Re: [IRCA] GROUNDWAVE RANGE ON MEDIUMWAVE

[Glenn Hauser <wghauser@xxxxxxxxx>]

This thread petered out on the IRCA list, but continued in DX LISTENING DIGEST.
For those who have not seen that, I have rounded up further responses from
several DXLD issues, trying to avoid anything that was already on the IRCA
list: Glenn Hauser

Re DXLD 8-032: If you see fading on your S meter and hear audio phase 
distortion on the medium frequency signal then the propagation mode is 
sky wave. If you hear a steady signal most of the time, with 
occasional fading on your S meter and audio phase distortion then the 
propagation mode is a mixture of ground wave and sky wave. 

During winter time and especially at the low part of a solar cycle, 
(like we are experiencing at the moment) at daytime virtually 100% of 
medium frequency propagation past the normal ground wave reach of a 
particular station is via sky wave. 

Even in the summer time at the low part of a solar cycle the majority 
of medium frequency signal propagation past the normal ground wave 
reach of a particular station is via sky wave, especially at mid and 
high latitudes. This occurs as the absorptive D layer is weak to even 
non existent. 

During summer time at a moderate and high phase of a solar cycle 
virtually all long haul propagation via medium frequencies is via 
ground wave. This occurs as the background x-ray solar flux level is 
greater than A0. increasing signal absorption of medium frequencies 
via the D layer. 

You can read more about it at KN4LF 160 Meter Radio Propagation Theory 
Notes: http://www.kn4lf.com/kn4lf8.htm under 1.) Medium Frequency 
Radio Wave Propagation Overview- under .1) .b) .d) .f) and elsewhere 
on the website. 

As I write this email at 1430 UT I'm listening to the Turks and Caicos 
Island station R. Cristobal [sic] on 530 kc and it is coming in via a 
mix of ground wave and sky wave. A bit earlier the same with WWL 870 
kc in new Orleans, WCNZ 1660 kc from Marco island, FL and WSB 650 kc 
from Nashville. 73, (Thomas F. Giella, KN4LF Lakeland, FL, USA, March 
10, dxldyg via DX LISTENING DIGEST) 

[this item later clarified; maybe it wasn`t Angola]
In 2001, while in Accra (Ghana) I had groundwave reception of Luanda 
(Angola) on 945 kHz in the middle of the day. A distance of around 
1,300 miles, almost all of it over salt water. Very weak signal but 
with confirmed audio. Undoubtedly groundwave, not skywave, as this is 
a trans-equatorial route so D-layer absorption would be total in the 
middle of the day (also, it was sunspot maximum). Receiver was an Icom 
IC-R8500 with a good long-wire aerial about 50 feet above ground. I'm 
not claiming a world record - in fact I'm hoping that someone can beat 
that 1,300 miles, especially as the listed power on 945 is only 25 kW. 
Two essentials are an all-ocean path and a low local-noise level at 
the receiving end (Chris Greenway, UK, March 10, DX LISTENING DIGEST)

Chris, While still in the employ of Uncle Sam I visited Signal Hill in 
St. Johns, NF in September 1988, at the peak of Solar Cycle 22. At the 
time I was an SWL, not yet licensed as a Ham, which came in December 
1989. I had with me a Sony ICF-6500W receiver and at daytime on ground 
wave I was able to clearly copy WQAM 560 kc 5 kw in Miami, FL. At the 
time WQAM's single tower was out in Biscayne Bay. That was an 
approximate distance of 2158 km, 3474 mi. Part of the ground wave path 
in NF was over land but the signal probably skewed along and around 
the coast to Signal Hill. 

BTW I returned to Signal Hill in December 1995 at the bottom of Solar 
Cycle 22 to see what I could hear on the LF and MF AM broadcast bands, 
as well as 160 meters. At this time propagation conditions were 
identical to what was in existence when Guglielmo Marconi heard the 
famous "S" in December 1901 [?]. At daylight a myriad of signals were 
received from Europe using a Radio Shack DX-390 receiver via sky wave. 
That of course did not prove that Marconi heard the "S" but 
propagation conditions certainly would have allowed it if his 
receiving equipment had been up to the task. 73, (Thomas F. Giella, 
KN4LF Lakeland, FL, USA, dxldyg via DX LISTENING DIGEST)

Groundwave propagation on mediumwave: This statement

>> "At 0.5 MHz over average ground, the ground wave predominates over
the sky wave from the transmitter site out to distances of about 150 
km, where the two signals are equal. The signals add as vectors, and 
destructive and constructive interference can occur. At distances 
beyond 150 km the sky wave is the predominant signal. At a signal
frequency of 1.5 MHz, the distance where the two signals are equal 
reduces to 45 km, because of the increased loss at the higher 
frequency." <<

is not related to the question how far groundwave reaches out (which 
can be answered only for a certain fieldstrength) but instead to the
situation at night. It describes the problem of ground-/skywave
congestion for which in German the dedicated term Nahschwund exists.
Sophisticated antenna designs suppress steeply upwards radiation to
avoid this problem, they radiate only at rather low take-off angles,
thus the first skywave signals come back to earth only at a distance
where no ground-/skywave congestion arises anymore. Another solution 
is to let the antenna the other way round radiate steeply upwards and
produce no groundwave signal (using dipoles with no grounding grid). 

Of course such systems can be used for nighttime service only. Not 
much of them have been ever built although the concept works pretty 
good; Berlin-Britz (990 kHz, dismantled after further use of this 
antenna had been banned because of too high fieldstrengths outside the 
transmitter site), Madrid-Arganda (1359 kHz, hardly if ever on air 
nowadays?), Sarnen (1566 kHz, dismantled), Mainflingen and Burg 
(1539/1575 kHz, respectively, in everyday use) are the ones I'm aware 
of. See http://www.waniewski.de/id200.htm and further links there
(Kai Ludwig, Germany, March 10, dxldyg via DX LISTENING DIGEST)

Glenn, Re all the discussion, groundwave distance, daytime skywave, 
etc., can be confusing. Here is some (simplified) basic data:

1.  Groundwave propagates along the half-space surface, attenuated by 
the ohmic losses of the earth. It can exceed 1/R only in VERY limited 
situations of layered conductivity. (San Joaquín Valley, Kuwait and 
maybe Iraq near the mouth of the Tigris/Euphrates, the Arctic over sea 
ice are the exceptions I know about. J. R. Wait wrote a whole book on 
the subject. And >1/R conditions can exist only for limited areas 
because of the laws of conservation of energy.) Thus for a 1 MW omni 
1/4 wave antenna, E = ~ 10,000 mV/m at 1 km, so at 1000 km E = 10 mV/m 
unattenuated. But the attenuation is, even for sea water at 500 kHz, 
substantial: 20 dB/1000 km, so received field would actually be 1 
mV/m. At the upper end of the band the attenuation over sea water is a 
little over 30 dB/1000 km. Any path over land has far greater loss.  
At 500 kHz even very good ground has about 36 dB/1000 km loss, while 
at 1.6 MHz it's over 110 dB. 

2.  Daytime skywave probably accounts for most N. America reception at 
distances greater than 4 or 500 miles or a little further (over the 30 
mS/m conductivity in the Great Plains region, for example). And 
despite the fact that the Fuzzy Confusion Commisariat won't consider 
the concept of daytime skywave, it's clearly a factor where powers 
greater than the Region II 100 kW limit are used, and is certainly 
observable from time to time in N. America as well. I have certainly 
seen (or more correctly, measured) it, particularly where the ground 
conductivity was poor and skywave predominated at relatively short 
distances from a high power site with DA gain. ITU-R Recommendation 
P.1147 ("Prediction of Skywave Field Strengths......") at Annex 2 "A 
discussion on daytime sky-wave propagation" item 2, "MF cases," 
states:  "/Available data show that midday sky-wave field strengths 
display a consistent seasonal variation pattern with maximum occurring 
in winter months. The average winter-month field strength is about 10 
dB stronger than the annual median value and the winter-to-summer 
ratio can exceed 30 dB. The annual median value of midday field 
strength is about 43 dB lower than its counterpart at six hours after 
sunset. Field strength exceeded for 10% of the days of the year is 
about 13 dB stronger than the annual median value. See also the ITU-R 
Handbook - The ionosphere and its effects on radiowave propagation."

3. The reason a good ground system is important for producing skywave 
is that it produces the field from the "image" antenna that is below 
the "half-space." (Ben Dawson, Hatfield & Dawson, WA, March 11, DX 
LISTENING DIGEST)

Ben, Tnx but even this is a bit over my head, starting with what 1/R 
signifies. Aside from theory, is there any way with non-professional 
equipment to determine once and for all whether WGN-720 is getting 
here at midday by groundwave, skywave or a combination?

If it is skywave, why don`t I get higher-frequency Chicago-area 
stations even better? 1160 might be a possibility (clear frequency). 
And there was 1690 which I did think was skywave altho not IDed. But 
the skywave factor obviously dropped off below the X-band, or below 
1500.

What about WNAX 570 SD which I can hear any day mixing with KLIF? 
Steady, not fading, unless there is a SAH. Such distances correlate 
well with the lower-the-frequency-the better, and thus groundwave. It 
really seems counterintuitive that this should more likely be skywave.
73, (Glenn to Ben, via DX LISTENING DIGEST)

Glenn, 1/R merely is the equation for "inverse distance" - that is, at 
twice the distance you get 1/2 the signal, at ten times you get one 
tenth. R is Radius, which is just the conventional usage. There is 
frequency dependence in skywave transmission as well as in groundwave, 
and although in N. America it's considered to be greater signal the 
higher the frequency, in the rest of the world the data is considered 
to be the opposite of that. And it varies, day to day, hour to hour, 
just as the signal itself does. 

*****
Conductivity between Chicago and Yankton toward you is generally 
pretty high, so it probably is groundwave, particularly if it does not 
vary from hour to hour. If the average conductivity is 30 mS/m, 
Chicago should give you about 13 uV/m, Yankton about 55 uV/m. Average 
conductivity of 20 mS/m would drop that 6 dB, but still a useable 
signal with good gear in a low-noise environment (Ben Dawson, ibid.)
*****

I happened to be out driving in the middle of Enid, March 12 at 1902 
UT (one semihour after local mean noon), and tuned 720 on the caradio 
as I was parked on the south side of Starbux (I haul their grounds to 
garden, not buy their coffee), and there was WGN news, quite audible 
even tho there was some line noise. So I don`t even have to expedition 
to a quiet country parking spot to get it. As I drove away, between 
high noise powerline spots, I checked 670, and there was The Score 
with sports news and talk, mixing with but slightly atop KLTT Denver. 
780, 890 and 1000 are blocked by OK stations, but the next Chicago 
clear is 1160 --- nothing audible there; nor 1690 which I would expect 
to be showing at topend, if skywave were in play. Essentially the same 
results next day around same time (Glenn Hauser, OK, DX LISTENING 
DIGEST)

Glenn, A couple of points need clarifying about Ben Dawson's notes in 
DX LISTENING DIGEST 8-034:
 
1. The formula 1/R - "at twice the distance you get 1/2 the signal" is 
incorrect. the relationship is logarithmic, not arithmetic. The 
groundwave signal reduces in inverse proportion to the square of the 
distance. So, at twice the distance you get a quarter of the signal, 
not a half.
 
2. The laws of physics are universal, so "in N. America it's 
considered to be greater [skywave] signal the higher the frequency, in 
the rest of the world the data is considered to be the opposite of 
that" seems odd. In Europe we are very familiar with daytime skywave 
reception on mediumwave in the winter and it is definitely more 
prevalent in the higher part of the band. Also, mid-day skywave on 
longwave is never observed - confirming the same point. 
 
Finally, well-known German MW DXer Martin Elbe has cast doubt on my 
2001 logging of 945 Angola from Accra. He says it was probably São 
Tomé that I heard. Fair point, especially as both would be in 
Portuguese. My memory is unclear. I thought I had confirmed 945 as 
Angola by checking against the parallel SW frequency, but I can't 
remember for certain now. Unless I can produce documentary evidence in 
my archives (a log note showing a confirmed ID or parallel broadcast, 
or a recording), I will have to withdraw my claim. Accra to São Tomé 
is only 600 miles, so no sweat for a groundwave signal over an all-
water path. One factor to check is which side of the island the Sao 
Tome transmitter is on. If not the side facing Accra, then Angola 
might still be the more likely station I heard (Chris Greenway, 
England, March 15, DX LISTENING DIGEST)

[Re 8-035]: Glenn, 1.  Well, Mr. Greenway is dead wrong about MF 
groundwave propagation. Physics is indeed immutable, he just hasn't 
done his homework. It is NOT free space propagation, which is 1/r^2, 
but propagation in the half-space, which is 1/r. 

I will quote the physics gospel, from the Radio Engineers' bible 
(Radio Engineers' Handbook, McGraw-Hill, 1943) according to Dr. 
Terman: "If the heights of transmitting and receiving antennas are low 
enough ... the surface wave is given by

E surface wave = A(2E0/d)" 

NOT d^2. And the scholarly references are Norton and Sommerfeld. All 
one has to do is look at the ITU or FCC groundwave curves to see that 
they are log-log charts where groundwave is related to attenuation 
greater than the no-loss 1/r condition.

2.  I didn't say that the physics was different in N. America and 
elsewhere (although the location of the magnetic North Pole does make 
N. America fairly anomalous from a propagation standpoint); I just 
said that the historical interpretation of the data has led to the 
observation that skywave fields are higher at the upper end of the 
band in N. America and at the lower end elsewhere, according to ITU 
publications.  

If you examine the ITU skywave databases, you will quickly conclude 
that the data is sparse, and some of it very old, and was often based 
on very incomplete knowledge of the transmitting antenna 
circumstances. The skywave databases are not quite as bad as anecdotal 
observation, but I am skeptical of much of the older data. There are 
at least seven different skywave propagation algorithms which have 
some legal standing somewhere in the world, and the fact that they all 
differ demonstrates just how subjective the interpretation of the data 
actually is.

3.  The São Tomé government medium wave transmitter (if that's the one 
on 945 - I know the antenna installation, but I can't remember the 
frequency for sure) is at the VOA site on the east side of the island, 
at Pinheira, about 4 or 5 kliks S. of São Tomé city. It's the same 
site originally established by the Portuguese in colonial times. Last 
time I was in Sào Tomé - a little more than 10 years ago - the VOA 
1530 and the government station were the only MF in the country (Ben 
Dawson, WA, March 18, DX LISTENING DIGEST)


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