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LAA++ loop & mast coupling
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Mark Scudder
Good Evening, Just looking for some wisdom on the following; I've installed a rotator on a steel tripod, which then clamps onto my Laa++ via a pvc pipe. Since mounting the loop on the rotator, it does seem noisier, and I'm just wondering if it is coupling to the tripod, which is steel?.... The loop itself still receives incredibly well outside, as it did before mounting it on the rotator & mast, but the noise floor is higher. Keen to get any thoughts on it - thanks. Best regards, Mark. |
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Tex
Hi Mark,
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Perhaps cathodic action? I assume that the rotator has a Zinc-based metal shell. If it has, that in contact with the steel may be causing a small but significant signal due to dampness in the air. It might be worth while putting an insulating layer between the two, say a layer of rubber or plastic. regards tex On 6 Mar 2023, at 20:46, Mark Scudder via groups.io <mark.scuds@...> wrote: |
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Chris Moulding
One possibility is that RF noise is coming up the rotator control cable from the RF noisy mains earth and coupling into the loop.
Try some clip-on ferrites along the rotator control cable where it leaves the building to see if this lowers the noise floor. Regards, Chris |
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David Cutter
The great thing about those clip-on ferrites is that you can move them up and down to find the sweet spot.
David G3UNA
From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 07 March 2023 12:08 To: CrossCountryWireless@groups.io Subject: Re: [CrossCountryWireless] LAA++ loop & mast coupling
One possibility is that RF noise is coming up the rotator control cable from the RF noisy mains earth and coupling into the loop. |
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Mark Scudder
Thanks for the suggestions gents. I tried adding clip on ferrites, with no appreciable change. Disconnecting the rotator feed also made no change; I have a connector installed about a foot from the rotator, so leaving very little wire for any signals, plus the ferrite. The loop is clamped to the rotator by pvc, so shouldn't be any kind of cathodic or galvanic action. In the end I took the laa++ amplifier off the loop, and attached a copper tube loop I had made previously, sitting the loop on a piece of wood near the ground helped lower the noise floor a little. Interestingly, when I reassembled the amplifier onto the main loop, the noise had dropped about 5db. It seemed to stay at this level consistently...I'm putting it down to a poor connection to the coax or the loop connections, which by disconnecting and reconnecting has seemingly cured the issue. In terms of the rotator, I use a mobious loop arrangement, and it seems that rotating doesn't have a huge effect for a broad part of the rotation, but there is an incredibly sharp and deep null, whereby the signal level falls right off a cliff, then pops back up just as sharply! I'm not graced with a massive garden, and live in a corner house, so really only have one open side towards the road, with the rest being in fairly close proximity to neighbouring house walls, so it may be as much a symptom of location as a feature of the mobious loop arrangement. Thanks and regards, Mark. On Tue, 7 Mar 2023, 12:54 David Cutter, <davidg3una@...> wrote:
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Simon
A noise cancelling unit plus a noise antenna may help alot..( feed against the rx loop)
I found it essential for my use in London. Simon g0zen |
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Martin - G8JNJ
A few clip on ferrites with a single pass of cable will not provide a high enough value of choking impedance.
You would need at least 30 to make an appreciable difference on the LF bands, and 50 is getting to be good. Better to use larger ferrite rings such as FT240-33 or FT 240-43 with multiple turns. If you have already fitted connectors, then a very large clipon core such as Mouser part number 623-0431177081 with something like 8 turns works well, but at a price. Regards, Martin |
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Mark Scudder
Thanks for the assistance. The cause was actually down to the (choice of) coax. I had used some rg58, which it transpires, had a solid core. I'm surmising at this stage, that the solid core has a break in it, which was very likely caused by the action of the rotator! I have some Hyperflex 7, terminated with M&P soldered BNC connectors, and when substituted, that works just fine. Best regards, Mark. On Mon, 13 Mar 2023, 21:10 Martin - G8JNJ via groups.io, <martin_ehrenfried=yahoo.com@groups.io> wrote: A few clip on ferrites with a single pass of cable will not provide a high enough value of choking impedance. |
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