Sunday, August 13, 2017

W6LVP Loop Trial

After reading many reports about some of the "new" broadband, amplified loops and having had considerable experience with large unshielded tuned loops, and also having a vacation coming up to a coastal area, I thought it might be a good time to spring for one of them and give it a try,  especially given the increasing and intermittent high noise floor in my neighborhood.

For ease and quick shipping and a somewhat lower price,  I chose to go with the W6LVP loop after seeing several good reports among the Facebook DX groups that I have been frequenting.

I will say that the customer service, method of secure  payment and swift  delivery was very good and the antenna arrived in short order, well packed and of apparent good construction. Assembly, such little of it that there was, was very simple and intuitive.  The antenna is very light and is attractive.

I fired it up inside the shack only a couple feet off the floor and fed it into the R-75 only a few feet away.  the power supply was very quiet and there appeared to be no noise coupling from it even with the close proximity that I found it to be to the loop in the initial test.

Noise inside my house is a bit high due to multiple cell phone chargers, wifi, televisions, cable boxes and computer power supplies,  but with judicious rotating of the loop, noise was lower than the vertical out in the yard and considerably lower than the sloper.  Comparing signal strength of WWV and CHU showed about three S-units down from the outside forty foot vertical over 60 buried radials, but due to the reduced noise, they were all at least as readable on the loop inside.

Noise on the MW broadcast band and Low  Frequency band was comparable to the vertical. To be totally fair, rotating the loop inside the house showed noise coming from various locations,  with two of the main sources just about 90 degrees apart, so nulling both would be just about impossible no matter how good the loop would be.

The next day,  I mounted the loop on a temporary mast in the back yard about 20 feet from the house.  It was up about fifteen feet  above ground in the same general area of the yard as my vertical ( about ten feet away) and about 20 feet east of where the sloper traverses the yard.

Firing it up at that location gave it a much better chance of showing off its performance. In fact, it was a whole different world from when it was inside.   Nulling the major noise source was much easier, though there seemed to still be a secondary noise source whose null would require a position mutually exclusive to the position for nulling the worst noise source.

The first test run was done in the MW broadcast band at 0000 GMT July 23. This is over an hour before dark at my location in Woodway, on the west side of Waco, Texas.  To get an idea of just where I am, if you look at a map of Texas, look on the west side of Waco along Highway 84, a couple miles west of its intersection with Loop 340/State Highway 6. The following signals were logged as ground wave signals on the loop feeding the R-75:
XEMU     580 kHz   5 kw  Piedras Negras, Mexico  S-5 and steady
KLIF        570 kHz   5 kw Dallas, Tx S-9+10 db
KLBJ        590 kHz   5 kw Austin, Tx  S-9 + 20 db
KTBB       600 KHz  5kw  Tyler, Tx  S-5
KILT         610 kHz   5 kw  Houston, Tx S-7
KESB       620 kHz    5kw  Dallas, Tx S-8
KSLR       630 kHz    5 kw San Antonio, Tx S-7
Unk          640 kHz     1 kw  Norman, Oklahoma S-5
KSKY       660 kHz   20 kw  Dallas, Tx S-9+20 db
KKYX      680 kHz   50 kw  San Antonio, Tx S-8/S-9
KSAH       720 kHz   10 kw  San Antonio, Tx S-8
WBAP       820 kHz   50 kw  Fort Worth, Tx S-9 + 40 DB
KONO      860 kHz     5 kw  San Antonio, Tx  S-7
Unk           930 kHz     5 kw San Antonio, Tx S-7
WOAI      1200 kHz   50 kw  San Antonio, Tx S-9
KRZI        1660 kHz   10 KW Waco ( local) full scale

These were logged in a quick sweep mostly of stations I could identify by presence to get a quick idea of what was going on via groundwave before too much night effect prop would begin.

At 0100,  still a bit before sunset and still full sun at the WWV transmitter site,  a quick sweep of time and frequency stations yielded the following:
2500    WWV  S-5
3330    CHU    S-4 ( their transmitter site in darkness)
5000    WWV  S-9
7840    CHU    S-7
10000  WWV  S-9+20 DB
14670  CHU    S-7
15000  WWV  S-9+10DB
20000  WWV  S-7
25000   WWV Just audible carrier

The R-75 in all of these tests was being run with neither pre-amp on. Ambient noise on the loop was about S-1, while on the vertical was S-3.  It should be noted that the vertical had been put up in the quietest spot in the yard by walking a portable receiver around tuned to 500 kHz.

A quick tune around showed the Voice of Greece, a strong evening regular on 9420 at S-9+20 DB. A check of Radio Encyclopedia from Cuba on 530 kHz showed it at S-7, well above the noise and listenable.  On the vertical it usually runs S-9 but with some noise in the background.

A quick test of the low frequencies showed, as expected, it was well too early for the European and African Long Wave broadcasters to be heard. I quickly ID'ed a few non-directional aircraft beacons:
ARM  245 kHz  Wharton, Texas   S-5 ( about 200 miles)
PQF    248 kHz  Mesquite, Texas  S-7 ( about 100 miles...Mesquite is on the east side of Dallas)
ROB   400 kHz  Robinson, Texas  S-9+20 db ( local NDB 10 miles away)

A quick ham band test in the 40 meter cw portion showed:
0227 GMT   OK2RRR   7007 kHz  Czech Republic RST 579
0238 GMT   F5IN          7011 kHz   France               RST 579
0247 GMT   W0LI         7017 kHz   USA                  RST 589
0248 GMT   K9OM        7017 kHz  USA                  RST 599
0249 GMT   W7FW        7018 kHz  USA                  RST 599

Again, these were on the R-75 with no extra preamps on and with 250 hz filters in.

This being at the end of a long day and with other evening chores still ahead, this was the end of the first days testing.

The next day ( July 23, 2017) allowed time for a little more testing under daylight conditions.  Unfortunately my operating set up did not allow quick A-B testing between the loop and the vertical because I have no remote antenna switching and I was actually using the feedline that normally goes to the vertical to feed the loop.  The transmission line is about 100 feet of RG-8 X that is routed in an indirect route along fence lines to allow the shortest run across open lawn to the antennas. The RG-8X is not buried.

In a run beginning at 1436 GMT or about two-and-a-half hours after local sunrise, a run of the time and frequency stations yielded the following:
 25000 kHz   WWV   S-5
20000 kHz     WWV  S-7
15000  kHz   WWV   S-9
14670  kHz    CHU    S-4
10000 kHz     WWV  S-9 ( No WWVH)
7850  kHz     CHU     S-4
5000  kHz     WWV   S-8
3330 kHz      CHU     inaudible
2500 kHz      WWV   Just audible carrier

A run through the 20 meter amateur band resulted in  a logging of showed numerous USA stations at S-9 or better  At 1444 I heard VE2WU calling CQ on 14017 about S-5 followed by XE2AAW in Mexico at S-7.  No Europeans were heard in a quick sweep. WRMI on 9455 was S-9 at 1448 GMT. At about this time, rains were coming in and the loop was taken down from its temporary mast because the connections had not been waterproofed for this quick test.  The next few days saw several periods of thunderstorm activity, so testing was pretty much halted. The rest of the week was also taken up by preparations being made for the vacation trip that would include testing the antenna at the Gulf Coast.

This would be a real test as we were going to the coast in a passenger car rather than our usual Chevy Suburban and would have no room for large mast sections usually carried on the luggage rack on the roof of the Suburban.  The loop would be the only antenna taken.

We arrived at our coastal location about midday July 31. Radio activity would take place in the environment of family activity, so it would not be a full five days of all-out testing but it was hoped that a fair amount of " wringing out" of the antenna would take place.  It was mounted on a camera tripod with a short piece of PVC pipe extending above it to keep the loop away from the metal of the tripod.  The antenna was set up on a balcony about 15-18 feet above the ground and about a hundred yards from the water.

The location was at Crystal Beach, Texas on the Bolivar Peninsula about 12 miles east of Galveston, Texas.

The first listening came late in the afternoon of the first day and was a short one due to other activities including unpacking,  running errands to a local grocery to stock up on supplies and the first steps into the salt water ( priorities!!!)

A quick check at 2300 GMT showed our old favorite, the Voice of Greece on 9420 at S-9+20 db.
WWV on 10 MHz was S-9 with QSB and on 15 mHz was S-5 with QSB. A quick check of a few Medium Wave stations  showed WTAW on 1620 KHz, 10 kw,  from College Station, Texas ( about 160 miles) S-9 + 10db. KRZI on 1660 from Waco, also 10 kw was S-9, and while they were still on daytime power, there was some evidence of night effect as there was some QSB. KOGT 1600 from Orange, Texas with 1 kw about 75 miles away was S-9+10 db, but it should be noted that it is almost a water path from that location.  Thus ended the first evening of testing with swimming and dinner taking over!

With testing the next morning some disappointments began to show up. It was obvious that there was difficulty in nulling noise and many signals were just not what they should be. particularly signals to the north were poor. It was then discovered that the reason for this is that the beach house had been built with metal studs in the walls and the wiring for lights on the balcony were running within a foot of where the loop was set up. Tilting the loop to get it away from the walls of the let it " see around the house" as it were and to get it away from the house wiring helped considerably. Signals via groundwave from medium wave stations to the north and east of us jumped 20-25 db or more and the noise was nullable. This would appear to be a consideration for anyone planning to use one of these loops made by any manufacturer.  Metal framing might be a bit of a problem, though other testing with the loop inside and near windows without metal screening outside showed fine results in the direction of the opening.  Turning the lights off on the balcony where the wiring ran so very close to the loop took care of  most of the noise problem. It would appear that the antenna will work very well inside if some care is taken with placement.  No antenna can perform miracles if not given a chance!!

After the antenna rearrangement, reception on the low frequencies was quite good.  The dial was full of low frequency non directional beacons,  with dozens heard very well beginning the next morning about 1600 GMT ( 9 a.m. local time) with many heard from all over Texas, Louisiana and a few from Mexico.  The noise floor after antenna rearranging and nulling was about S-2.  The carrier for the WWV station on 60 kHz was even heard.

Daytime reception on medium wave was quite good. A sampling of more " interesting" MW loggings that mid morning ( starting about 9:30 a.m. local):
KTSA  550  5 KW  San Antonio  S-7
KLVI   560   5 kw   Beaumont, Tx S-9 + 30 db
KLIF    570   5 kw   Dallas, Tx  S-5
KJMJ   580    5 kw  Alexandria, Louisiana  S-4
XEFD  590    5 kw  Reynosa, Mexico S-9
XEGH  620    1 kw  Reynosa, Mexico S-7
KSKY  660    20 kw  Dallas, Tx  S-6
KKYX  680   50 KW San Antonio, Tx  S-9 + 10 db
WQNO 690   10 kw  New Orleans, La S-5
KEEL   710    50 KW Shreveport, La  S-5 ( a loooong way for daytime groundwave!)
KSAH  720     10 kw  San Antonio, Tx  S-9
KTRH  740     50 kw  Houston, Tx  Full scale.

Rotating the loop seemed to indicate a pretty broad main lobe but a fairly deep and narrow null.

I ran through 31 meters about mid afternoon, at a time I thought would be before the night time enhancement of those frequencies with a later run through the same band near sunset. Here are a few samples with the sweep beginning at 2000 GMT, or 3 p.m. local time ( actually 2 p.m. local sun time given that we are on daylight savings time...something easy for me to forget!)  This was with the loop attached to a eight foot long piece of PVC pipe and extended out from the balcony to get it away from the metal in the walls and the wiring in the  ceiling.

V. of Greece           9420 S-5
Voice of Turkey    9460  S-7
R. Saudi                 9555  S-8
R. Marti                  9565 S-7 plus jamming...could null the jamming!
Voice of Turkey     9635 S-5
R. Guinea               9650  S-4
R. Saudi                  9675  S-7
R. Saudi                 9870  S-5
V. of Greece           9935   S-5
WRMI                    9955   S-9+10db

The noise floor was about S-2 with the loop extended about four feet away from the balcony.

Another run through 31 meters beginning at 0030 GMT or 7.p.m. local or a little over an hour before local sunset with the loop in the same position as above:

V. of Greece    9420   S-9+20 DB
WRMI             9395    S-9
WBCQ            9330    S-9+10 DB
Strong rtty sig 9317     S-9
WINB             9265     S-9+10 DB
Nauen, Ger.    9450      S-7
WRMI            9455      S-9
CRI Kashi      9470     S-6
Issoudon         9490    S-9+20 DB
R. Transmundial 9530   S-4  (Brazil)
R. Havana       9555     S-9
R. Boa Ven.    9550     S-5 Brazil
CRI/Rom.       9570      S-9+ 20DB
CRI/Cuba       9580      S-9+ 10 DB
CRI SP kasha  9590     S-4
R.Cancoa N.   9675      S-5 Brazil
RRI                 9730      S-9+ 10 DB
V. of Turkey   9830     S-9+ 10DB
VOIRI            9880      S-5  ( Iran)
V. of Greece   9935      S-9+10 DB
These are all on the R-75 with no extra preamp turned on.

Later at 0200 R. Sonder Grense on 3220 from Meyerton, S. Africa was in very solid at S-9 and listenable without objectionable noise.

I hope this is not getting too boring with too much listing, but I figure that this is the best way to show the performance of the antenna, particularly for those in the Central US and hopefully for those elsewhere looking at a map and sort of imagining tuning and listening get some idea what one could get out of this antenna.

Below is a quick run through of the "usual" Mexican  and Cuban MW stations heard nightly, previously on wire and vertical antennas beginning at 0250 GMT just getting into post dusk darkness:
XEX              730         Mexico City  S-9+20 DB
CMBC           890         Cuba              S-7
XEW             900         Mexico City   S-9+20 DB
XEQ              940         Mexico City   S-9+20 DB
XEOY          1000        Mexico City   S-9+10 DB
XEG             1050        Monterrey, Mex  S-9+20 db ( 150 kw)
XEEP            1060       Mexico City   S-9+ 20 DB
XERF           1570        Ciudad Acuna, Mx  S-9+30 db
R Encyc.         530       Cuba                S-9

All of these signals are more than comparable to how well they are received at home on both the vertical and the sloper, again with noise floor measured at 520 kHz of S-2.

The last " acid test" I gave the antenna was the look at the sunrise Pacific/Asian opening the next morning beginning at 1130 GMT or 6:30 a.m. local time, just as light is beginning to appear on the horizon. Noise floor measured at 2800 khz S-2
2850  KCBS North Korea  S-4  very readable
2500  WWV S-8  with WWVH audible in background
3320  Pyongyang BC S-4
3325  Bougainville and Indonesia mixed  S-5 "bouncing"
3480  Voice of the People S Korea S-5
3910  Voice of the People presumed S-5 and jamming
3925  R Nikkei S-5
3930  Voice of the People S-5
3945  R Nikkei S-5
3985  Echo of Hope  S-5 and jamming
4055  R Verdad S-7 QSB ( interesting notably with not as good a signal as at home!)
4212  WLO  CW/SITOR  s-9+10 DB
4735  R. Tarma Peru S-4.

There were some thunderstorms that developed in the area the next couple days and this led to disappointment in doing more low frequency work and I did not hear any of the European or African Long Wave Stations or MW stations.

Overall,  for its size, the antenna performed admirably well.  It was great to have an antenna to take on a trip that was not a huge chore to pack and set up. It might have been good to have some mast sections that could have allowed the antenna to be set up at a distance from the house and more in the clear.

I have noticed the same here at home.  While it works well indoors, at least much better than an indoor random wire, it does much better outside and in the clear.  Getting it up fifteen feet or so  really seems to help.  The next plan at home is to put it up on a telescoping mast up about thirty feet.

One observation is that other metal objects very near do seem to affect the ability of the loop to null noise. Dropping the wire sloper at home that had been running near it greatly reduced the noise that apparently was being coupled into it.  If one is using one of these type loops it would proibably be worth the effort to keep it at least a moderate distance away from other antennas,  particularly large wire antennas.  If those other antennas pick up noise where they run,  they could couple that right back into the loop or provide an additional place to be nulled, thus " nullifying" one of the advantages of the loop.

The loop does result in somewhat lower S-meter readings on some signals, but the lower noise floor more than makes up for that.

QSB does seem to be more pronounced than on the larger antennas but that is probably just a result of the smaller aperture and less of a "diversity" effect thereof.

During the test period, I noticed that the antenna did seem to perform better on the lower frequencies, but that might easily have been the result of band conditions,  so consider that a caveat.

I was hoping to hear some DX on 160 meters,  but during the week and during a non contest period there is not a huge amount of activity on that band, so that should not be misconstrued.

All in all,  this antenna has proved worth the expense and for those with limited space or even living in an apartment, I can highly recommend it as a way of getting some reasonable DX.  If you have a balcony, all the better...and if you can get it extended out beyond the balcony, even better yet.  As with any antenna,  giving it an even chance to work by putting it in the best possible location is a given.  If you are in a home with metal framing ( aluminum studs in the walls, etc) do your best to get it at least near a window without metal screening.

I am already planning a way to get the radio and antenna out totally away from wires and walls.  Running the R-75 and the loop both off a 12 volt battery is easily possible.

One note: Despite being in the " hot lobes" of directional antennas from three different 50 kw stations including one that  effectively "pinned" the S-meter on the R-75 ( OK, drove all the lights on...) there were no overload issues.  The Galveston station on 1540 khz runs 2500 watts but its directional had its main lobe right over our vacation location with only salt water between us and  it was not a problem.

There is always a risk in evaluating an antenna over a short period of time given how band conditions can vary.  That goes not only for this report or for any antenna you might try or put up. Poor bands can make the best antenna seem lousy on the first try and listening with extra care on a new one can sometimes give an impression in the other direction.  Always give one time,  and particularly with small antennas like loops,  try different locations and give them an even break to give you what you want.

Again, I hope the station listings were not too boring, but figured it was the best way to show what the thing did. As always, comments welcome.

WWCR                  9980  S-9

Saturday, August 12, 2017

By What Path Do They Get Here

I was asked in one of  my Facebook groups how signals travel to their destination, or by what path do they come. The simple answer is " by a Great Circle path."

What does this mean?  Well if you think back to geometry class ( I know that is asking a lot!!) the definition of a great circle on a sphere is  " a line on the surface of the sphere defined by the intersection of a plane passing through the two points in question and through the center of the sphere"

OK, so that is a little esoteric. Think of it this way. Take the equator line and tilt it so that it passes through the two points, or cities, that you are looking at.

If you look down on the line while holding a globe,  this path looks like a straight line.  but if you look at it on a flat map it will look much different,  most likely as a curved line. If you are familiar with what is known as a polar projection, or a flat map made up as a circle with the center being the north or south pole you can get a better idea of what is going on. A really good way to look at it would be if you could find a polar projection based on your own location.  There are computer programs that can do this for you and I would be willing to bet with a little judicious searching on the internet you could find a website that can do it.  You would just need your latitude and longitude to enter.

Sometimes the direction from your place might be much different than you would intuitively think.
Like who would think that the beam heading for Alaska and Japan would almost be the same from Central Texas.  Of that the beam heading for Europe and East Africa would be almost the same.

You will notice if you do this mental exercise or even look at a globe with the two points actually on the equator that there are two paths between the points: the short one and the long one.  Thus the definition of " long path" and " short path".

Logically the shortest one is the one by which the signal you are hearing arrived,  and most of the time this is true. However, there are times and conditions under which the signal can arrive the other way round, or in some cases by both.

Which way it comes depends upon the time of day, frequency and general band conditions. If you are where I am, in Central Texas, the shortest distance to Australia is to the southwest over the Pacific Ocean.  If I want to hear or work an amateur station in Australia on forty meters, the best time for short path is early in the morning my time. That insures that the signal will have a darkness path most of the route.  Often the window is short depending on where in Australia the station is located, because the sun will be either just going down or has been down a little while  the sun is almost about to come up here. Propagation on forty meters ( 7 MHz) the other way around in the morning my time is simply not going to happen because that path is in full sunlight most of the way.

But let's take a look at " the other end of the day." Just before sunset in Texas, in some parts of Australia the sun is just rising, or just about to rise. The path the long way round is in darkness most of the way.  Prop on forty meters usually lasts a little beyond sunrise at most locations, sometimes by an hour or more.  If on that particular day, conditions are such that the Maximum Useable Frequency happens to be fairly low. it just might be that prop can begin a little before sunset and continue until a little after sunrise,  just enough to allow the signal to get through, and you get your signal via long path!

Now what direction is the signal going? Logic might try to tell you to the southeast from Texas, but that is not correct.  The signal still follows the Great Circle path,  which means it goes Northeast, up and over Europe, then down toward Australia.

Long path prop does not happen every day or on every frequency. There are a number of factors that might determine whether it will occur or not.

First, for the lower frequencies, there still must be darkness over much of the path. There might be some stretching at either end with some light if the first hop could still be in darkness. This can occur if the frequency involved is at the higher end of the range that can be propagated in darkness. For example, my most frequent success on the amateur bands for long path prop to Australia from Texas has been on the 30 meter band. There are times that rather long hauls can be made in the late daytime or near dusk that might make the first hop possible even a couple hours before sunset. The subsequent hops would then be in darkness.

For shortwave listeners,  the closest approximation might be the 31 meter broadcast band.  In the winter hemispheres, 25 meters might be too high for good prop after dark at the higher latitudes and would not make it,  but 31 meters might. We all know that 31 meters does well until a good ways after sunrise as evidenced by NHK from Japan and Radio New Zealand being listenable after sunrise in North America ( and of course, the now gone Radio Australia on 9580 was often listenable well after sunrise while it was still on the air)

There are times that the 40 meter amateur band and the 41 meter shortwave broadcast band can provide the same kind of performance.  The only difference is one must be much closer to darkness for it to work.

There may be exceptional times where prop can occur over both paths at the same time. I have noted this most often at higher levels of sunspot activity on the higher bands that can still sustain prop at night. This kind of prop is characterized by a pronounced echo on the signal brought about by the different transit times for the two paths. My earliest experience with this occurred listening to the VOA relay station in the Philippines back in the early sixties.

As a side note, echo does not always indicate both long and short path prop.  There are also times that I have noted Pacific or Japanese stations with pronounced echo in the mornings that is the result of something else altogether. It is a phenomenon known as " Backscatter". This occurs most often when a station in the Philippines or Japan is beaming a signal away from North America. Some of the signal arrives direct path off the back of the antenna. ( One must note with care when looking at beam headings listed for broadcasts.  Just because a certain beam heading is indicated does not mean that there is no signal sent in other directions.  Even if the front to back ratio of an antenna array is 20 db or even more, if the station transmitter is using high power in the 100-250 kw or more range and the effective radiated power in the main lobe is nearly a megawatt, 20 db down in the opposite direction is still a power level high enough to provide a fair signal. Twenty db down from an ERP of a megawatt is still 10 kw!)

In backscatter, signal that arrives at a distant point from a transmitter often has some bounced back toward the transmitter, and if the prop is good, can hop again toward a listener off the back of the antenna, too.  The difference in transit time can give the echo effect. Some times because the backscatter signal has originally come off the front of the antenna with much greater power and the "direct" signal was radiated with less power,  sometimes the echoed signal can be noticeably stronger than the direct signal,  giving a really strange effect of the echo being louder than the first part you hear.  Sometimes this effect is so pronounced that it can be difficult or impossible to understand the words being spoken.  On a cw amateur band signal,  the delayed dits and dahs can fill in the spaces and make the signal absolutely impossible to copy.

This is a bit of a digression, but because backscatter is an interesting phenomenon perhaps it should be included here. And in a way it fits because it can provide an anomaly in the direction from which a signal appears to come.  This happens most noticeably on the ham bands, but conceivably could happen with broadcast stations, too.

There are times when a relatively nearby station--that is, one too far away to be heard via groundwave but within the "skip zone" or area where the signal is usually not heard because it quite literally "skips over" the receiving site--can be heard, usually with a fairly weak and often very fluttery sound.  What is happening in this case is that the signal is being heard totally via backscatter. That is, the signal is going from the originating signal through the first hop distance, then when it hits the ground or water, while a good bit of the signal goes forward for the next hop,  some of the signal sort of "splatters" and usually most of it goes back in the general direction from which it came, making it audible in the general region where it originated.

A good example of this would be a Texas station being heard on 10,15, or 20 meters by other stations in Texas and Louisiana perhaps well beyond groundwave range but " too close" to be heard by skip. It has been my general observation, by no means meaning that this is the only time it happens,  that this occurs usually right before the band goes out to the original target area.

When this happens, some of the backscattered signal might go off in a range of azimuths, allowing the station to be heard in other areas besides where it was originally targeted or where the "regular skip" path would have taken it.  This would lead a receiver of the Texas signal in, say, Mexico or Central America, to say it appeared to have come from the west or southwest, making it appear that the signal came by the odd path if the receiving station were using a rotary beam of some kind.  It would peak up as coming from the point of the back scatter rather than from whence it really came.

This is where I believe the fabled phenomenon some times called " one-way skip" comes from.  If the station hearing the Texas station via backscatter were to try call or answer the station,  the contact would never be made because the chances of the answering station making the trip back to the original station via backscatter from a different angle would be very small indeed.

Other echo effects can occur on signals whose paths take them through the auroral zone in the arctic.
Signals get tumbled and jumbled and can take on a watery or echoey sound.  This often happens in the amateur bands in the Central US when listening to signals from Sweden, Norway, Finland and north-central Russia. As in the case of backscatter,  this can make a phone signal hard to understand or cw all but impossible to copy. On the amateur bands, when trying to work a station in Scandanavia or northern Russia on cw under these conditions,  the old school guys know the thing to do is to SLOW DOWN and put more spaces between characters so the echo doesn't kill your intelligibility.  This is why I always keep a straight key at the ready along with my Vibroplex bug and electronic keyer!

Gray line prop is another condition that can often make signals appear to come from a different direction than they " should"  There are lots of theories about what brings about so-called gray line enhancement, in which signals seem particularly strong along the boundary between daylight and darkness.  I make no claims to understand with any certainty what actually occurs,  but have learned to take the " bonus " signals or signal strength and enjoy it. There are times when the signals seem to come from other directions than they should.  Sometimes the best thing to do is just log 'em and don't worry about it.  If using a directional beam antenna,  just rotate for best signal strength and don't look at the azimuth indicator.  The bottom line: get them in the log!

One other time in which signals can appear to come from a different direction than they should is during Sporadic E propogation on VHF frequencies.  I have noted times when it almost appears a signal has taken a right or left 90-degree turn when arriving.

This happens when the signal arrives by multiple hops.  Sporadic E occurs when highly ionized patches or clouds form in the mid level of the ionosphere with the ionization levels high enough to provide reflection of signals well into the VHF region.  Sporadic E can also extend into lower frequencies, but usually only down to 25 MHz or so.

If there happens to be two different sets of E layer clouds and IF a signal bounces off one, strikes the round in such a way as to scatter and perchance strike a second E layer cloud somewhat off azimuth from the original path,  the signal path could in effect, be bent.

Sometimes during a really wild sporadic E opening one can almost wear out a good antenna rotator trying to figure out where best to point the antenna. Again, its often best to just leave it where the signal is best readable and not worry about it.  Truth be told,  often Sporadic E signals come down at such a steep angle that they strike the antenna from high above and it probably matters not which direction its pointed.

How do we predict these things?  Well,  that could be a really tricky business.  One could spend so much time trying to do it that there would be no time left for DX-ing.  And perhaps this is where differing philosophies come in.  Whether it be double hop Sporadic E,  grey line prop, long path prop or whatever,  there are some who would try to assign numbers, develop models,  look at the physics of the thing and basically geek themselves almost into a coma trying to predict and figure them out or explain what's happening.

It is my personal feeling that while this is well and good and a great academic exercise,  for me THIS IS A HOBBY!  While there are some fishermen who do the same thing,  others just go out and fish.  I go out and listen.  For me, what is more fun is to turn on the radio,  tune around and get a feel for what's happening and then intuitively shop for the best DX.

I have often said that DX-ing is a lot like fishing.  One learns to read the signs and then just know where to look and how to look. Experience has taught me that some indicators indicate certain conditions and to let that guide where I look.  There are some tools that can help a bit, like the prop forecasts.  Though if I had paid attention to prop forecasts that called for poor conditions or some kind of disturbance, I might never have turned on the radio and missed some great stuff.  But I have learned that when there is supposed to be no prop,  often folks do just that and there is little activity.  But if there is a little atmospheric noise and one tunes around, someone might just find somebody rare and distant hopefully calling CQ.  I well remember stumbling across my first Guam, Johnson Island, Banaba, Christmas Island and a few others just that way!!

Sometimes another "new school" barometer to look at is DX Summit or some of the other DX reporting sites that post real time signal spots.  Take a look and just see where the stuff is coming into various areas and on what frequencies.  This is even useful to the non ham or listener who is not interested in ham stuff.  But what is happening on the ham bands can be a really good barometer on what is happening on the nearby shortwave broadcast bands.  Forty meter spots being a good barometer for 41 meters and to a lesser degree for 49 meters. Twenty meter and seventeen meter spots are good indicators for 19 and 16 meter shortwave stations.  Thirty meter spots are good for 31 meter shortwave conditions and to a lesser degree 25 meter shortwave broadcast spots. Sixty meter spots are good for, well, the 60 meter shortwave band. And so on.....

But I am wandering a bit off track here.  Hopefully this will help some get a feeling about how things appear to me to work. This is based not on textbook theory, but over fifty years of observing what really happens out there.  Sometimes it seems better not to worry so much about the why's of something and to just jump in and take advantage of it.

Good DX-ing to all, and as always, I am happy to hear from anyone with their own observations and ideas through the comments section of this blog or through the Facebook groups you can find me on.
Don't forget,  if the bands sound dead or the signals sound weak,  don't turn the radio off-get in there and dig around.  You never know what might be lurking in the radio shadows.