This thread has drifted from the original question, of 'How effective is an earth in reducing noise on AM?' To which my answer would be 'not very'.
Furthermore, in my experience, whilst putting up longer wire aerials if space permits may marginally increase the signal strength, it has the undesirable effect of increasing the background noise level too. What are often termed 'long wire antennas' are in reality 'short wire' antennas. My understanding of a long wire antenna is that it is at least 1.5 wavelengths long, so on 200 Metres, it would need to be 300 Metres long.
About the best that most of us with suburban gardens could manage is 20 Metres (in my case exactly that). Height wise, most of us would struggle to get a wire antenna up more than 5 Metres, that's 1/40th of a wavelength long. 'Back in the day', that's what most householders managed with, but of course, they were not beset with the proliferation of noise levels that exists today.
In my view - and I'm not alone - for low noise and good signal strength, magnetic loop antennas are far superior to wire antennas of any length. I guess that's why Wellbrook are still in business selling their own magnetic loop version at eye watering prices.
All lot of experimentation and construction of 'home-brew' amplified loop receiving antennas has been undertaken since 2016 by Gary Tempest, who will be well known to BVWS members. The three versions of Gary's designs that I've built worked first time and I'd commend them to anyone who wishes to receive MW stations at good strength with minimum background noise. (It should be said at the outset that they're they connected to the aerial and earth sockets of AC only radios and not designed for live chassis sets such as the ubiquitous Bush DAC90A).
Gary Tempest originally bought a Wellbrook Loop and in 2016 but the Amp failed while under guarantee, so Wellbrook replaced it. It had lasted until a few weeks ago then that too went low gain with gritty noise, so rather than pay out for a replacement Gary built a new Amp. He reported that performance of his latest version into an HMV 650 was 'back to stunning again - crystal clear R4 and RTE better than before. MW is excellent on many stations and SW better than he can remember it, not that there is anything of much interest on the bands'.
BVWS members will know that Gary wrote two articles on building Mag Loops in the BVWS Bulletin. For his most recent amp he went for the simplest design with least components that he could string together using the 'Manhattan' construction technique to replace the second failed Wellbrook one, using the same power and signal feed (12V at 100mA). The power is spread over 4 transistors (Hfe: Tr1/2 >130, Tr3/4 >80 and matched) rather than just two in the WellBrook.
He was originally inspired to investigate and experiment with magnetic loop antennas by the home-brew design by a Dutch radio amateur, PA1M:
https://www.pa1m.nl/simple-active-receive-loop/
Details of Gary's recent 4 Transistor version can be found at this link:
https://golbornevintageradio.co.uk/f...d.php?tid=8065
His 2016 five transistor version, one of which he gifted to me is 2016 (which is still performing excellently in my garden workshop) is here:
https://golbornevintageradio.co.uk/f...d.php?tid=5944
I constructed one myself for indoor use and wrote it up in this thread:
https://www.vintage-radio.net/forum/...t=Loop+Antenna
Gary’s 2 transistor version based on the Dr George Smart ‘Wellgood’ 'Welbrook clone' article can be found here:
https://golbornevintageradio.co.uk/f....php?aid=18052
In Spring 2019 I built that 2-transistor version and posted details in a now closed thread entitled 'Clone of 'Wellgood' Magnetic Loop Receiving Aerial'. at this link:
https://www.vintage-radio.net/forum/...d.php?t=156263
I installed that loop in my brick garage loft. I spend a lot of time in the garage where my metalworking lathe is sited and where I make larger woodworking projects, so the loop is in use most days, connected to one or another restored valve, which I change every few weeks to give them an airing.
At Dr George Smart's website there are very clear instructions and diagrams on how to wind the little binocular transformer, and I had no problem in doing that (or with the little transformers in the other designs):
https://www.george-smart.co.uk/projects/wellgood_loop/
(It will be evident from George Smart's investigations that the Wellbrook Amp is built not on a PCB, but on a piece of stripboard, which only became apparent when he X-Rayed the Wellbrook).
In each of Gary's designs he used the 'Manhattan' construction technique with little 'tiles' of PCB material stuck to a piece of PCB laminate to obviate the need for a PCB, but for repeatability, I designed a PCB using Gary's layout. In each case, the diagrams and photos make it clear how to construct the amplifier. Minimal expense and effort for maximum enjoyment - Id rather be indoors soldering, than up a ladder outdoors faffing about with wire antennas to no good effect!
A nice winter project.