Mini-Circuits PSA4-5043 preamp
Kenneth Wyatt- October 2, 2012One of my favorite companies, Mini-Circuits, developed a (really!) low-noise, broad band, preamp (model PSA4-5043+) earlier this year for use as a front-end amplifier for mobile telecom applications, such as GSM, CDMA, LTE and WiMax. However, it would also be ideal to amplify spectrum analyzers and the low-noise feature would lower the effective noise figure of the analyzer, allowing you to see low-level signals better. This would not only be useful for amplifying near-field or current probe outputs, but would work well to boost the antenna output in semi-anechoic chambers - especially if there is a long run of coax cable.
While the PSA4-5043 costs about $2.50 in quantities of 20, Mini-Circuits is good about providing free samples. But, rather than ordering the device itself, note that Mini-Circuits sells the amplifier already built into a high-quality test board and brass housing (model # TB-653+) for just $59.95 in single quantities. It's orderable right off their web site.
The MMIC amplifier is based on E-PHEMT technology and is spec'd from 50 MHz to 4 GHz with an amazing noise figure of 0.73 to 1.44 between that frequency range. The output power at 1dB compression is about 16 to 20 dB and the third-order intercept ranges from 28 to 31 dB. It should operate moderately well in high dynamic range environments. It's really quite good for a single four-legged SOT-343 device. In addition, it's also rated Class 1B (HBM) at 500 to <1000V for ESD.
Figure 1 - here's the packaged PSA4-5043+ broad band preamp. The top two SMA connectors are for test purposes only and are not a part of the preamp.
Figure 2 - the flip side of the test board and brass housing. The upper two SMA connectors merely connect to a spare bias-T network and is used for test purposes, only. The actual preamp is connected to the lower two SMA connectors.
I tried measuring the preamp using my Rigol DSA815TG spectrum analyzer (with tracking generator) and found the gain to vary from 25 to 15 dB from 1 to 1,500 MHz (the upper limit of the analyzer), just as the data sheet specifies. Note that, despite Mini-Circuit's spec of 50 MHz for the lower limit, I found it would amplify all the way down to 5 MHz. To power the preamp, I took a spare USB cable and cut off the larger end, leaving enough to reach the USB port on the analyzer. On my cable, the +5V was the red wire, with black was the return. Be sure to verify your cable using a volt meter before connecting to the preamp.
I adjusted the tracking generator output to -20 dBm, so the preamp wouldn't saturate. I also changed the vertical scale from 10 dB to 5 dB per division, so I could observe gain changes more easily. After normalizing the analyzer, I adjusted the offset so the positive gain would display properly on the screen.
Figure 3 - The test setup is pretty straight forward. The tracking generator output is connected to the preamp input and the preamp output connects to the analyzer input. The unit is powered from +5V and I rigged up a USB cable to power it, which merely plugs in to the USB port on the analyzer.
Figure 4 - the gain of the preamp from 1 to 1,500 MHz (the limit of the analyzer). It varies from 25 to 15 dB as per the Mini-Circuits spec sheet.
You'll want to print out this gain versus frequency plot (or save as a calibration table) in order to provide a calibration factor for certification testing or for accurate current probe measurements. Otherwise, for general EMC troubleshooting, it's relatively immaterial, as you normally just need to compare a baseline measurement with a measurement following a circuit change ("A-B" testing).
Why pay hundreds of dollars for a broad band preamp when you can get one for under $60 bucks?