The SULA antenna

[JohnGreen-SWL]

Noted on the correct mast height specs ie 3m to bottom corner of antenna.
I will make up a mast extension and repeat the SW test . SULA vs JHG mag loop.
Busy with some work at the moment and WX raining. Thanks for your input Andrew.

[Andrew (grayhat)]

Noted on the correct mast height specs ie 3m to bottom corner of antenna.

As for the SULA setup, all the data can be found here

viewtopic.php?t=55

including height

[JohnGreen-SWL]

Yep got a copy but does not specify 3m to bottom corner of triangle for height.

[Andrew (grayhat)]

Yep got a copy but does not specify 3m to bottom corner of triangle for height.

well, it does, if you check the image you'll see that the support pole is 3m, and at the top of it there's the PVC pipes structure supporting the loop

[JohnGreen-SWL]

That is the same as I made my one

[Andrew (grayhat)]

That is the same as I made my one

Now I'm confused, if your support pole is 3m and your cross structure is above the pole, then the height of the bottom corner of the SULA should be about 3m from ground... then ok, you tested the SULA inside so no support pole, the antenna sits near ground and suffers from reflections/coupling, plus the lobe will be quite distorted, anyhow... hope you'll be able to give it a proper test sooner or later !

[JohnGreen-SWL]

Hi Andrew my mast is in two sections short bit for indoors about 1m and balance 2m extension used outdoors..
Hope that makes it clearer.

[Andrew (grayhat)]

just a short note about how to route the coax feeding the SULA; the image below shows the effect of routing the coax outside the SULA or inside it (through the center), as you can easily see, routing the coax toward the center (second image from top) heavily changes the pattern, the backside "null" disappears and the vertical lobe raises, so even if having a "dangling" piece of coax isn't visually nice, it MUST be routed that way if one wants to obtain the real SULA performance

[rayb]

Hello,
I just found this forum, as well as the info on the Sula antenna. Looking over the four pages of info on this post, it seems to be a very good "all around" antenna for swl'ing, as well as it having the benefit of only one null instead of the usual loop dual null.

Ok, I'm going to be "shooting from the hip" here, but I'd like to make a comment/suggestion on the previous post to mine by Andrew. He points out that the Sula's nice cardioid pattern is degraded when one attempts to make the antenna "visually nice" by routing the coax as pictured in the lower pictorial.

I thought about that for awhile and came up with an idea/modification I'd like to suggest to someone who can either model same in software, or actually incorporate the idea into their Sula.

My idea is to still use the "visually nice" routing as pictured, but instead of connecting coax to the feedpoint at the corner, connect a twisted pair of wires to the low impedance output of the 9:1 balun. Run the twisted pair, as shown in the lower diagram of Andrew's attachment. The twisted pair will terminate in a watertight enclosure, perhaps a foot below the lower corner of the Sula.

You have a choice now, in that enclosure ...

(1) You can either connect that twisted pair to the input of a low impedance balanced preamp that will feed your coax to the shack.
(2) You can place a 1:1 balun made up of a binocular 43 material in that enclosure... 5 or so turns each side, then connect one side to the twisted pair, the other side to the input of your unbalanced input preamp... output coax to shack.

Imho, the twisted-balanced pair should allow the "visually nice" configuration to work without disturbing the desired pattern of this fine antenna. Again, I'm shooting from the hip here and just "theorizing" what should work to achieve the best of both worlds, so to speak.

What say ye? Is the idea worth someone modeling it in software or actually trying the mod out on their Sula?

rayb

[Andrew (grayhat)]

Hello,
I just found this forum, as well as the info on the Sula antenna. Looking over the four pages of info on this post, it seems to be a very good "all around" antenna for swl'ing, as well as it having the benefit of only one null instead of the usual loop dual null.

Ok, I'm going to be "shooting from the hip" here, but I'd like to make a comment/suggestion on the previous post to mine by Andrew. He points out that the Sula's nice cardioid pattern is degraded when one attempts to make the antenna "visually nice" by routing the coax as pictured in the lower pictorial.

I thought about that for awhile and came up with an idea/modification I'd like to suggest to someone who can either model same in software, or actually incorporate the idea into their Sula.

My idea is to still use the "visually nice" routing as pictured, but instead of connecting coax to the feedpoint at the corner, connect a twisted pair of wires to the low impedance output of the 9:1 balun. Run the twisted pair, as shown in the lower diagram of Andrew's attachment. The twisted pair will terminate in a watertight enclosure, perhaps a foot below the lower corner of the Sula.

You have a choice now, in that enclosure ...

(1) You can either connect that twisted pair to the input of a low impedance balanced preamp that will feed your coax to the shack.
(2) You can place a 1:1 balun made up of a binocular 43 material in that enclosure... 5 or so turns each side, then connect one side to the twisted pair, the other side to the input of your unbalanced input preamp... output coax to shack.

Imho, the twisted-balanced pair should allow the "visually nice" configuration to work without disturbing the desired pattern of this fine antenna. Again, I'm shooting from the hip here and just "theorizing" what should work to achieve the best of both worlds, so to speak.

What say ye? Is the idea worth someone modeling it in software or actually trying the mod out on their Sula?

rayb

already modeled, was there, done that it won't work, the only way to preserve the cardioid pattern is to route the coax outside the loop.