External Antenna VSWR monitoring


#1

Does anybody know manufacturer who could supply a VSWR monitoring device which I could install on the external antenna line and which would trigger an alarm (SNMP trap or C contact) when the VSWR exceed a preset threshold?

I’m aware of many manufacturers which provide that kind of device for higher power transmitter (10 Watts to 100 kW), but I can’t find any which would be suitable for a device like a MC7354 or MC7455.

I found a chip which I believe could do the job if properly integrated with directional coupler, (Maxim Integrated MAX2016), but I can’t find anybody who made such integration with that chip or a similar chip.

Any help will be appreciated, thanks in advance.


#2

Hi, could you provide some additional details on what you are trying to do? Perhaps we could suggest an alternate way provide this functionality. For example, are you trying to detect an antenna short/open (i.e. if the antenna is disconnected or shorted to ground).


#3

Thanks for the reply,

In short, I’m trying to detect poor antenna performance, not only short or open, but any VSWR exceeding, say 3:1.

I have about 1500 of these modem installed in fixed location and 2000 more mobile units. To my knowledge, the modems can’t provide me the antenna condition.

I’m definitely open to any suggestion to enable the detection of underperforming antenna.

For instance, I had a fixed site where the signal was looking good, RSRP at -94 dBm and RSRP at -11 dB. This site was causing a lot of issues due to packet loss I assume. frequent error or no response to command sent. We found out that a connector on the antenna line was not well done and probably causing a 10 dB loss, which would be a strong reflected signal which appeared to be sufficient to desensitize the receiver.

On the fixed location, it is relatively simple to compare the measured signal values with the values measured at installation. On the mobile unit it is not applicable.


#4

Thanks for the details. I’m not aware of any fully integrated, off the shelf options to monitor VSWR. This would likely have to be a custom design as you mention in your original post.

Even if RSRP and RSRQ are good you should also take into account SNIR. SNIR >0 is ideal. Anything << 0 and throughput and packet loss can be significantly affected…even in good signal. Noise from other cellular products as well as other radios can impact this