting reduces the audio level of anything below a certain level, but doesn't eliminate it altogether. So you hear the hiss between stations, but at a lower volume.

That explains why when I was trying to DX FM in my BMW and it was cutting in and out almost like a squelch would. And that soft muting feature was acting quite aggressive and I could hear some blending action too!