Stylophone Site Redesign!:

The work to complete the new extra pages has been delayed. I had hoped to have completed the pages by now, but sadly life has got in the way again. I now hope to have the site completed by the end of 2026. (no guarantees!)

Check it out: Norm's (redesigned) Stylophone Site

Review:

The Si-Tex SX-Micro 90, hereafter called just Micro 90, is a very nice VHF marine radio handset made in 1995. It has all the features you would expect on a quality marine radio. It's rated to do 5 watts RF power output, and after all these years, the two Micro 90's I've got still do the full 5 watts.

The receive is as good as expected, and easily matches or beats other marine radios I've tried (XM 2000/Icom IC-M12/Maracom M6000).

RX Audio is loud and clear. One of my micro 90s had very quiet audio, but a replacement speaker cured that.

BATTERY: The original battery pack uses a Sanyo Cadnica 9.6 volt, 600 mAh, 8 cell NiCd pack. Since the radio was produced in 1995, its likely that the pack is dead, but it may (if you're very lucky) be ok.

These packs can be easily re-celled with a 9.6v pack from an RC car, but if you put in a pack with a much higher capacity, you may need to modify the charge circuit, since it will take too long to fully charge.

CHARGER: The charger should be 12 volts and around 500mA (not critical). I'm using a 1000mA charger and it works great. Both the charger socket on the side and the EXT PWR socket are tiny 1.3mm x 3.5mm x 9mm DC plugs. They are wired centre NEGATIVE!!! Be aware of this because most commercially availible power packs or chargers are centre positive.

Plugging in a centre positive supply won't damage the radio or the supply, since both sockets are protected with diodes, so it will only pass current with the correct polarity.

The radio can be powered directly from the charge socket, but this is not recomended, since that socket is current limited, to prevent overcharging the battery pack. Thats why they added the second EXT PWR socket at the top. I guess they could have used a single socket for both, but chose not to.

The user manual states that a 6 hour charge will give a full battery, but my tests have shown that a 6 hour charge gives a 90-95% battery.

The SX-Micro 90 uses a Low Pass Filter (LPF) to cut some of the high end hiss on the audio

As seen in the pic above, it is a simple r/c (resistor/capacitor) filter, with a 1000pf capacitor across the speaker, which is fed through a 4.7 ohm resistor, giving a 33.863 kHz cut-off frequency.