The small SWL beam (1...30 MHz)

[13dka]

as for changing the feedline routing, if you'll have a chance, it would be interesting trying the modified loop at home, while walls will cause reflections and the pattern may be distorted, it will at least tell if the backside minimum is where we expect it to be

The backside minimum seems to have shifted a few degrees to the west using RAI 900kHz but since that's a skywave signal this doesn't have to be the antenna's fault (dammit, that's exactly where a 2nd prototype would come in really handy!). Edit: I can't get over how well this works on MW, apart from the gain - I wasn't aware that Romania is blasting 909 kHz with 200 kW underneath BBC Radio 5 from various locations including Moorside Edge with 400 and Brookman's Park with 200 kW. It boggles my mind how much I can separate these stations with this antenna (this is with the LANA HF taken out and the 705 preamp at +18dB):



Other than that and mostly independent from that question, I can now say with some confidence that the TTY signal interfering with Radio Rebelde 5025 kHz is coming from the east, 20m is as difficult to tell as before, which also has to do with a local QRM source coming clearly from the NW, messing with SNR and the meter readings. That the QRM source can be nulled out so precisely may say something too.

My overall indoor impression is that this may have improved things a little bit but that may be placebo effect. Unfortunately I'm on the 3rd floor (US, 2nd floor elsewhere) and that means I'm high enough to get weird lobe splitting on higher frequencies, 2 nulls on 15MHz and all that stuff on top of the building influence. I'm confident that it didn't deteriorate things tho, except for the mechanical complications coming with attaching everything outside of the loop maybe.

[Andrew (grayhat)]

The backside minimum seems to have shifted a few degrees to the west using RAI 900kHz but since that's a skywave signal this doesn't have to be the antenna's fault (dammit, that's exactly where a 2nd prototype would come in really handy!).

well, the shift may be due to the antenna coupling with surrounding stuff, what's important is that it's there as predicted by the model

Edit: I can't get over how well this works on MW, apart from the gain - I wasn't aware that Romania is blasting 909 kHz with 200 kW underneath BBC Radio 5 from various locations including Moorside Edge with 400 and Brookman's Park with 200 kW. It boggles my mind how much I can separate these stations with this antenna (this is with the LANA HF taken out and the 705 preamp at +18dB):

And this seems to further confirm that tne "null" is there and that it's "deep" enough to null out a relatively near and high power station, heck, just by turning the antenna one can cut-off one of the stations and listen to the other w/o interference, it seems a pretty good result to me; as for the preamp, in my opinion, using it or not depends from the band and from the receiver internal preamp, a preamp may be needed going down in frequency, but then, while the antenna offers good match, it's small, so not really suitable for LW, I think (then maybe I'm wrong); the idea behind the design was to give some overall decent performances from MW and up

Other than that and mostly independent from that question, I can now say with some confidence that the TTY signal interfering with Radio Rebelde 5025 kHz is coming from the east, 20m is as difficult to tell as before, which also has to do with a local QRM source coming clearly from the NW, messing with SNR and the meter readings. That the QRM source can be nulled out so precisely may say something too.

The next time you'll be at the dike, if the TTY can be received there, it would be interesting to check the source direction that would tell how much the indoor setup causes antenna lobe distortion as for directions, if you don't already an azimuthal map centered on the dike, it may be useful printing one and having it at hand just to have a quick reference

My overall indoor impression is that this may have improved things a little bit but that may be placebo effect. Unfortunately I'm on the 3rd floor (US, 2nd floor elsewhere) and that means I'm high enough to get weird lobe splitting on higher frequencies, 2 nulls on 15MHz and all that stuff on top of the building influence. I'm confident that it didn't deteriorate things tho, except for the mechanical complications coming with attaching everything outside of the loop maybe.

Well, an antenna indoor is subject to reflections and parasite coupling, so I think that the only test would be trying the antenna "in the clear", yet, reading what you reported, the indoor test seems promising; what else... oh yes, I just ran the NEC model of the antenna (the latest one) to check for currents, and currents on the feedline are pretty low, so maybe chokes won't be needed, also, looking at current nodes with the antenna at 3m from ground and the feedline going all the way down, the NEC model shown a node (current minimum) near the base of the vertical support, if that's correct, then placing the chokes there will have higher effect and, at the same time, would solve the "weight" issue, the image below

sdl_current.png (23.92 KiB) Viewed 1031 times

shows the currents distribution and magnitude, as you can see there are two usable nodes, but the first one is near the feedpoint while the second is near the feedline bottom and more convenient, also looking at the magnitude it's easy to see that the feedline shows a current of around 1.7mA while the antenna loop a current around 220mA, the only segment showing high current is the bit of feedline running horizontally below the antenna, but that shouldn't be a problem given that the real antenna has an "arc" of coax; I may simulate that if needed, but would require putting together a bunch of short segments to simulate the curve <sigh>

[Andrew (grayhat)]

As for support, maybe it's a crazy and too complex idea, but just to play some "brain storming", check the pic below

sdl_supp.png (25.1 KiB) Viewed 1023 times

the idea is to use some PVC pipes to form a cross, the left of the pipes cross hosts a "T" junction which is used to tie the cross to the (non conductive) vertical mast, a rope tied between the top of the cross and the upper section of the mast supports the cross, the coax runs vertically from the feedpoint (where the cross is tied to the mast) so there's no "dangling" coax

Again, probably it's too complex and/or not robust enough, not sure, it's just an idea off the top of my head

[Andrew (grayhat)]

As for the idea of adding a switch so that one will be able to include the resistor, exclude it or open the loop at the corner, here are the radiation patterns in the three configurations



now, being able to change the patterns just by flipping a switch would be cool, the problem is that, if we remove the resistor, the impedance at the antenna feedpoint changes a lot, as shown in this image



it's easy to see that w/o the resistor in place, the resistive part of impedance becomes very low while the reactive one raises, this in turn causes losses and may probably cause problems if using the SDL with an external preamp or with a receiver which doesn't "like" too much impedance mismatch (like the Belka), so while running some experiments will be cool, I doubt that there will be real benefit in adding a switch to change the antenna config

[13dka]

As for support, maybe it's a crazy and too complex idea, but just to play some "brain storming", check the pic below

Thanks for the effort, Andrew! But the problem isn't so much the dangling coax (which is ~1m, neither much to dangle nor much weight), it's the weight distribution on a rather flexible fiberglass pole. The antenna has more weight on one side of the horizontal boom of course, which in turn may bend the affordable portable fiberglass poles, which would be a natural companion for this antenna. The smallest of these masts would suffice for the SDL but they're pretty thin and therefore sensitive to this.

I'm currently using the 10m HD mast sold by WIMO and only the lower 4 segments of it, which have some reasonable diameter and that's pretty OK. In fact the additional weight of the ferrite beads was worse than the slightly longer lever and the coax (which had put a weight on the arm anyway). Another problem is the weathervaning effect, which is already something to consider if the antenna is balanced and centered on the pole. I was out at the dike despite rather adverse climate -- it was pretty cold (13°C), wet (showers) and windy (with gusts during the showers) because I was really curious about the changed feedline arrangement and the antenna kept turning southwest and after some gusts it lowered itself to a safe height (some mast segments collapsed) a few times.

Re the changed feedline...

Fig.1: 5 out of 10 passing cars step on the brake when they spot this. Damn heathens...

SDL_mod_dike_evening.jpg (18.52 KiB) Viewed 1004 times

This evening I could observe the directionality for the first time on 20m, previously considered to be the "problem band". I heard a Japanese station and when I was just about to turn the antenna to the north an Italian station called, pretty loud. While I was turning the antenna that station dived considerably into the background and another station calling came up. (That sounds like QSB/AGC action but there was no QSB, it's all me turning the antenna, sorry for the lazy filming of the recorder):



That this antenna seems to love Japan is very likely due to the fact that I can easily turn this straight to the north and cover all northpole and greyline paths between 290° and 70° at once due to the pretty wide beam. The LoG is usually pointing ESE-WNW, with one null pointing more or less towards short path Japan. Next is a pretty much failed attempt at showing the effect on RNZ 15720 kHz. Unfortunately there is too much wind noise, which I didn't hear of course when filming the antenna rotation, but you have to admit the glowing feedpoint illumination is cool:



A few minutes later the rain started, the wind picked up momentum. Next thing I now is that the antenna was down to 1.5m. The rain stopped just in the right moment for Australia VOLMET. Sorry again for filming the recording (too tired to pry the SD-card out of the Icom and find the adapter to transfer the file, convert it yada yada). First thing you (don't) hear is the station while the antenna is turned off axis, then I FFWD to the point when I have turned the antenna to the north, then after the antenna was raised to 3.5m again:



This is another demonstration that the antenna can still deliver true DX at very little height. I packed up early around 4:00am between showers, conditions were pretty down so I couldn't play with ZL signals on 40 etc. I did pick up some extra difficult TA MW DX tho - first time I tried that in summer and I could pickup Bloomberg Radio from NY on 1130kHz, not good enough to understand entire sentences or ID the station but hey, the lines on the waterfall are back!

Long story short: The antenna seems to work as expected, but only if the expectations are reasonable. By this I mean the directionality, its sensitivity has yet to be examined further, that the elevation angle is flat is very much supported by the results so far, more insight will come when I finally get to the dike early enough in the evening to put up two antennas.

[Andrew (grayhat)]

Thanks for the effort, Andrew! But the problem isn't so much the dangling coax (which is ~1m, neither much to dangle nor much weight), it's the weight distribution on a rather flexible fiberglass pole. The antenna has more weight on one side of the horizontal boom of course, which in turn may bend the affordable portable fiberglass poles, which would be a natural companion for this antenna. The smallest of these masts would suffice for the SDL but they're pretty thin and therefore sensitive to this.

Hmm... I see, now here's an idea (no masterpiece of art !)

SDL_setup.png (47.63 KiB) Viewed 1003 times

not sure it will solve the fiberglass pole issues, but at least may allow to better distribute the load thanks to the additional supporting rope; I wonder if, by using some PVC pipes inserted over the larger section of the fiberglass pole it may be possible to reduce/solve the issue

Re the changed feedline...

Fig.1: 5 out of 10 passing cars step on the brake when they spot this. Damn heathens...

but ... but ...

This evening I could observe the directionality for the first time on 20m, previously considered to be the "problem band". I heard a Japanese station and when I was just about to turn the antenna to the north an Italian station called, pretty loud. While I was turning the antenna that station dived considerably into the background and another station calling came up. (That sounds like QSB/AGC action but there was no QSB, it's all me turning the antenna, sorry for the lazy filming of the recorder):

pretty impressive, and further demonstrates how, changing the antenna orientation it's possible to attenuate or "null out" an undesired transmitting station !

That this antenna seems to love Japan is very likely due to the fact that I can easily turn this straight to the north and cover all northpole and greyline paths between 290° and 70° at once due to the pretty wide beam. The LoG is usually pointing ESE-WNW, with one null pointing more or less towards short path Japan. Next is a pretty much failed attempt at showing the effect on RNZ 15720 kHz. Unfortunately there is too much wind noise, which I didn't hear of course when filming the antenna rotation, but you have to admit the glowing feedpoint illumination is cool:

Well, as for the horizontal beam width, I'm fiddling with that in NEC and trying to find a way to make it narrower if possible, the idea at the moment is to experiment changing the size of the loop sides with the latest config and checking the effect, will post an update if I'll find some working "hack"

This is another demonstration that the antenna can still deliver true DX at very little height. I packed up early around 4:00am between showers, conditions were pretty down so I couldn't play with ZL signals on 40 etc. I did pick up some extra difficult TA MW DX tho - first time I tried that in summer and I could pickup Bloomberg Radio from NY on 1130kHz, not good enough to understand entire sentences or ID the station but hey, the lines on the waterfall are back!

I won't thank you enough for your efforts in building and testing the antenna ! As for the height, that, along with reduced size was one of the requisites I had in mind when designing this antenna, as you know the idea was/is to find an antenna which could fit even on a terrace or small garden and yet offered decent DX performances, also, one of the "features" of the antenna can be seen by running a 3D rendering of the lobe and looking at the bottom side of the pattern, you'll easily see that it's "cyan", that means that ground waves will be highly attenuated, and that, if the antenna is placed on a terrace, should allow to reduce interferences from the building below the antenna, or at least that's my hope

Long story short: The antenna seems to work as expected, but only if the expectations are reasonable. By this I mean the directionality, its sensitivity has yet to be examined further, that the elevation angle is flat is very much supported by the results so far, more insight will come when I finally get to the dike early enough in the evening to put up two antennas.

Well, I don't think "miracle antennas" exist, so... well, this one seems to work decently well (note: Thomas saw that Radio Romania VS BBC video and wrote "That is INSANE! Most impressive!" and also "I look forward to an article that might not only help others built, but also use one" ) and may help (or at least that's the hope) many SWLers and Hams

Thanks again !!!

[edit]

Forgot, the NEC predicted radiation pattern for the current design is shown in the image below



as you can see, when going up in frequency, the vertical lobe becomes narrower but at the same time, the backside "null" becomes less pronounced, this probably explains why, by turning the loop you weren't able to completely null-out that station on 20m

[Andrew (grayhat)]

Here's another idea to "balance" the antenna structure, instead of hosting the preamp inside the same box hosting the balun, move it to the point where the coax is tied to the vertical pole, in such a case a "drop cable" will come from the feedpoint to a box hosting the preamp and, from there, the main coax will go down to the receiver, this would allow moving the weight of the preamp to the antenna support pole and possibly have a better balance; also notice where the chokes are placed in my "masterpiece" (previous post), that is near the bottom of the pole, this is because, from NEC simulation, with the bottom of the antenna at 3m from ground, there should be a current minimum at that point, and this will increase the effect of the snap-on ferrites; the only drawback in moving the preamp to the pole is that you won't have that cool "direction indicator" light anymore", oh well

[13dka]

Hmm... I see, now here's an idea (no masterpiece of art !)

SDL_setup.png

not sure it will solve the fiberglass pole issues, but at least may allow to better distribute the load thanks to the additional supporting rope; I wonder if, by using some PVC pipes inserted over the larger section of the fiberglass pole it may be possible to reduce/solve the issue

What I described earlier is this:

Offset_mount.jpg (26.59 KiB) Viewed 990 times

The antenna is mounted to the pole on its center of gravity (like Yagi beams) using another piece of plastic profile. But then again, this prevents folding the booms for transport unless this gets screwed on and off...maybe too much hassle, I like that I just have to unscrew one of the 2 screws joining the 2 booms. The actual weight imbalance with the balun box, the preamp and the coax is maybe 100-200grams since the ferrite beads are not weighing this down anymore and that little weight could be added somehow (what's a good non-metallic weight?) as a counterweight on the other side if need be. I have to order one of these small portable poles to see how that works out practically. For fixed installations this is likely a non-issue anyway.

Well, as for the horizontal beam width, I'm fiddling with that in NEC and trying to find a way to make it narrower if possible, the idea at the moment is to experiment changing the size of the loop sides with the latest config and checking the effect, will post an update if I'll find some working "hack"

Sorry for being sceptical - I'm not quite sure if that's always practical or desirable, if that's even possible at all. For example if the noticeable minimum is traded in for a narrower lobe, it will be harder to find the direction of a signal using the sharp minimum while it will be still hard to find it using the maximum and having these minimums is certainly a valuable asset (think pinpointing QRM sources by walking around, this antenna is still quite lightweight and handheld-portable). Having both at the same time might be a really tall order.

The narrower the lobe, the more need to rotate the antenna for faint off-axis signals etc. It's always a trade-off and my feeling is that for the intended general SWL purpose, the ~170° wide lobe may have the most benefits with the least amount of downsides? I imagine that making the lobe narrower will likely not come with more gain and the achievable reduction of the lobe width is possibly not that high? For hardcore MW DX the lobe can't be narrow enough of course but that antenna may not become the weapon of choice for that purpose due to the low gain down there anyway. Using a custom preamp instead of the 2 NooElec parts could change that of course, and searching for an optimum beyond the "easy to obtain off Amazon parts" restrictions may be a rewarding thing.

BTW, the limits of the NooElec LANA HF could indeed be an issue. I have previously tried it with the 20m LoG and it reacted with intense intermodulation to the partially not so small signals on 49/41/31m. Not a problem with the YouLoop but with the SDL I can see very faint beginnings of intermodulation in the otherwise dead VLF range only. When I saw this I checked said bands for big signals from the usual suspects but there wasn't anything really big, so maybe that was caused by something on FM or elsewhere.

one of the "features" of the antenna can be seen by running a 3D rendering of the lobe and looking at the bottom side of the pattern, you'll easily see that it's "cyan", that means that ground waves will be highly attenuated, and that, if the antenna is placed on a terrace, should allow to reduce interferences from the building below the antenna, or at least that's my hope

Exactly. It could retain as much benefits of regular SMLs as possible while doing away with their worst disadvantages, which would make them the closest thing to a...

"miracle antenna"

I compared it with the YouLoop indoors of course -- the shielded design does have some advantages in that quite extremely noisy place and the 2-turn Moebius trick gives it great properties on MW. This advantage disappears - typical for SMLs - at the latest above 10 MHz and what gives the YouLoop the edge below is probably mostly its sharp and deep nulls. What I want to say is that the SDL could even be a better indoor option for shortwave in many cases where the local QRM is less extreme and diverse and if the room is not on the 23rd floor of a high-rise but most likely it may be a better option than any SML in a backyard, terrace or balcony indeed. Of course, whether or not it actually is "better" depends on a lot of factors, for example, do you even play radio at a time of day when this antenna could play its winning cards etc.

Well, I don't think "miracle antennas" exist, so... well, this one seems to work decently well (note: Thomas saw that Radio Romania VS BBC video and wrote "That is INSANE! Most impressive!" and also "I look forward to an article that might not only help others built, but also use one" ) and may help (or at least that's the hope) many SWLers and Hams

Yes, so far it looks really promising to me, not only for application in noise- or space-restricted cases , I hope I finally get to compare it directly with LoG and SML this weekend (though summer break in all federal states now may get in the way of that, I can't have a whole bunch of RVs around, disturbing me and the antenna patterns grrr) to verify its benefits over these antennas. A draft for an article is already in the making, I have like 1000 words so far.

Forgot, the NEC predicted radiation pattern for the current design is shown in the image below



as you can see, when going up in frequency, the vertical lobe becomes narrower but at the same time, the backside "null" becomes less pronounced, this probably explains why, by turning the loop you weren't able to completely null-out that station on 20m

One thing the article presenting this antenna should make very clear is what to expect from this antenna, staying away from any kind of hype. That's what I meant by "the antenna works as expected if your expectations are reasonable". Most people reading that may have zero first-hand experience with beams (like yours truly) that were not made for TV reception and may be disappointed otherwise, but even if they have.... the minimum on the backside is not what a Yagi-style beam would have to begin with, but its existence doesn't mean it will make signals disappear. I want to make sure that people understand that this won't work like a flashlight, that 3 S-units difference mean nothing on an S9 station and that the null is not a null most times, even if it looks like that.

[Andrew (grayhat)]

What I described earlier is this:

Yes, that's another possible way to arrange the loop, I just wonder if the additional complexity when it comes to deploying or dismantling the antenna, for portable use, may be worth

Sorry for being sceptical - I'm not quite sure if that's always practical or desirable, if that's even possible at all. For example if the noticeable minimum is traded in for a narrower lobe, it will be harder to find the direction of a signal using the sharp minimum while it will be still hard to find it using the maximum and having these minimums is certainly a valuable asset (think pinpointing QRM sources by walking around, this antenna is still quite lightweight and handheld-portable). Having both at the same time might be a really tall order.

Probably you're right and I'm just trying to "chase ghosts" here, all in all the SDL is pretty good at what it does, the only drawback is that due to its small size and the resistor its gain is pretty low, but even then, judging from your tests it seems to be a nice choice for people w/o too much available space; also, I've been fiddling a lot with NEC model variations but had no real improvement, the only thing I didn't try (yet ) is flipping the loop horizontally so, in practice, turning it into a "mini rhombic" antenna, I think I'll give the idea a spin, just for curiosity

BTW, the limits of the NooElec LANA HF could indeed be an issue. I have previously tried it with the 20m LoG and it reacted with intense intermodulation to the partially not so small signals on 49/41/31m. Not a problem with the YouLoop but with the SDL I can see very faint beginnings of intermodulation in the otherwise dead VLF range only. When I saw this I checked said bands for big signals from the usual suspects but there wasn't anything really big, so maybe that was caused by something on FM or elsewhere.

In own experience, here in EU the FM stations are the culprit for a lot of IMD issues, and if you consider that the LANA HF works up to 150MHz, it's more than possible that some FM signals overload it causing the issue; as a note, I had to buy an FM bandstop filter time ago since some of the SDR units I was testing shown "ghost" images due to overloading from FM stations <deep sigh>

Exactly. It could retain as much benefits of regular SMLs as possible while doing away with their worst disadvantages, which would make them the closest thing to a...

"miracle antenna"

Nay, I don't think it's a miracle, just a small loop with some tweaks

I compared it with the YouLoop indoors of course -- the shielded design does have some advantages in that quite extremely noisy place and the 2-turn Moebius trick gives it great properties on MW. This advantage disappears - typical for SMLs - at the latest above 10 MHz and what gives the YouLoop the edge below is probably mostly its sharp and deep nulls. What I want to say is that the SDL could even be a better indoor option for shortwave in many cases where the local QRM is less extreme and diverse and if the room is not on the 23rd floor of a high-rise but most likely it may be a better option than any SML in a backyard, terrace or balcony indeed. Of course, whether or not it actually is "better" depends on a lot of factors, for example, do you even play radio at a time of day when this antenna could play its winning cards etc.

As for physical height vs "electrical" one, my bet is that installing the SDL on a terrace at the 23rd floor and on a 3m pole will still give a pattern similar to the one of the antenna sitting at 3m from ground, at least if we consider that the floor of that terrace usually contains metallic net and/or metal bars, so the antenna will "see" it as the ground (plane)

Well, I don't think "miracle antennas" exist, so... well, this one seems to work decently well (note: Thomas saw that Radio Romania VS BBC video and wrote "That is INSANE! Most impressive!" and also "I look forward to an article that might not only help others built, but also use one" ) and may help (or at least that's the hope) many SWLers and Hams

Yes, so far it looks really promising to me, not only for application in noise- or space-restricted cases , I hope I finally get to compare it directly with LoG and SML this weekend (though summer break in all federal states now may get in the way of that, I can't have a whole bunch of RVs around, disturbing me and the antenna patterns grrr) to verify its benefits over these antennas. A draft for an article is already in the making, I have like 1000 words so far.

COOL, I was thinking to ask if you'd like to put something together, also since I'm not so good at writing documentation or the like; oh, by the way, I never meant to "make money" or whatever with this antenna, it's just an idea, but if you think you may earn something, absolutely go for it, the design is public and free, anyone willing to can use and abuse it

One thing the article presenting this antenna should make very clear is what to expect from this antenna, staying away from any kind of hype. That's what I meant by "the antenna works as expected if your expectations are reasonable". Most people reading that may have zero first-hand experience with beams (like yours truly) that were not made for TV reception and may be disappointed otherwise, but even if they have.... the minimum on the backside is not what a Yagi-style beam would have to begin with, but its existence doesn't mean it will make signals disappear. I want to make sure that people understand that this won't work like a flashlight, that 3 S-units difference mean nothing on an S9 station and that the null is not a null most times, even if it looks like that.

Totally, absolutely agreed, as I wrote I don't think it's a "miracle", and presenting it as the "final solution to all SWL evils" would be a very bad idea, it's a honest antenna presenting some peculiarities and which may improve reception; as for the "null" (notice the quotes) I know that it isn't a "total canceller" (although the BBC vs SSR shows pretty well how it works )

[Andrew (grayhat)]

the only thing I didn't try (yet ) is flipping the loop horizontally so, in practice, turning it into a "mini rhombic" antenna, I think I'll give the idea a spin, just for curiosity

tried it, no cigar

oh well