Active Ferrite Aerial Project

[Geaney]

The gadget now works pretty well. For anyone interested in seeing the final setup, it's here:

https://www.youtube.com/watch?v=ytuNa79Gep8


I still have some cosmetic work to do - and will replace the coarse tuning pot, etc.

I'm very happy with the performance of this little gadget so it will definitely come in handy.

Cheers, John

[pwdrive]

I saw the video, excellent improvement on the weak signal, proper job.

Lawrence.

[Geaney]

The electronics must be in another discussion thread? I could give you a 10-turn pot, and for that matter, a ceramic switch too. Lots of them in the junk box.

Thanks Alan, right now I've replaced the cheapo pot with a decent one and things are much better. It's a lot easier to tune it when using my PYE P53 as there is greater travel in the radio dial versus the little Radialva.

I did not mention the electronics in any great detail as the project is from a magazine article - EPE September 2000 - and one of of our colleagues on this forum kindly etched a PCB for me so all I had to do was populate the board. I'll dig out a link to the article and post it.
Cheers, John

[AlanBeckett]

It's a lot easier to tune it when using my PYE P53 as there is greater travel in the radio dial versus the little Radialva.

Rightly so.
You'll advance to a 39J/H one of these days

Alan

[Radio Fixer]

And now for a Magnetic loop John: http://www.wellbrook.uk.com/

Can apparently connect the coax output to the aerial and earth connections of a domestic radio, or even devise a matching transformer (50 to 300 Ohms say).

Needs someone to try this ...

But well done with the ordinary loop project.

Gary

[pwdrive]

I spoke to Andy Ikin (Wellbrook) a few years ago, I asked if impedance matching would be required between the loops output cable and the typical input impedance of my comms receivers which is around 400 ohms, he thought that impedance matching between the loop and receiver wouldn't make a great deal of difference in the reception stakes.

Lawrence.

[Skywave]

If a source of voltage has an impedance of 50 Ω and is connected to a load of 400 Ω, the reflection coefficient (RC) = (400 - 50) ÷ (400 + 50) = 0.778.
The resultant return loss (RL) = 20.log(RC) = 20 X 0.778 = 2.2 dB approx.

So on that basis, I would say that the effect due to the mis-match is not ignorable, but, on the other hand, is not likely to cause a significant problem in practice. Personally, I would choose a broadband impedance matching transformer.

Al.

[Radio Fixer]

All calcs. for you at the moment Al.

I never came across reflection coefficient, is that something that Hams get into when dealing with aerial systems?

Return loss I am familiar with or was as its common on cable systems as well. In the mists of time though ...must be 40 years ago that I made those sort of measurements. Wow! time flies by.

thanks Gary

[Radio Fixer]

I am tempted by one of those Mag loops ... early Birthday present to myself.

Could start off with it on the window sill in the Den, as shown on one of the Web site pics and then maybe go for outside mounting later.

Yes! I should try making one myself and messing about but always short of time and it looks like a lot of development has gone into the item. At the moment I am without even a decent long wire after new UPVC windows being fitted.

Gary

[Skywave]

At the moment I am without even a decent long wire after new UPVC windows being fitted.

O.K., that bit I appreciate. But do you have an external TV aerial with its downlead, outside the house, and coming through a hole drilled in the wall? If so, then perhaps you could get permission to drill another one to feed in the downlead from a 'longwire' aerial.

Al.