Mag loop aerial for the Den

[pwdrive]

My guess is that it shows an undefined distance between the loop head and the receiver/power supply.

Lawrence.

[AlanBeckett]

That's the Co-ax between the Aerial/Amplifier combination and the Power Feed/Signal Pick-off.
It's just a funny way of describing it, at least I think so.

Alan

[Murphyv310]

Hi.
I'm really pleased that the loop you've built Gary is doing the business, so cheaply too, I'm a great believer in homemade stuff it gives a good feeling when it all works as it should.

Regarding the Wellbrook and the ferrite I've no idea how far into the loop it extends. It may only be at the ends but that's conjecture.
The thing about the Wellbrook that made me wonder was when my loop broke away from the original amplifier. there was no visible electrical contact to the alloy loop and I took it as some form of RF coupling via the ferrite. Wellbrooks replacement amplifier to repair the problem I had has two wires you screw to the alloy loop so it must work on the same principles as our little two transistor balanced amplifier we are using. Wellbrook say that their replacement amplifier gives exactly the same performance as the original set up.
So for £90 I decided to make my own and for a couple of quid my old loop works perfectly. So I'm still mystified about the ferrite, it's purpose and whether it's actually there for a reason.

[Radio Fixer]

As Alan said David "That's the Co-ax between the Aerial/Amplifier combination and the Power Feed/Signal Pick-off."  But I choose not to do it that way as the loop wasn't going to be remote from the radio location (down the garden say).  I just feed the power by a couple of 4mm bananas as I had those in the  cupboard.  If you want to feed power by the coax you will need another small project box for those components.

Yes! you are right Trevor its nice to make things rather than buying and it works so well.

I wonder if there is a ferrite mixture you can just pump in... might do a web search but I expect Lawrence will beat me to it

Gary

[pwdrive]

I Googled Wellbrook loop and ferrite the other day, not a lot turned up, as Trev says it might be something to do with coupling the loop to the amplifier, I've seen ferrite used for that with single turn tuned loops, just a toroid slipped over the loop at a low impedance point (opposite the gap) with some turns wound around the toroid for the take off.

Lawrence.

[Radio Fixer]

Or could it be bridging the gap Lawrence? Be fun to try.

Gary

[Radio Fixer]

Tried the loop on a couple of 5 valve (no RF stages) Supies and it transforms those.

One was an Ekco AC97 not renowned for great performance.  Here Trevor's matching transformer was tried and the 'eye' pics show a worthwhile improvement.

   

   

I will make that up into a small box and sort the connectors out so its easy to use on any sets in here.

Gary

[Radio Fixer]

Thinking of a square or rectangular loop it would be easy to join the two with a ferrite rod with some turns around it. Might not work and the performance of the Den loop doesn't really need any improvement (especially with the matching transformer).

Another way I could have made this loop is just to have got some heavy gauge cable and clipped it beneath the window sill and then up one side, and tie wrapped it above the curtain rail, and down the other. But its done and is unobtrusive now its painted flat white.

Gary

[pwdrive]

Goes to show that matching can make a meaningful difference for receivers/antenna, a lot of folks say it doesn't matter for receivers but I've always reckoned it does, when I used to do SWL with a random wire antenna I used a simple L match which made quite a bit of difference to the signal level.

Lawrence.

[Murphyv310]

What a brilliant thread chaps.
I'm really enjoying what we have achieved here.