The SULA antenna

[Andrew (grayhat)]

Just opening this thread as a place for people willing to try the SULA, the idea is to post here questions, discuss modifications or improvements and post test results.

To start here are the links to the SULA informations from "The SWLing post"

https://swling.com/blog/2022/08/introdu ... can-build/

https://swling.com/blog/2022/08/small-u ... ion-notes/

https://swling.com/blog/2022/08/small-u ... s-answers/

which I recommend anyone willing to build a SULA to read, since they show you what the antenna is and isn't and how to build it; following the above, for the ones in a hurry, here's a pic showing the structure of the SULA antenna

SDL_struct.png (39.02 KiB) Viewed 40925 times

the top part is a cross, formed using PVC pipes or similar material, it serves to support the wire forming the loop, to the left corner of the "diamond" there's a 530 Ohm (approx) resistor, it may be obtained by combining some resistors in series/parallel, to the right corner there's the feedpoint, where the 9:1 BalUn sits, the antenna is fed using some decent 50 Ohm coax (75 Ohm will do as well), the coax vertical drop from the feedpoint, to the point where it reaches the support pole should be about 1 full diagonal, that is about 1m, at the point where the coax joins the pole it's possible to place a preamp (optional but recommended) offering a gain of 20dB or more, from there, the coax drops down along the pole and, at bottom it's possible to place a common mode choke, the latter may be built using some (6 or more) snap-on ferrites closely grouped together and helps minimizing whatever CMC, the support pole must be made of insulating material, be it fiberglass, wood, a bamboo or whatever, as long as it is insulated it will be ok, the lenght of the pole should be enough to keep the bottom corner of the loop at about 3m height from ground or roof/terrace/balcony/porch... floor, in case the pole isn't installed on ground, and in case the surface (floor) isn't a conductive one (e.g. concrete reinforced with steel bars or grid) a piece of metallic "chiken net" may be placed below the antenna to give it a decent ground plane

The 9:1 BalUn may be homebuilt using a binocular toroid core (6 turns + 2 turns on a #43 or #73 binocular core will do) or either the commercial NooElec 9:1 V2 Balun will fit, the same goes for the preamplifier, any preamp working on the desired range (the SULA is effective from MW up to about 500MHz) and offering about 20dB of gain will fit, be it homemade or commercial, a couple cheap commercial preamps may be the NooElec LANA HF or the SV1AFN GALI-84+ but other preamps will work (or you may also build the SULA w/o a preamp although performance on lower frequencies will suffer), the remaining bit, if your receiver doesn't offer Bias-T power over coax or if you don't already have a suitable unit, is a Bias-T power unit, a cheap "chinese" unit like (e.g.) this one may fit, or you may pick any suitable one, as long as the frequency range matches your desired listening range

For the ones willing to experiment and fiddle with modifications (I suggest to start with the antenna "as is" before trying mods), my suggestion is to pick a copy of the free 4NEC2 modeling software and then using it to load the SULA model found below (just save it as "sula.nec")

Code: Select all

CM ----------------------------------
CM File: SULA.nec
CM ----------------------------------
CM
CM Small Unidirectional Loop antenna
CM
CM feed using a 9:1 balun transformer
CM keep the bottom corner at 3mt from 
CM ground to avoid pattern distortion,
CM use a non conductive pole to raise
CM the antenna, optionally add a 20dB
CM or more preamp to raise the gain
CM
CE

' symbols definition
SY freq=7.100               ' test frequency
SY hght=3                   ' height of bottom corner from ground
SY side=0.762               ' length of one side
SY diag=(sqr(2)*(side/2))   ' half diagonal
SY wire=0.00125             ' wire radius
'SY wire=0.00635            ' 1/2" copper pipe
SY vres=530                 ' loading resistor value
SY segm=13                  ' number of segment in wires
SY segs=5                   ' short wires segments
SY wfed=1                   ' feedpoint wire
SY sfed=segm                ' feedpoint segment
SY wres=4                   ' wire hosting the resistor
SY sres=1                   ' segment hosting the resistor
SY drop=hght-diag           ' coax drop section length
SY coax=0.00250             ' simulated coax radius
SY spac=(coax*3)            ' spacing for coax routing
SY dist=diag+spac           ' spacing for coax feedpoint


' wires geometry
'  ID seg    x0     y0   z0         x1     y1     z1          wire rad
GW  1 segm     0     0  hght      -diag     0   hght+diag       wire
GW  2 segm     0     0  hght       diag     0   hght+diag       wire
GW  3 segm -diag     0  hght+diag     0     0   hght+(diag*2)   wire
GW  4 segm  diag     0  hght+diag     0     0   hght+(diag*2)   wire

' coax feeder "simulation" (may be changed to TL)
GW 20 segs -dist     0  hght+diag -dist     0   drop            coax
GW 21 segs -dist     0       drop     0     0   drop            coax
GW 22 segs     0     0       drop     0     0   spac            coax

' ground parameters
GE  1
GN  2  0  0  0  13  0.005

' wires loading
LD  7    0     0    0 2.1 wire    ' insulation
LD  5    0     0    0 58000000    ' copper wire
LD  1 wres  sres sres vres   0    ' resistor

' enable extended kernel for calc
EK

' feedpoint
EX  0  wfed sfed 0 1 0 0

' initial test frequency
FR  0  1  0  0  freq  0

' end
EN

at that point it will be possible to edit/modify the model and simulate whatever modifications one wants, to see the result, before going on and testing the modification on the real antenna

That's all, for the moment, this thread is open for anyone in need of further details/infos or willing to give feedback on the SULA

[13dka]

While more serious experiments and comparisons with other antennas are still due, I felt like just practically experiencing the SULA the last few times out at the dike, particularly when the condx were briefly recovering between flares. Just like Thursday last week, when the solar indices looked better than during almost the entire development time of the SULA, it turned out next day that yet another flare happened just at the time when I drove to the dike, with many more to follow:

CONDX-Aug-25th_sml.jpg (38.59 KiB) Viewed 40805 times

fusilade.jpg (104.24 KiB) Viewed 40805 times

These wildly changing conditions are one reason why a reference antenna is needed to assess relative performance on the spot. But how is generally living with the SULA, compared to the other antennas I like to use at the dike?

Deployment:

My least favorite part of being a "DX nomad" is putting up antennas, particularly when this is requiring tools and assembly, or launching ropes into trees to pull up wires and whatnot, which was what I did before I started thinking that through. Even worse is that I have to pack that all up again at the end of a session, when I'm tired, hungry and I really want to go home. That's one reason (the other is the performance of course) why I quickly fell in love with the simple monopole antenna at the dike - hook in the end of the antenna wire on the top segment of a fiberglass pole, zip-tie the pole to a fence post and extend the other segments. Attach coax at the bottom, plug the other end into the radio - done. This can be done in less than 5 minutes and brings fantastic results at the dike: The vertical wire benefits enormously from the soil at the dike and the seawater on the other side of it, it has a really flat elevation angle to that side and performs brilliantly. Same goes for the LoG, it's just as easy to deploy and works like the monopole (just with less output). The problem: These antennas only work that well with an ocean literally a stone's throw away

Overall, deploying the SULA does not require many additional steps: My version needs to be "unfolded" and (this is actually pretty optional) secured with a second screw pictured in its "parking" position here:

SULA_Second_Screw.jpg (23.06 KiB) Viewed 40805 times

Then I can snap in the wire at the ends of the booms and zip-tie the antenna to the fiberglass pole. Since the SULA needs only 3m of height I have to pull out only a few of the mast segments and use 2 cable ties to attach it, the preamp needs another cable tie. Of course some of the steps can be skipped if you have a bigger car than me so you don't have to "fold" the SULA, or even detach it from the pole.


Impressions:

Let me begin with how playing with this has changed my perception of (and taught me a lesson about) my listening post and the antennas I'm using there: Blinded by the best results I ever had so far and the ability to listen really deep into the western hemisphere, I didn't really ask myself why I hear the West Coast pretty fine (in the morning) but almost never Alaska, and I took the pretty rare reception of Japanese stations as a given, geographical disadvantage. I was aware that the LoG antennas I'm often using there are kind of bidirectional but didn't really bother with changing their orientation and my vertical wire monopole is omnidirectional anyway. Or is it?

Well, while testing the SULA we had a lot of radio blackouts happening, often taking out the sunlit west when I arrived at the dike in the evening. But without failure, I could hear Japan every evening when I had put up the SULA, and then again next day before noon. When the ionosphere settled a bit, I also heard Alaska more often than ever.


Video: JE8AGX from northern Japan


Video: KL7HRN (near Anchorage) working Malta, never heard Alaska in the evening before!

Here's more Alaska next morning, this time the west of the state (Bethel, AK):



So what's up with that? When I use a LoG at the dike, I usually have its lobes covering 290°/110°, perpendicular to the dike. Hence the "nulls" are pointing 020°/200° - Japan is 30-45° short path. Western Alaska is 355°, 25° to the left of the LoG minimum, just like Japan is up to 25° to the right. Likewise, I heard stations long path (240°-270°) from Australia in the morning but not so much short path (60°-90°) in the evening. The LoG doesn't really have "nulls", it's more an oblong shaped pattern and not figure-8, and I didn't bother with turning it because I got more or less the same results on the vertical, which is omnidirectional. But why?

The most likely explanation is that the ocean to the west is greatly bending the pattern to that direction, while most over-the-pole paths mean "soil" at my location, not water. The antennas have signal gains and a low elevation angle to the west, but not necessarily to the north and east. Cue the SULA: This antenna is not overly impressed by the ocean to the one side, and does likewise not rely so much on the soil to the other side to maintain a beneficial takeoff angle.


Video: WWVH (350°, same as Alaska) on August 26th, in the middle of more flares causing unsettled condx.

In practice, the "preselection" of stations due to the unidirectional pattern has a bigger impact than I could imagine. Turning it e.g. to the north is visibly changing the band's "population" on the waterfall, with southern Europe losing several S-units and e.g. Japan gaining a little, suddenly I can find them much easier while tuning across the band simply because they stick out more. It's actually a fun antenna! However it has a few...

Downsides:

For example, there's the sensitivity on MW. Here are quick band scans before and after sunrise:


Video: MW band scan before sunrise


Video: MW band scan after sunrise

Obviously this isn't that much of an issue during the night and it likely doesn't prevent picking up transatlantic DX. Here's Bloomberg Radio with the SULA (and the ML-200 for comparison):


Video: WBBR, first proper reception this year.

The SULA likely doesn't dig up low power POTA stations from the East Coast as convincing as the 10m high monopole antenna but that's a small sacrifice given the advantages on the other sides, also that advantage for the monopole would not be there on a non-coastal location. The SULA was also not quite as good as the ML-200 on 5 Mhz but these marginal differences aside, I can e.g. still hear the 75m US ragchewing nets hours before sunrise with the SULA:



Back to the upsides and while I'm dumping videos here anyway, here's another high-quality (with recorded audio merged with the video) demonstration of the horizontal pattern on 10 MHz:


Video: Gander Radio on 10 Mhz

Here's the pattern on 70cm, using a repeater on Helgoland island, ~60km/37mi out in the North Sea. The pattern turns into a bidirectional pattern and rotates 90° for the fist time around ~100MHz, another rotation of 90° happens around ~250MHz so reception is again along the loop plane (but 180° reversed). Depending on frequency, the bidirectional pattern can be somewhat asymmetrical.


Video: 70cm horizontal pattern demonstration

Good results on VHF/UHF are yet another reason why this is a fun antenna for me even at the dike, the monopole is not quite as good (despite the top being 7m higher) and a loop on the ground on FM... Should tropo or sporadic E happen, I have something sensitive and bidirectional to harvest FM DX, and an antenna that's generally very useful from 1 to 150MHz and still good enough on 450MHz.

There's one more thing I want to mention: Maybe you can imagine that spending nights at the dike is coming with a certain blood tax, despite trying to keep the door closed, display light and my odor is attracting a lot of mosquitos and I'm usually getting a lot of bites. Not so much while testing the SULA: The white LED on the LANA HF preamp is pretty darn bright (it actually illuminates the ground and the dike a bit!) and an awesome distraction for the mosquitos, so I suffered at most one or two bites each night, despite having the door much more open due to getting out of the car and turning the antenna!

[Andrew (grayhat)]

just a very quick note (I'm on holidays at last ), nothing forbids a Ham to use the SULA as a receive-only antenna, for example using a vertical or an endfed for TX and the SULA for RX to help fighting the noise and attenuating signals from undesired directions

also, NEC simulations show that the SULA is usable from 0.5MHz although it start doing good from 1 to about 35MHz with an unidirectional lobe toward the feedpoint then the pattern starts showing two lobes perpendicular to the loop and with a number of "fragmented" sub-lobes, moving up to around 250MHz the unidirectional lobe is restored, but in the opposite direction, that is toward the resistor, also, at these higher frequencies the SULA shows positive gain, so the preamp may be omitted/bypassed, and... Ollie, your "real world" tests seem to confirm the above

as for mosquitoes... I'll need to find how to simulate them in NEC

[JohnGreen-SWL]

SULA-JHG.jpg (63.05 KiB) Viewed 40604 times

I have just completed my SULA antenna which at the moment is restricted to indoor use due to the WX at the moment but we are at the start of Spring I am using 2.5mm stranded copper wire as suggested a commercial 9:1 balun and for the resistor a piece of veroboard (stripboard) in an ADSL filter box with a 470 ohm and 56 ohm resistor in series. The mast and extension to 3 meters is 25mm conduit and the crossbar polycarb tubing 16mm. The wire is attached to the frame using cable ties. The LNA amplifier is from the old version MLA-30. The QTH at the SW tip of Africa is on the slopes of a hill and is a villa and has a good take off over the Atlantic Ocean. So far I have tried SW and MW and both seem to bring in stations on the SULA. I will see if I can get any Transatlantic MW stations from Brazil or USA before sunrise.
Many thanks to Greyhat and 13dka for this innovative antenna looking forward to seeing how it performs compared to my JHG amplified magnetic loop antenna

[Andrew (grayhat)]

SULA-JHG.jpgI have just completed my SULA antenna which at the moment is restricted to indoor use due to the WX at the moment but we are at the start of Spring I am using 2.5mm stranded copper wire as suggested a commercial 9:1 balun and for the resistor a piece of veroboard (stripboard) in an ADSL filter box with a 470 ohm and 56 ohm resistor in series. The mast and extension to 3 meters is 25mm conduit and the crossbar polycarb tubing 16mm. The wire is attached to the frame using cable ties. The LNA amplifier is from the old version MLA-30. The QTH at the SW tip of Africa is on the slopes of a hill and is a villa and has a good take off over the Atlantic Ocean. So far I have tried SW and MW and both seem to bring in stations on the SULA. I will see if I can get any Transatlantic MW stations from Brazil or USA before sunrise.
Many thanks to Greyhat and 13dka for this innovative antenna looking forward to seeing how it performs compared to my JHG amplified magnetic loop antenna

Hi John; nice build and thanks for building and posting, I see one issue, though

The MLA-30 preamp is designed with a pretty high input impedance and to be connected directly to a loop, whereas the SULA, due to the resistor and the 9:1 BalUn presents a 50 Ohm impedance over the whole operating range, this means that the mismatch may and probably will result in less than optimal performance (set aside the other MLA preamp issues), so it would be a good idea considering to replace the preamp with a better unit, that said, using the MLA preamp is still an interesting experiment, please, post back your results !

Oh and... the coax dropping from the feedpoint should be longer and dropping down more or less vertically otherwise being too near the antenna wire it will distort the pattern

[edit]

regarding the MLA-30 preamp, more infos about its issues can be found here

https://www.g8jnj.net/activeantennas.htm#MLA30

now, if you still want to experiment with that preamp, try this; remove the BalUn and replace it with the MLA-30 preamp directly connected to the loop wire, don't know how it may behave, but will be an interesting experiment, just ensure to let the coax from the preamp drop down smoothly (see the pics posted by 13dka)

[edit #2]

remember that the SULA is unidirectional, so to improve reception of a given station you should aim the antenna feedpoint corner at the desired station, a customized azimuthal map like this

viewtopic.php?t=9

will help aiming the antenna

[Andrew (grayhat)]

John... is that you ?

https://youtu.be/Dpo6RCgM2V8

https://youtu.be/B0kbRO12Ftc

[13dka]

There's more, I hope John doesn't mind linking them all here, I'm just so exited to see other OMs using the SULA!





Thanks for trying the SULA, John! It's really rewarding to watch these videos!

[Andrew (grayhat)]

Yes, saw those, pity the SULA is just inside (while the doublet is up in free air) and pity the preamp isn't the best one, yet I believe that the results are quite impressive ! I'm waiting for an outdoor test with the SULA aimed toward some station(and opposite to it, just to check the backside attenuation)

[JohnGreen-SWL]

Hi Andrew thanks for your input.
I will remove the balun and replace it with the preamp as suggested also alter coax feed to vertical drop. I will see if I can find a local sourced LNA that is more suitable as the courier costs to here are high.
The WX seems to be improving so will try the SULA outdoors. 73 John

[Andrew (grayhat)]

Hi Andrew thanks for your input.
I will remove the balun and replace it with the preamp as suggested also alter coax feed to vertical drop. I will see if I can find a local sourced LNA that is more suitable as the courier costs to here are high.
The WX seems to be improving so will try the SULA outdoors. 73 John

Hi John, placing the MLA-30 preamp at the feedpoint will be an interesting experiment, but it's untested so I don't know how it will behave; as for LNAs Amazon offers a number of possibly usable ones, regarding the outdoor tests, remember that the optimal height for the SULA is about 3m from ground (or a ground plane if installed on a balcony/terrace/roof/porch - in such a case, a piece of chiken fencing may replace the ground, if needed), the usable height range goes from 1.8m to 4m

as for the preamp and the Bias tee

https://www.amazon.com/Amplifier-50K-2G ... B07NLT9XMV

https://www.amazon.com/10K-2GHZ-Amplifi ... B076Y4N483

https://www.amazon.com/gp/aw/d/B07QGD5FCT

the above are just examples, but may be suitable, notice that since the above LNA doesn't have an embedded bias-t circuit, to use it one will need two external bias tee units, one station side to inject the DC over coax and a second one antenna side to pick up the DC from coax and power the LNA