Radio reception now vs back then

[frankberry]

Nothing said in this thread about AM receivers, whose technology hasn't really improved in about 20 years.

A lot of these interference issues might be a result of the quality of receivers. And the lack of FCC enforcement or rulemaking in this area.

AM receivers are designed to detect changes in amplitude. Impulse noise causes a change in the amplitude of the signal being received. Back in the 80's, there was an attempt to standardize the performance of AM receivers.
One of the requirements was an impulse noise reduction circuit (Part of the AMAX standard) which was designed to minimize the impact of interfering impulse noise.
It was a good idea which went nowhere.

 

[TheBigA]

Too bad manufacturers haven't done anything to improve AM quality or reception, and the losers are the radio owners.

 

[rbrucecarter5]

Long Island is essentially a sand bar. The conductivity is just terrible.

Daytona Beach Shores was essentially a sand bar, too - but reception was incredible! The NYC clears (except WOR) all day long, no matter what season of the year! A whole lot of other East Coast clears as well. I assumed it was salt saturated sand causing spectacular ground conductivity. I moved a few miles inland, all gone! Normal ranges on AM.

 

[gar hi]

Here's a little table on the resistivities of various soils.

When you consider that continued expanding development on land that was once forest, field, or wetlands involves a lot of concrete, it would suggest that it does have a negative impact on the propagation of medium wave ground wave signals.

The resistivity for soil is between 100 - 10,000 ohm-cm if you include clay too

https://books.google.com/books?id=3...k#v=onepage&q=soil resistivity ohm cm&f=false

The resistivity for moist concrete is 10,000 ohm-cm and it's significantly higher with dry concrete.

http://trid.trb.org/view.aspx?id=102173

 

[1L6E6VHF]

Daytona Beach Shores was essentially a sand bar, too - but reception was incredible! The NYC clears (except WOR) all day long, no matter what season of the year! A whole lot of other East Coast clears as well. I assumed it was salt saturated sand causing spectacular ground conductivity. I moved a few miles inland, all gone! Normal ranges on AM.

Not salt-saturated sand, rather salt-saturated WATER!

Sea water is the best "soil" of all. Typical soil is a "4" or an "8", the legendary prairie soils are a "30", but sea water is said to be a "5,000"!

And yes, such signals from far across the sea "drop dead" just a short distance inland.

I'm surprised you would get NYC stations from Daytona by day. Much of that path is on land- NJ, DE, MD, VA, ALL of NC are in the way.

 

[rfry]

One of our resident experts .... 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.

Below are the two graphics referred to above, although the descriptions above aren't spot on.

There is apparently a difference between putting buildings on the groundwave 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.

Conductive components in low-/medium-rise buildings also can re-radiate MW fields. But that effect depends a lot on how close to that structure those fields are measured, and the path distance and azimuth orientation of that structure from the DA array.

In general, and as shown by the fields near the hospital in the 2nd graphic below, MW fields diffract around such structures quite well, as those structures are relatively small compared to wavelength.

 

[Carltheradioguy]

You think daytona beach has great reception, check Cape Cod Haha

 

[cyberdad]

And then there's the example of one of our favorite getaway spots, Perdido Key, Florida. This is a sand bar extending about 23 miles southwest of Pensacola. Daytime, with one exception, the Pensacola AMs, via land path, are for all practical purposes not listenable on most radios. Meanwhile, about a half-dozen signals each from New Orleans and Tampa Bay are present. About 150 and 400 miles respectively. In fact, WWL is very listenable, with a signal exceeded in strength only by a 25kw semi-local (WEBY). WDAE (620) from Tampa routinely trips scan buttons on car radios. Which is something most Pensacola AMs can't do.

 

[boombox4]

I think receivers -- I'm talking standalone radios here -- have improved, at least in overall performance. In the 60's & 70's most radios, solid state or tube, were variants of the All American Five, most without an RF amp, much less a TRF stage. With the widespread use of IF chips with an RF amp stage, as well as 'whistle reduction', hot AGC and other features, even a Walkman or boombox had good AM performance.

Now we have companies like Sangean making shower and kitchen radios with hot digital IF chips and decent loopsticks, making them decent performers. Light years better than your typical portable or clock radio of the 60's & 70's.

The actual sound of AM may not be as pleasing now, but I think the quality of the radios is overall better.

 

[Steve Green NEPA]

@ David E ...

'Long Island is essentially a sandbar'.

Yessir on that point. For those not familiar with 'New York City's Bedroom', the most heavily populated areas live on flat land, like 8 feet above sea level on the South Shore. As you go north along any point from the South Shore's skinny stretch though, the elevation slowly increases until you reach North Shore villages like Oyster Bay, Sea Cliff, Port Jefferson, et al. You have then reached, and for a long stretch of population, cliffs.

My observation/question about that spot in southeast Nassau County was based on seeing several coverage maps.
True, they are Radio-Locator maps. But there is a decided blockage of signal at that densely populated suburban spot -- Levittown, East Meadow, Plainedge, Massapequa Park -- on just about every signal I've brought up on R-L.
Plus, the transmitter sites in NJ send their signal southeast ANYWAY.

Here are merely the first two New York City stations on the dial, as an example.

http://radio-locator.com/cgi-bin/pat?call=WMCA&service=AM&status=L&hours=D

http://radio-locator.com/cgi-bin/pat?call=WSNR&service=AM&status=L&hours=D

Both those station signals come to a halt at essentially the same spot -- southeast Nassau County. I imagine that the thousands upon thousands of cement-slab foundations in that area after WWII and Korea *might* have something to do with repelling AM signals. Now, the Pine Barrens stretching to the east from the Nassau-Suffolk line, the central Long Island 'spine' -- obviously contribute to the substandard propogation of those NYC signals.

I just feel that the wild 50's overdevelopment in southeast Nassau County is also a factor. No full basements. Only a crawl space, the floor of which is a cement slab.

 

[schmave]

AM receivers are designed to detect changes in amplitude. Impulse noise causes a change in the amplitude of the signal being received. Back in the 80's, there was an attempt to standardize the performance of AM receivers.
One of the requirements was an impulse noise reduction circuit (Part of the AMAX standard) which was designed to minimize the impact of interfering impulse noise.
It was a good idea which went nowhere.

Bingo. The receivers keep getting worse, but in fairness, so does the man-made interference.
I haven't had a really good AM receiver in a car I have owned in over 10 years. I live with it, but I don't like it. By contrast, my parents' Ford Escape SUV has a wonderful AM unit. Maybe I am just too cheap

 

[TheBigA]

With the widespread use of IF chips with an RF amp stage, as well as 'whistle reduction', hot AGC and other features, even a Walkman or boombox had good AM performance.

My point is receiver technology hasn't improved since that, and you're talking about 30 years ago.

 

[rbrucecarter5]

Not salt-saturated sand, rather salt-saturated WATER!

Sea water is the best "soil" of all. Typical soil is a "4" or an "8", the legendary prairie soils are a "30", but sea water is said to be a "5,000"!

And yes, such signals from far across the sea "drop dead" just a short distance inland.

I'm surprised you would get NYC stations from Daytona by day. Much of that path is on land- NJ, DE, MD, VA, ALL of NC are in the way.

Not as surprised as me! The real shocker was WLW - all day long! I actually considered if a neighbor nearby was re-broadcasting them or something and went on a car ride. Up and down the barrier island, they were all there. The moment I started up one of the bridges - GONE! I was right by the Dunlawton bridge, close enough to walk. I took the GE Superadio 2 with me on a walk - same thing as the car radio. As I got away from the soil of the intercoastal waterway - gone. I took the radio to the beach two blocks away, reception on the beach was even better. It was repeatable at different times of the year. Amazing! I haven't experimented at Galveston like I wanted - but I am greatly hampered by not speaking foreign so I can't identify things from Mexico. My resident Spanish language speaker from last year has left to be on her own, and she was very immersive in English, preferring it to Spanish anyway.

 

[boombox4]

My point is receiver technology hasn't improved since that, and you're talking about 30 years ago.

True, but I don't know what further improvements could be made to receivers to 'improve' the quality of a bandwidth reduced signal coming from a radio station. YOu can't add fidelity that isn't in the signal to begin with.

Noise reduction improvements could be made, and the digital chips used in many radios now may have a way of doing that in the future.

 

[rbrucecarter5]

i think the radio manufacturers settled on the "radio on a chip" design for home radios - with one IF filter AM and one IF filter FM many years ago. As long as you aren't too close to towers, one IF ceramic filter is enough. But if out of band signals punch in too strong - the ultimate stop band reception of a single ceramic filter is only about 50 dB, so you can get quite a mess! Their response is to make the ferrite bar very small, and not have an FM antenna at all beyond what they attenuate off of the headphone wire in a broadband ceramic filter. Drop 20 dB or so, and if there is still too much signal have a local / DX switch on the radio that breaks the antenna connection completely, leaving an inch on the PC board or something as the FM antenna. Or put an insulated metal strip on the power line and steal whatever FM is leaking into the power line. This stuff is cheap, easy to produce, small, and reliable. And local stations come in for the most part. Radio - distilled down to just what is absolutely necessary, nothing more. I've even seen radios that delete the ceramic filter entirely, putting a ceramic capacitor there instead. All of the AM selectivity comes from the ferrite bar and tuning cap - and the radio becomes effectively a tuned RF radio and not even a superhet. FM selectivity entirely from the antenna coil and tuning cap. They make AFC ridiculous, and the five or six strongest FM stations come through as you tune across the dial. This is in the really low cost small stuff, but I've got pictures of the innards of these radios - this is what they have inside! Put a ceramic filter in, they get a lot better.

The future is bleak. SiLabs has a line of IC's where you can't even get close to the IF - it is entirely integrated "what you hear is what you get". RF in, frequency programming lines in, audio out - that is the IC. I've got one of their FM radios on a USB stick. It actually does pretty well, with a fair amount of sensitivity and selectivity. So far though the chip is expensive enough to keep it out of a lot of radios.

I also think the AM in my car radio is entirely DSP algorithm. I can't find any components you would expect with an AM section in the radio. You know what? Its a good AM section - a 50 kW clear 250 miles away comes in absolutely free of static with a 31 inch whip on my car. Can't complain about that!

 

[TheBigA]

True, but I don't know what further improvements could be made to receivers to 'improve' the quality of a bandwidth reduced signal coming from a radio station. YOu can't add fidelity that isn't in the signal to begin with.

But we know that the fidelity has the potential to be better than it is. The reason it isn't as good is because of the selectivity of the receiver and its ability to resist interference. My sense is it that manufacturers simply don't care. The profit margin is higher for other devices, so they just do bare minimum for broadcast radio, and radio stations are powerless to do anything about it.

 

[semoochie]

But we know that the fidelity has the potential to be better than it is. The reason it isn't as good is because of the selectivity of the receiver and its ability to resist interference. My sense is it that manufacturers simply don't care. The profit margin is higher for other devices, so they just do bare minimum for broadcast radio, and radio stations are powerless to do anything about it.

Today, I was downtown, attempting to listen to a local non-directional 50KWer on 1550. I was within the 5mv/m contour of the station. It was completely obliterated by noise. I switched to a one and a half watt LPFM that was probably within its 30dbu contour. It was fine. It makes you wonder.

 

[MarioMania]

You all didn't talk about IBOC HD that causes Noise also from the AM Band also

 

[TheBigA]

Also

 

[boombox4]

You all didn't talk about IBOC HD that causes Noise also from the AM Band also

I think the IBOC "problem" is overblown. I say this as an AM DXer as well as an AM listener.

Here in the Seattle metro there are 2, count 'em, 2 frequencies basically wiped out by IBOC (1080 and 1100).

I can still DX those channels on rare occasions with my most selective radio. Right now I can hear 1080 ESPN Portland, with some interference from 1090's IBOC, but the station is still clearly audible on my PR-D5 (IBOC interference covers any stations from the east or west, but the Portland station is clearly audible from the south).

I can also hear KFAX 1100, with minimal IBOC interference, although when I aim my PR-D5 E-W, the IBOC is audible.

I'm getting more interference from my computer monitor and router cable on other channels right now than IBOC.

There are two more frequencies higher up the dial that are affected by IBOC (1170 & 1530, and to a lesser extent, 1390), but I have still heard DX through them.

So, unless you're in a metro where IBOC wipes out half the AM dial, I think the negative effect it has on the AM band is minimal.

If digital could save AM, I'd be all for it, even though it wreaks some havoc on adjacent channels on an analog AM receiver.

Unfortunately, it looks now like it may not 'save' AM, although maybe 15 or 20 years from now the remaining AM stations may be all digital.