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Hello,
lots of great info here. I am new to the group IO format, just created an account. I have been paging through the topics and tags but I cannot seem to find anything that deals directly with the shape of the loop material. I have been debating building an upgraded receive only loop. I see most loops are made of round material, either tubing, wire, coax etc.. i am wondering if using sheet metal cut to a certain width then passed though a 3 pin roller to achieve the correct diameter would be OK? The 3 pin can also take up to 3/8" solid or hollow round stock. How wide would be too wide??
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Thanks a lot
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Hi
Welcome.
We need much more info on what you intend to make before advice can be reliably given.
Ie.. active pre amped no tune loop antenna,( ie lz1aq type,) high q tuned? Dia of loop, frequencies of interest etc etc.
However, in general there is no such thing as too big a tube diameter.( dia of tube not loop.) Its usually limited by what you have/ can get/ bend/ not worth the effort due to no real world gains, etc.
A name to call you?
Regards Simon g0zen
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On Mon, Jan 13, 2025 at 12:47 PM, Simon wrote:
However, in general there is no such thing as too big a tube diameter.
Hi, Simon
A thicker tube diameter causes a higher loop capacitance and therefore has an impact on the self-resonance frequency of the loop.
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regards, Fred
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currently using an mla30+, I am incapable of not tinkering.?
pre amped, probably will use LZA1Q but wouldn’t mind something stateside.?
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Possibly tuned with dual gang capacitor.?
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really my question is can I use sheet metal instead of tubing? I have a sheet metal shop and access to copper and or aluminum sheet and coil. If we are looking for the lowest inductance would for eg a 1m diameter loop made from 6” wide copper be acceptable??
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Thanks by the way. Forgot to add that in my reply ??♂??
John is my name.?
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Not to the point of conductor diameter, but one of my reservations using sheet metal.? Considering a mag loop must support large RF currents, I'd be a bit hesitant to use sheet metal.? It is not a particularly good DC conductor which indicates it is not a good conductor of RF currents.? Since skin depth depends on resistance of a material at frequency, a bad conductor is bound to introduce more I^2 x R losses.? Since the mag loop configuration is roughly 15 to 20 dB below a full sized dipole at the same frequency and identical physical surrounds, I'd be cautious of introducing any more loss.
Just my take on your proposal.
Dave - W?LEV
Thanks by the way. Forgot to add that in my reply ??♂??
John is my name.?
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?Hi Dave
John said rx only.
Dave , at time of my reply where I said bigger the better no frequency was specified..ie if was for vlf then all good etc. obvs if for hf then there is a limit along with dia of loop. Thats why I asked for more info.
Regards Simon
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I'll contribute with my additional question (ouch):
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When the thing is a small NON-resonant magnetic loop, for RX-only... is the loop material thickness meaningful?
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73, Jukka
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It is generally accepted that copper and aluminum are very good conductors of RF currents...
Maybe Dave missed that message & assumed the OP was referring to sheet steel or tin. Regardless, for a Rx antenna, it is of little consequence.
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A circle encloses the
largest area for a given length of material, so the largest
received signal. Loops made of wire are generally square for the
simplest support structure. Loops made of tubing can be
self-supporting and are often squares or octagons using 90 or 45
degree elbows to avoid having to bend tubing.? With a metal
shop, you are pretty much unlimited.
On 1/13/2025 4:47 AM, Simon via
groups.io wrote:
toggle quoted message
Show quoted text
Hi
Welcome.
We need much more info on what you intend to make before advice can be reliably given.
Ie.. active pre amped no tune loop antenna,( ie lz1aq type,) high q tuned? Dia of loop, frequencies of interest etc etc.
However, in general there is no such thing as too big a tube diameter.( dia of tube not loop.) Its usually limited by what you have/ can get/ bend/ not worth the effort due to no real world gains, etc.
A name to call you?
Regards Simon g0zen
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wow, thanks for all of the replies.?
yes. I could use 16 or 20oz copper sheet or .032 aluminum.?
I see many people modify existing loops to use copper pipe. Is it necessary to use a round material? Does the cross section of the loop material matter on a rx only loop??
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Just wondering if using a sheet of material and rolling your own tube would really be any cheaper or provide any significant benefit over just using readily available copper water tubing available at big box stores for like 20 dollars? Or aluminum fuel tubing? (Not sure of the cost)
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Tom
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It would be left flat. Not tubular. So it would be a circle of 6” wide copper sheet I have a lot of scrap laying around. Mainly my question is does the element need to be round. ?My loop would be more like a tunnel I suppose. Instead of using tubular material I’m going to use flat metal. Wondering how wide would be too wide. I’m pretty much unlimited in the diameter I could make it. Was thinking about staying at 1m-1.5m diameter.?
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So the loop would resemble something like . The antenna in the picture is horizontally mounted but can be mounted vertically as well. There are manuals on the web as the Isoloop has not been manufactured in decades. Tubing gives a bit more structural regidity but there is no reason why a flat strip of the proper type of metal cannot work as long as properly supported.
73, kevin kc6pob
On Monday, January 13, 2025 at 05:24:08 PM PST, Superlite via groups.io <superlite17@...> wrote:
It would be left flat. Not tubular. So it would be a circle of 6” wide copper sheet I have a lot of scrap laying around. Mainly my question is does the element need to be round. ?My loop would be more like a tunnel I suppose. Instead of using tubular material I’m going to use flat metal. Wondering how wide would be too wide. I’m pretty much unlimited in the diameter I could make it. Was thinking about staying at 1m-1.5m diameter.?
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John, there is nothing wrong with flat material....except dimensional stability and wind loading.? Even for TX, people have used aluminum flashing to build loops (look up "midnight loop").? It's appealing because no special roller dies or welding/soldering are needed.? Maybe there is a small increase in AC resistance (relative to the same width rolled into a tube) due to proximity effects, but this would probably be small even for a TX loop and completely insignificant for RX as others have pointed out.? If you really want to use sheet stock and can form it into a "U" cross-section, or something similar, for mechanical stability, you'd probably be happier with the overall result.
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Dan - K3GMQ
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If you remember when MFJ first was selling its transmit loops, the short period when these were contemporaneous with the AEA Isoloop, MFJ touted that their loop
was not a flat element, was instead round tubing. Supposedly, the not crowding of the RF currents in the middle of the flat strip, away from the thin edge dimension, was an advantage
of the MFJ antenna. But i don’t believe their ad; this “loss” would be, i think, minor compared to other small transmit loop losses.
-Hue Miller
Newport, Oregon, USA
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thanks for all the replies everyone. Much appreciated. I’ve been ruminating on the connection point. Supporting and fabricating the loop is the easy part. I don’t think having a squared off end of loop will be good. Possible I will taper the sheet to a smaller size at the connection. Possibly have multiple bolts or even a bar type connection at the amp housing. So many possibilities. I will just start experimenting and post my results. Thanks everyone.?
john.?
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john
Go look at Lz1aq website.. much info on there re loop antenna fabrication..plus much much more.
Chavdar is a well know and respected wealth of knowledge.. ie on here one can buy from USA his modded preamps etc. see Everett..
Regards Simon g0zen
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Back when I was working with several radio sites, we were using 2" wide flat copper ground strap; because it was supposedly lower impedance than wire ground conductors. [Lightening as you know is NOT a DC impulse.] Mmmm. At what frequencies do flat strap conductors stop being lower impedance than round conductors or vice-versa?
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On the other hand, flat strap in the open air outdoors would tend to flap and twist in the wind, making it unsuitable for an outdoors antenna.
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Phil, K0TWA
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The higher in frequency you go, the more you need ribbon conductors to deal with monsterous currents line lightning strikes.? The reactance does not change.? Its reactance can easily be calculated using:
????????? X(L) = 2 x pi x f x L
pi = 3.14159 f = frequency in Hz L = Inductance in H
Both the ribbon and cylindrical conductors exhibit inductive reactance.? For a unit length of each the wide ribbon conductor exhibits less inductance than the cylindrical conductor.? As the reactance increases (wire is worse than ribbon conductors) AND the frequency increases,? the copper ribbon and the cylindrical conductor become less and less capable of handling very large currents.
Dave - W?LEV
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Back when I was working with several radio sites, we were using 2" wide flat copper ground strap; because it was supposedly lower impedance than wire ground conductors. [Lightening as you know is NOT a DC impulse.] Mmmm. At what frequencies do flat strap conductors stop being lower impedance than round conductors or vice-versa?
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On the other hand, flat strap in the open air outdoors would tend to flap and twist in the wind, making it unsuitable for an outdoors antenna.
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Phil, K0TWA
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Superlite
Robin Midgett