Using a TinySA Spectrum Analyzer on undocumented transceiver - Page 1
Forum section: electronics / rf-microwave

author: figment
author_rank: Contributor
timestamp: July 31, 2025, 12:59:02 pm
content: I have a question for someone with more experience with RF than myself.I purchased a TinySA Ultra Spectrum Analyzer, and want to know if there is a way to safely connect it directly to each antenna port, one at at time, and measure what frequency each port is transmitting on. The TinySA will probably be fried if I just connect it without some kind of RF power reduction between the TX and TinySA.I have an undocumented WiFi radio transceiver with 2 onboard radios and 8 antenna ports on the circuit board.Only some of the antenna ports transmit, the others are receive only.The WiFi radios on the circuit board are capable of transmitting on the 2.4ghz and 5.8ghz WiFi bands.I can't simply use a cheap handheld spectrum analyzer because the device has 8 antenna ports, and all are in use when the device is powered on. I have to discern the TX freq of each of the 8 ports.

author: tszaboo
author_rank: Super Contributor
timestamp: July 31, 2025, 01:22:06 pm
content: I would assume that any Wifi device would only transmit with +30dBm or 2W.For the TinySA the damage level is on the input is 10dBm, but you don't target the damage level. Let's target 0dBm. That means that a 30dB attenuator should be used. I would also use a DC block, if you have one.If you need to buy stuff to make this measurement, I would buy some cheap connectorized 2W attenuators, one with 20dB two with 10dB. And connect those. Once you know the level, take out as many as you don't need.

author: Kean
author_rank: Unknown
timestamp: July 31, 2025, 01:42:05 pm
content: As mentioned by tszaboo you need at least one attenuator to bring the signal level down. You likely don't care about signal level accuracy so quality of the attenuators isn't too important.The tricky bit is that the WiFi transmissions are short and easy to miss.You will want to set your frequency span to just one band at a time - i.e. about 2400-2500 MHz for 2.5GHz band and 5100-5500 MHz for 5GHz band.Use max hold feature to capture short transmission and leave it running for a while.Considering there are multiple potential transmitters in close proximity, you should probably ignore any low level signals you capture as they are likely crosstalk.

author: tggzzz
author_rank: Super Contributor
timestamp: July 31, 2025, 01:55:05 pm
content: Quick and cheap: put an antenna on the SA (any bit of wire will do) and put that "antenna" near the UUT antenna. Near is a few inches.You will also pick up other transmissions, but they will be many 10s of dB weaker.

author: Kean
author_rank: Unknown
timestamp: July 31, 2025, 02:05:04 pm
content: Forgot to mention that you will need to adjust your RBW (resolution bandwidth) setting to keep the sweep speed fast to help capture any transmissions.With a slow sweep you have blind time and can easily miss the short & infrequent transmission. This is where a real-time spectrum analyser comes in as it has no blind time as it captures a wide frequency span all at once (up to the specified RT bandwidth of the SA).Once you capture any transmissions you can then adjust the RBW and span to narrow down on the particular frequency, but based on your other topic you really just want to see if there is any transmission at all. With patience and a device like the TinySA Ultra can probably show you this. I have one but not really tried capturing WiFi signals as more WiFi info is generally readily available with other tools easily.Quote from: tggzzz on July 31, 2025, 01:55:05 pmThe OP is dealing with a WiFi Pineapple which had 5 radios and 8 antennas housed in a single unit. They want to check each radio/antenna independently.See their previous post.https://www.eevblog.com/forum/rf-microwave/hak5-wifi-pineapple-enterprise-antenna-question/

author: figment
author_rank: Contributor
timestamp: August 01, 2025, 05:08:53 pm
content: Thank you to allI ordered a handful of attenuators and will try the suggested techniques. I've been unable to use CLI commands on the device, the software running on the device is OpenWRThttps://openwrt.org/Correct, this is basically the same question I posted here;https://www.eevblog.com/forum/rf-microwave/hak5-wifi-pineapple-enterprise-antenna-question/