Reddit mentions of Eton Corp. NGAN200 Grundig Indoor Antenna

I'm going to focus on AM broadcasting in my reply. I'm not going to go into the whole groundwave/skywave thing, since others are going to address that. But, this could serve to be a very interesting introduction to AM DXing.

AM broadcast stations, during the day, operate differently than they do at night.

https://www.fcc.gov/media/radio/am-stations-at-night

TL;DR, Many AM broadcast stations DROP their power significantly at nighttime or cease operations, so they don't interfere with other AM broadcasters.

So, an AM station like WABC out of NYC broadcasts at 50kw daytime and nighttime.
WABC-AM

HOWEVER, same city, WNYC (public radio) transmits at 10kw during the day, but at 1kw at night.
WNYC-AM

Now, for the cool part... I went to college in Indiana. During the night, I could hear 770 WABC out of NYC. So, I could listen to Yankee games. So, that leads me to...

Something really fun to do at night is AM DXing, especially during winter. You don't need much. A "solid" sort of portable AM radio, like a portable SW receiver that has a ferrite core. A passive AM antenna.

You don't even connect the antenna to the radio. You just put the two of them next to each other, and you just tune the antenna to create nulls in different directions to pull-out AM stations that you want to hear.

Anyway, here is a URL to get you started in AM DXing if I have piqued your interest: http://www.amdxing.com/

It's quite possible that you're overloading the front end when you clip it directly to the antenna. Placing the antenna wire near the radio creates an inductive coupling, similar to how one of these works for the AM broadcast band.

It's fantastic with this loop.

>would a ferrite loop work at all inside a 22 gauge steel box,

Not well at all, no.

>is there a standard port I could add to the cabinet to suport an external removable AM antenna,

Use whatever connector you have lying around that's easy to work with. It doesn't matter very much. 1/8" audio jacks would be good. You could probably repurpose an antenna for a Countycomm GP-5.

Or maybe something like this:

https://www.amazon.com/Eton-NGAN200-Grundig-Indoor-Antenna/dp/B001PNNXGO

https://www.amazon.com/Eton-NGAN200-Grundig-Indoor-Antenna/dp/B001PNNXGO
For low power, these RX mag loops work nicely for transmitting. I use one when demonstrating radio to young'ins at the museum.