How to build a magnetic loop antenna for HF reception?

[debojitacharjee]

I need to build a magnetic loop antenna to receive HF bands from 3 MHz to 30 MHz. Please tell me how to calculate and design it?

Is it also possible to use a mag loop to receive MF bands?

 

[AK9R]

Have you Googled "DIY magnetic loop antenna"?

 

[debojitacharjee]

Have you Googled "DIY magnetic loop antenna"?

Yes, I did but looking for the formula instead of a calculator. I need to know how to calculate the bandwidth of a mag loop.

 

[W1FRV]

This might be a good place to revive the DIY loop antenna thread.
Have been getting very good results with small loops not over .1 wavelength.
Since the net signal plus noise at a the loop terminals is ( from low effective height ) a very low level should I use a low noise pre-amp at the loop??

Also am using a 4 turn litz wire by 7' diameter loop on 630 meters. Today am trying an LNA at the loop to see if net signals are more useful S/N wise.

Any comments welcomed..

I found some hacks like isolating with a toroid at each end of the lead in run to isolate shack noise from reaching the loop, also center tapped the loop to local ground rod seems to help..

 

[ka3jjz]

<sigh> We have several homebrew designs in our Loops wiki

Loops - The RadioReference Wiki

wiki.radioreference.com

Mike

 

[W1FRV]

Hi Mike,
I found this thread on the net so thanks for pointing to the great source of information..
Kudos to radioreference.com
W1FRV ( first radio voice) call is used to commemorate Reggie Fessenden who first put voice on to radio waves..
He ended up with about 500 inventions and loop antennas were one of his development efforts.
My W1FRV loop on 630m and W1NMF ( U.S. Coast Guard radio station ) loop on 30m shows good results by using small loops for receiving.
www.radiocom.net/Fessenden
TNX de Dave AA1A

 

[prcguy]

A simple 1m diameter loop of wire presents a fairly constant impedance over a very wide range like below 1MHz to 30MHz on the order of 140 ohms or so. Many commercial loops use a balanced low noise preamp with an input impedance matched to the loop impedance with a modest amount of gain and a 50 ohm output impedance.

I made a 1M shielded loop using coax for the loop where the coax braid in the center of the loop is severed then used a broad band 4:1 current balun at the feedpoint. The balun sits in a small metal box that also has two coax connectors on either side and the coax loop has coax connectors so it jut screws onto the metal box with a third connector at the bottom for the output. Using a 15dB gain HF LNA it works very well, although my commercially made W6LVP has more signal output with its roughly 25dB gain preamp.

My point here is that it’s easy to make a broad band no tune loop that performs really well. My shielded loop using coax is probably a little less sensitive than a simple loop of wire so my 15dB gain LNA would probably work better with a simple loop. I can post pictures of my home made loop with more details like the balun if there is interest.

 

[W1FRV]

Hi PRC walkie!!

Am glad to have someone to talk with about this loop hole..
Started off with all the noise QRN around and now am finding years to hack at it..
This is on the W1NMF loop..
I'd like to know the difference between + or - loop circumference length and the .1 wavelength rule.
How do the patterns at that point differ?? Go to .01 wavelength without losses then have super conductor, eh?
Been using loop toroid coupled primary/secondary..
Then change to1/5th diameter loop secondary to receiver..
Will be trying a large ferrite single turn new loop then secondary append..

Way to proof good on WSPR.. A million field strength meters..

Glad I landed here, TNX from Newbie..

 

[prcguy]

Hi PRC walkie!!

Am glad to have someone to talk with about this loop hole..
Started off with all the noise QRN around and now am finding years to hack at it..
This is on the W1NMF loop..
I'd like to know the difference between + or - loop circumference length and the .1 wavelength rule.
How do the patterns at that point differ?? Go to .01 wavelength without losses then have super conductor, eh?
Been using loop toroid coupled primary/secondary..
Then change to1/5th diameter loop secondary to receiver..
Will be trying a large ferrite single turn new loop then secondary append..

Way to proof good on WSPR.. A million field strength meters..

Glad I landed here, TNX from Newbie..

You might be thinking of a tuned loop with the % of wavelength rules and primary/secondary loops. Those would be an open loop with capacitor across the open end and fed with a smaller loop. They also need a very large diameter conductor for lowest loss. The untuned broad band loop I described above avoids most of the rules and since it’s about 140 ohm impedance, you can use small diameter wire with no loss to worry about. The only thing you can’t do with it is transmit.

 

[W1FRV]

Just strung up a modified loop for 160m.. Nothing new, only different applications of coupling, feed and tuning..
The W1NMF ( US Coast Guard Comm Sta commemoration ) loop is on now and seems to be the best tried @ this QTH thus far..
It consists of silver plated 1/2" copper tubing at about 14' length ( 4.3' diameter ), certainly less than .1 wavelength..
The open end ( tuning ) is currently approx. 1.22 nF of C and the current side of the loop consists of three #75 mix toroids to make the loop look like around 6uH.
Two turns of hook up wire through the middle toroid produces a resonance with about 32 db of return loss..
Now to try one on 630m.. I found this site by accident and am glad to be a newbie..

Big helper: Impedance Nomograph

 

[W1FRV]

Been having very good luck with vertical loops on MF/LF mainly 160 and 630 meters.
Recently started to digest the EWE loop theory and see that it's inventor makes a great case.
https://hfdxarc.com/technical-pages/aerials/the-ewe-antenna/
Next I will try to show some improvement to the loops here. At least the noise from the back direction should improve overall performance.
Let's say I go up 20' vertical and 40+ feet horizontal. ??
Instead of driving ground rods at the bottom of the verticals, just run a #10 copper wire along the ground to each vertical bottom??
Start with a #75 mix ferrite beginning with 3:1 turns ratio at the feed side and a tuned LCR series combo at the far side may be good for now.
Is there an argument for a run of wire between the bottom of each vertical element? Or is ground rod best? My thinker stops here.
Will post findings as soon as I try this out.
Right now I have run out of operational improvements with the present loop and the S/N on DX is best I can get @ 630m.
Have changed out the 72 ohm KW TX twin lead feed running on the ground from the receiver to the loop bottom to 75 ohm coax. Seems to be less common mode and less noise now. Also at each end of the feed I use a ferrite ring for matching and isolation plus an in line choke for common mode. That's the best I have arrived to at this point.
W1FRV is on 630m and W1NMF is on 160m.. Hoping the next improvement shows some lowering of local noise.
Thanks for any thoughts. de Dave / AA1A
.

 

[MUTNAV]

Been having very good luck with vertical loops on MF/LF mainly 160 and 630 meters.
Recently started to digest the EWE loop theory and see that it's inventor makes a great case.
https://hfdxarc.com/technical-pages/aerials/the-ewe-antenna/
Next I will try to show some improvement to the loops here. At least the noise from the back direction should improve overall performance.
Let's say I go up 20' vertical and 40+ feet horizontal. ??
Instead of driving ground rods at the bottom of the verticals, just run a #10 copper wire along the ground to each vertical bottom??
Start with a #75 mix ferrite beginning with 3:1 turns ratio at the feed side and a tuned LCR series combo at the far side may be good for now.
Is there an argument for a run of wire between the bottom of each vertical element? Or is ground rod best? My thinker stops here.
Will post findings as soon as I try this out.
Right now I have run out of operational improvements with the present loop and the S/N on DX is best I can get @ 630m.
Have changed out the 72 ohm KW TX twin lead feed running on the ground from the receiver to the loop bottom to 75 ohm coax. Seems to be less common mode and less noise now. Also at each end of the feed I use a ferrite ring for matching and isolation plus an in line choke for common mode. That's the best I have arrived to at this point.
W1FRV is on 630m and W1NMF is on 160m.. Hoping the next improvement shows some lowering of local noise.
Thanks for any thoughts. de Dave / AA1A
.

Would this be helpful, if you hadn't seen it already...




Although I had seen this chart elsewhere... This is where I got it.

The SuperLoop: A super-sized terminated corner-fed broadband loop.

Hope it's helpful. PLEASE let us know any results you get ! !

Thanks
Joel

 

[W1FRV]

Thanks Joel, that was useful and now I see the difference between a 4 sided loop and 3 sided with ground rods with earth return.
Guess it would be good to find the difference between the two loop version.
The last known improvement by the author was to add the series RLC circuit.
May be that tuned instead of broad band needs some more research, will advise..