Loop Aerials - Does Size Matter ? - UK Vintage Radio Repair and Restoration Discussion Forum

E93AFAN · 14th Sep 2023, 12:51 pm

My house is subject of a restrictive covenant in respect of aerials and my local council very critical of anything other than a UHF aerial or small dish, one local amateur was forced to remove his aerials recently. So for many years I used a long wire hidden amongst my garden trees, which was "adequate" but neither high enough or long enough.

When a new supermarket opened RFI made reception on medium wave nigh impossible. On this forum I discovered loops and bought myself a 1 metre metal hula hoop to which I have added a preamp. The results are a revelation, I can once more read all the remaining MW local stations as far away as South Somerset, listen to Classic Gold from London at all times, Manx Radio, Caroline and many European and North African stations come alive at dusk. Performance is also improved up to about 30 Mcs, which is the limit of my interest anyway.

I have researched the following questions and whilst I feel I should already know the answers, I can't find anything definitive.

1. What impact does the size of the loop have on reception - is bigger better ?

2. If bigger is better at MW, will performance at higher frequencies by adversely affected ?

3. A US forum suggests two side by side loops of the same size are better than one - true ?

4. Some suggest a "traditional" multi turn copper wire frame aerial outperforms a metal loop ?

In earlier times I enjoyed MW DX and so as European stations wane I foresee the possibility of some long range finds if my aerial is efficient enough and so if improvements can be made I'm happy to spend time investing in these.

As always I'm sorry this is low level stuff to most of you, but I do thank you in anticipation of your views, which are always helpful to me.

Radio Wrangler · 14th Sep 2023, 1:07 pm

Larger loops subtend more area and catch more signal energy than smaller ones. Go very large (in terms of frequency) and resonant effects enter the fray. Very good if the resonance is on your wanted frequency.

Smaller loops couple less well to free space and their impedance looks more reactive leading to higher Q making tuning more ticklish (and greater losses if transmitting)

Unless you're at the upper end of the HF bands or into VHF, then communications aren't much limited by receiver noise. So the small amount of signal power captured by small loops is not a problem.

Smaller loops are lower in Z and so more awkward to get low loss transformation to something better suiting amplifiers and input stages. Not much of a problem for receiving.

All loops have nice nulls which can be planted on your worst interferer, but if you can't rotate them then you get stuck with null directions. Small loops are easier to rotate.

Frame aerials with normal tuning capacitors work quite well and can be fun to play with. Again, expect high Q and touchy tuning. On long wave they can be narrower than the modulated signal you're trying to receive which cuts treble.

Plenty to play with.

Put up a TV antenna use the feeder as an HF verical with the TV aerial working as a capacity hat!

David

G6Tanuki · 14th Sep 2023, 6:50 pm

For me, the 'untuned' loop type antennas [Welbrook/Welgood] with amplifiers always seem a compromise though they work OK for some people.

My dislike of them is based on the idea that they are innately broadband - so they don't really do anything to exclude RF energy at the image frequency [assuming we are talking feeding the output to a superhet receiver] or similarly-superhet-implied +/- image-and-local-oscillator-harmonic frequencies.

I like high-Q resonant antennas. They generally don't respond to harmonics, and they have the additional benefit of excluding broadband noise that can also cause intermodulation/mixing in the front-end of the receiver which raises the 'noise floor'.

Most historical receiver-tests for intermodulation/overload etc. generally use a couple of frequencies maybe 50KHz apart; they don't really map well into a world of SMPS sharsh, powerline-data, ADSL and plasma-TV emissions where you have potentially hundreds of relatively-low-power carriers spaced only a few KHz apart - and whose aggregate energy can be significant.

A tuned loop helps exclude such nonsense.

Recently I have been playing around with a DDRR Hula-Hoop antenna, as developed by Northrop in the 1950s for US for military applications.

See http://www.orionmicro.com/ant/ddrr/ddrr1.htm

and "Hula-Hoop Antennas: A Coming Trend, J. M. Boyer, Electronics, January. 11, 1963"

It's a horizontal loop mounted only a few inches above an 'ideally' perfectly conducting groundplane.

My version uses 15mm copper microbore heating tube mounted above a cut-open-and-flattened old-fashioned copper immersion-heater tank.

I'm using a WWII-era 60+60pF air-spaced variable capacitor to tune it; this thing has around 1/8-inch plate spacing.

On 28MHz it tunes-up well. It's really high-Q, initially I was trying to tune it up while only a few inches from the capacitor, but the stray capacitance between me and the antenna detuned it so when I walked away it shifted 20KHz high.

Solved that by remote-adjusting the capacitor using a 6-foot length of plastic electrical conduit as a 'remote' drive.

The result seems to work rather well; 20W of SSB on 28MHz gets me across Europe and into Texas, New Mexico, and the Caribbean.

Playing with antennas is fun!

G6Tanuki · 14th Sep 2023, 7:21 pm

More historic info on loop antennas, from US Military research:

https://apps.dtic.mil/sti/tr/pdf/AD0406463.pdf

Enjoy those Smith Charts!

Bazz4CQJ · 14th Sep 2023, 9:04 pm

Quote:

Originally Posted by G6Tanuki

For me, the 'untuned' loop type antennas [Welbrook/Welgood] with amplifiers always seem a compromise though they work OK for some people.

The effort:reward ratio is quite good for those kinds of loops if used purely for listening.

But of course, if you transmit through them, the effort:reward ratio gets very bad indeed

.

B

Craig Sawyers · 14th Sep 2023, 11:42 pm

The wellgood amplifier and bias T arose because the guy who designed it transmitted into his wellbrook and fried it.

Wellbrook have shut up shop now as a result of the founder retiring. So the wellgood amp is the only well designed and mature show in town now.

Craig

murphyv310 · 15th Sep 2023, 8:46 am

Hi
I've used loops for years. The original was a Wellbrook loop which worked very well till the preamp physically broke! This was then removed and I constructed a simple two transistor balanced amplifier with is crucial for reducing localised noise and giving deep nulls. The amp is heavily biassed to reduce intermodulation effects and now I build them with 2N3688 transistors. My local is so close I can see the antenna from the bedroom window, I literally have no intermodulation effects, harmonics etc. The loop is effective from below 60khz and still gives gain on Band 2 FM but no nulls evident at those frequencies.
I've also built two transmitting loops neither use the small coupling loops as IMHO they reduce efficiency considerably especially on TX. I use a 1:1 balun on the opposite side to the tuning capacitor and get resonance and correct impedance by altering the position of the feed point. Two contacts were initially made on 20 meters using 500mw from a tr(u)SDX on SSB into the Orkney Islands with a signal of 5/9+30 & the UN in Austria with 5/9 the antenna was at 6ft above ground level. I've also made a three turn version for 80 meters which works reasonably well, with considerably less received QRM.
Unfortunately there are a lot of Loop dissenters out there, done properly and often not following the crowd with different ideas and methods will produce incredible results. Amateurs should experiment and not take what's written as gospel, I for one have proved by practical experience that a lot of so called experts can be wrong.
Have a play and get the rewards.

murphyv310 · 15th Sep 2023, 9:22 am

Quote:

Originally Posted by Craig Sawyers

The wellgood amplifier and bias T arose because the guy who designed it transmitted into his wellbrook and fried it.

Wellbrook have shut up shop now as a result of the founder retiring. So the wellgood amp is the only well designed and mature show in town now.

Craig

The original Wellbrook amplifier was made on veroboard, a poor way to construct anything that handles RF. I also believe that it was over priced but that's my personal opinion.

It's easy done transmitting into a loop if you use it with a transceiver and your sequencer is not working etc, I fried my 2N3866's in my home made one by shoving 50 watts up the coax!

David G4EBT · 15th Sep 2023, 11:36 am

Since 2016 I've made several magnetic loop antennas based on Gary Tempest's BVWS Bulletin articles, and have posted threads on the forum about them. The first was a 5 transistor version, then a 4 transistor version, and lastly, a 2 transistor version of what might be termed a Wellgood' clone.

But this thread is simply about whether the size of the loop has any material difference on signal strength, so I'll focus on that.

Gary had a Wellbrook loop which failed and was replaced under warranty, so he had that to use as a comparison. The Wellbrook was 1 metre diameter. Gary experimented with a large rectangular loop made from 15mm copper tube. In 2016, he kindly gifted me an amplifier to evaluate. I too used 15mm copper tube to make a square loop with 2 Metre sides, installed on the outside of my workshop.

In 2019 I made a 2-transistor version of Gary's 'Wellgood' loop clone for which I made a 1 Metre loop of 15mm copper tube. I erected that in the loft of the inside gable end of my brick garage, in the same orientation of the 2 Metre square loop on my workshop. (The 'Wellgood' used ZTX237 transistors, but I used 2N3866s, kindly gifted to me by David, Radio Wrangler). As well as my workshop, I spend time in my garage where my metalworking lathe is situated, so both loops are in regular use.

Both the 2 Metre square loop and the 1 Metre circular loop perform exceedingly well, with no discernible difference in signal strength, though I only used a radio with a magic eye as an indicator, rather than say an 'S' meter.

The main benefit of a magnetic loop antenna is not simply the improved signal strength but the very low noise level. The other obvious benefit is that it can be mounted in a loft, on a balcony, on a garden fence, or at ground level in the garden.

Pic 1: 2 Metre square loop on end of workshop.
Pic 2: Sketch of the layout and orientation of that loop.
Pic 3: 1 Metre circular loop.
Pic 4: 1 Metre loop in garage loft on gable end wall.
Pic 5: Sketch of the circular loop.

Hope that might be of interest.

Footnote:

Gary Tempest's articles on loop antennas published in the BVWS Bulletin are:

'Loopy about Loops' Autumn 2016. Can be viewed/downloaded a this link:
https://www.bvws.org.uk/publications...letin_41_3.pdf

Magnetic Loop Aerials Part 2, Spring 2018:
Covers the Wellbrook, Wellgood, and and the 2-transistor clone of the Wellgood.

'Second repair of Wellbrook ALA1530 Mag Loop Aerial'. Winter 2020.

E93AFAN · 19th Sep 2023, 5:03 pm

Just back from holiday and thank you very much for your replies, David has answered my query succinctly, there would seem little to be gained from changing my existing loop and Wellgood amplifier. As always thank you for your time and patience, it is much appreciated.

Apropos absolutely nothing the BVWS publication in which "Loopy about Loops" appears features the Bush TV22. We didn't have electricity in my village, but one of my relatives lived in Bath and I remember being enthralled watching BBC TV on one of these sets when we visited and seven family members huddled round the tiny screen! My relatives later rented a 14 or 16 inch set when ITV started up in 1955 and the little Bush was consigned to the garage.

Electricity came in 1958, before that a 1920's Lister D "runs on anything slightly volatile" paraffin engine with a 24 volt ex-US army generator supplied night time lighting and some bench machinery power. My older brother begged the TV22 and after replacing the EY51 and fitting a 12 inch tube the set was put in the corner of our parlour without a case and worked just fine.

We used this set right through the early 60's; I remember watching TWTWTW with the gorgeous Millicent Martin and the not so appealing David Frost; until my parents purchased an ex rental 17 inch set and we had the glories of ITV, which my father born in 1893 thought far too racy.............. Happy days.

14th Sep 2023, 12:51 pm	#1
E93AFAN Tetrode Join Date: Mar 2022 Location: Chippenham, Wiltshire, UK. Posts: 53	Loop Aerials - Does Size Matter ? My house is subject of a restrictive covenant in respect of aerials and my local council very critical of anything other than a UHF aerial or small dish, one local amateur was forced to remove his aerials recently. So for many years I used a long wire hidden amongst my garden trees, which was "adequate" but neither high enough or long enough. When a new supermarket opened RFI made reception on medium wave nigh impossible. On this forum I discovered loops and bought myself a 1 metre metal hula hoop to which I have added a preamp. The results are a revelation, I can once more read all the remaining MW local stations as far away as South Somerset, listen to Classic Gold from London at all times, Manx Radio, Caroline and many European and North African stations come alive at dusk. Performance is also improved up to about 30 Mcs, which is the limit of my interest anyway. I have researched the following questions and whilst I feel I should already know the answers, I can't find anything definitive. 1. What impact does the size of the loop have on reception - is bigger better ? 2. If bigger is better at MW, will performance at higher frequencies by adversely affected ? 3. A US forum suggests two side by side loops of the same size are better than one - true ? 4. Some suggest a "traditional" multi turn copper wire frame aerial outperforms a metal loop ? In earlier times I enjoyed MW DX and so as European stations wane I foresee the possibility of some long range finds if my aerial is efficient enough and so if improvements can be made I'm happy to spend time investing in these. As always I'm sorry this is low level stuff to most of you, but I do thank you in anticipation of your views, which are always helpful to me.

14th Sep 2023, 1:07 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,246	Re: Loop Aerials - Does Size Matter ? Larger loops subtend more area and catch more signal energy than smaller ones. Go very large (in terms of frequency) and resonant effects enter the fray. Very good if the resonance is on your wanted frequency. Smaller loops couple less well to free space and their impedance looks more reactive leading to higher Q making tuning more ticklish (and greater losses if transmitting) Unless you're at the upper end of the HF bands or into VHF, then communications aren't much limited by receiver noise. So the small amount of signal power captured by small loops is not a problem. Smaller loops are lower in Z and so more awkward to get low loss transformation to something better suiting amplifiers and input stages. Not much of a problem for receiving. All loops have nice nulls which can be planted on your worst interferer, but if you can't rotate them then you get stuck with null directions. Small loops are easier to rotate. Frame aerials with normal tuning capacitors work quite well and can be fun to play with. Again, expect high Q and touchy tuning. On long wave they can be narrower than the modulated signal you're trying to receive which cuts treble. Plenty to play with. Put up a TV antenna use the feeder as an HF verical with the TV aerial working as a capacity hat! David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

14th Sep 2023, 6:50 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,465	Re: Loop Aerials - Does Size Matter ? For me, the 'untuned' loop type antennas [Welbrook/Welgood] with amplifiers always seem a compromise though they work OK for some people. My dislike of them is based on the idea that they are innately broadband - so they don't really do anything to exclude RF energy at the image frequency [assuming we are talking feeding the output to a superhet receiver] or similarly-superhet-implied +/- image-and-local-oscillator-harmonic frequencies. I like high-Q resonant antennas. They generally don't respond to harmonics, and they have the additional benefit of excluding broadband noise that can also cause intermodulation/mixing in the front-end of the receiver which raises the 'noise floor'. Most historical receiver-tests for intermodulation/overload etc. generally use a couple of frequencies maybe 50KHz apart; they don't really map well into a world of SMPS sharsh, powerline-data, ADSL and plasma-TV emissions where you have potentially hundreds of relatively-low-power carriers spaced only a few KHz apart - and whose aggregate energy can be significant. A tuned loop helps exclude such nonsense. Recently I have been playing around with a DDRR Hula-Hoop antenna, as developed by Northrop in the 1950s for US for military applications. See http://www.orionmicro.com/ant/ddrr/ddrr1.htm and "Hula-Hoop Antennas: A Coming Trend, J. M. Boyer, Electronics, January. 11, 1963" It's a horizontal loop mounted only a few inches above an 'ideally' perfectly conducting groundplane. My version uses 15mm copper microbore heating tube mounted above a cut-open-and-flattened old-fashioned copper immersion-heater tank. I'm using a WWII-era 60+60pF air-spaced variable capacitor to tune it; this thing has around 1/8-inch plate spacing. On 28MHz it tunes-up well. It's really high-Q, initially I was trying to tune it up while only a few inches from the capacitor, but the stray capacitance between me and the antenna detuned it so when I walked away it shifted 20KHz high. Solved that by remote-adjusting the capacitor using a 6-foot length of plastic electrical conduit as a 'remote' drive. The result seems to work rather well; 20W of SSB on 28MHz gets me across Europe and into Texas, New Mexico, and the Caribbean. Playing with antennas is fun! __________________ I played a blank tape at full volume. The mime-artiste who lives next door complained.

14th Sep 2023, 7:21 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,465	Re: Loop Aerials - Does Size Matter ? More historic info on loop antennas, from US Military research: https://apps.dtic.mil/sti/tr/pdf/AD0406463.pdf Enjoy those Smith Charts! __________________ I played a blank tape at full volume. The mime-artiste who lives next door complained.

14th Sep 2023, 11:42 pm	#6
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,875	Re: Loop Aerials - Does Size Matter ? The wellgood amplifier and bias T arose because the guy who designed it transmitted into his wellbrook and fried it. Wellbrook have shut up shop now as a result of the founder retiring. So the wellgood amp is the only well designed and mature show in town now. Craig __________________ Doomed for a certain term to walk the night

15th Sep 2023, 8:46 am	#7
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,388	Re: Loop Aerials - Does Size Matter ? Hi I've used loops for years. The original was a Wellbrook loop which worked very well till the preamp physically broke! This was then removed and I constructed a simple two transistor balanced amplifier with is crucial for reducing localised noise and giving deep nulls. The amp is heavily biassed to reduce intermodulation effects and now I build them with 2N3688 transistors. My local is so close I can see the antenna from the bedroom window, I literally have no intermodulation effects, harmonics etc. The loop is effective from below 60khz and still gives gain on Band 2 FM but no nulls evident at those frequencies. I've also built two transmitting loops neither use the small coupling loops as IMHO they reduce efficiency considerably especially on TX. I use a 1:1 balun on the opposite side to the tuning capacitor and get resonance and correct impedance by altering the position of the feed point. Two contacts were initially made on 20 meters using 500mw from a tr(u)SDX on SSB into the Orkney Islands with a signal of 5/9+30 & the UN in Austria with 5/9 the antenna was at 6ft above ground level. I've also made a three turn version for 80 meters which works reasonably well, with considerably less received QRM. Unfortunately there are a lot of Loop dissenters out there, done properly and often not following the crowd with different ideas and methods will produce incredible results. Amateurs should experiment and not take what's written as gospel, I for one have proved by practical experience that a lot of so called experts can be wrong. Have a play and get the rewards. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

15th Sep 2023, 11:36 am	#9
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,577	Re: Loop Aerials - Does Size Matter ? Since 2016 I've made several magnetic loop antennas based on Gary Tempest's BVWS Bulletin articles, and have posted threads on the forum about them. The first was a 5 transistor version, then a 4 transistor version, and lastly, a 2 transistor version of what might be termed a Wellgood' clone. But this thread is simply about whether the size of the loop has any material difference on signal strength, so I'll focus on that. Gary had a Wellbrook loop which failed and was replaced under warranty, so he had that to use as a comparison. The Wellbrook was 1 metre diameter. Gary experimented with a large rectangular loop made from 15mm copper tube. In 2016, he kindly gifted me an amplifier to evaluate. I too used 15mm copper tube to make a square loop with 2 Metre sides, installed on the outside of my workshop. In 2019 I made a 2-transistor version of Gary's 'Wellgood' loop clone for which I made a 1 Metre loop of 15mm copper tube. I erected that in the loft of the inside gable end of my brick garage, in the same orientation of the 2 Metre square loop on my workshop. (The 'Wellgood' used ZTX237 transistors, but I used 2N3866s, kindly gifted to me by David, Radio Wrangler). As well as my workshop, I spend time in my garage where my metalworking lathe is situated, so both loops are in regular use. Both the 2 Metre square loop and the 1 Metre circular loop perform exceedingly well, with no discernible difference in signal strength, though I only used a radio with a magic eye as an indicator, rather than say an 'S' meter. The main benefit of a magnetic loop antenna is not simply the improved signal strength but the very low noise level. The other obvious benefit is that it can be mounted in a loft, on a balcony, on a garden fence, or at ground level in the garden. Pic 1: 2 Metre square loop on end of workshop. Pic 2: Sketch of the layout and orientation of that loop. Pic 3: 1 Metre circular loop. Pic 4: 1 Metre loop in garage loft on gable end wall. Pic 5: Sketch of the circular loop. Hope that might be of interest. Footnote: Gary Tempest's articles on loop antennas published in the BVWS Bulletin are: 'Loopy about Loops' Autumn 2016. Can be viewed/downloaded a this link: https://www.bvws.org.uk/publications...letin_41_3.pdf Magnetic Loop Aerials Part 2, Spring 2018: Covers the Wellbrook, Wellgood, and and the 2-transistor clone of the Wellgood. 'Second repair of Wellbrook ALA1530 Mag Loop Aerial'. Winter 2020. Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.

19th Sep 2023, 5:03 pm	#10
E93AFAN Tetrode Join Date: Mar 2022 Location: Chippenham, Wiltshire, UK. Posts: 53	Re: Loop Aerials - Does Size Matter ? Just back from holiday and thank you very much for your replies, David has answered my query succinctly, there would seem little to be gained from changing my existing loop and Wellgood amplifier. As always thank you for your time and patience, it is much appreciated. Apropos absolutely nothing the BVWS publication in which "Loopy about Loops" appears features the Bush TV22. We didn't have electricity in my village, but one of my relatives lived in Bath and I remember being enthralled watching BBC TV on one of these sets when we visited and seven family members huddled round the tiny screen! My relatives later rented a 14 or 16 inch set when ITV started up in 1955 and the little Bush was consigned to the garage. Electricity came in 1958, before that a 1920's Lister D "runs on anything slightly volatile" paraffin engine with a 24 volt ex-US army generator supplied night time lighting and some bench machinery power. My older brother begged the TV22 and after replacing the EY51 and fitting a 12 inch tube the set was put in the corner of our parlour without a case and worked just fine. We used this set right through the early 60's; I remember watching TWTWTW with the gorgeous Millicent Martin and the not so appealing David Frost; until my parents purchased an ex rental 17 inch set and we had the glories of ITV, which my father born in 1893 thought far too racy.............. Happy days.