Overall, do you think radio reception has improved from 30+ years ago? AM+FM. I've heard a few different theories but I want to hear what people think
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Radio reception now vs back then
- Thread starter Carltheradioguy
- Start date
Back then
No IBOC & less Stations
No IBOC & less Stations
Most aspects of reception have to do with the laws of physics and don't change: ground conductivity, propagation, etc.
Then there are things that change over time such as the influence of the 11-year sunspot cycle on AM propagation, as well as things like the Aurora Borealis, summer and winter natural noise levels. And on FM, inversion layers and such introduce a variable.
All these have always affected reception.
New influences: rapidly increasing man made interference that reduces the listenable coverage of all AMs. More stations and higher power on FM, particularly since Docket 80-90 have congested the band.
But within any station's primary coverage are, very little except man made interference has changed.
One thing I have noticed is that some of the new voltage control devices actually put interference into the FM band and beyond, making it difficult to hear weaker stations.
One thing we don't have that we used to is the harmonics from the 15,750 Hz Sync Oscillator from TVs. These harmonics could be heard on AM radios from neighbors' TVs, even if you didn't have your own TV on. Miniaturization and harmonic filters seemed to improve this over the years. You probably remember when you were a kid going into a department store where they had dozens of TVs on in the department, and the colors were all a little bit different, and hearing that high pitched whine from the TVs. That was the fundamental being coverted to audio by all the huge electromagnets in the TVs. In order to avoid this interference (630 and 1260 were right on the frequency), you sometimes had to wait until the TV stations signed off and your neighbors shut it down for the night.
One thing we don't have that we used to is the harmonics from the 15,750 Hz Sync Oscillator from TVs. These harmonics could be heard on AM radios from neighbors' TVs, even if you didn't have your own TV on. Miniaturization and harmonic filters seemed to improve this over the years. You probably remember when you were a kid going into a department store where they had dozens of TVs on in the department, and the colors were all a little bit different, and hearing that high pitched whine from the TVs. That was the fundamental being coverted to audio by all the huge electromagnets in the TVs. In order to avoid this interference (630 and 1260 were right on the frequency), you sometimes had to wait until the TV stations signed off and your neighbors shut it down for the night.
I think FM may be better because of more advanced technology providing more sensitivity and separation.
AM is worse, not only because of more stations but more development on land means a weaker ground wave.
And all the electronic gadgets we now have along with those 'eco friendly' light bulbs make for an AM DXer's nightmare.
AM is worse, not only because of more stations but more development on land means a weaker ground wave.
And all the electronic gadgets we now have along with those 'eco friendly' light bulbs make for an AM DXer's nightmare.
Carl.... For whatever my opinion is worth, FM reception has actually improved on balance during the last 30 years. Better receivers and better transmission methods and facilities. It's true that the band is more congested, but the net effect seems to be more stuff to listen to.
Unfortunately, for AM, things have generally gotten somewhat worse. More stations that used to be daytime only are now operating at night, which due to the nature of the band, means more interference. But the other two big culprits are deterioration of transmitter sites....many of which are now well over 50 years old.....along with the increase in both ambient noise and urban development. The causes for the noise have already been described. As for urban development, the short oversimplified explanation is newer construction around what used to be remote open-area towers has the effect of "soaking up" some of the signals. Combine this with a possibly deterioriating ground system, and you've got a recipe for reduced signal strength.
One of our resident experts, jfry, presented in another thread graphs showing field strength at equal distances from an AM tower of an obstructed path (large building) and an unobstructed one (fields and low growth). There was no difference.
There is apparently a difference between putting buildings on the goundwave path and putting reradiating metal objects, like cell towers and electric transmission lines with metal support structures. The latter will distort directional patterns, of course.
There is no doubt that AM signals can bend around some obstructions. However, many sources say that paving over a town with much concrete will reduce effective conductivity. The usual quoted value is 1 mS/m. Plenty of proof of performance measurements on DAs also bear this out, even when there is no reason why consultants might want to underestimate conductivities. There have been some challenges to measurements. But you cannot deny that MANY signals are far below M-3 prediction, based on observation, and have been for the 50 odd years I have been observing them. And they don't suddenly pick up further down the line in the vast majority of cases.
I saw an interesting observation a while back that the depleting of the water table in areas where such resources are routinely tapped for city water supplies may have as much to do with changes in conductivity in some metros as pavement and buildings do.
When I see that portions of the central valley areas of California have sunken as much as 10 feet over time, I have to wonder what effect that has on propagation at AM frequencies.
I also wonder if, in come cases, conductivity improves with urbanization. Take Long Island or the Coachella Valley or even much of the area around Traverse City where conductivity is as close to 0 as possible... do the combined products of urban development have greater conductivity than the native value? Or is that a stupid question?
Thanks for all the responses so far, I agree about the AM, The interference of gadgets can often kill reception. Like right now, I hardly AM Dx because first off the band is terrible during the summer for the most part and secondly my air conditioner destroys any AM Signal that isn't local or extremely powerful. While I do agree idk if i'm 100% sold on the gadget thing because i've been in old houses with limited electronic "stuff" and it happens to be worse. I have noticed the FM dial is better(especially now) but it also seems unpredictable but that's often summer propagation. I also never thought of Aurora Borealis either.
I've wondered the same thing. Definitely NOT a stupid question. If you pave over 0.1 mS/m conductivity with 1 mS/m material, would it increase? I will look at skin depths at 1 MHz and conductivity of construction materials and see if I can formulate a theory, unless rfry has information readily available. I think skin depth is about zero for concrete, and probably 0.5-1 mS/m conductivity.
It all depends on the market and the radio you have. In a growing market like Charleston, where we've added 13 new FM signals in the last 15 years, distant FM radio reception has gotten tougher. But radios have gotten better. HD stations have taken away several frequencies.
AM reception though is about the same. The only thing I can notice here is that WSB, which used to be barely listenable almost all year, is only available now in the winter. Probably that is because of all the development around WSB's transmitter, but the ground conductivity is not very good there, and never has been.
AM reception though is about the same. The only thing I can notice here is that WSB, which used to be barely listenable almost all year, is only available now in the winter. Probably that is because of all the development around WSB's transmitter, but the ground conductivity is not very good there, and never has been.
How about IBOC on AM?
I'm noticing more interference on FM due to new gadgets and electrical things. There are traffic lights in my neighbourhood that make some of the weaker FM stations impossible to listen to. The flashing don't walk signs create a hash that blows the stations right off the dial when they are on, but when they flash off the station pops back in. When they're solid, forget about it. This affects at least 4 local FM stations in Ottawa. Some computers and electronic gadgets also cause FM interference. In my Office, FM radio is impossible on all but 2 stations, and that's only because their towers are 5 blocks away. AM is fine on the locals and even 3 out of towners from Montreal make it in At night if you can hear it half decently the signal gets in. The only problem on AM in the office is if the receiver is too close to a monitor.
I have no deep understanding of skin depths, so will be rather anxiously awaiting your conclusions and theories.
R
rbrucecarter5
Guest
FM - too many new stations, too much IBOC interference on adjacent channels. Previously listenable rim shots are now blocked by interference.
AM - besides too many stations and IBOC - the biggest problem can be summed up in three words: "switching power supplies". What used to be pretty rare and difficult to design is now commonplace. But - analog design, particularly power supply design - is a dying art. Thanks to semiconductor manufacturers, there are hundreds of controller IC's. Each one with a nice schematic on how to use it. But those schematics do not take the PC board into account. What really needs a 4 to 6 layer board - with good internal planes, broken up by function - is implemented on a 2 year or worse yet one layer. Critical feedback loops are never analyzed. They let an ARTIST - not an engineer lay it out - the layout monkey slops the parts on the board anywhere they want, and the result is long traces on switching waveforms pumping out interference. Oh and vastly reducing the efficiency of the supply - but electricity is free, right?! The person making the parts list for the supply doesn't bother to read the notes about power rating on resistors or voltage rating on the caps. I just had a massive case of interference caused when a 1/16th watt resistor was used instead of the required 2 watt. It eventually burned out, of course. The supply I replaced it with also burned out the same resistor. Different company, different PC board - same exact problem.
I used to gripe about CFL lamps, light dimmers, home networks, etc. But these switching supplies are pervasive, everybody has one on their cell phone charger, cable box, wireless LAN box, etc. I'm convinced this is a huge and undocumented problem.
AM - besides too many stations and IBOC - the biggest problem can be summed up in three words: "switching power supplies". What used to be pretty rare and difficult to design is now commonplace. But - analog design, particularly power supply design - is a dying art. Thanks to semiconductor manufacturers, there are hundreds of controller IC's. Each one with a nice schematic on how to use it. But those schematics do not take the PC board into account. What really needs a 4 to 6 layer board - with good internal planes, broken up by function - is implemented on a 2 year or worse yet one layer. Critical feedback loops are never analyzed. They let an ARTIST - not an engineer lay it out - the layout monkey slops the parts on the board anywhere they want, and the result is long traces on switching waveforms pumping out interference. Oh and vastly reducing the efficiency of the supply - but electricity is free, right?! The person making the parts list for the supply doesn't bother to read the notes about power rating on resistors or voltage rating on the caps. I just had a massive case of interference caused when a 1/16th watt resistor was used instead of the required 2 watt. It eventually burned out, of course. The supply I replaced it with also burned out the same resistor. Different company, different PC board - same exact problem.
I used to gripe about CFL lamps, light dimmers, home networks, etc. But these switching supplies are pervasive, everybody has one on their cell phone charger, cable box, wireless LAN box, etc. I'm convinced this is a huge and undocumented problem.
Here's a link to a skin depth calculator, and a discussion of soil effects on signals at various frequencies. Can't figure out how to get the program to work. I'll try later on a PC.
http://www.smeter.net/grounds/rf-skin-depth-in-soil.php
I guess my question would be how thick would a layer have to be to affect conductivity. I do know of one AM site that is close to a dump with a bunch of cement slabs and pieces in it, about 1/2 mile North Northeast of the land that it is on. I wonder if that is why the signal in that direction is much worse than a similar facility a few miles away on a close frequency and virtually identical maximum IDF. In other close directions, such as North Northwest, the signals seem much closer in FI. This is taking into account the different patterns, which have a different beamwidth.
http://www.smeter.net/grounds/rf-skin-depth-in-soil.php
I guess my question would be how thick would a layer have to be to affect conductivity. I do know of one AM site that is close to a dump with a bunch of cement slabs and pieces in it, about 1/2 mile North Northeast of the land that it is on. I wonder if that is why the signal in that direction is much worse than a similar facility a few miles away on a close frequency and virtually identical maximum IDF. In other close directions, such as North Northwest, the signals seem much closer in FI. This is taking into account the different patterns, which have a different beamwidth.
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@ OP Carl : There has been much talk about deteriorating AM ground systems, which can't be helping transmission much. Copper thieves and general equipment erosion played a part in at least two stations up this way.
@ Schroedinger: You'd be hard-pressed to find a NYC AM station that doesn't run into a wall as it tries to go east onto Long Island. Here's WEPN 1050, for example.
http://radio-locator.com/cgi-bin/pat?call=WEPN&service=AM&status=L&hours=D
That signal-stifling area of southeast Nassau County -- under the 'o' in New York -- is where thousands of cement-slab Levitt homes were built in Fifties. If memory serves, that region used to be all farms ; ducks, potatoes, whatever.
I don't know if that is a factor, or if that spot on Long Island is just naturally a conductivity black hole. Perhaps both ?
And naturally, Long Island is VERY watchful of their water-table stuff. Always has been.
@ Schroedinger: You'd be hard-pressed to find a NYC AM station that doesn't run into a wall as it tries to go east onto Long Island. Here's WEPN 1050, for example.
http://radio-locator.com/cgi-bin/pat?call=WEPN&service=AM&status=L&hours=D
That signal-stifling area of southeast Nassau County -- under the 'o' in New York -- is where thousands of cement-slab Levitt homes were built in Fifties. If memory serves, that region used to be all farms ; ducks, potatoes, whatever.
I don't know if that is a factor, or if that spot on Long Island is just naturally a conductivity black hole. Perhaps both ?
And naturally, Long Island is VERY watchful of their water-table stuff. Always has been.
Long Island is essentially a sand bar. The conductivity is just terrible.
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