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

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13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

A box with 525 resistors is on its way to me (plus another one with 500 capacitors because I needed one of those too). :D Going to source 2.5mm wire tomorrow and I already have 1m plastic cable channel profiles to craft a cross-shaped support from (76cm sides is an extra challenge for 1m long profile pieces).

The feed point at the front looks interesting in that the F/B ratio and horizontal pattern shape seems considerably better, that may be worth the extra complication re practical design of the balun box. :)
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

13dka wrote: Tue Jul 12, 2022 3:03 pm A box with 525 resistors is on its way to me (plus another one with 500 capacitors because I needed one of those too). :D Going to source 2.5mm wire tomorrow and I already have 1m plastic cable channel profiles to craft a cross-shaped support from (76cm sides is an extra challenge for 1m long profile pieces).

The feed point at the front looks interesting in that the F/B ratio and horizontal pattern shape seems considerably better, that may be worth the extra complication re practical design of the balun box. :)
COOL !! Really, due to this "@#!&*" wrist I can't go on and build it, grr, well at least you can do it now :D !!

And... yes, I was seeking for a way to improve the pattern, after trying moving the resistor around, changing height, adding elements and then some, I thought to move the feedpoint and DANG ! That did the trick, I even simulated the effect of the coax and, while it isn't "disruptive", adding some snap-on ferrites on the horizontal portion of the feeding coax should care that; the net advantage is that now, going up in frequency, the horizontal angle doesn't widen as much as it did with the previous design so the antenna directional pattern is mantained throughout the whole range; tried changing the terrain to "sea water", well, I won't anticipate what I saw, just pick the latest NEC model, give it a spin and tell me what you think ;) :D

[edit]

forgot, on a totally different topic, I sent you a PM with my email, in case you'll send me an email and won't hear back from me, send me a PM and I'll check if your message was locked ... and "whitelist" you
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

as for the balun box and the loading resistors, I think that a pair of small "electrical junction" boxes may fit pretty well, and willing to add a preamp, a third box, placed below the bottom of the diamond should fit
13dka wrote: Tue Jul 12, 2022 3:03 pm I already have 1m plastic cable channel profiles to craft a cross-shaped support from (76cm sides is an extra challenge for 1m long profile pieces).
shortening the sides a bit should be ok, I just changed the sides from 76cm to 63cm and the pattern seems to be ok over the whole range and, by the way, the diagonal then becomes 90cm, which fits for 1m supports; I choose 76cm since I kept the same size of KK5JY "SRL" antenna
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

Yes, played with the mode (thanks!) and this looks incredible. The F/B ratio seems to be whopping 20dB minimum above 10 MHz, can also be 30dB elsewhere, of course we're talking losses and not gain here but still, this seems too good to be true - a 3-ele Yagi has typically 13dB or something. It still wants to fly low but the h/v patters are super consistent and it that works even half as good as the simulation suggests, that would be the receiving antenna you want to stick into the sand on the beach but also the antenna you want to have in the backyard with the back facing your house to eliminate the noise coming from there. Can't wait to have this on the dike! :)

Re junction boxes, that's what all my stuff lives in and I think I'm going to make the "big" version first to have a reference, the profiles I use come in sizes that fit into each other for some telescoping style setup. 2.5mm flexible litz wire should be good to make that contraption foldable so I end up with 1.1m parts still fitting into my trunk.
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

13dka wrote: Wed Jul 13, 2022 12:13 pm Yes, played with the mode (thanks!) and this looks incredible.
I knew you'd like that; on saltwater or coastal terrain this little loop seems a miracle :D
The F/B ratio seems to be whopping 20dB minimum above 10 MHz, can also be 30dB elsewhere, of course we're talking losses and not gain here
Sure, but then let's reason a bit; on 40m the NEC models tells we have -43dBi at the front and about -63dBi at the back, if we add a 20dB preamp at the antenna we'll have -20dBi at the front and -43dBi at the back, not bad as front/back and not bad for "setting the S/N" too :D all in all, how the LoG and other "lossy" antenna demonstrated, when it comes to receiving, it's all about S/N, and now we have both, S/N and directivity :D !
a 3-ele Yagi has typically 13dB or something.
And then, a 3-ele yagi for the 40m (or the 160m) won't be so "portable" and will need to be raised more than just the 3m of this loop
It still wants to fly low but the h/v patters are super consistent and it that works even half as good as the simulation suggests, that would be the receiving antenna you want to stick into the sand on the beach but also the antenna you want to have in the backyard with the back facing your house to eliminate the noise coming from there. Can't wait to have this on the dike! :)
Well, as I wrote the proof will be "when the rubber meets the asphalt", so at this point I believe it's a matter of waiting and testing, but I'm confident that the antenna will perform as expected; as a note I also ran further experiments, I started by changing the vertical/horizontal ratio of the "cross" and found that, by reducing the horizontal arm size at about 1/3 (and proportionally increase the vertical one), the antenna shows a lower and narrower vertical aperture, but then, the horizontal aperture is widened to about 170° so, I'm not sure such a modification may be worth, I also tried a circular model but that one too doesn't show much improvement, aside from 3dBi more in gain (-40dBi for the round one vs -43dBi for the diamond one), so I think that the diamond shape should be the best compromise
Re junction boxes, that's what all my stuff lives in and I think I'm going to make the "big" version first to have a reference, the profiles I use come in sizes that fit into each other for some telescoping style setup. 2.5mm flexible litz wire should be good to make that contraption foldable so I end up with 1.1m parts still fitting into my trunk.
If you can arrange the "full size" version, go for it, also since simulations were done on that size, so having the real thing will tell how well the model matches the real world antenna, but then again, I think the difference won't be too marked

Another thing I was thinking ... reading the infos floating on the 'net, the Belka receiver seems to be rather "picky" when it comes to antennas, that is, if an antenna doesn't offer a good match, the Belka may have problems, now... this loop presents a very good match to the 50Ohm coax, so I think that the Belka may like it :D

A last consideration; imagine adding a preamp like this one

http://www.arrl.org/files/file/QEX_Next ... Steber.pdf

to the antenna, just add some relays to switch the "L1/L2" section and cover the whole HF and add a controlbox with a tuning potentiometer and a switch to select the band (through relays) and the result will be a remotely tuned, directional, preamplified antenna :D .... but now maybe I'm pushing things too far
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

Just for fun, if the antenna stands to the "real world test", I think we'll need to find it a name, now, I was thinking to something short and easy to remember and following the acronym "tradition" (LoG, SRL, NCPL, ...) I think that this one may be called SSB (Small SWL Beam), but I'm not sure, since that would clash with "Single SideBand" and then someone may say "I was listening to RNZ on AM with the SSB..." :lol: - well, any idea for a name ?
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

Hmm... I have no experience with naming antennas other than giving mine the "crap" prefix, craploop, crap-pole...because I initially thought they are cheap and simple so they must be crap :mrgreen: Crapbeam sounds not very attractive.
The Greyhat
SLB (Small Loop Beam)
Small Unidirectional Greyhat Antenna Rectangle (SUGAR)
SMall Unidirectional Reception Feat (SMURF)
FLat Elevation Unidirectional Receiving Antenna (FLEURA)
Uni-Directional Diamond Enhancing Reception (UDDER)
Directional DX Diamond (Triple-D)
FLat Elevation Angle Beam Antenna, Low Level (FLEABALL)
Flat Inclination Antenna Thingamabob, Unidirectional, Non-Obtrusive (FIAT-UNO)
Flat Elevation Rectangular Reception Antenna, Really Inexpensive (FERRARI)
Convenient Receiving Antenna Project (ok the loop is closing here) :)

Acquired the rest of the needed materials today, just need to find time to build it in a not too crappy way now.
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

13dka wrote: Thu Jul 14, 2022 10:55 pm Hmm... I have no experience with naming antennas other than giving mine the "crap" prefix, craploop, crap-pole...because I initially thought they are cheap and simple so they must be crap :mrgreen: Crapbeam sounds not very attractive.
The Greyhat
SLB (Small Loop Beam)
Small Unidirectional Greyhat Antenna Rectangle (SUGAR)
SMall Unidirectional Reception Feat (SMURF)
FLat Elevation Unidirectional Receiving Antenna (FLEURA)
Uni-Directional Diamond Enhancing Reception (UDDER)
Directional DX Diamond (Triple-D)
FLat Elevation Angle Beam Antenna, Low Level (FLEABALL)
Flat Inclination Antenna Thingamabob, Unidirectional, Non-Obtrusive (FIAT-UNO)
Flat Elevation Rectangular Reception Antenna, Really Inexpensive (FERRARI)
Convenient Receiving Antenna Project (ok the loop is closing here) :)
:lol:

Ok, I think we may stick with "SDL" (Small Directional Loop) or "SDRL" (R for Receiving)
Acquired the rest of the needed materials today, just need to find time to build it in a not too crappy way now.
Cool, I do really hope this loop will stand to expectations; my only remaining doubts about it are the effect of the feeding coax (in real world) on the radiation pattern, I ran some simulations and those shouldn't be a major issue as long as the horizontal run of the coax is choked with snap-on ferrites, but then that was just the NEC simulation ...
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

As a thought, the "SDL" may be built using off-the-shelf stuff, a spool of wire, some resistors, some PVC pipes, a NooElec 9:1 v2 balun, some snap-on ferrites and optionally a NooElec LANA HF (or a similar low noise preamp) will suffice to put together the antenna; add two or three (if using the preamp) electrical junction boxes (to host the balun, the resistors and the preamp) and that will be everything needed to build it, and if one doesn't want to solder (resistors) a terminal block will do

As a note, the difference between a 530 Ohm or a 540 Ohm load resistor is negligible, so 2x270 Ohm resistors in series will just fit, the resulting SWR curve between 0.05 and 33.05 MHz
sdl_swr.png
sdl_swr.png (49.83 KiB) Viewed 551 times
shows that the antenna presents a good match over the whole range, this as I already wrote, allows to use whatever preamp (after the 9:1 BalUn) and in any case, offers a good match to the receiver and minimizes cable losses caused by mismatch
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

Andrew (grayhat) wrote: Fri Jul 15, 2022 7:08 am Ok, I think we may stick with "SDL" (Small Directional Loop) or "SDRL" (R for Receiving)
I suggest SLOB then, you know it really helps if the acronym is a word (took me 2 years until I could memorize "NCPL" and 10 for "G5RV/HB9CV/W3DZZ"), or the antenna has a completely unrelated name like "Double Bazooka" for a "coaxial folded dipole antenna". :) Hmmm...Bazooka...
Screenshot 2022-07-15 at 09-45-27 Bazinga.png
Screenshot 2022-07-15 at 09-45-27 Bazinga.png (160.28 KiB) Viewed 548 times

Andrew (grayhat) wrote: Fri Jul 15, 2022 7:08 am those shouldn't be a major issue as long as the horizontal run of the coax is choked with snap-on ferrites
Not sure what you mean by "horizontal run"? In my mind the coax will likely not make that much of a horizontal run, depending on its bending capability) (which is admittedly not so great for the H-155 I'm using), the more snap-on ferrites it gets, the less it will be able to bend. Do you thing that short piece of horizontal-ish coax will be a problem? BTW that is the part that causes me the most headaches, having this NooElec Balun sitting horizontally in its junction box at the end of the boom, with the coax putting some pull on the boom and the prospect of chaining another box with the preamp to the balun box. I should have thought of that, there are 90° SMA plumbing pieces available on Amazon. :/

Re preamp, I want to try it with the LANA HF, because it's easy to obtain (and I already have 2 of them) and is ready to be powered via Bias-T. It may not be necessary on shortwave but on MW the SDL/SLOB :) has 10dB more losses than the (already not so great) LoG and I find the idea of a small, very unidirectional loop working OK on MW while putting 20dB attenuation on EU stations for transatlantic DX very compelling. If I turn that to 330° up here I'd have all the "offenders" between Spain and Romania on the backside.

Hmm.. maybe it's better to try the initial version first? I have 10m of that 2.5mm wire, enough for 3 antennas.
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