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Mag Loop and other info

David Cutter
 

This site may help a few builders.  I just came across it an hour ago and have had only a cursory look. It contains a lot of useful info on other topics as well.  You need to scroll down to section 7.  https://www.qrz.com/db/k4hkx


Just for amusement I built an aluminium strip loop using a 12ft x 4ft 20swg aluminium sheet forming a tube 4ft long by ~4ft diameter.  Tuning accomplished with several interleaving vanes 4ft long by 4" wide attached to the open ends of the tube. It was a monster.  Eventually I got it to work in a contest on 20m and it had a 48dB front to back ratio to null out the noisiest of Mediterranean and Russian mega-stations.  The pick up loop started life as 4ft square 20swg aluminium sheet to form a tube 4ft long by ~1ft diameter.   Then I moved house and scrapped it and I'm still using bits of aluminium from it 30 years later. Crazy days, fun and educational on several levels, ie learn by doing. 

73 David G3UNA


Re: Help making a decision

Tom Crosbie G6PZZ
 

Decision made, order placed! Gone for STD rather than VLF

Thanks all.

Tom G6PZZ

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 16 January 2021 13:04
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Help making a decision

 

Tom,

If you are using the loop antenna inside you will not need the extra gain of the base unit.

The extra gain is really only useful for an inefficient loop or insensitive receivers. I know of one customer who uses one with  a 1930s regenerative receiver with remarkable results!

Regards,

Chris


Re: Covid..and making phased loop antenna array..

Simon
 

Hi

Its a possibility..but issue is finding space in the nw/se direction..
Sw/ne not a problem..( long( ish.) very thin front garden ..


Simon


Re: Covid..and making phased loop antenna array..

Martin - G8JNJ
 

On Sun, Jan 17, 2021 at 03:03 PM, Simon wrote:
looks like the sla is not suitable for my gth..space and not in open.
the loops will have to do
Hi Simon,

As they only have one central support pole and the elements are made from wire, I'd suggest that it could perhaps be easier to conceal by incorporating it as a garden 'feature'.

In December I saw some LED illuminated 'skeleton' Christmas trees that looked very similar.

Regards,

Martin


Re: Covid..and making phased loop antenna array..

Simon
 

Hi Chris

Thank you..

Simon


Re: Covid..and making phased loop antenna array..

Chris Moulding
 

Tomorrow evening (I don't have time this evening or tomorrow) I'll use the 4NEC2 antenna modelling tool to model two cardioid loops in end fire and broadside configurations.

I'll set it up so that users can easily change loop spacings, loop height and loop size.

I'll report back tomorrow evening and add the 4NEC2 files to the cardioid loop web page.

Regards,

Chris


Re: Covid..and making phased loop antenna array..

Simon
 

Hi Chris

I think that may be a good guess about copying..but a patent should have covered that?

Ok then..let’s assume 110r it is..
Let’s assume loop can be anything, so mine will be copper tube as self supporting.( with plastic separator at top and 110r.) and have lots of.

Is there on your modelling/ testing an optional height? C and s show it low to gnd.

Any luck on broadside spacing..come up here with nothing other than Martin..ie min 14m..
Modelling??

May well also alter my endfire array to use cardioid loops..again nw direction..makes them smaller and more directional, though will lose nw se choice..but would like to try broadside first

Also (SORRY.) anything to gain with increasing cardioid loop dia? Say 1.5m?

Thank you Simon


Re: Covid..and making phased loop antenna array..

Chris Moulding
 

From the information I have on the C & S loop antennas they use a two loop design to reduce the inductance so that it resonates with the capacitance across the loop ends above 30 MHz.

An article in the RSGB RadCom Technical Topics (I do miss that!) by one of the C & S engineers who was also a radio amateur stated that the resistance at the top of the loop was 110 ohms.

This ties in with my antenna modelling and prototype antenna for best front to back ratio.

I don't know where the idea of it being an inductance came from. Maybe when it was first launched to avoid copying of the design?

Regards,

Chris


Re: Covid..and making phased loop antenna array..

Simon
 

Hi David

looks like the sla is not suitable for my gth..space and not in open.
the loops will have to do...until  we eventually move.

preamps i use have good imd and sensitivity..looking forward to trying out a pair of Chris’s new ones when ready..

i have the cardioid loop now working..altered input matching to prreamps.

would love to get more info on the c and s cardioid loop.
it must work differently to Chris  design due to they state needs low inductance loop ( and shows 2 parallel loops to lower the inductance)..and Chris design does not.
seems to state they use inductance at top and not a resistor, though that is vague.

Mag loop Simon 


Re: Covid..and making phased loop antenna array..

David Cutter
 

Simon

Re sensitivity / signal strength v f/b ratio: if you have a good amplifier then sensitivity might not be an issue.  I would rather reduce strength of other signals getting in to increase signal to noise ratio.  It's also useful to prevent overload in the amplifier chain, though Chris's amplifiers are good in this respect. 

David G3UNA

On 16 January 2021 at 21:48 Simon <ohhellnotagain@...> wrote:

Hi Chris and Martin  and anyone else reading

i can get 14m separation on broadside..for 2..( at a push!)

i have now mounted the cardioid loop up at 3m to base, ( was 1.5m) so now sense aerial is longer..this has  ( will recheck) reduced the nulls on the sides, but increased the back to front ratio..b to f about 15db on 160m..( was 12.)
i would rather have the greater nulls broadside to the loop, but if the forward gain is better at 3m then that is a winner..( to be checked.)

i notice the c and s design uses a low inductance loop.( 3 parallel ali bars welded together.) it also mentions using inductance at top rather than resistance..

any thoughts on this??

looking good now..just need 160 to open to usa..


As is now..facing sw. yes pic on side..
Simon 


Re: Covid..and making phased loop antenna array..

David Cutter
 

It's been around for a few years now and has undergone a little massaging. Need to take care of the mechanics of stringing wires and cords in the air but I'm told they work well, if quite expensive. Sensitive to sloping ground and reflections from nearby objects.

David G3UNA

On 16 January 2021 at 23:03 Simon <ohhellnotagain@gmail.com> wrote:


Hi Martin

Shared apex loop looks interesting..

Simon


Re: Covid..and making phased loop antenna array..

Simon
 

Hi Martin

Shared apex loop looks interesting..

Simon


Re: Covid..and making phased loop antenna array..

Simon
 

Hi Chris and Martin  and anyone else reading

i can get 14m separation on broadside..for 2..( at a push!)

i have now mounted the cardioid loop up at 3m to base, ( was 1.5m) so now sense aerial is longer..this has  ( will recheck) reduced the nulls on the sides, but increased the back to front ratio..b to f about 15db on 160m..( was 12.)
i would rather have the greater nulls broadside to the loop, but if the forward gain is better at 3m then that is a winner..( to be checked.)

i notice the c and s design uses a low inductance loop.( 3 parallel ali bars welded together.) it also mentions using inductance at top rather than resistance..

any thoughts on this??

looking good now..just need 160 to open to usa..


As is now..facing sw. yes pic on side..
Simon 


Re: Covid..and making phased loop antenna array..

Simon
 

Hi Martin..yep i agree about bigger.. but no chance here..hense the loop experiments..

Simon


Re: Covid..and making phased loop antenna array..

Simon
 

Ok

Added 16:1 from loop to amp..

Big difference..now noise is s7 from s0ish..TALKING aiming at smpsu noise local to me..not general noise floor!
Will try 9:1 and 25:1..just to see..

Back to front about circa 12db..loop is abit egg shaped due to gravity and bodge job on fibreglass pole plus short sense antenna?
Off sides very good nulls still..

1m dia loop. Bigger needed?? 160m optimised.

Will also try loop up higher once get it more circular and not eggy..lol..this to lengthen sense wire. Say 3m?

Ok looking better now..should have worked this out earlier..i bad..

This is using my preamp..not ccw..( which is currently in use.) maybe my preamp has lower input impedance, but i think not.

Need to improve back to front ratio if possible..

Endfire cardioid loops now look a good idea! Facing nw..

Simon

Sorry if boring people with all this..but hope others gain something from my experimentations..

On 16 Jan 2021, at 15:40, Simon via groups.io <ohhellnotagain=gmail.com@groups.io> wrote:

Hmmm

Thanks for replying..

Ok using your loop amp i have..how would you suggest getting more output from amp..?

Issue i have is virtually nothing out..

I maybe misunderstanding how it is working, but if your loop amp wants to see very low inductance ( current amp.) then the cardioid loop is showing high..thus poor performance.input mismatch..hence why when using my big quad loops changed input transformer windings to gain much better performance.

( ie normal loop aimed at local noise a good s7-9.. cardioid loop just hear it in noise..)

I cant imagine i have made the loop wrong..its just a 1m dia thin copper tube with 110r at top..( no hula hoop to hand!) with 1.5m of wire from one side of preamp input to gnd via copper earth stake ( good sodden clay gnd.)
Wire to gnd too short??

Simon ..









Re: Covid..and making phased loop antenna array..

Martin - G8JNJ
 

On Sat, Jan 16, 2021 at 02:05 PM, Simon wrote:
Thank you..! I found nothing regarding spacing on net..have looked hard too..
Plenty on using them inline but not broadside..
The original C&S data is a bit vague, but for a four element end-fire array they suggest 7m spacing between loops, and for broadside it's about twice that.

If you want better LF band sensitivity then you probably need a bigger wire array, something like a Shared Apex Array, Flag or Pennant, which is what the serious LF band DX'ers tend to use.

The SAL is an interesting concept and they have their own IO group https://groups.io/g/sharedapexloop/messages

Regards,

Martin


Re: Covid..and making phased loop antenna array..

Simon
 

Hmmm

Thanks for replying..

Ok using your loop amp i have..how would you suggest getting more output from amp..?

Issue i have is virtually nothing out..

I maybe misunderstanding how it is working, but if your loop amp wants to see very low inductance ( current amp.) then the cardioid loop is showing high..thus poor performance.input mismatch..hence why when using my big quad loops changed input transformer windings to gain much better performance.

( ie normal loop aimed at local noise a good s7-9.. cardioid loop just hear it in noise..)

I cant imagine i have made the loop wrong..its just a 1m dia thin copper tube with 110r at top..( no hula hoop to hand!) with 1.5m of wire from one side of preamp input to gnd via copper earth stake ( good sodden clay gnd.)
Wire to gnd too short??

Simon ..


Re: Help making a decision

Simon
 

The idea ( again Chris may say otherwise, but think correct here.)
Is to get the greatest area in the loop,BUT with the minimum amount of inductance.
This means for a single loop the most efficient is a circle..inductance can also be lowered by using tubing not wire..

Simon


Re: Covid..and making phased loop antenna array..

Chris Moulding
 

I think that you are going in the wrong direction with a 16:1 transformer.

With a cardioid loop the amplifier will "see" the 110 ohm resistor plus the loop inductance.

Regards,

Chris


Re: Covid..and making phased loop antenna array..

Simon
 

Oh
Didnt see your reply..

Thank you..! I found nothing regarding spacing on net..have looked hard too..
Plenty on using them inline but not broadside..

Any thoughts upon min sense ( wire to gnd ) length? ( cardioid loop.)

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