Each year at the Dayton Hamvention, the folks at Mini-Circuits have a bunch of odds and ends they sell very inexpensively. Over the years I’ve gotten tons of SMA attenuators and jumper cables, and a few amplifier blocks. I’d never looked closely at one of the amp blocks until last week, when I noticed that it’s pretty interesting. It is a ZHL-20W-13X+ class A power amplifier rated for 20 watts output with 50 dB gain from 20 to 1000 MHz. The list price for this puppy is over $1300!
Since it’s a class A amp, it draws full current whenever it’s powered up. That’s about 2.5 amps at 24 volts. The standard version comes with a big heatsink and fan, but mine was missing those pieces. I found a heatsink on eBay and got it mounted. Then I set up to do some tests.
The rated frequency range is 20 – 1000 MHz; the data sheet says it’s usable from 15 to 1100 MHz. I swept it from 2 to 1500 MHz:
50 dB is pretty impressive gain! The amp looks pretty good even at 10 MHz, but unfortunately doesn’t quite make it high enough to cover the 1296 ham band.
Here’s the power output with about -10 dBm drive (the absolute maximum input level is -3 dBm):
A class A amplifier should be pretty clean, so I checked the harmonics when driven to about 10W output at 100 MHz (I used a 110 MHz low pass filter at the amplifier input, and there’s 40 dB of attenuation between the amplifier and the analyzer, so add that much to the power readings shown):
FCC requirements are for harmonics of transmitters of less than 25 watts between 30 and 225 MHz to be the lesser of -40 dBc or 25 uW (-16 dBm), but not less than 10 uW (-20 dBm). Sadly, the 2nd and 3rd harmonics don’t make the grade, so a low pass filter will be necessary to put this amp on the air below the 420 MHz band.
Here’s why it needs a good-sized heatsink:
And here’s a picture of the test setup: