The FT-817/818 has been in production for over 20 years and now that I own one, it is easy to see why. It is a fun radio to operate and fits a lot in a small package. There’s really just one thing that I don’t like about it: the wideness of its filtering can make operating difficult. The Hi-Per-Mite from the 4 States QRP Group offers an economical and easy to build solution to this radio’s shortcoming.
The receiver on the FT-818 hears about 1kHz to 1.5kHz of the band. This is probably fine for SSB, but it is less than ideal for operating CW on the weekend. I hear up to four stations at once while operating during peak times and conditions. I mentioned this to another operator while on the SKCC sked page and he recommended that I try out the Hi-Per-Mite kit offered from the 4 States QRP Group. Boasting a 200 Hz audio pass for only $28 shipped, it was a deal that I was eager to take advantage of.
The kit is small and easy enough for the beginner to complete as long as they can read a schematic and know how to solder. While the kit didn’t ship with instructions, there are some provided on the 4SQRP Hi-Per-Mite webpage.
All the parts came well organized from 4SQRP.
The enclosure I had on hand.
When building electronics, desk organizers help keep the bench neat and components off the floor.
Having pictures of the PCB before any components are placed
makes troubleshooting much easier
The rectangular, blue capacitors had to be squared after soldering
The instructions were slightly confusing at times and differed from the schematic in a couple of ways. In fact, I had some trouble getting it to work once I had all the components installed. Once I connected power and my FT-818 to the circuit, I was disheartened when the audio was horrendously overdriven. Through some conversations with members of the QRP-ARCI and NAQCC organizations on groups.io, I managed to troubleshoot the issue.
All the problems went away once I disregarded the long-form instructions and followed the schematic as it was drawn. This meant that I eliminated a jumper across D1. The audio issues went away! If I read the schematic correctly, I was feeding 12VDC into places where it wasn’t meant to go which caused harsh audio.
These jumpers constantly removed themselves from the header pins.
The tape was placed there to complete testing.
After confirming it was all working properly,
I soldered all the connections permanently.
Now that I have this audio filter working and in a nice enclosure, it permanently resides atop my FT-818. The performance is outstanding. I only hear one station at a time now even when the band is crowded. However, the audio adjustments are touchy at the radio now.
What I need now is a way to power it in a more seamless way. I’m considering adding a pigtail from my 12VDC supply cable to the Hi-Per-Mite so that there are fewer wires cluttering up the desk.
Port: 3.5mm stereo out
Jack: 3.5mm mono in
2.1mm barrel port: 12VDC in
Amateur Radio Station WB0ISG 