Recommendations for such an antenna would also be welcome
The antenna needs to be "fit for purpose".
Until that purpose is defined, it's difficult to be too specific.
The easiest way to test is to see if a phone, on the same frequency (and from the same service provider) as your modem, will work. Try tethering it, if you can. This will let you speed test the service. Beware, a lot of phones (and modems) may fall back to 3G if 4G is not working well. You can generally program modem behaviour to allow or prevent this.
Most modems vendors will recommend some specific small antenna. That's usually the best place to start when your signal is present, but marginal.
You can use the "
AT CSQ" command to detect signal strength:
Code:
Mar 23 18:17:20 pi4 chat[824]: send (AT+CSQ^M)
Mar 23 18:17:20 pi4 chat[824]: expect (OK)
Mar 23 18:17:20 pi4 chat[824]: ^M
Mar 23 18:17:20 pi4 chat[824]: AT+CSQ^M^M
Mar 23 18:17:20 pi4 chat[824]: +CSQ: 17,99^M
Mar 23 18:17:20 pi4 chat[824]: ^M
Mar 23 18:17:20 pi4 chat[824]: OK
Mar 23 18:17:20 pi4 chat[824]: -- got it
Adding this to the chat script can assist in antenna placement. The signal strength of "17" above is "good".
I have a 3g+ modem and live in a rural location in Australia. A small antenna won't work.
In my geographical context, 3G+ from my service provider operates at 900 MHz.
So I have an directional external antenna, tuned for 900 MHz, on top of a 6 m mast pointed at the service provider's tower in a town 10 km away.
The mast is just a galvanised steel pipe, sitting on a concrete tile, secured vertical with metal brackets attached to the floor joist and fascia board.
I oriented the antenna at night where the glow of lights in the town was discernible. I also had the option of using a compass, as all broadcast towers have their GPS coordinates and frequencies publicly documented (but pointing at the lights was much easier).
Not everyone will need a 6 m mast. But there are options you can try if a small antenna won't do what you need.
It may help to know that DAB (digital radio) uses the same coaxial cable standards (
SMA) as modems. The final pigtail connection to the modem is generally either a CRC9 or TS9 adaptor. Beware that these look similar, but different sizes, and are not interchangeable.