Bluetooth Poor Signal

Accourding to this topic(https://devtalk.nvidia.com/default/topic/1031479/jetson-tx2/bluetooth-class/post/5247673/#5247673), the class of bluetooth is 1.5.
So the signal should be available stronger than class 1 (100mW).

But currently, when I try to connect from iphone with Core Bluetooth, it can be connected only less than about 3cm away from jetson jx2.

Is this supposed to be? or could you give me some advice, please.

I set up the bluetooth based on the 'Bluetooth Device Settings’section of ‘NVIDIA_Tegra_Linux_Driver_Package/nvl4t_docs’
The current configuration is below.

*****@tegra-ubuntu:/var/app/ble$ sudhciconfig -a
hci1:	Type: BR/EDR  Bus: UART
	BD Address: 00:04:4B:A5:CF:B1  ACL MTU: 1021:8  SCO MTU: 64:1
	UP RUNNING PSCAN 
	RX bytes:2424 acl:24 sco:0 events:122 errors:0
	TX bytes:1880 acl:22 sco:0 commands:98 errors:0
	Features: 0xbf 0xfe 0xcf 0xfe 0xdb 0xff 0x7b 0x87
	Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
	Link policy: RSWITCH SNIFF 
	Link mode: SLAVE ACCEPT 
	Name: 'tegra-ubuntu #2'
	Class: 0x100000
	Service Classes: Object Transfer
	Device Class: Miscellaneous, 
	HCI Version: 4.1 (0x7)  Revision: 0x1000
	LMP Version: 4.1 (0x7)  Subversion: 0x610c
	Manufacturer: Broadcom Corporation (15)

hci0:	Type: BR/EDR  Bus: USB
	BD Address: 34:76:C5:A5:E7:81  ACL MTU: 820:8  SCO MTU: 255:16
	UP RUNNING PSCAN 
	RX bytes:1978 acl:0 sco:0 events:142 errors:0
	TX bytes:18799 acl:0 sco:0 commands:142 errors:0
	Features: 0xff 0xff 0xff 0xfe 0xdb 0xff 0x7b 0x87
	Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
	Link policy: RSWITCH HOLD SNIFF PARK 
	Link mode: SLAVE ACCEPT 
	Name: 'tegra-ubuntu'
	Class: 0x100000
	Service Classes: Object Transfer
	Device Class: Miscellaneous, 
	HCI Version: 4.0 (0x6)  Revision: 0xe2f
	LMP Version: 4.0 (0x6)  Subversion: 0xa041
	Manufacturer: Realtek Semiconductor Corporation (93)
*****@tegra-ubuntu:/var/app/ble$ cat /lib/udev/rules.d/50-bluetooth-hci-auto-poweron.rules
# Set bluetooth power up
#ACTION=="add", SUBSYSTEM=="bluetooth", KERNEL=="hci[0-9]*", RUN+="/bin/hciconfig %k up"

Do you connect the antenna?

No, which antenna should I use? Could you give me a link?

Could you refer to the devkit guidance on download center?

Jetson TX2 Developer Kit Carrier Board Specification

Ok so I will try with an antenna with my jetson tx2.
Thank you!