Aerials and early circuits - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Skywave · 24th Jun 2016, 12:02 pm

Quote:

Originally Posted by greenstar

https://www.youtube.com/watch?v=si3VV1Ba0vU
Meanwhile I found this - I have seen antenna loading coils used with very early sets. I guess this is the same as the ATU.

"Same as an ATU" (or AMU, for those who prefer that abbreviation): strictly speaking, not quite. A loading coil adds inductance to an electrically-short L.W. aerial so that the electrical length of the aerial plus loading coil produces an electrical quarter-wave length of wire at the aerial terminal of the set. A quarter-wave is desirable since this will be resonant (with a good earth connection). An ATU / AMU will also have a coil (usually with user-selectable tappings) but will also have a variable capacitor - and usually two. That way, a wider range of impedances (that the aerial + earth presents to the radio as the received freq. is changed), that can thus be accommodated. There are many configurations that are possible with one coil and two variable capacitors.

Al.

greenstar · 24th Jun 2016, 1:49 pm

Thanks, Al, this is starting to make sense.
Dave Schmarder describes a lovely ATU: http://www.makearadio.com/misc-stuff/antennatuner.php
What I like about the Youtube antenna loader is, it's very basic, cheap, old tech just as in the 20's, and makes a big difference. I also like the original DeMorgan design he shows, even simpler. I guess it's between something that works and something that pushes the boundaries. I always thought an ATU for a crystal set was for the extreme performance people - but it looks like a simple thing can also work well.

Skywave · 24th Jun 2016, 2:06 pm

The schematic for that tuner, as drawn, has one serious defect: it does not show any connection to the receiver!

Al.

ms660 · 24th Jun 2016, 2:12 pm

It's inductively coupled when placed next to a receiver according to the text, that should have been shown on the schematic as well maybe.

Lawrence.

Skywave · 27th Jun 2016, 10:57 pm

"Inductively coupled": I thought that might be the case.
"Should have been shown on the schematic": quite.

Al.

24th Jun 2016, 1:49 pm	#22
greenstar Octode Join Date: Jul 2011 Location: Leicester, Leics. UK. Posts: 1,684	Re: Aerials and early circuits Thanks, Al, this is starting to make sense. Dave Schmarder describes a lovely ATU: http://www.makearadio.com/misc-stuff/antennatuner.php What I like about the Youtube antenna loader is, it's very basic, cheap, old tech just as in the 20's, and makes a big difference. I also like the original DeMorgan design he shows, even simpler. I guess it's between something that works and something that pushes the boundaries. I always thought an ATU for a crystal set was for the extreme performance people - but it looks like a simple thing can also work well.

24th Jun 2016, 2:06 pm	#23
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Aerials and early circuits The schematic for that tuner, as drawn, has one serious defect: it does not show any connection to the receiver! Al.

24th Jun 2016, 2:12 pm	#24
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Aerials and early circuits It's inductively coupled when placed next to a receiver according to the text, that should have been shown on the schematic as well maybe. Lawrence.

27th Jun 2016, 10:57 pm	#25
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Aerials and early circuits "Inductively coupled": I thought that might be the case. "Should have been shown on the schematic": quite. Al.