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

[13dka]

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

Forgot this one: That may be true and I may have to try this more thoroughly but while I messed around with resistor values I noticed the massive increase in output (mostly QRM) of the antenna with one wire not yet attached to the resistor, that's why I ran this through 4NEC. If the preamp likes this arrangement there's no reason why the Belka shouldn't like the output of the preamp. The passive version of the loop works like the YouLoop with the Belka - almost not at all. With the preamp the Belka seems to be happy with the antenna of course. If the antenna would be adapted to the Belka's high impedance input, the little bugger could be attached directly to the antenna, which would be a cool RDF device. Edit: Maybe not that cool having the antenna pointing at the Belka's display.

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

Like I wrote, I wouldn't want to bother. TBH the only thing I like less than putting up antennas is packing them up again (collapsing the mast, coiling up antenna wires and the coax in a way that it can be conveniently deployed again next time...), so I want that all to require the least possible amount of steps/moves.

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

Too bad it didn't work out. A rhombic was always an antenna type I'd like to try and a mini version would be so cool. I didn't mean to discourage you trying to improve the design further though, of course a narrower beam also has benefits and if the would be easy to reconfigure for that - the more options the merrier.

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>

I tend to forget that because the closest FM transmitter is 20km away here and has pretty moderate power. When I was still living in the city I had not only a whole bunch of much closer FM stations but also a 100kW AM transmitter (Moorfleet 972kHz) giving all of the cheaper radios I had back then some frontend headaches. Today my very helpful test "enemies" are RRI, CRI and Vo Turkey and if they wouldn't be there I couldn't really assess radios at the dike. Speaking of which - as much as I regret having paid major €€€ for the ML-200, the preamp coming with it has no IP issues with those at all, not even when the 20m loop is up in a tree.

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

"Miracle" is a big word, even though the shape of the installation as shown above looks like a miracle is just what you'd ask from that thing. But it's definitely something I was dreaming of for a long time - a small, simple and very hassle-free unidirectional antenna for shortwave, whereas the relative independency from ground quality/conductivity and surprisingly low height requirements are a small miracle to me TBH, as much as I don't like to use that word.

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)

Yes, that may help of course, provided there is a sufficient size to the artificial ground plane. Being quite the opposite of an almost "isotropic"
SML it may be even very deaf to all the RFI racket from the floors below.

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

That's very nice, thank you! But I'm just such a great businessman as you are, so we are discussing all this in public instead of keeping that in private and have a container full of those antennas made in China to sell. I admire the spirit of making knowledge public for DIY and further development (and commercial exploitation) in ham radio and open software development but taking the cardioid loop design and removing the complications it has (ground rod, custom preamp) is a big achievement IMO. If this proves to be as good as I hope for*, this should have your callsign/name attached to it.

* I need to compare it with other "low flying" antennas, particularly SMLs and at less ideal locations than the dike and document the findings. Almost any contraption is good at the dike and LoGs work magic there - but how does that compare when the ground is only average?

[Andrew (grayhat)]

Forgot this one: That may be true and I may have to try this more thoroughly but while I messed around with resistor values I noticed the massive increase in output (mostly QRM) of the antenna with one wire not yet attached to the resistor, that's why I ran this through 4NEC. If the preamp likes this arrangement there's no reason why the Belka shouldn't like the output of the preamp. The passive version of the loop works like the YouLoop with the Belka - almost not at all. With the preamp the Belka seems to be happy with the antenna of course. If the antenna would be adapted to the Belka's high impedance input, the little bugger could be attached directly to the antenna, which would be a cool RDF device.

Well, experimenting may be worth, I just expressed some doubt about the problems which may arise if bypassing the resistor or opening the loop, in the first case, the loop will become a copy of KK5JY "SRL" (Small Receiving Loop) antenna, in the second case we'll have a vertical dipole, even if it's arranged as two "V"

Like I wrote, I wouldn't want to bother. TBH the only thing I like less than putting up antennas is packing them up again (collapsing the mast, coiling up antenna wires and the coax in a way that it can be conveniently deployed again next time...), so I want that all to require the least possible amount of steps/moves.

That's something I was pondering; I think the best way to solve the issue would be having the horizontal and vertical arms of the cross able to fold and/or telescope, that would add complexity to the build but would ease laying out or retiring the loop, also, if the vertical section of the cross extends below the loop for a bit, that would allow to fit the support pole inside that section when installing the antenna and pull it out when dismantling it; just a thought, by the way

I tend to forget that because the closest FM transmitter is 20km away here and has pretty moderate power. When I was still living in the city I had not only a whole bunch of much closer FM stations but also a 100kW AM transmitter (Moorfleet 972kHz) giving all of the cheaper radios I had back then some frontend headaches. Today my very helpful test "enemies" are RRI, CRI and Vo Turkey and if they wouldn't be there I couldn't really assess radios at the dike. Speaking of which - as much as I regret having paid major €€€ for the ML-200, the preamp coming with it has no IP issues with those at all, not even when the 20m loop is up in a tree.

well, nothing forbids using a different preamp for the SDL, I thought to the "LANA HF" just because it's cheap and easily available, but there are a number of other preamps which may be tried, I just believe that this SDL "experiment" should just allow to set some kind of baseline design, then there will always be room for improvement

"Miracle" is a big word, even though the shape of the installation as shown above looks like a miracle is just what you'd ask from that thing. But it's definitely something I was dreaming of for a long time - a small, simple and very hassle-free unidirectional antenna for shortwave, whereas the relative independency from ground quality/conductivity and surprisingly low height requirements are a small miracle to me TBH, as much as I don't like to use that word.

If so, then it isn't a miracle, just an idea which demonstrated to be good when put in practice (thanks again !) then ok, having a directional antenna with a wide bandwidth and a manageable size is a big plus, but I won't call it a miracle

Yes, that may help of course, provided there is a sufficient size to the artificial ground plane. Being quite the opposite of an almost "isotropic"
SML it may be even very deaf to all the RFI racket from the floors below.

Probably not totally deaf, but given the fact that the antenna has very minimal gain for signal coming from the bottom of the pattern, it may help relieving, to some extent, noise from the underlying building

That's very nice, thank you! But I'm just such a great businessman as you are, so we are discussing all this in public instead of keeping that in private and have a container full of those antennas made in China to sell.

While I don't want to underrate your work in improving the design, it could be probably considered "derivative work" based on whoever came up with the cardioid antenna and other antenna ideas put into the public domain in best ham spirit tradition. Developing that further in the same spirit is the way I like it, but of course have no stakes in that or knowledge or anything I could contribute. But who knows, if this turns out to be as good as I hope for, maybe some other people grab the baton and take it even further, that would be cool.

Well, I had to clearly state that the SDL is "open" then nothing forbids one from turning the design into a commercial product an selling it, all in all, someone did that with the LoG and then maybe someone in China will decide to copy the design, screw it badly and sell some kind of "clone" under a number of names

[13dka]

Well, I had to clearly state that the SDL is "open" then nothing forbids one from turning the design into a commercial product an selling it, all in all, someone did that with the LoG and then maybe someone in China will decide to copy the design, screw it badly and sell some kind of "clone" under a number of names

I edited my post above to sound less stupid/patronizing (4:00am is a bad time to post). If something like that happens (it really could be) it'll be your proof that your design was good. And yes, even though making a LoG is as simple as it gets, there will be people preferring to buy a finished product and throw $$$ at it, and I can understand that. The SDL sure has a lot of potential for that!

[Andrew (grayhat)]

I edited my post above to sound less stupid/patronizing (4:00am is a bad time to post). If something like that happens (it really could be) it'll be your proof that your design was good. And yes, even though making a LoG is as simple as it gets, there will be people preferring to buy a finished product and throw $$$ at it, and I can understand that. The SDL sure has a lot of potential for that!

No problem, I got the meaning, don't worry

As for the SDL, just to ensure the Chinese folks will copy it correctly, here's a masterpiece showing the overall setup

sdl_build.png (60.52 KiB) Viewed 13713 times

as already written, the 9:1 BalUn needs to be a galvanic isolation one with separated primary and secondary winding, willing to buy it, a NooElec 9:1 v2 will fit, the preamp may also be bought and a NooElec LANA HF will fit, otherwise it can be built following the design of the one used for KK5JY's "LoG" antenna; again, the preamp and the chokes are optional, but may be needed for some installations, the preamp can be a NooElec LANA HF barebones or any other decent preamp, the resistor may be a single one or a serial/parallel combination as long as the total value is around 530 Ohm, all the balun, resistor and preamp must be enclosed inside small weatherproof boxes, the loop support structure and pole must be built using non conductive material and the height of the bottom corner of the loop from ground (or floor, if installed on a concrete roof/terrace/balcony) should be about 3 meters, otherwise the loop pattern will be distorted

[Hank Michalenka]

If I used 75 ohm coax, should I increase the resistor value to around 800?

[Andrew (grayhat)]

If I used 75 ohm coax, should I increase the resistor value to around 800?

Hi there Hank !

No need to raise the resistor so much, leave it as is (530 Ohm), you won't even notice the difference; changing the resistor value may/will alter the antenna pattern, and at any rate the mismatch between 50 and 75 Ohm will be really small; to make an example, consider that the loop at 7 MHz shows an impedance of about 543+j67.5 this impedance is then transformed by the 9:1 to something like 61 Ohm and gives an SWR around 1.26, as you can see, changing the coax impedance won't affect things

[edit]

just in case, the antenna feedpoint impedance varies between 531+j4.86 at 0.5MHz and 759+j205 at 30MHz so the impedance value after the 9:1 transformation will fit pretty well for either 50 or 75 Ohm coax

for the sake of precision here are the SDL curves related to SWR and impedance over the 0.5 to 30MHz range

sdl_impedance.png (101.7 KiB) Viewed 13695 times

[Hank Michalenka]

just in case we all forget, which tends to happen too often, I want to say a giant "Thank You" for all the work you are putting in on this. I can't admit to understanding all of it, but I intend to construct one of these antennas when my wife, four-legged daughter and I move to Florida this fall. We have HOA restrictions about antennae of any type, so this may sneak under the radar [especially if I can put it up and take it down easily.]

[Andrew (grayhat)]

just in case we all forget, which tends to happen too often, I want to say a giant "Thank You" for all the work you are putting in on this. I can't admit to understanding all of it, but I intend to construct one of these antennas when my wife, four-legged daughter and I move to Florida this fall. We have HOA restrictions about antennae of any type, so this may sneak under the radar [especially if I can put it up and take it down easily.]

Hank, thank you for your nice words, as for "hiding" the antenna you may tell it's a religious symbol or something to allow birds to rest

[Andrew (grayhat)]

Just a quick note, while the purpose of this project was to obtain a relatively compact and directional antenna, nothing forbids one to increase the loop size; the chosen size was selected to offer good performance on the whole HF band, but willing to boost the antenna gain, in particular on the lower bands, one could increase the loop dimensions, to make an example, using the "standard" 76cm side loop, gain on 40m is -42dB, if we increase the side to 1m, the gain on 40m raises to -38dB, and the same increase may be observed on the other bands too, at the same time, the pattern is almost identical to the smaller version; the limit for the side size seems to be around 2m, above that, the antenna pattern will start changing, both for vertical angle and backside "null" depth; again, it's just a note in case someone would decide to make the loop larger.

Then if one wants to reduce the size, it can be done too, but gain will drop, for example, with a 50cm side the loop shows a gain of -49dB on 40m and lower going down in frequency, so I believe that the 76cm size for the loop side may be a good compromise between overall antenna dimensions and performances on the various bands; also, as Matt (KK5JY) correctly writes, making the loop larger means that at higher frequencies the loop perimeter will become a not negligible fraction of a wavelength, so its pattern and impedance will largely change, this may not be a problem if one is only interested in lower frequencies, but if instead one wants an antenna covering the MW and SW then it should be taken into account; in my opinion, 76cm is ok for all-round use, having room or using the loop on the field, 1m may give a bit better performance

[13dka]

At the dike, finally getting to compare antennas I just had the 2nd LANA HF dying on me on the SDL grrr. Now running only the one I bought that has less gain and the comparison with the amplified Youloop is over.

It was a bit pointless anyway because the YL (as a stand-in for an active SML) compared as predicted.. Maybe I get to put down the LoG later if the rain allows and the daylight is back. ++++13dka proving ground news bulletin out++++


Edit (back home): I really need to talk to the NooElec guys I think. I did nothing out of the ordinary, the LNA just went <poof> light out suddenly, the bias-T unit indicating short-circuit. Cutting the power and putting it back on the light comes on briefly then gets dim and flickering, I'd say it's the bias circuitry that went belly up while switching between the antennas. This is the older of the 2 LANAs I have bought 2 years ago (IOW out of warranty).