What's the differences between TX an RX cable loss?

[xinxin]

When measuring the performance of mobile phone through radiation connect using CMU200. we need make a compensation on TX & RX Loss .we found some phones made this compensation , RX loss was biger than it on normal phone , while TX loss sometimes need a biger compensation than it on normal phone . When we make a measurement on sensitivity through radiation , they both need to be setting. Could u tell me what's the problem when TX & RX loss get biger ? is it only due to the performance of anteena? thanks.

 

[vfone]

Theoretically the RX and TX loss shall be the same when is doing a radiated test. If antenna has different gain at RX and TX bands, will be a difference between losses.
Beware that CMU200 has in one of its inputs less RX dynamic range than other.
This will limit your distance for the radiated test. The best CMU RX input for radiated test is the one that support less input power.

 

[xinxin]

vfone , thanks for your message.
I found this problem when make a sensitivity for phone . I connected the shielding box to the CMU200 through the cable. the DUT is fold phone with inside antenna . Except the gain of antenna , Can it phone itself cause the differences of loss for TX &RX on CMU200, such as layout , data line radiation , something else?

 

[vfone]

If the antenna connector is common for both, TX and RX, should be no difference in conducted losses (because the calibration was done for both TX and RX at that point).
If the conducted calibration of one of them (TX or RX) is not good, could appear this discrepancy between radiated losses.
Radiated sensitivity usually is lower than conducted sensitivity, but this shall not affect this radiated loss issue.
If you use a shielded box, beware that this one by self has a funny frequency characteristic. I found some boxes that have the resonant frequency (waveguide cavity) exactly in the middle of the cellular band.

 

[xinxin]

vfone , thanks

We made some measurements on sensitivity for some differnets types phone , but only a type i metioned above has such a problem . It's OK when through the conducting mode. My question is if the citcuits could cause this problem.