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

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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

a crazy thought (maybe), I wonder if using the same approach, that is resistor and balun at the opposite corners, it may be possible to make the LoG directional; I'll need to run some NEC simulations to check the idea...
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

I was asking myself the same thing. :)

Making slow progress:

dirloop_wireguide_bits.jpg
dirloop_wireguide_bits.jpg (21.04 KiB) Viewed 464 times
(Detachable wire guide end bits, to tense the wire and make sure everything is symmetrical)

Edit: For stability and size considerations, I'll be using 4x2.2kOhms and 1x 22kOhms parallel = 536 Ohms
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

good !! I can't wait to read about the real world test !

as for the LoG, just put together a NEC model, place the wire at 1cm or so from ground, so NEC won't complain and see what comes out
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

OK, that took a bit longer than expected. :)

Hello_World.jpg
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Of course I can't really say anything about the function yet from trying if I get signal at all, and indoors 6-7m AGL... but so far...

- The passive output of the antenna seems to reflect what I saw on the 4NEC2 plots - it's really weak on MW, maybe a bit less output than the YouLoop on 80 but (guess) above 10 MHz it may be increasingly and considerably better than the YouLoop.

- It is already doing what it says on the tin in that is has one relatively pronounced and narrow null. I didn't play with it that much yet of course and tried only some hams on 80, I know where those fellas are (all S of here) but there was a station I didn't know and the null said clearly "East of me", turning the antenna 180° towards Berlin increased the SNR a lot and I noticed his accent, confirming what the antenna suggested.

Then I heard a noise and this happened:

Grrrr.jpg
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It's still working but I'll order a new one now. I usually simply tie a knot into the cable as relief but that doesn't work with 2.5mm wire and there's a bit much tension on the wire. Oh well... shit happens. :) I hope the weather allows for a first dikeside test tomorrow.
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

well, given signal reflections inside and all factors, the nulling seems promising; as for the balun... SIGH, but then it's a lesson I learned myself as well, ALWAYS use terminal blocks (if not using nuts and bolts) since they'll get the strain and not the balun, also, to lock the wires, a pair if nylon cable tiers, optionally with plastic "washers" will just fit

oh well, given the low signal at lower frequencies, a preamp may be due
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

Funny enough, I had small zip ties around the wires but then I noticed that I need to remove more insulation (the wire was slipping out of the terminal) so I had to cut them off and didn't replace them yet. The baluns have gone up in price, I ordered the v2 version (which comes with the green connector terminal set), that's 25 bucks now (the old one is 6€ (+50% or so) more now).

Edit: It reacts in partially unexpected ways to the preamp: +20dB lifts the signal on LW as much as needed to hear DCF77 and MSF, but it's definitely not a VLF antenna. :) But then I think I get a better SNR on Droitwich 198kHz than with the YouLoop, on MW the gain with the LNA is already hot enough to turn off the internal preamp and it really seems to kick the SNR, I think because I'm indoors and surrounded by QRM sources, the YL has two nice nulls in the otherwise omnidirectional QRM receiving pattern and the new antenna has a null in a hemisphere of attenuated QRM. Seems I can get more of 648 kHz Caroline this way (which is really a local QRM problem frequency here), so it might be a better indoor antenna in some situations too. On 80m it's already OK without preamp and the increasing sensitivity of the antenna itself shows above of course. On FM it's just getting insane and the "Overflow" signal is coming on - this doesn't happen with the YL plus LNA, the YL is actually pretty good on FM and 2m, and serviceable on 70cm but this thing has way more signal).

The antenna seems to be a bit cross-eyed up here in my den in that the null and the peak are not exactly reciprocal - e.g. the null for RAI 900kHz seems to be in the SW but the peak (which is interestingly noticeable and not as wide as expected) is straight south. But the antenna is surrounded by metal foil, metalized windows and metal structures so that could be it. I'm curious what the patterns will be in free space.
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

well

https://www.amazon.com/NooElec-Balun-On ... B00R09WHT6

and then, I have some v2, they work a bit better than v1, the other option is to pick a binocular core and wind the balun

as for the v2, check the download section here

https://www.nooelec.com/store/balun-one ... bones.html
13dka
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Re: The small SWL beam (1...30 MHz)

Post by 13dka »

Oh well, plus 7.75 shipping ends up more expensive than getting if from the German warehouses (but like I wrote, I ordered the v2 anyway). :)
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

as for weather... don't know how it is "up there" but here it's sunny, 31°C at the moment (09:08 AM)
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Andrew (grayhat)
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Re: The small SWL beam (1...30 MHz)

Post by Andrew (grayhat) »

13dka wrote: Sat Jul 16, 2022 9:53 pm Funny enough, I had small zip ties around the wires but then I noticed that I need to remove more insulation (the wire was slipping out of the terminal) so I had to cut them off and didn't replace them yet. The baluns have gone up in price, I ordered the v2 version (which comes with the green connector terminal set), that's 25 bucks now (the old one is 6€ (+50% or so) more now).

Edit: It reacts in partially unexpected ways to the preamp: +20dB lifts the signal on LW as much as needed to hear DCF77 and MSF, but it's definitely not a VLF antenna. :) But then I think I get a better SNR on Droitwich 198kHz than with the YouLoop, on MW the gain with the LNA is already hot enough to turn off the internal preamp and it really seems to kick the SNR, I think because I'm indoors and surrounded by QRM sources, the YL has two nice nulls in the otherwise omnidirectional QRM receiving pattern and the new antenna has a null in a hemisphere of attenuated QRM. Seems I can get more of 648 kHz Caroline this way (which is really a local QRM problem frequency here), so it might be a better indoor antenna in some situations too. On 80m it's already OK without preamp and the increasing sensitivity of the antenna itself shows above of course. On FM it's just getting insane and the "Overflow" signal is coming on - this doesn't happen with the YL plus LNA, the YL is actually pretty good on FM and 2m, and serviceable on 70cm but this thing has way more signal).

The antenna seems to be a bit cross-eyed up here in my den in that the null and the peak are not exactly reciprocal - e.g. the null for RAI 900kHz seems to be in the SW but the peak (which is interestingly noticeable and not as wide as expected) is straight south. But the antenna is surrounded by metal foil, metalized windows and metal structures so that could be it. I'm curious what the patterns will be in free space.

as for pattern, walls and metal can/will cause reflections, so it will be better checking the pattern on open field, as for FM judging from NEC model, the antenna shows two sidelobes there and has gain, so an FM bandstop between the balun and the preamp may be needed if the preamp is overloaded; getting back to pattern, it may also be distorted by coax, adding some chokes and/or trying to route it a different way may help
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