The magnetic loop

 

This is the mag loop  that has been  given by a ham radio operator, who designed it 3 years  ago and used not so often unless the weather was  good for outdoor reception .

In the start  i will  show several close up pictures of the so interesting   loop which is actually a Faraday loop.

The loop has been sent with all the parts packed in foam plastics to separate between.

The main loop has a circumference of ca 2 m and the secondary inductive loop is ca 40 cm and matches to the theory of Faraday loops This theory requires the secondary loop (Faraday loop ) to be the 1/5th of the main loop . It seems that the  supporting tube is raltively smaller than the required making the  loop in oval form but that really didn't matter  as its job is really very good as far as it meets its specifications.
 

The above picture shows a close up of the small inductive  Faraday loop. As you many see the joints of the  loop  made from RG58   cable are in reverse in order for the loop to work properly . What is not shown clearly here  is that also on the top of the sec loop there is also another cut area from the shield asnd protected with insulating tape.

The guy did a great job to make this design with nice plastic material for the axis including 'hratches' as we call the benders on the top of the loop .

The main cable is LMR400 as the maker of he loop advised me  with ca 2 m of length .

The above  picture shows the  capacitor base which is a  muλti-turn double  cap with a switch on the left upper part.

And this picture shows the base for the RG connector including a  banana socket should the base be used for uses other than this loop . I used it once with the 1 m square loop. 

And this is the last picture of the  mag loop showing the 'nippel' adaptor  system (fem to fem adaptor /bridge with two male plugs  )  for connecting  to portable shortwave radios thru the 3.9 mm plug.

After this  presentation  i  will notice my observations testing with several radios.

Range has been measured to  be between  8900- 29000 kHz for the fist capacitor &  5350-10100 KHz with the second (approximate frequencies ±150 kHz). Notice that there is an overlapped  band range.

Bandwidths  vary and here are some examples:

For 16 MHZ the range  is about 100 kHz

For 10 MHZ  is at 40 kHZ

For 8.9 MHz is below 30 kHz ...........using the lone condenser

For 8.2 mHz  is abt 200 kHz

For 6.8mHz  nearly same  (200 kHz )

For 5.6 MHZ about 50 kHz and less .............using both condensers

IN the overlapped band  range I prefer to use  the alone  condenser as the  twin condenser setup  offers lower Q (broader bandwidth)

This antenna as loop has the ability  to null out interferences as well as local  noise (QRN) His is inw of the reasons  i asked the antenna  from the radio amateur. The date i made this test there was not any significant QRN as for example 3 weeks  before , when a local machine (?) caused a  S7 noise across all  the bands (as tested with R75 ) that could not fully be nulled  out.

Still  this little  QRN could be  nulled out within 10 degs of turning the loop This has been  tested with 1102 and 1103 directly connected via the cable   My other 'cheap'  small radios  required a wire and female 3.5mm socket configuration to connect the one end to the ground and the other end to the antenna.Also a audio splitter  is required to separate the ground for the earphone otherwise no audio could be heard!

In contrast  to what i have been  noticed the loop can be used also inductively with small radios:
1. with the radio's antenna to inductively couple over the loop.

2. with a as thin as possible wire over the one part of the  big loop that can be then connected to the radio's antenna.This was my first on older times and the last experiment these days with it. And seems  to produce very good results .

This idea on the older times didn't work , but if a radio was connected  to the loop the above setup worked properly for remain radios. (all other radios that dont have plug socket ). I don't know if something happened to the cable but the loop  seems operating properly  .

The recent times the  loop was used (last and this year ) seems to work OK even a radio is not connected to it. The video below shows a demo of this inductive coupling tough that time the  antenna  was connected into the DE1103 radio

Verdict : 9/10 very good in its operation.

The only i don't know is to  which wire length this design  equals .The older times  i had the  idea  to redesign this antenna to include lower frequencies. My interest is mainly  between 4.5-15 MHz  a good idea is to double  the dimensions of this loop. The guy (radio amateur ) counter-proposed me to use a 3x1,5 mm cable (the typical cable for electricity connections) of ca 4 m length as loop and use the same capacitor system to tune it. I tested   this idea with the 1 m loop but found no results ....

(NEW )BTW  with kudos  to the designer he added me today  that the idea of the 3x1.5mm2 cable (3 wind looped form )after the making can be inductively coupled to the Faraday loop to be used for lower bands 

the blue texte are the new additions 

Unfortunately the loop was geting elder : the inner part of the Faraday loop has been cut and it was quite time consuming in my life to get it repaired> it can be rqiured either to  get it redesign it again or just repair it. However with the adtition of mthe new SDR itbe not be use this way ..