Help identify mystery RF mixer - Page 1
Forum section: electronics / rf-microwave

author: Testtech
author_rank: Regular Contributor
timestamp: December 27, 2024, 11:54:23 pm
content: I am working on a Rohde Schwarz FSP spectrum analyzer, and am troubleshooting the first front end board for low signal level.Unfortunately the only service data is a block diagram and a few signal levels.This mixer is right at the front end and generates the first IF of 3.476 GHz nominal. The LO power into this mixer is about 0 dbm, this seems low for a mixer LO, but without any spec on the mixer, or power level from the block diag., I am not sure.Anybody recognize this mixer?Thanks,Bob

author: KE5FX
author_rank: Super Contributor
timestamp: December 28, 2024, 04:56:17 am
content: That'll be aSynergy Microwavepart. There will almost certainly be something in the Mini-Circuits catalog that can replace it, but I agree that 0 dBm is much too low (assuming it's not an active mixer). The LO may be the problem rather than the mixer.Could be a bad YIG oscillator or something in the signal chain between the YTO and mixer.

author: Testtech
author_rank: Regular Contributor
timestamp: December 28, 2024, 02:28:25 pm
content: Thanks for the lead to Synergy, I have sent an email request for info.The LO for this mixer is locally generated on the front end board.Unfortunately I cannot extend this module during operation, so I must strategically attach test points and hope for the best..

author: eb4fbz
author_rank: Regular Contributor
timestamp: December 28, 2024, 10:41:40 pm
content: http://gbppr.net/mil/xband/MC3XSMX-3_-14.pdfProbably close enough, just different package option.LO should be 7dBm

author: Testtech
author_rank: Regular Contributor
timestamp: December 28, 2024, 11:10:01 pm
content: Thanks to all!I didn't provide enough info on the application:This is the "front end" mixer in R&S FSP spec an, input frequency range 9 KHz-3 Ghz, LO 3.4-6.6 GHz.As such, it is exposed to the user, and vulnerable to excess input.The RF input to the mixer is connected to the unmarked ( I?) terminal, the LO is input at the L terminal, and the IF is output at the R terminal.R&S had the forethought to allow the signals to be interrupted by solder pad jumpers for testing. I have set this up on the bench static, with sig gens and an SA at the IF output, and it doesn't seem to work too well.At 0 dBm 100 MHz RF input and 3.5 GHz LO@0dBm the IF is -29 dBm; at +10dBm LO the IF is -22dBm.I am not an expert in mixer design, but this seem like excessive conversion loss to me.What say you?

author: eb4fbz
author_rank: Regular Contributor
timestamp: December 28, 2024, 11:44:22 pm
content: Conversion loss should be well under 10dB so that mixer is probably broken. You could make a replacement board using Minicircuits SIM-83+Could you check the RF port output level at 6GHz when injecting -10dBm IF at 1GHz with 10dBm LO at 5GHz?

author: Testtech
author_rank: Regular Contributor
timestamp: December 28, 2024, 11:59:56 pm
content: Same connection as before, but with your suggested levels and frequencies the IF is 6 GHz -17 dBm.

author: eb4fbz
author_rank: Regular Contributor
timestamp: December 29, 2024, 08:46:02 am
content: Quote from: Testtech on December 28, 2024, 11:59:56 pmThat looks right, it’s a conversion loss of 7dB.