Does the headphone jack antenna connection work with AM?

[Skrapshak]

Hello everybody!

I am curious. The ATS Mini v4 is advertised as being able to use your headphone cables as an FM antenna, like a Walkman. Can that same connection be used as an AM antenna?

I'm wondering because I have a Sangean ANT-60 antenna reel that has the 3.5mm jack interface. It would be nice to be able to use it, if possible.

Just a curiosity. Thanks!

[G8PTN]

Hi,
On the ATS-Mini V4, the headphone socket is only usable for the FM input as shown in the circuit below by DB9JG.

It should be noted that users have identified interference issues with the implementation in FM mode, due to the PCB tracking arrangement. The recommendation is to remove the capacitor as shown, which disconnects the headphone connection.

#267 (comment)

73, Dave

[G8PTN]

Hi,
There should be negligible effect on the 150kHz 30MHz bands with the capacitor fitted or removed. It is only for the broadcast VHF band.
73, Dave

[DB9JG]

Hi,
The effect on the shortwave path is not very strong.
The reverse-engineered circuit diagram may help explain why.
The MiniRadio V4B now has a removable coaxial cable connection, which provides better shielding against internal ESP32 noise — although it uses a coupling capacitor with a rather unusual value.

There are still some things to improve ... work in progress:-)

[DB9JG]

FYI:

Community driven V4 evolution!

I received feedback from AMNVOLT team and several user reports revealing that there has been a very rapid evolution of versions V4, V4a, and V4b between October 2025 and January 2026, driven by community feedback.

The latest version V4b shows much improved behavior with regard to:

• the Theremin effect, as a small coil has been added at the SMA pin,

• FM interference, thanks to an internal (removable) coaxial cable now used for the headphone FM antenna connection, and

• the internal audio ADC input at IO11, which has now been equipped with an RC low‑pass filter supporting RTTY and CW detection and maybe more as it has a 3kHz cut-off

Apparently, the community’s suggestions have been heard at the far eastern workbenches :-)

How to distinguish V4, V4a, V4b ???

Outside they sadly look the same :-(
A good indicator is inside at the speaker socket:

• V4b = capacitor + resistor at the audio connection
• V4a = a resistor only
• V4 = two empty solder pads

[ghplw]

That certainly explains why I haven't been able to reproduce any of the quality problems people have been having. I would have been very confused If I had opened it up before seeing this.

Confirmed mine has the capacitor + resistor and the coax from the headphone jack. Didn't want to pull off the shield but as I haven't been able to reproduce the theremin effect and I have the other things I'm assuming it's under there.

[DB9JG]

Some additional information about V4, V4a, V4b