How to check for a RF output?

[uslrs]

Hi, I would really appreciate some help with this issue - I have a number of PCB's with damaged RJ sockets/battery carriers, etc which are a relatively straight forward to repair.  These boards communicate with a base unit to identify location and alarm situations and as far as I can make out, this is accomplished using an Si 4431 chip, which according to the data sheet, can be programmed to operate in the 240-930 MHz range.  The layout on the board looks similar to the example schematic in the data sheet (attached).  I am looking for a (simple?) way to identify there's a RF output, so I'm not wasting time and money on pointless repairs but I'm not trying to interpret or capture the output in any way. I have a 60MHz scope. logic analyser and  the usual range of multimeters, etc, but I'm struggling to think of a quick and simple go/no-go test.   The board has an aerial with what appears to be a test point but I can't see anything on the scope  - I've shown the connection point to the Si4431 in red - Any ideas?
 

[Miti]

You could buy an RF Explorer spec an and diy a passive rf probe. They are quite cheap and, in this case, it would do the job.

Edit: On second thought, reading the datasheet, I see that the chip supports frequency hopping so it may be hard to catch with a spec an. Maybe use one of those cheap power meters from ebay.

[PA0PBZ]

Does the board include the microcontroller? The chip will not do anything unless instructed to do so.

[Muttley Snickers]

These boards communicate with a base unit to identify location and alarm situations and as far as I can make out......(snip)

Many wireless security system devices were designed to transmit their alarm conditions not more than once every minute to conserve the batteries. Some systems required the battery cover to be removed or a jumper link to be enabled before the device could be enrolled or registered into the main control panel or receiver, this process would also enable longer transmission times which is what you may require to verify their operation.   

[uslrs]

You could buy an RF Explorer spec an and diy a passive rf probe. They are quite cheap and, in this case, it would do the job.

Edit: On second thought, reading the datasheet, I see that the chip supports frequency hopping so it may be hard to catch with a spec an. Maybe use one of those cheap power meters from ebay.

Thanks Miti - I've found this one on Ebay: RF Power Meter Digital Radio Frequency Attenuation Value -75~+16 dBm Detection
Is that what you're suggesting? They appear to operate in the range 1-600 MHz, so not sure if that's adequate?

[uslrs]

Does the board include the microcontroller? The chip will not do anything unless instructed to do so.

Yes, the board has an ATXMEGA32A4U mpu connected to the Si4431 on pins 16 & 17 as in the datasheet example.

[uslrs]

These boards communicate with a base unit to identify location and alarm situations and as far as I can make out......(snip)

Many wireless security system devices were designed to transmit their alarm conditions not more than once every minute to conserve the batteries. Some systems required the battery cover to be removed or a jumper link to be enabled before the device could be enrolled or registered into the main control panel or receiver, this process would also enable longer transmission times which is what you may require to verify their operation.   

Thanks Muttley - there does appear to be a delay/repeat capacity, but there's no jumper/link/switch on the board - the alarm/call buttons are used in sequence to program the location and ID for each unit, but I don't think there is any associated inhibit function .

[Muttley Snickers]

I probably could have explained that last statement a bit better but what I was trying to relay is that generally speaking most wireless security devices do not transmit continuously and short periodic bursts can be difficult to identify, handheld remote keyfobs on the other hand can transmit at will.

[BFX]

Cheap SDR will do the job.

[NiHaoMike]

Look up the FCC ID to figure out what frequency it operates at, then use a RTLSDR.

[uslrs]

Cheap SDR will do the job.

Please excuse my ignorance - is this (SDR) a software-defined radio?  If so, could you point me to an example.  Many thanks.

[uslrs]

Look up the FCC ID to figure out what frequency it operates at, then use a RTLSDR.

I can't find anything relating to a FCC ID and would this be appropriate? RTL2832U DVB-T Tuner Dongles

[David Hess]

Before spending a lot of money, I would hack together a simple RF probe for my multimeter using some small signal schottky or germanium diodes.

https://www.electroschematics.com/rf-probe-circuit/

[uslrs]

Before spending a lot of money, I would hack together a simple RF probe for my multimeter using some small signal schottky or germanium diodes.

https://www.electroschematics.com/rf-probe-circuit/

Many thanks David - this looks perfect for my requirements!!

[uslrs]

Before spending a lot of money, I would hack together a simple RF probe for my multimeter using some small signal schottky or germanium diodes.

https://www.electroschematics.com/rf-probe-circuit/

I've made the RF probe and am very happy to report it works like a dream!  Had all the components and took no time at all to put together, so well pleased.  Thanks again David.