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

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

Andreas — Fri, 11 May 2018 07:55:18 GMT

Hi,

Good news on the reduction in signal strength variation.

Yes, 0xFFFF can be used per v5 Spec.
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.
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

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

liu — Thu, 10 May 2018 06:46:34 GMT

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

liumanjinkobe@126.com

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

Andreas — Fri, 27 Apr 2018 09:10:06 GMT

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

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

liu — Fri, 27 Apr 2018 01:15:59 GMT

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

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

liu — Thu, 26 Apr 2018 14:35:51 GMT

Hi,

Andreas.

Thanks for your help very much.I think i should make some experiperments to test it according to your suggests.

Liu

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

Andreas — Thu, 26 Apr 2018 09:03:41 GMT

Hi Liu,

OK, the ground information is valuable, that should be fine then.

The input impedance of the chip will differ when the radio is off, from when it is in RX or TX, meaning it will not have 50 ohm input when off. This will alter the S-parameters of the power dividers, and probably cause more of the power to be directed towards the other device (the one that is on).

When the chips are erased, the radio will be off all the time, so the received signal strength should be consistent all the time. If the chips are loaded with a Softdevice application the radio HW will switch itself on and off, meaning received power in one device will fluctuate between the levels given when the other two devices are on or off.

Similarly if instead of erasing the application of one or two devices, if you load an application that has the radio in RX continuously, you should read a signal strength that does not fluctuate.

Best regards,

Andreas

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

liu — Wed, 25 Apr 2018 15:21:59 GMT

Hi,

My PCB board is 4 layers.The second layer is GND totally.

So,there have solid ground underneath all RF paths,and through it we made 50Ω impedance.

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

liu — Wed, 25 Apr 2018 15:10:18 GMT

Hello,

Andreas.Thanks for your reply.

I am sorry for my expression not clearly. I mean received power is jumping about 4dBm,because my gateway only be used for scanning. Program is burned means NRF52832 is loaded softdevice and application program.

Program is loaded when it is erased means chips have no programs.

I find received power is jumping when chips are loaded programs but which is stable when chips have no program.But what's caused it?

Thanks.

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

Andreas — Wed, 25 Apr 2018 12:32:51 GMT

Hi Liu,

This is a very uncommon application for our devices, so please understand that we have very little knowledge on this.

Troubles:

1. I do not understand what is jumping, transmitting or received power? Which program is burned? Which program is loaded when it is erased?

2. The difference in signal strength is probably a combination between trace length and the middle trace just passing through 1 power divider, even though it is 3-way division. Also there should be solid ground underneath all RF paths, without ground, and with a trace passing underneath one direction, you do not have control that it will be similar.

3. Using the RSSI module in the nRF52 is an inaccurate way to characterize this. It would be better to use a signal/spectrum analyzer. A network analyzer could be useful to see how different the loads seen by the nRF52 are.

Best regards,

Andreas