Since I’ve been using my Icom IC-705 on the QO-100 satellite I’ve been getting no end of unsolicited great audio reports with one Op even saying I have the best audio he’s ever heard on the satellite.

Most people are surprised when I tell them that I am using the stock fist mic that comes with the radio. It’s nothing special, in fact it’s rather cheap and plastic, not particularly good quality however, it does seem to have a good sounding mic insert.

The other great thing about the IC-705 is that it has a two channel parametric equaliser built into the radio. Many people don’t realise this and miss out on the massive improvement they can make to their transmitted audio with just a few simple adjustments.

The stock fist mic has a very flat response across the audio frequency range out of the box and doesn’t sound particularly inspiring. Many see this as a negative and often just replace the mic with either a headset (probably from Heil), a boom mic (again probably from Heil) or another, better quality fist mic. All of these options cost varying amounts of money when in reality none of them are necessary.

Starting from a flat audio response is actually a good thing as it makes the equaliser adjustments more pronounced, making it easier to adjust the settings to suit your voice.

We all have different voices but, there is one thing that is pretty much the same for everyone and that’s the frequency range in which the articulation of the words and sounds we make can be found. It’s this part of the voice that is often lacking when we struggle to understand what the DX station is saying.

It’s become common place on the HAM bands these days for stations to boost the bass frequencies and reduce the mid and high frequencies with the net result of a horrible bass ringing sound and muddy mid range often making it very difficult to understand what is being said.

Having spent some considerable time watching the great videos on audio from the late Bob Heil, K9EID it’s clear that the most important frequencies to enhance are those around 2.5khz as this is where all the articulation is in the human voice.

To this end I set about setting up the audio on my IC-705 QRP radio so that my voice sounded such that it is easy to comprehend even in the most difficult of situations on air. This doesn’t mean that it has to be very harsh and overly bright, quite the opposite in that to be heard clearly in all conditions on air one’s audio needs to be balanced across the frequency range with an enhancement in the 2.5Khz frequency range.

To reduce the unwanted, muddy bass the first thing to do is change the transmit bandwidth for the “Wide” setting to 200-2900Hz. This will cut off the bottom 100Hz from the voice reducing the overall bass output from the standard fist mic that comes with the radio. This will ensure a 2700Hz wide SSB signal, the recommended max for QO-100 operations and the preferred bandwidth on the HF bands.

On top of this I made a further reduction of 2dB on the TX Bass setting to help balance out the overall audio response of the mic insert.

Next I set about enhancing the higher frequency response of the mic insert and found that it required an increase of 4dB to bring out the articulation of my voice. This enhanced my audio considerably compared to the standard output from the fist mic and improved the intelligibility of my voice considerably, especially in difficult band conditions.

To complete the setup I set the compression to 3 and mic gain to 35 so that the overall drive level is increased slightly giving a greater average output from the radio.

Once I’d got the audio setup correctly I enabled the configuration by setting the Transmit Bandwidth (TBW) to the “Wide” config in the IC-705 Function menu so that the correct settings were made active.

Ever since making these relatively easy changes I have had no end of unsolicited great audio reports from stations asking me what mic I am using and how I’ve managed to get such good audio from the IC-705. Many are surprised that I am using the OEM fist mic that comes with the radio and I’m sure there are those who don’t believe me!

Of course all voices are slightly different and these settings may not be perfect for your voice but, all those that have tried these settings have told me that their audio sounds better than ever and that DX stations often comment on how good their audio is.

I also went through the same exercise with my Yaesu FTDX10 with it’s standard fist mic and again achieved excellent results with it’s 3 channel parametric equaliser. I’ll go through the somewhat more complicated setup for the FTDX10 in another article soon.

It was sad to hear that Bob Heil, K9EID, is now a Silent Key. Bob passed away on February 28th, 2024 after a year-long battle with cancer. 

Bob was the founder of HEIL SOUND which is well known for audio equipment like microphones and headphones for the amateur radio community and music industry.

HEIL HAM RADIO released the following statement... "Our beloved founder, Dr. Bob Heil, K9EID, is now a Silent Key. Bob fought a valiant, year-long battle with cancer, and passed peacefully surrounded by his family. Bob’s lifelong passion for amateur radio was clear to everyone involved in the hobby. Everything Bob did for the betterment and growth of amateur radio - from his instructional handbooks and countless presentations to his support of the ARRL and youth programs - was based on the foundation and spirit of service. Bob was an Elmer to all of us. While Bob’s presence will dearly be missed, his impact on the hobby and everyone in it will forever be felt. On behalf of Bob to all ham radio operators worldwide, 73."

Dr. Bob Heil, K9EID (October 5, 1940 – February 28, 2024)

1) Wikipedia link

Heil Pro-Set Ear Pad Replacements. After seven months of use, I have to say these ear pad replacements are much better than the stock Heil ear pads!