Opened the box and its just a ferrite ring transformer !!
Read the article on mag loops but haven't given myself enough time to get around the maths. Anyone any idea how much more sensitive a loop constructed on ferrite is compared to not? I'm obviously not going to do that but just wondered.
I want to make a mag loop for the den and have a fixed window pane in the middle, this has sides of roughly 1.2 m so I could mount a construction to blend with that. Initial thought is just wood covered on one side with the aluminum self adhesive tape. But would it be better to make the loop multi turn with copper wire? I have got the transistors and ferrites for the circuit shown in the article first posted by Trevor. Also for the output Xformer I'm thinking of not making it 1:1 as shown but more matching to a radio as per Trevor's construction (6 turn primary say and 40 turns secondary)
. Looking at Trevor's ferrite I would need to buy some larger ones as the circuit devices are very small and I doubt I would get the wire on !
thanks for any thought Gary
Hi Gary, a few thoughts on using a loop around a window frame. My workshop window is 1 by 1.5 mtrs, dbl glazed and has an aluminium sealing section all the way round the glass i.e. a shorted turn. I built a single turn loop using the same 2 transistor cct that Trevor used and tried it up against the window and seemed to work fine, no reduction in signal when the loop is placed against the window. this surprised me a bit, maybe the al. sealing is not continuous. That loop is now in the loft along with the year old Wellbrook which is on a rotator. I have to say the Wellbrook is the best aerial I have, mainly because of its quiet background.
Peter
Hi Guys.
Peter, I wonder how the modified Wellbrook loop compares to your 1 year old genuine Wellbrook? I also wonder what difference a 1 meter loop made from the same diameter alloy tubing as the Wellbrook would compare with their Ferrite/Alloy construction.
Wellbrook themselves can supply a replacement amplifier but it connects just like the mod I've done with the two transistor amp. I just wonder if the Ferrite/Alloy is the real answer.
I'm going to my local engineering shop in the two or three weeks and will ask them to make up a 1.5 meter loop made of alloy tube to try a slightly bigger loop.
This brings me to Gary's post. If you look at the calcs the cross sectional area of the "wire, tubing etc" makes a difference to the signal level so I personally wouldn't use alloy tape. It may work but perhaps not as good as it could.
The 1:1 toroidal transformer is there for two reasons.
1, to add the phase differences between each side of the loop/amp
2, to allow 12v to the amp and couple the RF to the down lead.
A multi-turn loop will be tunable, a 1 meter loop with 7 turns requires a tuning capacitor up to 500pf to cover the MW band, to cover Long Wave satisfactory you need around 20 turns plus the cap. Tunable frame aerials have really good gain but the sharp tuning can be a pain if the aerial isn't close to the radio, they also are not as good as a single turn loop in noisy situations.
Hi Guys, my thought was that the aluminium tape in double glazed windows would act like shorted turn. I was surprised how little effect it had. Maybe the al. tape had much more resistance than the 2.5 sq mm copper of my loop. When the weather improves I could bring down my wellbrook for a direct comparison.
Peter
My intention is to leave the aerial I make in the window, the work bench and display area is close to it so its convenient. I didn't intend to feed the 12V in the manner shown Trevor. I can just have a Walwart plugged in at the back of the bench and supply the power separately. That was what set me thinking of not using the transformer shown but your design which hopefully would have some direct matching to the radio input.
OK, tape not a good idea so how about 15 mm Yorkshire tube and elbows? I hadn't thought of the ali surround inside the dbl glazing Pete so pleased it doesn't affect things adversely.
thanks and soon will have some time to do a little experimenting.
Gary
(20-02-2016, 03:43 PM)Eddystonepete Wrote: [ -> ]Hi Guys, my thought was that the aluminium tape in double glazed windows would act like shorted turn. I was surprised how little effect it had. Maybe the al. tape had much more resistance than the 2.5 sq mm copper of my loop. When the weather improves I could bring down my wellbrook for a direct comparison.
Peter
Hi Peter.
That's going to be a long time then! It's either pouring or freezing cold.
Hi Gary.
A one metre loop will need 3.14 metres of tubing, a good old pi calculation
Well not so Trevor as it would be a square loop, painted white so that its acceptable to SWMBO, of 4 X 1.2m so comes out at 4.8 m. Tube is sold in 3m lengths so two of those but I may have some old in the shed so could cost less
Gary
(20-02-2016, 05:49 PM)Radio Fixer Wrote: [ -> ]Well not so Trevor as it would be a square loop, painted white so that its acceptable to SWMBO, of 4 X 1.2m so comes out at 4.8 m. Tube is sold in 3m lengths so two of those but I may have some old in the shed so could cost less
Gary
Hi.
Copper brake pipe or bundy tubing will do too. I used to make loads of aerials with brake pipe in the good old CB days.
Or 8/10mm Microbore Central Heating Tube?
Alan