QUESTION

Question

Hi,

I built a project that uses Quectel BG96 for GPS and LTE communication. For GPS I use M20047-1 antenna but it looks like something is unmatched while I "see" 11 satellites but can't get a fix. Can you provide information on how to properly test the antenna using a VNA? I found for M20057 here:
https://ask.antenova.com/746/what-im-measuring-when-the-active-antenna-20047-is-powered-on?show=746#q746
so I suppose the procedure is similar, but R1 is on some other place... Thanks

Gabrijel

Answer 1

Hi Gabrijel,

What are the C/N values you are seeing from the satellites? If the BG96 module has a LNA it could be a case of the receiver being over saturated as the M20047 has a LNA already.

The process to connect the M0047/57 to the VNA is the same.

Best regards,

Yu Kai Yeung

Answer 2

Hi Yu Kai Yeung,

As noted in the Quectel BG96 HW design (v1.3, p.54), there’s no integrated LNA.

Initially, I didn’t focus on satellite SNR during testing, assuming a matching issue due to my custom PCB. I’ll retest and monitor SNR more closely.

I powered the antenna using M20047 and Quectel documentation. The only variation was the DC blocking capacitor—100pF (Quectel) vs. 22pF (M20047), for which I followed the M20047 datasheet.

I found VNA connection guidance for the M20057 (linked in my first message), but I’d appreciate help on how to connect a VNA to the M20047.

Kind regards,
Gabrijel

Answer 3

Hi,

I have tested the device in open sky and got this SNR values:
sat. num/snr: 33/36
sat. num/snr: 38/35
sat. num/snr: 39/34
sat. num/snr: 40/36
sat. num/snr: 42/35
sat. num/snr: 46/34
sat. num/snr: 48/34
sat. num/snr: 51/34

This should be enough to get a clear 3D fix but I waited for half an hour and nothing. Can it be the interference from LTE modem on the same PCB? I have been reading here that, if LTE and GNSS are on the same PCB, better to use M20057-1.

Gabrijel