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Author Topic:   Icom Microphone
BellBoyBob posted 08-08-2007 12:02 AM ET (US)   Profile for BellBoyBob   Send Email to BellBoyBob  
Have any of you experienced this problem: I was out cruising with a friend in separate BellBoy 19'classic glass cruisers. We were checking the newly installed radios in our boats. I have the Icom 402A and he has the Icom 502. Intermittently, when I would transmit to him he would report that my signal was very weak. When I would press the transmit button on the mic more forcefully, he reported that I came in 5x5. It did not seem to be a problem with the high (25 watt) transmit setting. Also, we are having trouble connecting using the DSC feature. I can call him, his radio beeps in response, but then we are not sure how to commence a radio exchange on DSC. Any ideas?


jimh posted 08-08-2007 08:04 AM ET (US)     Profile for jimh  Send Email to jimh     
When your signal was reported as being weak, are you referring to the strength of the signal or to the level of the modulation?
Chuck Tribolet posted 08-08-2007 08:47 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I suspect he's talking about the audio volume, which doesn't
have anything to do with the transmit power in FM (I know ham
jimh knows that, but BellBoyBob may not) I'd be
thinking defective switch in the mike. New radio, it's ICOM's

As far as the DSC goes: Read The Fine Manual. ICOMs have
have an agravatingly complex process to answer a DSC call.
Standard Horizon, you just pick up the mike and talk. I've
read somewhere that ICOM has improved this in their most
recent radios.


bluewaterpirate posted 08-08-2007 09:52 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
Chuck ..... what are you talking about in regards to complexity of ICOMS protocol in answering a DSC call. After receivng a DSC call the ICOM swtiches to channel 16 you pick up the mic and talk. If you don't have Auto Ack (which is selected as a preference by the user) you push enter to respond to a information call such as a position request. To clear the DSC call from your display you push the Clear Btn .... this is trained ape stuff.


BellBoyBob posted 08-08-2007 03:22 PM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
I was referring to a precipitous DROP in voice modulation when my boating partner said that in some exchanges he could "barely hear me". When I would firmly depress the mic key, he would report a 5x5 reception. I think it may be mechanical on my end.
The DSC is complicated because I am installing his equipment / training my novice mariner with an Icom model other than mine. Tricky.
jimh posted 08-08-2007 04:13 PM ET (US)     Profile for jimh  Send Email to jimh     
As a professional broadcast engineer licensed for thirty years, and an avid amateur radio operator for 43 years, I can tell you that in theory the audio recovered from a frequency modulated transmission should not vary with received signal level as long as there is sufficient received signal to put the receiver into saturation.

A good reference for modulation level is to adjust the receiver audio output while tuned to a commercial station such as a continuous marine broadcast from a NOAA weather radio station. After you set the receiver gain on that transmission, switch to a VHF channel and compare the audio you are getting from the transmitter being tested.

The other day I was sitting in the harbor reading the mail on boats calling the harbor master, and the variation in audio modulation level among all these transmitters was very wide. Some boats came in loud and clear and others had barely a whisper of modulation on their signal. Hand held radios seem to be the worst in this regard. Also much of the variation can be due to microphone technique and speaking level. There is a tendency among radio transmitters in the VHF Marine Service to have the microphone gain set for someone who is yelling above a loud motor noise when transmitting.

bluewaterpirate posted 08-08-2007 04:23 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
or it could a cheap antenna or a good antenna with a bad connection.

These are the top two problems I find when troubling shooting reported bad radios:

1. Substandard connection between the VHF antenna and the radoi.

2. Neatly coiled & bundled excess antenna cable.

BellBoyBob posted 08-09-2007 11:24 PM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Ok, so we had both boats in the garage and tried different DSC scenarios. Every call that the 502 made was recievable by the 402a but only sometimes could the 402a send a DSC call (all ships and POS request would go through) The individual DSC call from my 402a was never received by the 502. When doing straight communication my radio could not be heard through his even though the Tx was illuminated on my 402a. Then, suddenly he could hear my radio call. I think I have determined that my radio has either a faulty mic or a bad connection to the Shakespeare antenna. FRUSTRATING!


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