Receiveing signal strength is jumping and different from each other of NRF52832 Gateway

[liu]

hello,

Now i have two troubles in NRF52832 Gateway.

1.Planning  introduce：

  The only function of NRF52832 Gateway is to scan beacons' advertisements.  With beacons‘ number is so huge，so we use three NRF52832 chips and scanning on 37/38/39  channels respectively.But we only use one antenna(SMA footprint) in this gateway. So  rear of this antenna is a LNA chip,after LNA chip is power separator chip(1 to 3).Three NRF52832 are connected to power separator directly like image1.     

2.PCB introduce:

F2 is LNA，U4 is power separator.RF lines(green )have made 50 Ω.Like photo 2.

3.Our testing method.

SMA antenna is linked with a Signal generator to gerenter a 2.4GHz&2MHz bandwith ble signal.We give the signal strength is -40dBm.

NRF52832 ANT pins is linked to spectrometer to see the waveform.

4.Our finding troubles.

1. Three NRF52832 chips‘ peak point of waveform is jumping about 2dBm when  it have burned programs.After erased the program, Three peak points of waveform is stable.

2.Middle NRF52832's signal strength is better than others 4dBm.
5.My Qus:

1.I guess the reason of these two troubles is length of RF lines is so long and not equal each other.
2.How to measure to find the reason causing this two thoubles,Network analyzer?
3.My testing method is appropriate or not.

Eager to get you help.  Eager Eager...

Thanks,thanks,thanks.
liu

[email protected]

[liu]

Hi,

I want to know the role of  3.9nH linked to RF pin of NRF52832.I wonder if i shoule adjust the value of it according to the impedance or length of RF lines.

Liu

[Andreas]

Hi Liu,

 

The 3.9 nH is part of the matching network of the nRF52, ensuring 50 ohm input impedance and harmonic rejection. Adjusting it (and the parallel 0.8 pF capacitor) is often needed, as the optimal values will vary from layout to layout. The layouts of the 3 chips are quite similar though, so even if not entirely optimal you should get equal insertion loss to all three, provided the transmission lines(RF_OUTx) are 50 ohm lines.

 

Best regards,

Andreas

[liu]

Hi,Andreas

Thanks.

Scanning waveforms of three NRF52832 chips were not jump as i adjusted BLE_GAP_SCAN_WINDOW_MIN and BLE_GAP_SCAN_INTERVAL_MIN (they are always equal) from 20ms to 10.24ms.So, as your said, 

 input impedance are differ when you open or close radio.

Success! strength gaps of them have become smaller.

Now, i have three questions:

Qes1:

BLE_GAP_SCAN_INTERVAL_MAX and BLE_GAP_SCAN_WINDOW_MAX are0XFFFF in sdk15.0, but it is 10.24s(0x3FFF) according to ble specification 4.2.

I wonder if it can be use as 0xFFFF in ble 5.0.

Qes2:

What can i do to adjust RF 3.9nH and  0.8 pF capacitor according to my PCB.Using network analyzer?

Actually, i know little about RF design.

Qes3:

In SDK15.0, if i want to maximize RF sending power, i should use sd_ble_gap_tx_power_set(BLE_GAP_TX_POWER_ROLE_ADV,m_adv_handle,+4).

But i wonder why it must be behind of advertising_init(), because it is random in S110 of SDK8.1.

Best regards,

Liu

Beijing,China

[email protected]

[Andreas]

Hi,

 

Good news on the reduction in signal strength variation.

 

1. Yes, 0xFFFF can be used per v5 Spec.
2. You probably need to use a combination of network analyser (S-parameters or input impedance) and spectrum analyzer (nRF output power). The output power is the most convenient way to determine if the match is good or not, but there are some variation to output power between devices, so to not be tricked by this you should verify by measuring the input impedance or S-parameters of the matching.
3. Not sure I understand your question correctly, but this has to be handled by the softdevice to not be reset. I suppose you could call the function various places, not necessarily in advertising_init.

 

Best regards,

Andreas