DX...Skip and dead areas......questions

[M.Casey]

Hi Don,

I guess you could call it a "Dead Zone", although, the area could more 
correctly be described as a signal cancelling zone, or just a weak signal 
area. There's all sorts of variables involved, and I don't know all of 
those, and I don't have a degree, but here's a few of those variables that 
I've experienced and some that I have talked over with AM engineers much 
smarter than I. From what I've seen as a AM DX'er since the early 60's is 
that the zone is affected mostly by the type of transmitting antenna the 
station has and the day to day and seasonal variances in the atmosphere.

Not in any order.

A. Signal Cancelling--
The words "signal cancelling" could be thought of as somewhat of a misnomer, 
but most times there is some, usually partial cancellation of signal 
received at a location where both the groundwave and skywave signals are 
present.

B. AM propagation variances--
The atmospheric influences. Some times there is no dead zone at all, and 
skywave will be so strong that it is received well within the station's main 
groundwave area. Years ago, I heard skywave a number of times on WTIC AM, 
(1080 khz) within sight of the towers at only 22 miles away, and within a 
reasonably strong groundwave contour, 24 hours a day.

C. AM Antenna design variances--
The basic design will determine the angle of radiation. And that angle will, 
in a large part, determine where the strongest reception areas are. (Note 
the exception of signal propagation over salt water and coastal areas.) This 
could change in differing antenna systems. There are many 50kw stations that 
have a very good skywave signals, and some not so good, even when taking 
into account directionality issues. The basic efficiency of an AM antenna 
system is a major factor also. Maybe some of our Radio Engineering friends 
can weight in on this. (Goes along with (D.) below--skywave limiting 
antennas)

D. AM Skywave Limiting Antennas--
A number of years ago designs for skywave limiting antennas were 
popularized. I don't know how many were built, but they were advertised as 
being able to increase signal strength in the main service area at the 
expense of skywave. For the sales dept,, if it worked, it would really make 
sense--almost no stations made money on the skywave audience, and electrical 
noise was increasing and folks moving away from AM because of the increased 
noise, so any increase in signal to get over the noise would translate into 
more listeners. A Hartford area engineer friend told me that WTIC AM rebuilt 
their antennas to this design about 20 years ago, but the performance did 
not match the expected.  Maybe WGY has one of these also. I have also found 
that WGY does not have a very good skywave signal anywhere I've been. I do 
not believe that most of the major New York City stations have these 
antennas. WFAN, WABC, WCBS, WINS, 1050, 1560 all appear to be as strong on 
skywave as they were in the 1960's & 70's--some maybe stronger.

E. Frequency--
With available AM broadcast band receivers, skywave is usually stronger, the 
higher the frequency. At night, AM BCB skywave is usually present from 530 
right up to 1700, but it's nearly always a little stronger as you get toward 
1700. That "dead" zone might be affected by the frequency, but I haven't 
really seen that to any extent. Just my opinion, but I don't think that the 
difference between 810 and 1030 alters the "dead zone" to any large degree, 
and probably not at all. I think the difference between those 2 stations is 
mostly due to antenna system design differences.

F. The listener's radio and antenna--
Makes a huge difference. Car radios are almost always better all around, and 
better at night also.

I listen to WBZ AM for at least a few minutes, almost every evening around 
10pm on a decent Sangean portable radio. The signal is usually lousy--just 
noise/cancelling/fading making a mess. But, I put up with it because I want 
to keep up with what's going on in Boston and what Dan Rea has for a 
discussion subject. Sometimes, it so bad I just give up trying to listen. At 
10pm, If I am in my car in near home the WBZ signal is always much better 
than on the home radio, and it is reasonably listenable, but that is a 
function of both the car radio and the car radio antenna. I'm in that ZONE 
you are talking about--85 miles west of Boston, just east of 
Springfield--probably not far from Martin.  The day signal isn't stronger, 
it's just that there aren't 2 signals fighting it out, so it's easier on the 
ears to deal with a slight constant low static that the night mess. Daytime, 
Without the skywave fighting/cancelling, the HD signal will pop in and out 
in this area east of Springfield, but never stay in for long.
Most nights, WBZ's groundwave signal is very reliable to about 10 miles east 
of Worcester.

I do not think WBZ ever incorporated any anti-skywave elements into their 
system at Hull, but maybe one of their engineers will comment. WBZ certainly 
has one of the best skywave signals in the country. But part of that may be 
due to their directionality toward the West. WWL in New Orleans has a 
similar situation--on the coast and directional inland toward the rest of 
the USA. In WWL's case, directional toward the north. You might think the 2 
Los Angeles big stations, KFI at 640 and KNX at 1070 would use directional 
antennas toward  the east since they are on the coast, but that's not the 
case--they are omni. Maybe if they didn't waste the signal on the fishes, 
they'd have a better night skywave signal to the east. But, maybe the omni 
signal gave them better coverage up and down the coast--where more listeners 
lived when those stations were designed in the 1930's and 1940's.

WBT in Charlotte, NC, at 1110,  also has one of the best skywave signals. 
It's directional NNE/SSW with null to the West. It's about as reliable as 
skywave can be and the strongest skywave that can be heard in both the 
Northeast and Southeast most nights. So, if you go to Florida sometime, try 
comparing WBT's signal in Orlando or Melbourne to its signal in Boston or 
Hartford.

Even the best skywave signal is not the greatest thing to behold on any AM 
station. Although somewhat reliable in some areas 100-700 miles from a 50kw 
station, it still fades down often. The skywave signal from different 
stations seems to be the strongest at different distances, so I think that 
goes back to (C.) WBZ's skywave seems to be strongest at about 200-400 miles 
out. I've received the HD signal at night for extended periods at these 
distances, but not very often at 600 miles even though the basic skywave 
signal at 600 miles is much, much better than any night WBZ signal here near 
Springfield.

Here's an interesting note. It's rather rare night, but every so often, 
skywave almost completely disappears. If I remember correctly, that happens, 
sometimes, when there is a strong aurora. Then you can hear some local and 
regional stations that are usually covered up by skywave signals of other 
stations.

YMMV
Mark K1MAP


-----Original Message----- 
From: Don
Sent: Saturday, June 06, 2015 2:20 AM
To: boston-radio-interest@lists.BostonRadio.org
Subject: DX...Skip and dead areas......questions

>From what I  understand, stations with big DX signals like the former clear
channels, maintain their groundwave/local signal at night...and as you move
away from that area there is a "dead zone" before the Skywave/Skip/DX signal
coverage begins.

WBZ claims a big signal at night...but if you drive due west from Boston,
you will find that after Worcester, WBZ's signal is fluttering and
unreliable.  But when you get to Albany it's pretty strong and reliable.

Someone from this list (I think it was Martin Waters) was in CT, and said he
couldn't get a decent signal from WBZ day or night.  When I think about it,
WBZ has a lot of listeners in Mass, NH, and even RI...but not so much in
Vermont, W Mass, and CT.  Which is strange (to me anyway) for a station that
covers 38 states.

Here's the question:  Does the area of the "dead zone" depend on the
frequency of the station?  i.e....I mentioned that WBZ (1030AM) is pretty
reliable in Albany and Upstate NY.  However, WGY (810AM (which is
directional towards New England) is occaisionally listenable, but not a
reliable night signal.  You would think it would be pretty equal going both
ways.

Does the difference between 810 and 1030 alter the area of the "dead zone"
between ground wave and sky wave?

Thanks for your help...this is something I've never understood fully.  ;-)

D




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