I've been part of this message board for a while and have seen the topic of AM skip mentioned a couple of times. I have a basic understanding of what is happening when I can pick up a distant station at night. What I don't know is why stations seem to fade in and out. Is this because the signal is bouncing off different parts of the ionesphere? What else would cause this? Sometimes the skip signal seems stronger just before sunset or just after sunrise. Does the curvature of the earth have something to do with this? I think the farthest station I ever picked up was when I lived in central California and was able to pick up WWL (New Orleans) and WLW (Cincinatti).

Free space path loss (signal energy lost in traversing a path in free space only with no other obstructions) is continually changing. Propagation of RF is 4 dimensional. x,y,z,t (A specific point at a specific time).

Why it is continually changing is because the state of the conditions along the path are not constants, and there are other obstructions

The curvature of the earth is one of these changing conditions (the earth is not a sphere, nor its orbit around the sun circular).

The changing light and heat of daily conditions are always a factor as well.

The more consistent the sum and total of all the conditions are, the more reliable skywave is. The predictions of skywave take some of this into account "but accurate predictions are difficult to achieve because of the extreme spatial and temporal ionospheric variations."*

*
http://adsabs.harvard.edu/abs/1981icap.conf..258T

I've read that skip often occurs when the E and F layers of the ionosphere meld together at night. This thickened layer is apparently what helps cause radio waves to bounce back down toward earth.

Given what Andy notes, my guess is that the thickness of that joined layer is not always consistent.

Herb

Andy, I feel the need to go back to college to understand your last post. But I'm still intrigued.

Another question...why did it seem easier to DX AM's in the 70's than today? Is it receiver quality, or some other explanation?

Easier because it was less crowded. The AM band has more RF energy total because of the growth of the population and the need to serve new markets as well as the shoehorning in of many frequencies into the major media markets and the restructuring of allocations led by the big conglomerates to rob bandwidth from the lesser markets to increase presence elsewhere and global warming and the changing amount of ozone in the atmosphere .... just off the top of my head. Receivers are better at receiving signals once too weak to capture and reject better the causes of receive interference, but I don't think it's that big a factor. The antenna you use is a bigger factor probably. Skywave has always behaved the way it does. Oh, yeah, don't forget sunspots.

The AM band today is more crowded, and more stations are on the air in the evening, even at severely restricted power. Oh, yes...the noise from other electrical interference as in LED traffic lights and electronic devices adds to the clutter...

Loved DXing AM back in the day. Today's talk programming makes me feel that signals are harder to tell apart from one another, and not as easily identified. Frankly, I always thought the music helped the audio cut through the clutter!

Today, finding music on AM at night is an event in itself...

I think these are the major factors. Not necessarily in order of significance:
1. Receiver/Antenna Quality - now is worse
2. More sources now of electrical noise near your radio.
3. More stations now on at night (fewer "clear" frequencies, etc).

Yep, there was a time when you could pick up KFRC 610, KGW 620, and KFI 640 all at the same time throughout the western US. Now, almost impossible!

I count seven former "daytimers" in the Portland area alone, 750, 800, 880(was daytimer on 1460), 940, 1150, 1410 and 1480. There are also a sizeable number of newer sign-ons, three in the Portland area, 860, 1010, and 1040.

How about adding: 1360 & 1550. Even 910 was in the 1940's.

Of course you are correct, I missed 1360 altogether. However, in addressing the specific question regarding the 1970s vs. today, 1550's move to 24hrs "on December 24, 1976 at 3:38AM..." came several years prior to the dismantling of the daytimer/clear channel setup nationwide.

Into the 70s, you heard nothing local on the AM dial at night between KGW at 620 and KISN at 910!
That's how I got introduced to the hobby in the 60s...I got to hear San Francisco, Los Angeles, and even San Diego, not to mention Albuquerque, 150,000 watt border blaster XELO 800 across from El Paso in Ciudad Juarez, MEXICO! Even sent away for and got a QSL card from them.

Oh, yes... One time we went camping in a travel trailer for the first time in our lives in the late 60s. We stayed next to Fogarty Creek State Park on the coast. I took along a transistor radio with the single earplug. It was the first time ever I heard this strange-sounding dude on the radio from down south. His vocal quality was so unique from anything I ever heard before that I thought something was wrong with my radio. Turned out it was simply the unique presentation from another border blaster in Mexico in the middle of the night.

That was the very first time I ever heard Wolfman Jack playing the hits on 1090 XERB.

Those were great times for DX listening!!

I think I stumbled across 1090 XePRS, "The Soul Express" for the first time about 5 minutes after Wolfman left. Never got to hear him live.

The first time I heard The Wolfman was on XERB. And like Mark, by accident. It was around Spring 1968. My family was headed home to Beaverton from my Grandparents in Dundee late one night. We were all bored, so I talked Mom (ridding shotgun) into flipping on the radio and find something interesting. Well she stumbled on this deep Crazed Voice!

I had heard preachers before shouting but nothing like this! I couldn't believe it at first. I Was Transfixed! But it faded out and KING faded in. Mom tried to re-tune but we lost him. There would be other nights driving home, Mother would try and find that phantom station in the mist of the night. Sometimes she was even successful.

This would be one of the main reasons in later months, why I started DXing and learning the radio dial from my Grandfather, an avid DXer at the time.

I was driving between Portland and Grants Pass most weekends back about that time, Craig. I remember listening to the Wolfman all the time while driving down there at night. Had no interference from KWJJ or KING once you got south of Salem. I could hear him consistently without fade all the way from Eugene to Grants Pass/Medford. You are right. Something intriguing about listening to him. Mesmerizing. A lot of that sparkle was gone when he went to tv.

That was an example of why we listened to radio. I notice that KKSN still plays the same music now but without dj's. Although I like the music, I listen less without the live dj between the tunes. That is what makes it interesting because if I just want to hear the tunes, I can play my records, in the order I want.

I guess I am old fashion still living in the past.

Would be interesting to do the following experiment:
Have all AM stations agree to sign off one night. Go out into the country away from city and measure noise level across the AM band. Than take same measurments going back in time once per decade. This will tell us how much noise is being added to the atmosphere by all of the sources of electrical interference over the years. Repeat noise measurment test in city and suburb locations. Then allow some stations to come back on, only one per frequency, and see what happens.

This would be a great experiment... but how do we go back in time? You got an Art Bell machine?

I suspect that we would find less noise on the AM band, but there was still a bunch in the first part of the 20th century... "universal" AC-DC motors (with brushes), electric street cars, carbon filament light bulbs, early automobile ignition systems (before resistor spark plugs/wires), electric fences were contributers to the broadcast band noise level, which drove the development of FM.

To pick up on a thread on the "other side" I guess that I would rather DX in 1966 with the better radios that were available in 2006.

62kgw: Back in 1922-23 when most stations in the nation were on 360 meters (832.7kc), there were what the called "Quiet Hours" in Portland, when no station was broadcasting. Portland also had nights for DXing when all area stations agreed to stay off the air. This became very rare by the end of 1923 but by then stations were being moved to other frequencies anyway.

JR, I disagree about one thing. IMO, on the average, the average person had a better am radio (+ antenna) in 1966 than does the average person in 2006.

I guess thats another experiment for somebody to do. Do some side by side comparisons between typical old and new radios. Perhaps differing results for car, tabletop, handheld, stereo system, etc.

I think the effects of the various interference generating sources is very localized. Thats one reason for suggesting doing the test out in the country. Do all of the noise making equipment have a significant cumulative effect that gets into the atmosphere?

62kgw:
I don't disagree about the quality of the AM radio the average person might have in 1966 vs 2006, some of those old 5 and 6 tube super-hets were pretty good, and I did a lot of DXing with radios of that type. However, a GE SR III might do as well as the best of them.

But when you get down to ultimate DX performance, (and I was talking about DXing) most modern high end DX receivers from JRC, Icom, AOR, Ten-Tec and others have more to offer than DX receivers of the 60's, although some huge "boatanchors" such as the Collins R-390A (1959) or 50's era Hammarlund SP-600 JX do quite well.

I might try an old 6 tube Zenith vs SRIII tonight (if I can get the old Zenith to work).

I suspect that any noise event will contribute to the overall background but distance from the source will reduce the effect.

So many great AM DX areas being discussed! So, I'll start with RF interference. Fluorescent lights have become very popular and, the last time I checked, their peak RF output is about 600 KHz. Most devices were tightly controlled for RF output, but either the regulations have been relaxed or the enforcement. Ignition suppressors are no longer required on cars. The entire electrical infrastructure of most cities and especially rural areas is getting old, and is not being replaced. A noisy electrical transformer -- underground, in a substation or on a power pole -- got complaints and almost instant action from the regulators (Department of Communications in Canada, for example). Today, the cities and rurals areas are littered with RF-interfering transformers and no one cares. We even had a local station that was causing heavy interference up to 210 KHz above its frequency because of poor maintenance and monitoring, and no one (except me) reported the problem, or seemed to care. I worked for the owners, so got them to fix it, but no one else noticed.

Computers and halogen lights are pretty bad, too. And a local TV station says they had to build a microwave repeater downtown here because their portable truck couldn't communicate back to the studios at the edge of town during the lunch hour because every office worker was running a microwave oven. But, beyond RF interference, newer houses seem a lot more shielded. I have receivers on the North side of the second floor of a smallish house, but get very poor reception from the South.

Office buildings are a nightmare for AM reception inside. But they are also causing major problems outside, too. The large number of tall buildings has made CKNW Vancouver's somewhat distant transmitter site ineffective in covering areas with tall buildings, especially downtown. CKRM Regina is often dominant in and around tall buildings at night in Vancouver. Not to mention the bouncing of signals off buildings in the daytime causing phasing and other signal problems.

Overall, I'd say there is more RF noise now, especially inside a house, building or car. I get decent reception in my 2003 car, but am amazed how the background noise level decreases when I turn off the engine.

Well into the '70s, transmitter maintenance after midnight every Sunday night still gave you a reprieve from the huge number of stations that went 24 hours in the mid-1960s. But the real killer for most people being able to listen to distant stations almost every dark hour of the year was the death of 1-A clear channels. Based on discussions here, I've started a Web page on Clear Channels as they were originally intended to be at http://www.radiotribute.com/clear

But suffice it to say that West Coast folks could cruise through whole parts of the AM band where frequency after frequency was a distant station. So far, that page only talks about U.S. 1-A clear channels, but there were lots of frequencies with only 2-3 stations on the frequency. From memory, the range of those relatively clear channels were 540, 640-780, 800-900, 990-1140, 1160, 1180-1220, 1500-1580. That is a big chunk of the Broadcast Band.

On another thread (no clear channel for FM couplers) I was reminded of http://www.radio-locator.com/

Whoa, much improved since I saw it last. Invaluable since ID jingles are less common today, and digital tuners let you nail the freq.

The abandonment of the careful allocation engineering which prevailed in past decades is probably due to the increase in alternative delivery means. From the 20s through the 50s, the reliability of MW broadcast was an essential public need, particularly getting informative signals into the "white areas" (even if only a night) and for civil defense (even if that was a joke).

But considering the relative fragility of satellite-network delivery (either direct or through terrestrial affiliates or repeaters), and instances where a whole region's broadcasters can be knocked off-air (Katrina; think major earthquake), I still need some need for reliable long-range broadcasting. (The defunct WGU-20 was a stab in this direction.)

I still see a possibility for LW BC on this continent to take the place of the "clears," but it just doesn't fit today's business model here: There'd only be room for a dozen such, two dozen max. (Indeed, even back in the three-network days, Armstrong's FM network concept, implemented by General Tire as the Yankee Network, was crushed by RCA it threatened their biz model.)

However, I am surprised that Canada, where broadcasting remains largely public and satellite delivery was pioneered, and is now shifting to sat-fed FM, still operates a half-dozen low-powered domestic SW transmitters to serve remote areas but apparently hasn't looked at longwave.

It was examined for use here once back in 1931: http://ieeexplore.ieee.org/xpl/absprintf.jsp?arnumber=1671011&page=FREE

I used to cite http://www.ntia.doc.gov/osmhome/spectrumreform/responses/documents/A5-Substantiv e%20Written%20Comments.htm as a recommendation of implementing domestic LW, but upon rereading it tonight, realized it was half-baked.

who knows, maybe this post is, too.

For those who didn't know (that included me up to four years ago), Long Wave is serving a very useful purpose as a place for really Clear Channels that serve pretty much all of North America. And that is Time Signals. WWVB is on 60KHz and I have two watchs and two clocks that sync to it. The watchs can usually get reception in the day, but the clocks only after dark. And I'm pretty far North (Edmonton).

Reading my watch instructions, it is clear that Japan and Europe have equivalent services.

Funny thing, though. Canada's former Radio Shack just stopped selling all of the watches and clocks. I suspect it is an issue with the formula programmed into them for when Daylight Savings Time starts and ends. It has been constant since 1986, but changes this March.

"Canada's former Radio Shack" ?

Fascinating. Former RadioShack stores in Canada are known as "The Source by Circuit City." After selling its Canadian division to Circuit City, RadioShack forced Circuit City to stop using the RadioShack name. RadioShack then opened its own new stores in Canada, but the effort has failed. Good info here:

RadioShack at Wikipedia

Speaking of Wolfman Jack, here's a great video on the early days of radio.
http://www.amazon.com/Rock-Roll-Invaders-Radio-DJs/dp/1572524588

Here's a good AM Loop Antenna page.
http://www.mindspring.com/~loop_antenna/

"how do we go back in time? You got an Art Bell machine? "
There is a machine called a Tardis. Anybody know where we can rent one?

I really think that we DO need to go back in time to make my old Zenith perform well. Here is what I have found so far:

Zenith (model 6D030):
1. Is quite sensitive.
2. AGC functions well, many distant stations are nearly the same volume as locals.
3. Dial calibration is excellent.
4. Fairly broad tuning... At one time KOA Denver on 850 was an easy catch for this radio, but KPAM 860 now covers up 850. Same problem for KGO 810 (covered by 800), and anything close to KEX and KUIK (I live in Hillsboro)is covered.
5. Decent Sound Quality, It is easy to listen to.
6. Poor rejection of noise coming in on the line cord.

GE SRIII:
1. Is somewhat more sensitive than the Zenith.
2. AGC functions well, many distant stations are nearly the same volume locals. Perhaps a tie here.
3. Dial calibration is POOR, but I have marked the dial to provide adequate calibration.
4. Sharper tuning, 850 from Denver is no problem, ditto for 810 from Sf. 630 from Boise could also be separated (some splatter) from 620. The SRIII is a big winner here.
5. SRIII is also pleasant to listen to.
6. Noise from the power line is rejected better by the filtering in the SRIII...AND the SRIII can operate on batteries to further reduce line noise.

So I would conclude that the Zenith would work very well, in the days of clear channels, low line noise, less congested band condidions, and provide a decent listening experience, but today a fairly inexpensive, made in China radio is the winner!

Is that one of the uprights with a big loop? I had a friend who had a 1940 RCA that was amazing! You could usually get WNBC at night along with KIDO with no interference from KGW. He lived behind David Douglas High School.

Here is picture of one. Its a 1940's table top radio 6 tubes. Probably has small loop antenna inside back panel. It appears not to have a power transformer ("AC-DC"), which these transformerless radios often pick up noise from AC power line. Sometimes the noise can be greatly reduced by flipping the AC power plug 180 degrees in the socket.
http://www118.pair.com/pkonshak/z6d030.html

Yep! that's the puppy. Mine is slightly different in detail, in that it has black grille cloth, but is otherwise the same. Flipping the plug does indeed reduce the line noise somewhat.

Those big uprights were impressive, the one that I remember had an enclosed loop next to the speaker on the right hand side, below the chassis. There was a knob on the front panel and a chain arrangement so that the loop could be rotated for best reception. I think that it had about 10 tubes, which included an extra tuned RF stage, which would really improve selectivity. It perhaps had 1 or 2 more IF stages, push-pull audio output AND an eye tuning indicator.

The Zenith Stratospheres were the top of their line:

http://www.oldradiozone.com/strat.html

I would love to repeat the test with a stratosphere but they are quite rare and expensive today. I doubt that many *average* listeners in the 60's owned such a set, but many of these small 6 tube sets were still in use at that time. I used the 6D030 mostly for KVIX (OTR) until it went off the air.

IRCA and NRC were medium-wave (540-1600) DX clubs I was a member of in the late 1960s. They are still around, but I'm not. Most members, especially of IRCA, were teenagers back then. Which meant that few of us had much money. Some of us were able to save up and, after a lot of research, spent $100 on the best thing we could find. That generally meant a mass produced communications receiver aimed mainly at short-wave listeners and ham radio people on a tight budget. In my case, I picked one of the most popular, the Lafayette HA-230. I almost waited too long as I bought the last new one sold in Vancouver (Canada). There is a picture of one that looks better than mine did when it was fresh out of the factory-sealed box: http://www.radiotribute.com/dx

Hook that up to a hand-built 4 foot box loop antenna, and I was amazed at the difference between it and my previous DX radio: my parents' Philips late '50s transistor radio. The Lafayette's selectivity and sensitivity were unbelievably better. Sensitivity = stations were where noise or nothing at top volume on the Philips. Selectivity = no slop 20 KHz off a 50KW local with a directional pattern pointing right at me, from perhaps 10 miles away, when the Philips was almost unlistenable when that same station had only been 10KW with a much less tight directional pattern.

But, it was only a few years ago that I found out that the Lafayette actually had amazing frequency response. Playing old tapes, the high end is there. It just didn't sound like it because the receiver boosted audio around 250Hz by 6dB. Re-equalize and it sounds pretty good, though tape hiss can be an issue.

My point: in the '60s, the best AM DX receivers seemed to be some of the communications receivers meant for short-wave and ham enthusiasts. I tried some of the old stand-up console radios and found them nowhere near as good as my Philips, let alone the Lafayette. Nor did I know any of the DX'ers in either club that recommended them over communications receivers.

Today, of course, there are better receivers, as the few DX'ers I knew who are still at it have more money and have new equipment. We've touched on it before here, but there are also software approaches that automate the monitoring of different frequencies, and provide alerts. These same DX'ers now are old enough to have a driver's licenses, so the majority who are urbanites have to flee to the rural areas to get away from the Big City RF noise.

"My point: in the '60s, the best AM DX receivers seemed to be some of the communications receivers meant for short-wave and ham enthusiasts."

I agree 100%! I have always thought that communications receivers were best for AM DXing. The one that I grew up with, an old Hallicrafters S41G that my father bought shortly after WW2, was not the greatest however, many ordinary 5 and 6 tube table models could do nearly as well.

http://www.portabletubes.co.uk/boats/hs41g.htm

The question that I tried to address with the 6 tube Zenith vs the GE SRIII experiment was about the performance of a radio that an "average" listener in the 2 eras possibly would be using.

Was the HA 230 all solid state?

I think that Zenith radio was more of a (step above) average radio for average person, whereas the SRIII is a bit more of a specialty unit for budjet radio enthusists.
I had a similar wooden table top tube set back then I think it was GE that I got first tastes of top 40 and DX listening on. My brother must have taken it away.

No, all communications receivers that I was aware of (i.e. - less than $400) were 100% tubes, even the new ones that came out in the late '60s. If memory serves, the key factor seemed to be having separate RF and IF stages. Better receivers than my Lafayette had more than one RF stage.

As well as tuning the loop antenna's variable capacitor, I seem to recall having to tune an antenna trimmer on the receiver itself.

62kgw:
How about a 5 tube clock radio vs a cheap Sony "boom Box" ? What do you propose for the test ?

Adiant:
Thanks, I did not remember that SW receivers were so late in shifting to Solid State... Perhaps early transistors were subject to damage, caused by all the RF floating around the shack?

I don't think that frequency was the issue, as many decent FM tuners of the mid 60's (such as the Scott LT-112B that I built in '65) were solid state. I started FM DXing then, (Seattle and Vancouver BC were fairly easy in those days, during the summer). I did not really pay much attention to AM again until I got my first SW portable, a Panasonic RF-2200, in the mid 70's.

My father bought a Canadian-built (forget the brand) stereo receiver in the late '60s, in the sense of receivers today, with phono input, tape input and output, as well as AM/FM tuner built in. It was 100% solid state, but the AM receiver really sucked big time. The FM was great. Only major problem was that the transistors were all made of germanium. And they were very noisy. You could hear the white noise on headphones, through the speakers and even when you taped stuff off it.

All I can say about communications receivers is that, at the same time that I bought my receiver, around 1968, I friend bought the newer model Lafayette (since I had bought last HA-230), and it was still all tubes.

At that time, I think it would just be too expensive to buy all the transistors you'd need to build one or more RF sections, an IF section, etc. Tubes had advanced to the state where one could replace two or three transistors. Plus, the assembly lines and manufacturing would have been down pat for tube sets then.

5 tube clock radio vs. a new clock radio from Fred Meyer?
Actually what I want to see is comparison of 1960's car radios vs. todays typical car radios (tested only in AM mode, with engine running and lights on).

62kgw:
Well, my wife uses one of these that she got at Target a couple of years ago:

http://www.amazon.com/Sony-ICF-M410V-Portable-Weather-Radio/dp/B00006HOLO/ref=cm _cr-mr-title/104-3745945-9658362

Perhaps that vs her childhood Silvertone (5 tube) that it replaced ?

Anybody got a running 60's car with orig. radio ?

Seems reasonable.

OK, here is what I observed:

Silvertone 5 tube clock radio (Ch. 132.896)
1. Fairly sensitive, can receive many distant stations.
2. AGC action fairly poor, had to crank volume up and down quite a bit, while scanning the band.
3. Decent dial calibration.
4. Broad tuning...forget 850 from Denver and 730 from Boise, however I could make out 810 from Sf.
5. Sound quality ok.
6. Some line noise pickup.

Sony "liv" Portable clock radio (ICF-M410V):
1. Quite sensitive, could hear more of the weaker stations.
2. AGC functions well, many distant stations are nearly the same volume as locals.
3. Dial calibration right on (digital), however it only tunes in 10Khz steps... bad deal for DXing!
4. Fairly poor selectivity, KUIK (1360) covers 1340 to 1380! KOA Denver (850) was covered by 860 but 630 Boise was ok (some splatter). It did fine on KGO (810).
5. Sound quality ok... more bass (fewer highs ?) than the Silvertone. It sounded somewhat "muffled".
6. less line noise than Silvertone.

The old Silvertone is decent, but I would pick the Sony as the clear winner in reception.

Boise stations most likely to hear are 580, 630, 670(basically a clear in the west) and 1140. They used to have a daytimer on 740. I'll investigate.

It looks like they moved from 740 to 730 and added nighttime service at 500 watts.

Sorry for the mistake above... that should have been 630 from Boise in both cases. The old Silvertone could not not get 630 because of 620, but the Sony could receive it (with some splatter).

Having muffled audio is a big negative for all around performance. Its not only what you can hear, but also how well it sounds. Muffled sound on locals degrades the listening experience.
JR, I presume the silvertone is aligned as good as possible?

Communications receivers of the '60s often had problems with signal overload ("mufflued") on locals. Even with the IF gain turned all the way down, if you were lucky enough to have a receiver that even had an IF gain control.

Sorry, but the guys who designed these beasts weren't planning for them to be hooked up to high gain DX antennas less than 10 miles from an effective radiated power of 150,000 watts, which was what Vancouver DX'ers were faced with, given that, by the end of the 1960s, most of the 50KW local stations were just South of the City, and got their 50KW power increases by pushing most of their signal North, to protect U.S. and Mexican stations to the South and Canadian stations to the East.

62Kgw:
Agree, the Sony might be less pleasant to listen to for extended periods than the Silvertone (which some might say sounds a bit tinny). But remember, I was talking about DXing:

"To pick up on a thread on the "other side" I guess that I would rather DX in 1966 with the better radios that were available in 2006."

The alignment of the Silvertone is good.

I found a similar model on eBay:

http://cgi.ebay.com/Silvertone-3025-Black-Bakelite-Tube-Radio-c-1952_W0QQitemZ17 0071305873QQihZ007QQcategoryZ38035QQrdZ1QQcmdZViewItem

Similar, except the one I have (cat # 2026) is ivory bakelite, with a "basket weave" pattern on the front panel. The 4" speaker is behind the dial pointer, and sound exits through a 2.5" metal grille behind the pointer... could be why it sounds somewhat tinny.

Vacuum tube radio fans, check out this video.

http://www.youtube.com/watch?v=fmVC6HqEWYY

Steve,

Cool.

Reminds me of the old Heathkits I built.

In fact I still use the old tube amp out in my garage that I built in the late '60's . Of course, it's being fed from a Dish Network receiver.

Old meets new!