DXers Notebook - Vol. 68, No. 24

We’re going to focus this time on some propagation-type subjects, but first an additional report came in via regular mail from Mike Riordan in Salt Lake City, first on the "1140 mystery":

I have a Sony CRF-1 receiver with Radio West modified mechanical Collins filters. In my area of Salt Lake City I noticed on 1140 kHz a loud heterodyne pumping sound at night. This occurred from late December (!! – ed) to late February. I switched on the 1.9 filter position on my CRF-1. I discovered that KFSN in Las Vegas, Nevada was broadcasting off frequency. They were on 1138.5 kHz (1/5 kHz off frequency). I contacted the chief engineer, as of this date (3/14/01) problem corrected.

Mike also provides his opinion on the Select-a-tenna:

This antenna works great on some portables and others marginal. The Select-a-tenna works super well on my DX-440. It brings out the weak mediumwave stations loud and clear. It also helps tune out the garbage from strong local stations. I’ve never tried the Super Select-a-tenna. I’ve gotten various opinions on it in the DX community. Some people say that the gain is marginal compared to the original Select-a-tenna. One owner of the Super Select-a-tenna said that it is a broad-band amplified antenna. I could have problems with RF garbage in an urban environment with strong local stations. I am wary of the Super Select-a-tenna in a high RF environment. I would think it would work well out in the boonies.

Steve Francis <Pellisipi@aol.com>: I've heard 316 graveyarders over the past 30 years, and have yet to break the 800-mile barrier on any domestic catch! I did hear TGK-1240 in Guatemala City at 1516 miles in '77, but they're U1 5000/5000. My farthest domestic is KILE-1400 in Galveston, at 781 miles. 300 of the 316 are under 600 miles!

Barry McLarnon VE3JF <bm@lynx.ve3jf.ampr.org>: Your location clearly makes a big difference. You're immersed in the midst of the "GY cloud", which is good for hearing lots of stations, but not so hot for getting long distance catches. If you're on the outside of the cloud looking in, you can get those longer distances. I'm on the northern edge of the cloud, so there are fewer stations within a 600 mile radius, but I've had some luck hearing stations at longer distances - for example, WSBB-1230 (1162 miles), WGGG-1230 (1141 miles), WFOY-1240 (1107 miles), and WFAV-1400 (1186 miles) in Florida, and WMRK-1340 (1075 miles) and WDLL-1400 (918 miles) in Alabama...all heard in the past two years. No doubt most, if not all, had some help from auroral enhancement. I'll bet a lot of DXers in the northeast miss these GY catches because, when conditions are right, they're somewhere else chasing Latin Americans and such!

Mike Brooker <aum108@idirect.com>: For what it's worth (Buffalo Springfield, 1967)... my best graveyard catch from Toronto was WFOY-1240, St. Augustine, FL logged shortly after local sunset on Nov. 10, 1979. QSLed with a v/l and a cool Art Deco style card.

Robert Foxworth <rfoxwor1@tampabay.rr.com>: Two that I am sure I recall were made by Ernie Cooper, while on Cape Cod, both on 1240, the TGK recently mentioned here (and with 5 kW) and another one was his hearing ZNS-2 in Nassau, again during Auroral conditions, alone on the channel. But this was some years ago. This channel is a bit tough here with local on 1250 blasting away. Here in Tampa we have a local on 1340 and semi-local on 1450 and 1490, so I haven't heard as much here as I thought I would. Usually WFTL is big on 1400. I too have not yet had a confirmed outside-Florida logging, but haven't tried that hard.

Russ Edmunds <wb2bjh@nrcdxas.org>: I think that Barry also benefits greatly from being able to get some good GY resulting from auroral conditions, which Steve doesn't have for the most part. I'm somewhat in between the two, but even here, I've not seen the sorts of auroral GY receptions that others further North of me have over the past year plus.

Barry McLarnon VE3JF: Absolutely - I have notes on many of my GY loggings to the effect that there was suspected auroral enhancement. In addition to being in a good position for that, I'm blessed with relatively clear conditions on all six GY frequencies. The groundwave signals that I have on the GYs are not strong enough to be very troublesome at night, and I have no local stations adjacent to the GYs to splatter over them. I previously opined that a lot of good GY catches might be missed, since when conditions are best for long distance reception, most DXers will be busy chasing other targets and ignoring the GYs. To expand on that point a bit, I think there are factors other than aurora that can play a part in long distance GY DX. Just for grins, I took a look at all of my GY loggings that were over 600 miles (about 70 total) to see what time of year they happened in. The results were very interesting - the most loggings were in February, but every month of the year was represented. More surprising is the month with the second-highest total - July! From most to least, the order ran Feb, Jul, Jun/Nov (tied), Oct, May/Aug, Jan, Sep, and bringing up the rear, December. Granted that the numbers aren't large enough for real statistical significance, and that there are other factors involved (e.g., I was away for 3 weeks last Dec.), but I think the trend is interesting nonetheless. Of particular interest is the number of catches during the summer, despite longer days, higher noise levels and the usual summer distractions.

This brings me to my pet theory. :-) I'm convinced that sporadic E plays a part in AM DX. Es is of course best known for pushing MUFs high enough to permit long distance VHF reception. However, there is no reason why it cannot also have an effect well below the MUF. Skywave propagation at MW frequencies mainly results from reflections caused by the E layer, which has relatively weak residual ionization at night. If an Es cloud forms at night, it will have much more intense ionization than the E layer, and it seems reasonable that it would give rise to stronger reflections at MW. These clouds tend to be quite small, and as VHF DXers well know, for a given reception location, they usually support propagation from a small geographical area at any given time. If there is an enhancement from Es at MW, therefore, it would be most likely to be noticed to on a channel that is quite densely populated with stations (a la FM)... such as a GY channel. So, when you hear a GY station lifted well above the masses, it might be caused by Es enhancement. One difference from Es at VHF: at MW, there would be no skip zone, so Es could cause noticeable enhancement at any distance (out to the one-hop maximum, anyway). However, the closer the Es cloud is to you, the more likely it will be to enhance multiple stations (and closer stations that may be commonly heard), and thus be less noticeable. Thus the effects of Es enhancement would be more evident for those longer 600+ mile paths. Okay, show of hands - how many out there have tried GY DXing during the peak of the Es season (May-August at mid-latitudes)? That's what I thought. :-) I think that most folks have declared the AM DX season over by the time May rolls around. Despite less listening time, more than a third of my longer GY catches have been during those months. Of course, Es can happen at other times of the year too. I've heard some monster signals on GY channels from stations that are not normally heard, and aurora, sunrise/sunset effects, etc. were clearly not a factor. Sporadic E is the only mechanism that makes sense to me as an explanation. One nice thing about GY stations - since they are nearly all 1 kW NDA, you know that unusual signal levels are not caused by funny business with powers and pattern changes. This is all circumstantial evidence... I'm hoping to get a decent VHF antenna up later this year and look for correlations between VHF Es openings and MW enhancements. In the meantime, my message is: anytime is a good time to try some GY DXing!

Randy Stewart <jrs555t@smsu.edu>: Barry mentioned that many of his best GY catches have been in July... I'm not at home so don't have access to my DX notebooks, but I know that Robert Kramer's old articles on graveyard DX (which I think are still available as reprints...?) specifically say that summertime IS best for various reasons (the frequencies don't seem as crowded etc.). I don't think Es is one of the possibilities mentioned by Kramer, but it's certainly an interesting theory!

Barry McLarnon VE3JF: I haven't seen anything in print about GY DXing, or corresponded with other GY aficionados, but I'd sure like to hear about other people's experiences. Call me a masochist, but I find the GYs fascinating. I think it's somewhat akin to fishing. Has anyone written The Compleat GY Angler? :-)

Russ Edmunds: I have done a fair amount of summer GY DX'ing, although for a different reason. I, along with other DX'ers in the New York metro area years back, discovered that summer tended to yield good GY conditions to New England, and secondly, with fewer AN'ers then, baseball broadcasts provided for fairly easy identification of some good DX. We know that sporadic-E plays a role in bringing us unusual receptions during high geomagnetic activity by reflecting selected signals within the area of major absorption such that they sound almost 'normal', so there is some basis to suspect that sporadic-E could also have other effects. And, once again, given the Ottawa location, the geography is conducive. I don't have any receptions personally where I could easily go back and draw any conclusions as to this, but it's an interesting thought. And I actually did record the A-index values on my daily logsheets back then, but after some number of years, I wondered why I still kept the logsheets, and all of a sudden I trashed them....

Barry McLarnon VE3JF: At the risk of boring y'all, here's a piece that I wrote on the subject during the Es season last year. It was not posted to this list or printed in DXN, so it did not get wide exposure at the time... it sure didn't get much response, anyway. :-)

Sorry about the length of this, but hopefully it will provide some interesting fodder for the list...It seems that many DXers in the northern hemisphere give up on AM DXing at this time of year. It's true that the long haul stuff pretty much disappears (at least for us inlanders), and that noise levels can be high at times. Nevertheless, there is some interesting DX to be found these days, and if you're ignoring the AM band, you're missing out! Read on...

First a few words about MW propagation. As you probably know, ionospheric propagation is supported by two layers (a slight oversimplification, but close enough), the E layer at around 100 km and the F layer at 300-400 km. Below the E layer is the D layer, which causes massive absorption at MW during the daylight hours, but dissipates at night to make things interesting for DXers. :-) The layers that support reflections are characterized by their critical frequency, denoted by Fo (try and picture the "o" as a subscript), which is the highest frequency that the layer will reflect signals at vertical incidence. It will reflect signals at higher frequencies when they hit the layer obliquely instead of at a right angle. For a given path length along the earth's surface, the maximum frequency propagated for a particular layer is approximately given by the "secant law", which is the critical frequency Fo times the cosecant of the angle of incidence of the radio wave path with the layer.

When nighttime comes, the ionization of the E layer decreases, and its critical frequency (FoE) quickly drops from its normal daytime value (typically 3 MHz or so) to around 500 kHz. The F layer critical frequency also drops, but it normally remains well above the AM band (thus keeping the SW DXers happy!). Despite the low level of ionization of the E layer, it is the controlling layer for most paths at MW, as signals are usually reflected by this layer and thus do not penetrate to the higher F layer. This is a bit unfortunate, since the F layer would support single-hop propagation over much greater distances! (As an aside, I suspect that one reason long-range propagation is better in the winter months is that the longer hours of darkness allow the E layer to weaken further, to the point where signals can penetrate it even at oblique incidence and reach the F layer). In any case, the low FoE at night leads to an E layer "skip zone" in the AM band in which the signals for short paths (i.e., closer to vertical incidence on the layer) penetrate the E layer and are reflected by the F layer instead. The skip zone is negligible at the low end of the band, but it becomes significant at the high end. For example, if FoE is at 500 kHz, then the E layer skip zone will have a radius of about 350 km (about 220 miles) at 1000 kHz, and about 550 km (340 miles) at 1500 kHz. Stations inside the skip zone may be noticeably weaker than those outside it, for a couple of reasons: the greater distance traveled to be reflected off the much higher F layer, and the relatively high angle of radiation of the paths, for which the vertical transmitting antennas radiate poorly.

Okay, enough background... now let's get to the interesting stuff. What happens when we throw sporadic-E (Es) into the mix? The patchy Es clouds usually have much more intense ionization than the normal nighttime E layer, so they often have a much higher critical frequency (FoEs). When Es occurs, the FoEs is nearly always above the AM band, and it frequently gets to 5 MHz or more. On rare occasions, it hits 15 MHz or more, which is what is needed to generate MUFs that get into the FM band. All the excitement occurs on those occasions when FoEs gets high enough to support VHF propagation, but few people think about what Es might do at much lower frequencies. The fact is (okay, it's my conjecture rather than a fact!), any occurrence of nighttime Es could cause some enhancement of propagation in the AM band. It's just not going to be as dramatic as at VHF, since the enhancement occurs against a background of normal propagation rather than permitting propagation that wouldn't exist otherwise.

Since Es clouds tend to be small in extent and hence only support propagation to a limited area, it stands to reason that an Es enhancement would be more likely to be noticed on a frequency with a high geographical density of stations, such as (you guessed it!) a GY channel. Of course, the tradeoff is that any enhancement will have to fight off a higher background level of other stations. Hopefully, the enhancement will be great enough to lift one distant station above the rabble for awhile. A slightly different type of enhancement could occur if the Es cloud is quite close to you. This will do you absolutely no good at VHF, but in the upper part of the AM band it could enhance the signal of a close-in station that normally would be in that E-layer skip zone I talked about earlier.

Does Es enhancement at MW frequencies really exist? I don't have any proof, but I can offer some anecdotal and circumstantial evidence. To begin with, I've had pretty good luck with DXing the GY channels in the peak Es months - May/June/July. A couple of nights ago I snagged two new stations on 1490, both in Illinois. Just a coincidence? Maybe. Last week I logged one of my closest unheards - WEMJ-1490 in Laconia NH, just 248 miles away. On the same day last week (June 6), I heard WGRV-1340 in Greenville TN, 733 miles from me. According to Bill Hale's GY pages, the existing distance record for hearing that station is 69 miles! One of my all-time best GY catches was WINK-1240 (now WTLQ) in Fort Myers FL, at 1334 miles. This was on June 27, 1999, and it is well documented that there was intense Es activity on June 26-27 that produced skip as high as the 144 MHz amateur band. Just last night, I had a tentative logging of WCMA-1230 in Corinth MS (about 980 miles).

Have I convinced you yet? :-) Although Es peaks in early summer at mid-latitudes, there is a secondary peak in the winter, and it can occur at any time of year. A couple of other examples, and then I'll shut up. I was tuning around one night in early April (April 9, to be exact), and noting that all of the signals were significantly weaker than usual. This was in the aftermath of the geomagnetic storm on April 6, and things hadn't quite recovered yet. Then I found an exception: WTOP-1500 in Washington was at its normal strength, or maybe even stronger than usual. This seemed a bit odd.

Tuning down to 1450, I found instead of the usual jumble, a station totally dominating the channel. This was just before midnight. I nearly fell out of my chair when they ID'ed as WOR in Washington. I've only heard them one other time, and it was a weak and fleeting glimpse - this was certainly something else! So, there seemed to be a strong enhancement to the Washington area, perhaps made more noticeable by the depressed propagation to other areas. If it wasn't caused by Es, then I can't think of any other explanation.

One final example - on January 14 of this year, in the early evening, I came across a big signal on 1490 with C&W music, totally on top of the channel. I waited for the ID, expecting it to be pesty WIKE in Vermont, but was surprised to find out it was CKEN in Kentville NS, which is a whole lot farther away. I noted that CKEN had a // operation, CFAB-1450 in Windsor NS, so I tuned down and, sure enough, there they were - not as dominant as CKEN, but quite readable. I haven't heard either station before or since. Another probable Es enhancement.

I'm interested in finding more definitive proof that Es plays an important role in MW propagation (as far as DXers are concerned, anyway). One way to do this would be to identify some nighttime openings to specific areas at VHF that are clearly Es, and then do some listening on the AM band to try and spot stations from the same areas. Unfortunately, I don't have very suitable antennas up for FM/TV VHF reception right now. If anyone tries this and has some success correlating VHF and MW openings, I'd love to hear about it. And, don't assume that there is no Es just because you don't have any VHF openings - Es is actually quite common, especially this time of the year, but most of the time it doesn't produce VHF skip. I frequently check the digisonde at http://digisonde.haystack.edu/, and recently it's shown Es over the Massachusetts area nearly every day - in fact, it's showing Es as I type this. From here, that gives me a nice potential opening out into the Atlantic Ocean. :-) Comments?

Neil Kazaross <neilkaz@interaccess.com>: Yesterday, as it was finally a nice weekend day, I finished installing my "Squashed Delta" antenna here in Barrington IL. This is a modification to delta loop designed by K6SE for the Clipperton Is. DXpedition. I have the EZNEC program and what I did was to lower the height of the apex which lowers (theoretically) the backlobe's best null angle to the horizon. This is hopefully to reduce groundwave which is a huge source of QRM on AM. Perhaps some propagation expert can enlighten me as too what angles the incoming wavefront are from BCB stations. Anyhow with the null set north towards Milwaukee I was getting 25 dB to a bit more nulls across the band. I had calculated 40+ but that isn't easy in practice with my other antennas around and power lines and my DX truck etc.) However I don't think that I have finished optimization. Theoretically the side nulls are nearly 6 dB and I did indeed find that this cardiod clearly favored the south. This antenna doesn't provide as much signal as a big longwire but that is no problem as I could hear in full daylight WLDS 1180 with 1 kW a bit over 200 miles south of me. Will give more info when I get this antenna further optimized. I plan to phase two of them for further nulling…I moved it a bit to knock Milwaukee down a couple more dB...now -25 -30 dB and nailed a nice new catch on 620 - St. Petersburg. This antenna really works and does a good job at getting distant skip.

Barry McLarnon VE3JF <bm@lynx.ve3jf.ampr.org>: There is no simple answer to this question, as the tilt angle of the wavefront is a function of both frequency, and of the ground conductivity and permittivity. The tilt increases with frequency, and it also increases when the wave propagates over "poor" ground. The more tilt there is, the more the wave is attenuated, which is why low frequencies and "good" ground (with salt water being the best) provide the best groundwave paths. Unless your local ground conditions are exceptionally poor, the tilt angle at MW is probably no more than 2 or 3 degrees.

Kevin Redding <amfmtvdx@qwest.net>: Barry, I might be asking a stupid question. What is permittivity? Do you mean "permeability"? I dunno, just thought I'd ask.

Barry McLarnon VE3JF: The permittivity of a material is a measure of how good a dielectric it is - if you stuff it between the plates of a capacitor, the higher the permittivity, the greater the capacitance. In other words, it's a measure of how easily the material can become polarized and store charge in the presence of an electric field. Permeability is the analogous quantity for magnetic fields. Aren't you glad you asked? :-) According to one reference I looked at, high ground conductivity is the most important factor in having low attenuation of surface waves at LF, whereas high ground permittivity becomes the most important factor at HF - don't ask me why! I guess they're both important in the AM band. Not that this is of much practical use to DXers...

Neil Kazaross: OK so if I understand what you are saying, there is almost no tilt angle on BCB for groundwave. What is the angle of incoming wavefront for skip and it's tilt? For example, WCCO on 830 is about 315 miles NW of me and should be relatively high angle but is much weaker on my new delta than without and it is getting ripped up by the Spanish pop station in Louisiana often

Barry McLarnon VE3JF: Oops, guess I missed that you were referring to skywaves. This is actually easier to answer. :-) For the WCCO example, the elevation angle should be about 20 degrees. For other examples, you can go to my website at http://hydra.carleton.ca/ambc/aminfo.html, enter your lat/long and the station callsign, and get an estimate of the elevation angle for that station along with other info.

Sam Dellit <dellits@onthenet.com.au>: I recall that the surface/traveling/crossfield wave field intensity (the electric field axial to the direction of propagation to which the beverage antenna is designed to respond) generally falls exponentially as height above ground increases. has anyone out there calculated the heights above ground for various grounds, including fresh water and sea water (conductivity and permittivity) for reduction of field compared to the field immediately adjacent to the ground. I guess the yardsticks would be 1dB 3dB 6dB 10dB and 20dB. Here in Australia, we tend to try for long beverages wherever possible, generally in the range 1600ft to 3200ft, and keep the wire as high as possible through the trees, often 30ft plus to keep the velocity factor as high as possible, but I suspect this is too high over ground of good conductivity. anyone tackled this before?, I don't like to re-invent the wheel, well recycle it anyway.

Neil Kazaross: This is a variation of a flag or pennant antenna. Earl Cunningham, K6SE wrote articles in QST on these antennas and designed a terminated delta loop for use at the Clipperton DXpedition. Being interested in antennas and wanting a good back end null I played around with EZNEC and found that by shortening the height of the triangle and lengthening the sides I could reduce the best nulling angle of the back lobe to the horizon in an effort to reduce groundwave which is a big problem on AM. The calculated patterns show better than 40 dB F/B across the AM band at low elevation angles. I still get better than 20 dB at 30 deg. above the horizon and better than 15 dB calculated at 45 deg. Consider than a station 300 miles away arrives on skywave at about 20 degrees.

The antenna is simply a triangle of wire or delta. The apex is about 12 feet above the ground and the bottom wire is about 2 feet above the ground and about 40 feet long. These dimensions aren't critical and the antenna (theoretically) works just about as well if it is over double this size and provided more signal as well.

The cardiod pattern is produced thanks to the resistive termination which nulls the back end deeply. The resistor is connected at the far lower corner of the antenna and about 900 ohms is optimal. The resistor does not go to ground. The antenna is completely ground independent !!

The delta is fed with a flag or pennant transformer of about 18:1 value. If you punch in flag antenna in a search engine you'll find some details how to make this transformer. Or you can buy one from Array Solutions as I did. Others have used Mini Circuits transformers for flags but as I found out in my case (having a 9:1) handy, they can't handle strong RF very well and I had WSCR/WGN/WBBM where they didn't belong.

Anyhow...I set mine up Saturday as it finally warmed up a bit and was happy to get somewhat better than 25 dB nulls of Milwaukee stations to the north in the null. On 920 WBAA overrides WOKY daytimes now and there is very little WEMP 1250 audible. Last night on 620, WDAE in St. Pete was o/u WTMJ with Tampa Hockey...etc. etc. etc.

The cardiod pattern also has about a 6 dB null to the sides at low angles and that difference is noticeable. Also there still are decent nulls to the NW and NE as WCCO is way down at night and when North Bay ON on 600 was dominant on the Kiwa Loop I could barely hear traces of it on the Squashed Delta.

If it ever warms up here I'll try a taller apex like K6SE designed for 160 meters and also try a larger delta.

Jerry Monroe KC2UT <jerry.monroe@philips.com>: Neil I have operated a lot of 3.8 MHz DX the past two seasons, BCB propagation is not a whole bunch different. When working the Europeans from Central NY, there appears to be times when the propagation is from significantly different angles. My transmit antenna (full wave loop, perpendicular to ground) has a fairly high take off angle, but still much better than most close to the ground half wave dipoles. There are times when I am able to work Europeans quite well, even better than those "big guns" running 4 Square's (4 phased verticals, with big ground planes). The 4 square antenna really radiates well at low angles, and this is the proven winner for both 80 and 160 meters on DX. My point is however, that they're are times when the propagation angle does come in better from medium angle and not close to the ground angles (as is well thought, and is quite true for higher frequencies) for the really long stuff >3000 miles. Trying to null out nearby 100 mile or so stations at night can be really difficult, because you have the ground wave (low angle) component and the high angle sky wave >45 degrees competing with each other. (that’s why its so hard to hear those nearby 100 mile or so blowtorches at night). The trick is to ride your phase cancellation circuit for best results, as I think you are discovering. I would be curious how it works for long haul stuff in the daytime (without skywave).

Russ Edmunds <wb2bjh@nrcdxas.org>: Signal arrival angles are a function of 1) distance and 2) propagation type, thus this will vary by station but also by propagation conditions. I did a piece on this in Target DX early in the season or maybe last season, and I have some other info on the subject, just not immediately at hand.

Next time we’ll gave some more propagation talk, and also begin looking at some DX Targets from "hard-to-hear" states – a topic that comes up quite often. What state do you have trouble hearing? Which station from one of those states have you heard? See you then.