Mag loop aerial for the Den

[Radio Fixer]

Well you kicked it off Trevor, so really a great thank you for that. Got me started as I had been working in this Den for some time with just a length of wire for an aerial; pretty useless compared to the loop.

Watch this space as I'm thinking of buying more tube, say two lengths and building another complete with a mount and swapping it for the Wellbrook. It would be on the same 50 + ft of coax. Say 1m square, I have plenty of soldering elbows. The Wellbrook needs to come down anyway.

Gary

[pwdrive]

Gary, out of interest is your Wellbrook on a rotator?

Lawrence.

[Murphyv310]

Hi.
I use an Armstrong rotator, very nearly 62 years old and only recently has it been unreliable.

[ppppenguin]

Trevor, you forgot the smiley

[Radio Fixer]

Yes! it is on a rotator Lawrence.  Bought NOS for a very reasonable price.  I find for MW and LW it doesn't make a lot of difference into the HMV 650.  Its got a lot of gain and the AVC just takes care of it.  On a 5 valve Supie (AC97) you would be most disappointed with the Wellbrook (WB) and there the rotator does something.  With the loop facing N it is listenable at not great quality but if the rotator is used you can virtually get a null of the signal.   N just happens to be where the new window loop faces and I knew that was good as I had the WB on the window sill there when I started.

Just been checking the WB out before I take it down (a week or so and try a Home Brew loop) and check the WB to the 650 on a short coax.  If its as good as when I first got it should fold the 'eye' valve right back on itself.  Hard to think its coax loss as looked that up and was given as < 1/2 dB / 100 ft at 1 mHz.  Checked all the connections, no shorts and measures about 4 Ohms with a shorting plug on one end.  But to me it must be OK else it wouldn't get power and give any signal.

Here is how things are at the moment.

   

This pic is the 650 and here Trevor's   transformer makes not a lot of difference.

   

This one is obviously the 97, I guess as the gain is so low it does make a slight improvement but nowhere near to what it did on the window loop.


Gary

[boater sam]

Most of this thread is way over my head. The ferrite in the loop would seem to serve little or no purpose unless it is for coupling but then it seems so unnecessary . Found an article in Practical Wireless for frame aerials and amplifiers to give a balanced input, April 1973. has anyone tried this?
Sam.

[Murphyv310]

Most of this thread is way over my head. The ferrite in the loop would seem to serve little or no purpose unless it is for coupling but then it seems so unnecessary .  Found an article in Practical Wireless for frame aerials and amplifiers to give a balanced input,  April 1973. has anyone tried this?
Sam.

Hi Sam.
Now that's an article I'd like to see. Problem is I don't have that particular issue. Do you know if its available somewhere online?

[boater sam]

The full archive of PW and many more mags is available at http://www.americanradiohistory.com
A wonderful site, lots of patient scanning to produce it.

[pwdrive]

It's in here:

http://www.americanradiohistory.com/Arch...973-04.pdf

Nothing special, balanced tuned loop, unbalanced output, uses FET's

Lawrence.

[Radio Fixer]

Sam if you wander through the maths here :  http://sidstation.loudet.org/antenna-theory-en.xhtml  you will see that the magnetic induction of the loop is multiplied by the relative permeability  Ur of the ferrite.  This of course can be large and is why ferrite rods works so well.

How you would fill a loop with the stuff though is hard to imagine. I would think that ferrites are made under lots of heat and pressure. Hence Trevor's speculation that the ferrite is only at the ends and may be a coupling mechanism (or marketing).

Gary