Standard-Horizon GX1500 Improving Transmitted Audio

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
Posts: 11862
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula

Standard-Horizon GX1500 Improving Transmitted Audio

Postby jimh » Tue Dec 11, 2018 11:22 am

Author's note: this article is a revised and updated version of a similar article that was published earlier.

After making a modification to the microphone of the ICOM IC-M402 radio, the quality of that transmitter's audio modulation improved dramatically. (See a separate article that describes the microphone modification in detail.) I then made some comparison tests of the transmitter modulation of the M402 compared to my Standard-Horizon GX1500S. To my surprise, I heard the ICOM radio sounding clearer and better than my Standard-Horizon.

I used a third radio as a neutral test receiver, and I recorded its output into a digital audio recorder. This allowed me to replay the test transmissions many times to compare them. I even applied some amplitude leveling transforms to make the two signals more equal in loudness. Loudness always plays a part in deciding what sounds better. The ICOM IC-M402 radio transmitted audio still sounded better. This was quite an eye opener--or maybe an ear opener.

I decided to investigate the microphone of the Standard-Horizon radio. Upon disassembly, I found the microphone employed a similar water-resistant membrane in the sound path to the actual microphone element inside the case of the microphone, with a similar rubber cylinder gasket. The membrane was more porous than the one found originally in the ICOM. I removed this membrane, and, as I did with the ICOM, I replaced it with some water-resistance gauze material pulled from a plastic Band-Aid strip's pad. Because of the arrangement of the rubber gasket inside the Standard-Horizon microphone, I could not put the gauze in the cup-recess. Instead, I just pushed some gauze into the narrow center passage of the rubber gasket. I reassembled the microphone and retested.

The result of removing the membrane and substituting gauze was an improvement in the transmitter modulation of the Standard-Horizon radio. It was now the equal to or perhaps even better than the modified ICOM radio.

I am sure that removing the membrane in the sound path has compromised the resistance of these microphones to immersion in water. I will have to take more care with these microphones in any sort of wet environment. The improvement in the quality of the transmitter modulation is worth the risk of decreased water resistance, in my opinion and for my boat's operating environment, which is typically not completely open to rain or spray.