My Heltec board has a helical wire antenna for 2.4GHz on top, not the PCB antenna.
It also has a PCB antenna on the bottom side but that antenna is not connected.
The helical antenna sticks out above the display, not handy if to be mounted in a case.
WiFi reception with the helical antenna is poor. I was only able to detect 9 WiFi networks (max), while at the same location an ESP8266 ESP-12F module with PCB antenna detects 28 networks (max).
I wanted to improve the antenna so I hacked the PCB. I removed the helical wire antenna and mounted an U.FL connector so I can connect different types of antennas. This was possible because the antenna pad is surrounded with ground traces. While the modification is still not as good as the ESP-12F, I was able to detect 14 WiFi networks (max), which is an improvement of more than 50% (in detected networks).
I tried several 2.4GHz antennas, including 2 PCB types and a regular foldable type with SMA connector but the model shown on the picture below performed best.
Original
With U.FL connector mounted
With antennas