IC-M700PRO slightly off frequency ? or modulation problem ? .. How to trouble shoot ?

[finnstru]

When transmitting with the IC-M700PRO, and listening with a ATS-20 Arduino, I sound strange ??? (Tx on backstay, Rx down below in the cabin with the Arduino ATS-20).

I can not fine tune on the Rx side with the cheap Arduino receiver, but if the M700 is a bit off frequency, it's not much. And I just added an extra battery close to it to get rid of any voltage drops (and a couple of tantal and ceramic capacitors while at it).

I'm located in Norway, but the installation was likely done in the U.S. around 2002? aprox, and was done in order to enable reception of weather fax before sailing her over to Europe where she were used locally for aprox 20 years before I bought her aprox 3 years ago.

When I disconect shore power (to get rid of possible noise sources), and Tx (voice), some of the leds on the 12v distribution panel does light up a bit, and I've read that's normal, so I think much is working and o.k.

It's a formerly PreProgrammed 12Mhz channel I'm using for testing (simplex), (I haven't yet figured out how to re-program her, but I have googled and downloaded som stuff that I think can do it from a laptop with COM port).

So currently I only have that one channel that I'm legally allowed to Tx on (12,359.0 USB / C12).

I did try with a new microphone (from China, but says ICOM on it), maybe slightly better but not the cause for me not being able to understand myself.

It's not high pitched audio frequency, it's more like lack of modulation.

I don't know if this M700 was new in 2002? or second hand. He got it from someone running a weather fax service I think. And those channels (likely those) sound like they likely should (Rx) (When I was young I were using 300/1200 baud modems, sounds familiair what I can hear when audio listening to Rx-ing data streams (likely weather fax's)).

It has a tuner, Japanese one, with relays, seems to work like one could expect. And a lot of copper laid out down below, so likely done by someone who knew what they were doing (also underneath through to the sea a couple of places).

I bought a SWR meeter (with too thin? cable for having it in between), but it's likely not Power that's the problem.

Does anyone know (someone) who has some experience, if it could be some of the M700 PCB components that change with age ? (some types of capacitors does I think, but maybe not used for modulation ? .....

Any sugestions for further trouble shooting ? (I'm a former electronics engineer, but worked more with computers and software than with electronics).

Maybe I need a better receiver (fine tuning) to diagnose it further ?.

On the receiver side all background noise disappears when I transmitt, and if I go off frequency with several K?Hz the audio diminishes as one can expect, and I sound better with aprox 2Khz to 3Khz bandwith (less noise), but whatever I say verbaly it's like it's modulating it a fraction of a second (maybe too much), and then modulation too litle. ......... I'm watching the bars, trying to talk (eat the microphone) in order to have them aprox 20% to 80% of the scale.

It seems to be working 98%, but I can't understand myself.

I don't like to buy new if something can be repaired and maintained :-)

But I don't have a HAM licence, only a Marine one (LRC certificate for USB), and the VHF doesn't go too far offshore, which I'm still dreaming of doing without having to spend for modern technologies up front.

"LK9893"

[murofsresiurc]

Retired electrical engineer here, designed radios most of my career, but I have no experience with marine SSB.

1. Frequency drift over time is highly unlikely. Almost certainly, the radio has a synthesizer creating the RF signal from a crystal based reference. These don't change appreciably with age.

2. Are you sure the problem isn't with the Arduino receiver? It looks like this is a very inexpensive low end receiver compared to your top of the line Icom transmitter.

3. A lack of modulation could be anywhere in the circuitry between the microphone and the transmitter. To do any significant troubleshooting, you need an oscilloscope, a schematic/block diagram, and preferably a service manual. Since you are only looking at low frequencies almost any low end oscilloscope should work.

Good luck! Hope this helps.

[team karst]

tune in WWV on 10 or 15MHz, whichever is stronger. Put the icom on CW receive mode. report if the signal has a tone, indicating off freq.

but, my guess is the arduino is desensing in the HF field.

[stormalong]

Your receiver is overloaded, it is operating in an RF rich environment. To properly test the M700 either take your receiver at least a kilometer away from the transmitter or recruit another boat owner some distance away to do a radio test. There is simply too much RF power within your boat to do an effective test.

Also if you are in a marina your signal is being bounced off all the other masts nearby, adding distortion. Better to be away from the marina while conducting tests.