Today, I've been periodically checking 810 kHz, hoping to hear the KTBI signoff. Sometimes, this frequency is dead during the day from my location in Hillsboro; other times, there are are signals that pop in for a while. Earlier this afternoon, about 1:30 PM or so, I heard a religious program there that might have been KTBI. Later, around 3:00 PM, I heard Bob Brinker there, fading in and out (KGO's schedule has Brinker playing in this time slot). At 4:00 PM, I checked, and I heard news, followed by a KGO ID; the signal is pretty strong. There are no traces of KTBI.

Sporadic daytime skip on AM has fascinated me for many years because of what can mysteriously appear, only to vanish a few minutes later. Does anybody know what is responsible for this phenomenon (do holes somehow get punched in the D-layer)? Are there any web pages describing it?

Its skywave. in the winter there is less solar energy exciting the ionosphere. Its the solar excitation of the ionosphere which absorbs rather than reflects medium wave RF signals. Less solar in the winter means more potential for the ionosphere to reflect AM.

Typically skywave is still receivable in the "critical hours" two hours after local sunrise and for two hour before local sunset.

In the NW the short winter daylight hours mean longer DX times.

In the dead of winter it is not uncommon to hear skywave during the day.

I have heard KGO,KNBR, etc. at middle of the day several times.
Late December, Early Jan is best.
Often you can get at least part of the 9 oclock hour of Ronn Owens show.
If you get a good day, You can listen to the entire Ronn Owens program, before it goes away for a couple hours in the early afternoon. You got to position the radio carefully to get rid of Jammin 800.
I have also had daytime success with some of the Alberta 50KW stations.

I've noticed that the best winter DX times in the NW are right around sunset. Is there a scientific explanation for this?

i just gave the scientific explanation. the reason for around sunset is because in critical hours (sunrise sunset) stations in different time zones and locations are changing to and from directional patterns, not all at the same time.

Sorry, some of us less scientific soles need a more elementry explanation!

Hmm . . . so, being that the Northern part of the earth is in rather perpetual darkness around this time of the year, we ought to be hearing AM skip from Europe "over the top"?

Every winter DX'ers in northern Finland and Sweden send out plenty of reception reports to north American AM stations!

They use really long wire antennas and high end communications receivers.

the high end communications receivers would help you get european stations since the rest of the world has 9kHz channel spacing on AM instead of the 10kHz spacing here.

generally you need the specialty antennas and radios because of the many local AM's blocking out the distant stations on odd frequencies.

this is where a narrow band radio is quite usefull!

The ionosphere is a layer out in space surrounding the earth. At night, signals on medium wave frequencies(standard AM broadcast band among others)go out into space, bounce off of the ionosphere and return to earth at an unspecified location. Hopefully, this will give enough background information to be able to understand Notalent's explanation.

This Saturday AM when I was near McMinnville at about 11:30 I was suprised to be able to hear CKWX(News 1130) and KPUG(?) 1170 from Vancouver, BC and Bellingham respectively.

Both of these stations were received on a crummy car radio in the centre of an industrial area with lots of powerlines and metal buildings.

About a month ago we were on the Hawaiian island of Maui. While driving the Road to Hana about 4:15 in the afternoon, I was tuning the car radio and heard a familiar voice (Lars) on 1120. Turned out to be KPNW out of Eugene.

How many miles up in space do the reflections take place?

Would the astronauts in the space station be able to hear AM stations if they hung a wire antenna out of the window?

This morning perhaps forgot what time, I heard oldies (Dick Clark program) on 890 from Idaho on my clock radio.
Just looked it up KDJQ 50 KW. I dont remember hearing that one before.

given that the space shuttle only travels some 100-odd miles up, I bet 50,000 watt AM stations probably come in clear when on a transistor radio when they're nearby the broadcast antenna via direct signal (but not directly overhead).

Thanks for the explanations. The best daytime skip that I have heard has been during the winter months, so it would make sense that simply a thin D-layer (due to the sun's rays not charging up the ionosphere as much) is the cause.

For Paul, the ionosphere actually has different layers that interact with radio signals in different ways. The important ones for the AM broadcast bands are the D and E layers. The D-layer absorbs signals, and E reflects. The E layer is about 50 miles above the earth's surface, and the D-layer is closer. When the sun's rays are blocked by the earth, both of these layers start to dissipate, but the D-layer dissipates more quickly--and because the E-layer is up higher, it is exposed to sunlight for a little longer than the D-layer. If you tune in just around sunset, you're hitting a "sweet spot" where the D-layer has thinned out, but the E-layer is still pretty reflective.

AM broadcast signals probably wouldn't be too strong at 100 miles above the earth's surface because by this point, they would have been either absorbed by the D-layer or reflected by the E-layer. Signals above 10 MHz would still be pretty strong in this region because they are not acted on very much by the D or E-layers (the higher shortwave band signals are reflected by the F1 and F2 layers, which are about 200 miles above the earth's surface. Wikipedia has a pretty good article on the different ionospheric layers at: http://en.wikipedia.org/wiki/Ionosphere

ok, I stand corrected. AM signals probably will come in a bit fuzzy on a transistor radio on board the shuttle -- probably why astronauts carry iPods.

In the late '60s, some of us DX'ers made up rules for what we would consider "true daytime DX", and kept a separate log book for it. Our definition was 11am-1pm local standard time. In Vancouver, Canada, I often got 1550 Salt Lake City as my most distant reception, and never got anything across the Rocky Mountains.

But, about 5 years ago, late one Saturday morning, I noticed strong signaals on my car radio from KEX, Seattle and Vancouver stations here in Edmonton, Canada (across the Rockies), and e-mailed a DX friend in Seattle from back in those daytime DX days of the '60s. That same noon hour (Seattle time), he heard clear strong signals from Calgary and Edmonton stations, and even 540 CBC (CBK) Watrous, Saskatchewan, which serves both Saskatoon and Regina.

Every day is different. Back to the '60s, there was one noon hour when both stations in Nampa, Idaho, came in really well (still have tape of one advertising a Strawberry Alarm Clock concert in Nampa), but never heard them again in the middle of the day.

Both day and night, the DX conditions in different directions can differ widely. A few years back, I got nothing from the West Coast here, so was able to pick up 820 Dallas, Texas. Of course, directional antennas are the answer when reception is good in all directions.

Don't worry, Skep, they probably have Dish Network on the Shuttle, just like on Jet Blue. :-)

Andrew

A couple of years ago, I "discovered" KBRD (680 Khz, 250 watts) in Lacey WA (near Olympia). This was in the middle of summer and mid-day, when interference from KNBR (50 KW, San Francisco) was at a minimum.
KBRD was playing "really oldies" music, some from the 10's, 20's and 30's... pretty unususal stuff.
I listened to KBRD several times that summer, using a large loop pointed north (and south). Quite often, KNBR signal level would rise to the extent that KBRD would be totally wiped out! I never did find a relation to weather patterns, E-skip, solar flux or anything else that might explain these unusual summer daytime KNBR increases.

Presuming the space station structure is all metal and The windows may have metal screens also, therefore they would do better with an outside external antenna for AM reception. If the space station isnt allready equiped with an external AM antenna, then they could drill a hole and mount a car antenna, and connect it to a 1960s Delco radio.

Good job, notalent.

The only thing worth adding is don't forget that skywave, like groundwave, loses field strength over distance ... sooooooo the further up in the ionos reflection occurs, the less radio wave there is available to be reflected ... also, not all is reflected, some is refracted and is lost in higher levels.

Skywave may be fascinating, but it's totally unreliable in spite of it's so called predictability.

And for those wanting an even more ambiguous consideration, entertain the idea that reflected waves reenter the stratosphere and have to contend with all the groundwaves propagating around the metro and can get seriously dinged by strong adjacent channel, and A+B-C b.s. (even co channel in a market that happens to have that freq. in service)

Here's some sites with ionospheric info
http://www.ips.gov.au/HF_Systems/4/1/1

http://www.spacew.com/index.php

Another interesting point is that Class A AM stations, with their higher efficiency radiators (taller antennae) have better skywave signals because the shorter an antenna compared to the actual wavelength of the signal, the shorter the distance before the skywave comes back down.

It has to do with the angle of radiation of the skywave. Shorter towers radiate in a more circular pattern, like a sphere around the tower...

Tall towers (to a point) on the same frequency would radiate more like a donut... further out but not as high...

the best groundwave/skywave compromise has been found using a tower 5/8 of a wavelength tall.

with a shorter tower more energy goes straight up (since the radiation patter is theoretically spherical) thus when it is reflected by the ionospher it comes back down to the ground closer to the tower and possibly even within the range of the groundwave itself. This is when you get the fast beating throbbing type sound. the skywave will actually interfere with the ground wave and can even phase cancel it!

with the 5/8 wave tower the upward angle of radiation is much lower which brings the reflection back to earth farther away from the point of origin and hopefully outside the range of the groundwave.

This is why Class A AM's like KEX, KOMO, KFI, KFBK, KNBR, KGO etc have such tall towers compared to class B stations whose towers are normally 1/4 wavelength tall. This is also one reason that the Class A's have so much more skywave coverage than lower class statons... the other main reason being lack of other stations on channel or adjacent channel.

KFI currently experiences this problem while running on their 1/4 wave backup tower since their 700' main tower was knocked down in an aviation accident.

This concludes your antenna thoery lesson for today...

"aviation accident"

I'm betting it was fatal.

I quite frequently pick up KFBK (Sacramento) on 1530 on I-84 around Arlington during mid days... early afternoons. A couple weeks ago (Oct 30) I heard them about 2PM and they were as good as local. Also picked up KPAM past Pendleton and also picked them up in LaGrande around 9AM. KEX also but no KXL. KFBK all the time.

KFI tower crash story:

http://www.earthsignals.com/images/kfi/

They still throw a fairly decent signal toward Portland.

Wednesday's Orange County Register has a detailed report on the current fight over rebuilding the tower http://www.ocregister.com/ocregister/homepage/abox/article_1361504.php

How about shutting down the Fullerton Airport and put the new tower there?

Wasn't the tower there before Fullerton Airport? I would think that if concessions are to be made then perhaps there should be something done to make up for the potential lack of revenue? I don't know, it just seems to me that this situation falls into the NIMBY category. I think with proper lighting that the problem would be solved on both sides of the matter.

I decided to get some history....seems like there are more problems than just the tower issue.
From Wikipedia:
Fullerton Municipal Airport can trace its origins back as early as 1913 when barnstormers and crop dusters used the former pig farm as a makeshift landing strip. The site later became home to a sewer farm. The airport's "official" birthday is 1927.
The airport and surrounding areas have seen their share of aircraft accidents. Residents have complained that pilots often deviate from their mandated approach to the airport, following the Santa Fe Railway tracks. Pilots, in turn, complain that Fullerton and the neighboring city of Buena Park have permitted too much dense residential development in the area, which had been almost entirely agricultural when the airport was first constructed.
Since 1986, no fewer than 28 planes have crashed at or near the airport, killing a total of 11. Most recently, four were injured on September 27, 2004 when a 1986 replica of a Ford Tri-Motor crashed during an airport day.

NoTalent, KGO has 1/4 wave towers according to fccinfo.
It seems to do better then the others?

KGO beams its signal toward us whereas KFI just beams its signal.

I didn't actually fact check the KGO tower height before posting, oops... my bad I "assumed" that being a class A station its tower would be class A efficiency. I researched further and found that the KGO towers are 315' which is exactly 90 degrees (1/4 wave) at 810kHz.

50kw and no other stations on 810 at night help immensely as well as the physical location of their towers in the salt marshes of the Bay.

I stand corrected.

http://www.fccinfo.com/CMDProEngine.php?sCurrentService=AM&tabSearchType=Appl&sA ppIDNumber=249372&sHours=U shows that KGO's three tower pattern (day and night are the same) quite tightly protects the East and West, which means a lot more signal North and South. Admittedly, the pattern is a little off the North-South axis, but it means a lot more power pointing at Portland. KFI has always been non-directional.

KKOH 780 reno has 1/4 wave towers and somewhat similar beam pattern than KGO, althogh the west isnt squeezed off. Frequencies are close. Approx same distance.
So, is the difference the salt marsh? Sierra and Cascade mountain ranges?? or what? KGO seems to be almost allwasy stronger here than KKOH.
Does KGO signal travel up over the ocean coast and then curve inland?

I vote for the second option.

My engineering question is if a good ground plane (salt marsh) improves skywave propagation at all.

Hello all--

I know this may be slightly off-topic, but does anybody know where I can find a schematic and building information for a receiver (not transmitter, don't have an FCC license!) for the 10kHz-100kHz bands (or within this vicinity) on the Internet? PDFs preferred but I can also save regular HTML/Picture pages as MHT's.


No reason in particular, other than having never had a radio that has tuned this arrea of spectrum before, it has held an "air of mystery" for me since I found out about it in Elementary school. (Hearthwood, Vancouver WA - "Class of 1996" ;o)
Just curiosity, basically.

Thanks for any help I can get.

Now, just let me sway this thread back onto its original main topic of AM skywaves.........

swaying back to the fallen tower for just a sec. I recall seeing these photos before. Its the pilot's job as part of the flight plan to know of hazards in advance. IMO, the tower should go back up. Both Portland airport and especially Pearson Airpark in Vancouver have a MAJOR hazard directly in the approach/departure path -- the interstate bridge -- its reponsibility of the pilot to avoid -- not society's need to move obstacles.

back to skywaves . . .

without a good ground plane as a counterpoise for the vertical radiator part of the antenna the whole efficiency of the system suffers.

The quality of the ground plane is directly related to the ground conductivity of the soil in which the ground system half of the antenna is placed.

In reality the antenna of an AM has two parts, the virtical element and the buried ground radials. the above ground antenna wouldn't function well at all without a good below dirt system.

this would be the 180 wires place in the soil at 3 degree intervals extending out as much as 1/4 wavelength in a circle around the base of the antenna structure.

if the ground system is in highly conductive soil this improves the overall efficiency of the system.

if the ground system is in rocky unconductive soil the overall efficiency of the system suffers.

salt water marshes good, rocky mountains not so good. also sand not so good, witness AM's in places like Reedsport. KDUN with 50kw makes it about 40 miles in the daytime with an omni 1/4 wave tower. not so good.

being near an ocean does help significantly.

when the overall efficiency is better both the groundwave and skywave improve.

The best towers belong to KFBK by far, a superior arragement even for being at 1530 AM. Read about it here;

http://www.fybush.com/sites/2005/site-051028.html

re: antenna system

Would the construction of a fairly large pond (also called wetland restoration) around the antenna tower help the system efficiency?

What percentage of stations actually put money into an underground stystem for their towers?

Motozak: Google for "Lowfer" and "VLF" projects,there's lots of stuff!

Stations today must be concerned with meth heads stealing ground system metals ... do you know the story of WOR NY (in the Jersey swampland) and their drifting pattern in the late 60's early 70's?
I know when they fixed the problem they didn't replace all that stolen copper with copper. But even less than precious metals are at risk of being dug up by thieves.

Not to mention the expense, especially in a mud environment.

Not to mention all the moratoriums against any construction in areas that are wetlands.

Granted, a good ground system helps propagation, but the marginal utility in an already crowded AM dial would bring very little return on the invested dollar.

One thought was that mountains should not impede AM nighttime reception being that the signals are reflected by the atmosphere, whats on the ground shouldn't matter. Right?

If you have a salt water marsh, and a few pet alligators, you would have good security.

One Dude~

Thanks.....I will do that in a bittle lit. ;o)

Hang loose.............

"Not to mention all the moratoriums against any construction in areas that are wetlands."

True, but I'm talking about offering to restore wetland in return for a tower in the middle of it -- another thing entirely. Indeed, if located in the right place, one can create a bioswale or rainwater catch basin as a solution for city or county's envioronical problem at another place nearby. The city of portland is spending billions for Big Pipe -- something they wouldn't have to do if they could manage rainwater runoff on a large scale.

Why was 620 not allowed to keep their towers in the restored wetland at their former location?

That was by all measures a better site than the KEX location.

Perhaps some answers to your questions here:
History of Old KGW Radio Towers Site

notalent, thats true, but that was then, plus the KGW tower was on a wetland to begin with, today's local goverments are more aware of the need to including restoring wetlands in development plans. For instance most larger housing developments have bioswales and rainwater catch basins to collect runoff from the newer streets and downspouts.

Take the Convention center . . . the orginal building had little in the way of dealing with runoff, while the recent Convention Center expansion project spent millions to deal with the parking lot and rooftop runoff. You can see it on the South side of the building -- a series of waterfalls and catch basins - looks cool too.

Anyway, if Clackamas Town Center was being build today, the rainwater runoff has to be addressed. The KEX tower location would be a perfect site to use to handle the runoff from CTC. Heck I can see the developer buying the land and leasing it back to KEX for zero dollars. With the tower site in perpetual wetness, KEX will come in clear in SF as KNBR does here!

KEX used to be with KGW at the Delta Park site...
Why did they move to where they are if the old site was better?
Yeah, I know about the Vanport flood and that the water level was halfway up the top floor of the building.

But that was then...

KEX moved from Delta Park because it was no longer owned by The Oregonian, which owned the site along with KGW. KEX also need more room to build its new 50KW array.

As to the previous question about stations investing heavily in the ground conductivity, I interviewed a CBC engineer in Vancouver in the late '60s for a series of columns I was doing for my Province of the Month column in a DX publication.

He told me that the CBC Engineering staff got burned so badly in their failed attempt to serve both Edmonton and Calgary from a single AM transmitter in between (Stettler, I think it was) that they went all out in Saskatchewan. They picked the lowest frequency on the dial (540KHz), and buried copper wire in a radius of one quarter mile from the transmitter site in Watrous, Saskatchewan. And it worked. Both Saskatoon and Regina get a good solid ground wave signal. When I visited Edmonton in the late '60s, CBK was very listenable all day on my mother's car radio, though certainly not a local.

But the major investment that most stations make in ground conductivity is selecting a transmitter site. Swamps, river deltas, sloughs. Until the mid-'60s, every greater Vancouver (Canada) station had its transmitter in Richmond (or possibly Delta) on deltas of the Fraser River.

Even my High School Chemistry teacher told me about co-founding a private Saskatchewan radio station in the early '50s. The farmer's useless slough/wetland suddenly got expensive once he knew the buyers wanted to build a transmitter there.

As for the KFI tower issue, it seems pretty obvious that, tower or no tower, the airport should be shut down based on the other flight dangers in the area. Forget who came first, accept the reality of now, and make a decision based on it.

If necessary, vote on the airport's fate in the next local election, which would give the local government the right to expropriate the land at fair market value, then turn around and sell it for residential or whatever.

KGW was in the flight path of the airport. They'd been trying to get them to move for at least 20 years. Mixing from 1520 created a squeal in the southeast and Milwaukie areas.

All Access reports yesterday: Salem Talk KRLA-A/Los Angeles boosts its signal from 20KW to 50KW daytime. The new signal adds an additional 1.3 million potential listeners to the station's coverage area.

Good AM signals are a combination of low frequency (especially 800 and lower), tower height, ground system, and ground conductivity.

Most AM stations abandoned 5/8-wave antennas because there is a small high-angle lobe which tends to bounce off of the ionosphere and cancel the ground-wave signal. Most of the really big signals are from 1/2-wave towers which have a low angle of radiation.

Although at 1530, KFBK has stacked 1/2-wave towers, (which need no ground system), and is in an area of good ground conductivity. They suck in signal to the west and somewhat to the east (especially at night) and blast it north and south.

In Portland, only 1190 KEX (50 kW), 970 KCMD (5 kW), and 1640 KDZR (10 kW day/1 night) have 1/2-wave towers. With less than 1/2-wave towers, 620 KPOJ, 750 KXL, and 800 KPDQ still have the low-frequency advantage.

660 KXOR Junction City/Eugene has a great signal with 10 kW day and just a 54-degree tower (90 degrees is 1/4-wave). 550 KOAC Corvallis also has a great signal with 5 kW and 65-degree towers.

I remember while living in Astoria in the 1960s and 1970s I could hear KGO 810 all day in the winter. I could also listen to KGA 1510 in Spokane quite well. Year-round in the daytime I could hear CHUB Nanaimo and CBU Vancouver.

Astoria's ocean-front location gave you a huge advantage. In October 1979, driving through Coos Bay at high noon, the 40 watt CBC repeater in Uclulet (West Coast of Vancouver Island) on 540 had an excellent signal on a really crummy car radio.

Back in the 70's while camping out in Maine we picked up WABC 770 in New York City (actually in Lodi, N.J.) 50kw Non D 1/2 wave tower heard in 38 states back in the day.

Nostalgia site:

http://www.musicradio77.com/

check out the coverage page

http://www.musicradio77.com/transm.html

This was THE station when I was a kid, until the middle/late 60's when the first FM progressive stations made their appearance on the NYC FM dial, especially WNEW FM with the late Scott Muni, the late Allyson Steele and others spinning the likes of the Jefferson Airplane, Pink Floyd, Led Zeppelin, et. al. LONG before any of these groups were well known. Ah, those were the days.

Having the water around Astoria worked well for VHF too. On the north side, FM and TV from Seattle/Tacoma reflect off the Columbia river to put in a good signal, on the south side Portland FM and TV stations bounce off Youngs Bay. With the right antenna and location, I could hear Eugene to Vancouver BC on FM, the only receivable FM across the Cascades was KPQ Wenatchee.

Tonite I tuned to 1410 KBNP vs CFUN. Seems to me cfun is much stroger than usual here. Normally kbnp (reagan)is much stronger with the 9 watts, but tonite cfun (c2c) is louder with 2 or 3 "beats" per second. Comments anyone?

Last night was a great night for skywave propogation on the AM band. From Edmonton, WOAI-1200 in San Antonio was very strong much of the time, KXEL-1540 in Iowa was doing well, too, and KEX and KFBK-1530 in Sacramento were also there with great signals.

Even though CFUN protects South at night, such great DX conditions would still let a relatively low powered signal from Vancouver come in very well in Portland. For example, in the late '60s, around sunset in December in Canada's Vancouver (4:15-4:30 p.m.), KBGO-1580 in Waco, Texas, was very strong for several nights in a row. I remember checking sunrise/sunset maps at the time, and, unless someone messed up, they were on their 500 watt night-time pattern, rather than their 1000 watt day-time pattern. Admittedly, they had 4 towers, and I've lost the coverage map they sent me, so their directional pattern might have favoured my direction. But, still, that is a long way for such a low-powered signal.

I used to listen to CFUN all the time. After KPAM went of the air, it came right in, not quite as loud but close!

Note: a ground radial every three degrees would be 120 radials.

Note that the KGO transmitter towers are surrounded by salt water, "The conductivity of seawater is 5,000 millimhos per meter, resulting in the best propagation of AM signals" to quote the FCC. 50 kW, antenna system gain, and a "clear" channel helps, too.

You can see and download a ground conductivity maps of the U.S. at http://www.fcc.gov/mb/audio/m3/

The former VOA Dixon site, San Francisco Bay including KGO and Marin County are in a "30." KFBK is in a "15." KFI and the San Francisco peninsula appear to be in "8's." Portland is in a "4."

Here's a "A Pictorial Tour of KFI"

http://www.oldradio.com/archives/stations/LA/kfipix.htm