Re: Ground rod on a loop


Oene Spoelstra <spoelstraoene@...>
 

I saw that in a movie down here in the Netherlands with the Flying Dutchman. They made an airstrip with lights to make it possible for the plane to land in bad weather.

Op zo 7 feb. 2021 14:13 schreef Kenny Witt via groups.io <kennywtn=yahoo.com@groups.io>:

Nice article.......add to that the AM signal was used by aviation for navigation for many years with the ADF radio, which could be tuned to any AM station.  Then after verifying the “ident” via the transmitting station’s callsign, the pilot could plot the position, direction and speed of the aircraft, and subsequently determine the distance to their destination.  Of note, many a trans-Atlantic flights used this technique using this technique.


Kenny, KC4OJS 



On Feb 7, 2021, at 12:58 AM, WA8LMF via groups.io <wa8lmf=aol.com@groups.io> wrote:


On 2/6/2021 9:14 PM, Simon wrote:
Yep

No yanks on 160m

But mw lively..

1010 interesting..atleast 2 other usa stations competing against WINS..
Shame they don’t announce who they are often..
No make that 3 other stations competing against Wins.. 
all taking it in turns..

God they like adverts!!

 

Some general info on AM medium-wave radio in the US:


1)   There are approximately 5000 AM stations in the US on about 100 channels.  This means an average of 50 stations on every channel across the US.

2)    Legal station IDs are required at the top and bottom of each hour, although most stations mention their call far more frequently.  The legal IDs are plain voice, while the others each hour may be dressed up with music, sound effects or not even mention the legal callsign.    The real problem for DXing is that all the stations on a given channel are giving their legal plain-language IDs at the same time at :00 and :30 .

3)   US (and Canadian) stations are spaced on 10 KHz steps rather than the 9 KHz steps used in most of the rest of the world. This results in really nasty heterodynes when trying to DX US stations from the UK and Europe.  Euro carriers land in the middle of American sidebands and vice versa.

4)   US stations range from 500 watt locals in small towns to 50,000 watt long-range monsters. 

5)   The great majority of US stations go off the air at sundown local time, to avoid the massive interference from numerous co-channel stations propagating via long-range sky wave at night.  Or they sharply reduce power at night such as from 10KW day vs 500 w night.  The day vs night changes are based on local solar time and are calculated for the exact location (lat/long) of the station; they change each month of the year. These are actually part of the license document.  As a result, the "daytimers" as they are known have a much longer broadcast day in the summer than in the winter.


6)   With some exceptions, the low-power 500-watt - 1KW - 5 KW local stations mainly populate the upper part of the AM band, while the high-power 10 KW - 25 KW - 50KW regional stations occupy the lower part of the band. (Long haul daytime ground wave is better as lower.freqs.)


7)    In the early 1930s, before there were stations in thousands of small towns, the federal communications authorities created the "clear channel concept". For a lucky two dozen or so stations, all but one station on the channel was ordered off the air at night to produce interference-free long-range reception of a single high-power station over huge distances in rural areas at night.  Most of these 50,000 watt clear-channel stations were the early founders of AM broadcasting in the early-to-mid 1920s.

Most of them are distinguished by having 3 letter callsigns rather than the 4-letter calls that later stations have.  I.e. the "grand old calls" such as WWL (New Orleans), WGN & WLS (Chicago), WJR & WWJ (Detroit), WSM (Nashville), WLW (Cincinati), KSL (Salt Lake City), KOA (Denver), KFI (Los Angeles), etc.   With a few exceptions, calls beginning with "W" are east of the Mississippi River (which roughly divides the continental US in half), while calls west of the Mississippi begin with "K".  


8)    Most of the stations that started broadcasting in the 1920s and 1930s (i.e. the early entrants) have non-directional antenna patterns from a single 1/4-wave stick.  Later arrivals to the ever-more-crowded AM band have been obligated to protect the coverage of existing stations on each channel. This usually has meant multi-tower directional antenna patterns for the new-comers.   The most common directional array is three phased towers in a straight line.  (Broadcast antenna arrays almost always drive all elements, rather than have passive elements like HF yagis.)   Some arrays can get very complex. For example, there is one station in Detroit, Michigan that has 11 towers in two rows that create a weird amoeba-like pattern with multiple lobes and nulls in various directions to protect stations in Ohio, Indiana and Ontario, Canada.  

A lot of stations run higher power with a non-directional antenna in the daytime, and then switch to lower power and a directional pattern at night.   

For you DXers from the other side of the Atlantic, this is significant.   When the grey line reaches a given location (i.e. sunset), the signal from a particular station can actually instantly disappear or appear, depending on the day vs night pattern and power level changes.


9)    The most powerful AM stations in the US run 50,000 watts.  In the mid 1930s one station (WLW north of Cincinnati, OH) was allowed to experiment with 500,000 watts for a few years. This was the most powerful AM station that has ever existed in the United States.   [There were several 500KW  "border blasters" operating from Mexico, but directed to audiences in the US about the same time.]

A few years later, the US government tapped the engineering expertise of Crosley Broadcasting (owners of WLW) to build multiple 500 KW shortwave transmitters with monster rhombic antennas to beam news into Germany during WWII.  This site, about a mile west of WLW's site, consumed so much electricity that it was connected to both the City of Cincinnati power grid to the south, and to the City of Dayton grid to the north at the same time!   In the post-war era, this facility became one of only three Voice of America transmitters actually on American soil.   

The Bethany, Ohio VOA site was decommissioned about 20 years ago, and converted into a museum. If you ever visit the Dayton Hamvention, don't miss this museum which is about a 45-minute drive south down I-75 from the Hamvention site.  They keep the museum open for special extended hours during the Hamvention. The museum ham club has re-created some of the rhombics from the VOA era and has a commanding signal on the HF bands.  


Stephen H. Smith    wa8lmf (at) aol.com
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