A MMIC with some Muscle

Some folks have built HF gear using MMIC's (gain blocks) as either IF amps, receive preamps or pre-drivers.  I've used AG303-86's, MAV-11's, MAR-0685's and even a some hamfest SGA-6486's with few problems and with excellent repeatability.  50 ohm input and output, low external component count, relatively low noise figure and low distortion up to about 20dbm output at 1 db gain compression - what's not to like!  The issue I have with these devices is that they're a bit anemic for use use a QRP final amp or as drivers for 5+ watt PA's.  Recently, I bought a couple of SV1AFN's (SV1AFN) 1 watt driver, PHA-202+ boards to fill the need for 1 watt (approx.) gain blocks in a few projects.  This device/board can , indeed, deliver close to 30 dbm (at 1 db gain compression) output for 10 - 13 dbm input.  The down side:  the PHA-202+ is relatively expensive (Digikey's single unit price is around $16.64 (US)),  current consumption is rather high compared to less stout MMIC's, the driver board doesn't seem to be available, currently, and, of course, the actual device is SMT.

https://www.minicircuits.com/pdfs/PHA-202+.pdf?srsltid=AfmBOor_AzoQ9w_JlCPFYS7P9AN0N-oQ5wC6FeWmxvBknWgQrsF5Q-wn

While Makis' driver board is a small thing of beauty,  both physically and functionally, I wanted to see if I could duplicate its function with simple construction techniques that average hams use.  The PHA-202+ comes in a DL1636 case, ~5mm x 6 mm and contains an exposed "paddle" for grounding and heat transfer.  I figured I could fabricate a small, etched board and mount the device dead bug style.  I used a very short piece of solder wick as a low inductance ground strap (see photo below) and half baked thermal transfer link. I used very small lengths of #28 magnet wire (thermally stripped and tinned) to make the connections between the input/output pads and the strip lines on the board.  No hot plate or toaster oven was needed.  I did all the soldering using a fine-tipped iron, aided by a Donegan OptiVISOR.

I built this test amp mostly to the Minicircuits example schematic in their data sheet.  I added a hefty 22 ohm dropping resistor (bypassed, of course) in series with the DC feed to lower current consumption from ~350 ma to ~220 ma (at 12 v supply) because of the sketchy heat dissipation setup. 

I ran a few simple tests.  With the board powered-up and connected to my spectrum analyzer (with 50 db attenuation in front of it - just in case), I found no self oscillation. Input SWR was 1.66 to 1 at 20m.  Amplification behavior in the middle of the 20m band is shown, below:

1 db gain compression occurred at 28 dbm output.  Behavior was essentially identical at 10m.  I haven't looked at 2m or 70cm performance to date (don't care that much). My test board produced the same gain as Makis' board, but ~2 db less output at "full bore" - probably because of the lower device operating current in my incarnation.  The PHA-202+ passed the "finger test" (barely) after a minute at full output.  

I'm sure I could get marginally better results using proper SMT construction techniques, but there's no reason to let the good suffer in pursuit of perfection, especially below 30 MHz.  BTW - Minicircuits seems to be quite ham radio friendly.....


 

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