Hub Port-to-Port etc. Resistance Checks

Measurements

Model (Powered\|Unpowered)	Input-to-Port ±0.05 Ω¹	Port-to-Port ±0.05 Ω¹	Power-to-Input² ±0.05 Ω³	Isolation Confirmed?⁴
Old 4-Port Hub⁵ (P)	NC⁶	0.1	NC⁶
OEM 4-Port Hub (P)	NC⁶	<0.05	NC⁶
CLIPtec Combi-Hub & Card Reader (P)	Diode-like⁷	<0.05	Diode-like⁷
"Flower" 4-Port Hub (U)	1.3	0.1	N/A⁸
Gembird 4-Port Switching Hub (P)	Diode-like⁹	<0.05
Generic 4-Port Hub (EDO) (P)	0.2	<0.05	0.3
Generic 4-Port Hub (Sum Vision) (U)	13.3	2.5	N/A⁸
Hama 4-Port Hub (P)	NC⁶	<0.05	NC⁶
PowerSynch Tech. 3-port Hub & LAN adapter (P)	<0.05	<0.05	0.1
Pluscom 3-port Hub & Card Reader	0.1	<0.05	0.1
Pluscom UHBPC 4-port Hub (U)	1.3	0.2	N/A⁸
Pluscom UTO 4-port Hub (P)	0.3	0.1	0.3
Sweex 4-Port Hub (P)	0.2	<0.05	0.1
Targus "Cable-powered" 4-Port Hub (P)	Diode-like¹⁰	<0.05	Diode-like¹¹
Trust 3-Port + Camera "Port" Hub (U)	0.2	<0.05	N/A⁸
Trust 4-Port Netbook Hub (U)	0.3	<0.05	N/A⁸
USB Now 4-Port Hub (P)	0.3	<0.05	0.4
Conceptronic 4-Port, Cube Hub (P)	NC¹²	0.15	Diode-like
Generic 7-Port Hub¹³ - Front Ports (P)	0.1	<0.05	0.4
Generic 7-Port Hub¹³ - Rear Ports (P)	1.0	0.4
Generic 7-Port Hub¹³ - Front to Rear Port (P)	N/A⁸	0.3
2-port USB KVM Switch	Diode-like¹⁴	<0.05	N/A⁸

Power Isolation Cross-check


Isolating and "Back-power" Indicating Adapter

The adapter(s) above were used to cross-check power-to-input isolation where expected, or not, for some of the powered hubs. Column four has either when isolation was confirmed (LED not illuminated when a PSU connected to the hub) or when "back-powering" was possible (LED illuminated when a PSU connected to the hub). Whilst "back-powering" a Pi is reasonable if a single PSU is used to power both the Pi and the hub¹⁵, good isolation is necessary when separate (and similar) PSU's (one for the Pi, another for the hub) are used. The veroboard adapter part also includes a "track-break" to provide the necessary isolation of "back-powering" hubs for test purposes.