AM Commercial radio reception
Why is it that I can received WCBS @ 880kc fairly well at night but WABC @
770kc suffers from phase distortion like you wouldn't believe! (I'm about 175 miles from both transmitters.) They are both 50 kwatt stations. And why is it that both WBZ (Boston), WBT (Charlotte, NC), WJR (Detroit) and WBBM (Chicago) come in better than either of the New York City stations? Dave P. |
AM Commercial radio reception
Why is it that I can received WCBS @ 880kc fairly well at night but WABC @ 770kc suffers from phase distortion like you wouldn't believe! (I'm about 175 miles from both transmitters.) They are both 50 kwatt stations. And why is it that both WBZ (Boston), WBT (Charlotte, NC), WJR (Detroit) and WBBM (Chicago) come in better than either of the New York City stations? Dave P. ================================ Different frequencies, different directions, different sun angles (even when below the horizon), different ionospheric layer heights, different skip distances, different ground-path terrains and therefore different ground-path loss. ---- Reg. |
AM Commercial radio reception
Dave P. wrote:
"Why is it that I can receive WCBS @ 880 kc fairly well at night but WABC @ 770 kc suffers from phase distortion like you wouldn`t believe?" I havn`t looked up the directional patterns of the two stations and don`t know your location. If you should happen to be at the edge of a null in the nighttime directional pattern of WABC, that would likely cause distorted fading. WABC may be clear-channel non-directional day and night for all I know. Not many of these remain in the U.S.A. now. At 175 miles from both transmitters, you suffer interference between the ground wave and sky wave from either transmitter at night, at least occasionally. You probably have solid daytime reception from both stations, but at night, the signal may be stronger, though variable. The sky wave is susceptable to variations in the reflecting layers of the ionosphere at night. These are a function of frequency, reflecting carrier and sidebands differently at times. This can produce overmodulation at times in the received signal. Another factor is likely other stations on the same or adjacent channels which may fade in and out and cause variation from your automatic volume control action even when the interfering stations can not be readily identified. An Adcock, loop, or other directional antenna may produce a big improvement in reception of the desired signal. Finally, WABC is owned by the Walt Disney company. Maybe you should expect Mickey Mouse performance. Best regards, Richard Harrison, KB5WZI |
AM Commercial radio reception
Richard,
Both you and Reg have given excellent answers and I thank you both. By the way, you mention directional patterns and nulls. Is there any place I can find polar graphs of commercial broadcast station's antenna patterns? Thanks, Dave P. ==================== "Richard Harrison" wrote in message ... Dave P. wrote: "Why is it that I can receive WCBS @ 880 kc fairly well at night but WABC @ 770 kc suffers from phase distortion like you wouldn`t believe?" I havn`t looked up the directional patterns of the two stations and don`t know your location. If you should happen to be at the edge of a null in the nighttime directional pattern of WABC, that would likely cause distorted fading. WABC may be clear-channel non-directional day and night for all I know. Not many of these remain in the U.S.A. now. At 175 miles from both transmitters, you suffer interference between the ground wave and sky wave from either transmitter at night, at least occasionally. You probably have solid daytime reception from both stations, but at night, the signal may be stronger, though variable. The sky wave is susceptable to variations in the reflecting layers of the ionosphere at night. These are a function of frequency, reflecting carrier and sidebands differently at times. This can produce overmodulation at times in the received signal. Another factor is likely other stations on the same or adjacent channels which may fade in and out and cause variation from your automatic volume control action even when the interfering stations can not be readily identified. An Adcock, loop, or other directional antenna may produce a big improvement in reception of the desired signal. Finally, WABC is owned by the Walt Disney company. Maybe you should expect Mickey Mouse performance. Best regards, Richard Harrison, KB5WZI |
AM Commercial radio reception
There are undoubtedly official sources from the FCC, etc.
The best hand-held guide I could recommend would be the National Radio Club's "Night Pattern Book," a fantastic resource for MW DXers and broadcast listeners. Basically it is a book of maps of North America for each domestic broadcast frequency, with dots representing transmitting locations, and the night time radiation pattern around each. It's available from the following link: http://www.nrcdxas.org/catalog/books/ The 5th edition is sold out, but the new 2005-06 edition is scheduled to be out soon. Brent Taylor VE1JH Dave Pitzer wrote: Richard, Both you and Reg have given excellent answers and I thank you both. By the way, you mention directional patterns and nulls. Is there any place I can find polar graphs of commercial broadcast station's antenna patterns? Thanks, Dave P. |
AM Commercial radio reception
There are undoubtedly official sources from the FCC, etc. The best hand-held guide I could recommend would be the National Radio Club's "Night Pattern Book," a fantastic resource for MW DXers and broadcast listeners. Basically it is a book of maps of North America for each domestic broadcast frequency, with dots representing transmitting locations, and the night time radiation pattern around each. It's available from the following link: http://www.nrcdxas.org/catalog/books/ The 5th edition is sold out, but the new 2005-06 edition is scheduled to be out soon. Brent Taylor VE1JH Dave Pitzer wrote: Richard, Both you and Reg have given excellent answers and I thank you both. By the way, you mention directional patterns and nulls. Is there any place I can find polar graphs of commercial broadcast station's antenna patterns? Thanks, ====================================== Dave, http://www.nrcdxas.org/catalog/books/ Sounds exactly what you are looking for but may take some time to obtain. In the meantime, the basic groundwave radiation patterns of mediumwave broadcast antennas are either simple circles with the antenna at their centres, or heart-shaped with the antenna at the null. The first occurs when the antenna is a single vertical mast located near the centre of a large populated area. The second occurs when the antenna consists of a pair of masts, which radiate a very broad heart-shaped beam, located on one side of the populated area to be covered. Contour Maps of actual measured field strengths are useful when the basic groundwave patterns are distorted by the terrain, e.g., the existence of mountains, forests, rivers, built-up areas, high-rise cities, or seas, lakes or coastal regions. Radio frequency Field Strengths are usually measured in terms of "millivolts per meter" or in decibels relative to one volt per meter. ---- Reg. |
AM Commercial radio reception
"Dave Pitzer" bravely wrote to "All" (05 Nov 05 02:54:31)
--- on the heady topic of "AM Commercial radio reception" DP From: "Dave Pitzer" DP Xref: core-easynews rec.radio.amateur.antenna:219693 DP Why is it that I can received WCBS @ 880kc fairly well at night but DP WABC @ 770kc suffers from phase distortion like you wouldn't believe! DP (I'm about 175 miles from both transmitters.) They are both 50 kwatt DP stations. And why is it that both WBZ (Boston), WBT (Charlotte, NC), DP WJR (Detroit) and WBBM (Chicago) come in better than either of the New DP York City stations? DP Dave P. Perhaps there are a few mountains inbetween you and NYC that cause fringing effects? A*s*i*m*o*v .... Strip-mining prevents forest fires. |
AM Commercial radio reception
Dave P. wrote:
"Is there any place I can find polar graphs of commercial broadcast stations?" I have an old book, "Map Book, 540 kc to 1600 kc" published by "Cleveland Insritute of Radio Electronics". In it, WABC is 50 KW non-directional day and night. It shares 770 kc with KOB Albuquerque, 50 KW day and 25 KW night. Also, KUOM Minneapolis and WCAL Nortjhfield are both 5 KW and share the frequency on some schedule between themselves. WNEW St. Louis is on the frequency daytimes only, as is KWA Seattle, 1 KW. XEHB in San Francisco de Oro, Mexico is a 500 watt daytimer on the frequency, as are XELM, 150 watts at Lagos de Morens and XEDI at Queretaro, 1 KW. There is also CMDC, 1 KW at night when it could trouble you in Holquin, Cuba. So, at night there is possible same-channel interderence from New Mexico and Cuba. On 760 kc, you have WJR in Detroit 50 KW non-directional at night and on 780 kc, you have WBBM in Chicago 50 KW nondirectional at night. These non-directional 50KW adjacent channel stations may exercise your AVC. On 880 kc, WCBS has no same-channel night rivals but WLS (World`s Largest Store, Sears in Chicago) on 890 kc, onetime home of "The National Barn Dance", could work your AVC. Also, WWL in New Orleans occupies 870 kc with 50 KW. Good preselection will rid you of adjacent channel interference. I lived in Portugal for years and listened to WCBS nightly. I would rock my tuning from 880 to 870 for WWL during fades for my version of frequency diversity. Both stations carried the same CBS programs. My antenna was a Beverage aimed at New York. The receiver was a Hammarlund SP-600 which had plenty of preselection to avoid adjacent channels. Ed Murrow came in very well. Best regards, Richard Harrison, KB5WZI |
AM Commercial radio reception
On 2005-11-05, Dave Pitzer wrote:
Why is it that I can received WCBS @ 880kc fairly well at night but WABC @ 770kc suffers from phase distortion like you wouldn't believe! (I'm about 175 miles from both transmitters.) They are both 50 kwatt stations. And why is it that both WBZ (Boston), WBT (Charlotte, NC), WJR (Detroit) and WBBM (Chicago) come in better than either of the New York City stations? Dave P. WBZ in Boston is a clear channel station. I don't think they have any pattern restrictions; they run 50kw 24/7. |
AM Commercial radio reception
Richard Harrison wrote:
very well. Best regards, Richard Harrison, KB5WZI Slight change of subject, WCCO 830 and a couple others I've noticed, now have a tremendous amount of digital sounding crap around them that completely obscures stations such as KOA. Is this the new digital radio wonder weapon that I'm supposed to love? tom K0TAR |
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