Wellbrook Loop Performance Flex versus Rigid

[Andy-WParticipant]

I wouldn’t say the MLA-30 is useless below 500khz, but I have replaced the thin stainless steel wire with a longer loop of speaker wire approx 7 metres circumference in a rectangular shape attached to a fence panel. I find it pretty good as a general purpose antenna and something that can be experimented with…and at the price it is a great starter antenna. I have since bought a wellbrook which I have yet to install permanently .. it is definitely a better performer than the MLA and will probably use both in the future, possibly for diversity operation with the RSP Duo.

[Andy2Participant]

I’ve had a Wellbrook 1530 for ages and one of its advantages over the MLA is its LF response. It receives well down to about 30kHz and I’ve even picked up SAQ Grimeton on 17.5 Khz on it – but it’s well down at that frequency. As I have an interest in the LF end of things, a wee while ago I bought one of Wellbrooks LF loop amplifiers and added my own 3-turn loop (1m dia) and was delighted to see much improved signals below 30 kHz and SAQ comes in well now.
The 3-turn loop limits its HF response though so I’ve put both loops up on the same rotator, mounted at right angles so there’s no coupling between them.
BTW, I spoke to Andy Ikin a few months ago and he says he is reducing his product range and as he’s getting on a bit now he may retire soon. It might be time to stock up..

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[JHugginsParticipant]

It looks like we have a spammer. ^^^

I think I have a problem. I just got my Wellbrook FLX1530LN. I made my own 1 meter single turn loop. All my cabling is using RG6Q and BNC compression fittings, and all I’m picking up is a high noise floor. I thought for sure I would be able to pick up some MW local broadcasts but I get nothing.

Is there something about RG6Q that is suboptimal?

From https://www.loop-antennas.com/wellbrook/North_American/FLX1530LN-flexible-loop:
“The user provides the coaxial loop. It simply consists of 3-5m length of LMR400 or a much lower cost RG58c or similar with BNC males.”

Mike has a video showing his loop setup in an apartment in Florida and he’s getting a lot better results than I am!

[DaveRParticipant]

You ought to be getting very good reception using that cable. Compression fittings, though, can be difficult to fit correctly and, as you will be using only the braid for signal gathering, it’s possible that you’ve got a bad connection in one of the plugs. I suppose you’ve already checked the cable for end to end continuity? For preference, I’d use a soldered plug like the Cleqee P7001 every time over compression or crimp types, both of which have little mechanical strength and need proper weather protection if used outdoors.

Regards,
Dave

[JHugginsParticipant]

Hello DaveR,

Thanks for the reply!

I didn’t check resistance but I will. I also have yet to try moving my antenna upstairs. If that doesn’t help me get the local AM band I have a nice CCrane AM antenna to try too. I know wire lengths for AM broadcast need to be much longer than the 3.15 meters I have now to make the 1 meter diameter loop, but I got the impression it should work, which doesn’t mean I’m right in any way. I don’t seem to have trouble with other bands but too I’m just coming to grips with SDR Uno after some time struggling to understand its idiosyncracies but that’s another topic.

You said that only the braid is used for the signal, which makes me wonder, why use coax at all, compared to an equivalent that uses wire?

[DaveRParticipant]

Loop antennas and long wire antennas work completely differently, and even a smaller loop on the Wellbrook amp should pull in AM signals perfectly well. However, if you are trying to use the loop indoors it may be in a dead spot where the signals are completely overwhelmed by noise from within the house – you really need to try it outdoors or in an upstairs window to give it a chance. A few feet from your computer is not a good place for evaluation!

As for thin wire loops, they will also work, but not as well as something fatter, which is why most amplified loops use something like 20mm copper or alu tube instead. Coax cable when used in a loop simply becomes a tube of the same diameter as the braid, so it’s better than a plain wire but not as good as the 20mm tube. It’s all to do with getting the lowest possible inductance to get the biggest currents flowing around the loop, and the bigger the surface area of the conductor, the smaller the inductance – hence fat tubes are better than thin wires.

Regards,
Dave

[JHugginsParticipant]

Very interesting, thank you.

MY RG6Q goes braid/foil/braid/foil, and the braids together might give 80% coverage. Either braid layer alone provides quite incomplete coverage. And I don’t know how the foil affects things either. A metal tube has only one layer essentially and since that’s the ideal I want to get it right.

It seems a cable with one layer of well-wound braid would be more “tube-like” than what I have now. Bonito has some neat looking stuff and of course there is LMR400.

Do you know of a book or some other reference that addresses these questions?

[DaveRParticipant]

I didn’t know RG6Q is quad shielded, but that doesn’t make it any better for a loop antenna, as the inner braid and foil are shielded by the outer foil, leaving just the outer braid to do most of the work. The same goes for any other type of coax. LMR400 is nice and big, but it’s still only 85% coverage, and it’s very expensive unless you can find it in short lengths. Some 10mm copper microbore tube would be better, and 16mm or 20mm Pex-Al-Pex heating pipe would be better still (and a lot cheaper).

But first things first: where is the loop going to be mounted eventually? If it’s going to be outside, a few yards from the house, then make the best loop you can and you won’t regret it. If it has to be indoors then you may as well stick with the RG6, as the RF noise inside the house is always going to affect what you can pick up, especially around the MW band, so see what reception is like first.

I can’t think of any single work which goes into the pros and cons of various loop materials, but you can get lots of useful information just by searching for “small active loop antennas” (probably a lot more than you ever wanted!).

Regards,
Dave

[JHugginsParticipant]

Hello DaveR,

It looks like I won’t be able to get to my radio to do any testing for a couple of weeks due to unexpected travel but I will get back to the measurements and experimenting. Now I’m wondering if the shield alone has inductance and capacitance? As far as I know all those measurements are usually taken WRT the center conductor.

I can get an LMR400 BNC cable made at L-COM for less than $50, and one from Bonito for $75 or so if I remember rightly, and their Ultraflex cable is most impressive, but the L-COM seems like a bargain in comparison.

I had to look up Pex-Al-Pex. haha That stuff looks fantastic! I see a 32mm size as well as the sizes you mentioned. If I was to rig some of that up to my amp what would I do with the center pins on the BNC inputs? Are they unterminated?

The loop is to be used indoors, or outdoors in good weather rarely, so no worries about weatherproofing or anything really. I suppose size is the only consideration.
However there’s no reason I couldn’t make a really nice rigid one and just keep it in the closet. Then I could travel with the flexible cable and really do some DXing when I’m able with the rigid one.

[DaveRParticipant]

You can buy a lot of Pex-Al-Pex for the cost of those made up cables, and it will work a lot better, too – plus you’ll have the pleasure of making something yourself.

32mm Pex-Al_Pex would make a superb loop, as it would effectively be a 30mm tube – much bigger than anything you’d normally find (I’ve got 25mm myself), and you can bend it yourself by hand. Expose the Al tube by melting away the plastic with a soldering iron, then drill a hole to take a short 4mm bolt. The exposed Al only needs to be a little bigger than the bolt head, and drill through one side of the tube only. Use short lengths of coax with BNC plugs on one end to connect it to the amplifier (the centre pin will add some strength, even though it won’t be doing anything with the signals), and expose enough braid on the other ends to be able to tin it and wrap it around the shaft of the bolts, in between a couple of washers. Paint the bolted connections with lacquer or nail varnish, and the job’s done. BNC-BNC RG58 or RG59 patch leads are very cheap, so just cut about 5″ off each end to make your loop to amp connectors.

Have fun when you get back home!

Regards,
Dave

[JHugginsParticipant]

Hello DaveR, I’m back. A bit later than I had intended. 🙂

I can’t find Pex-Al-Pex around here. None of the hardware stores have even heard of it.
Since I don’t want to buy a whole reel from EBay I’ll have to wait and keep my eyes open.

A friend did donate to me a good length of LMR400, so I can try that next. I bought connectors and crimpers but haven’t got around to making the new loop yet.

My RG6QS will have to do for the moment.

Thanks for your advice, it was spot on.

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