Bob,
Welcome!
Welcome to Cruiser's Forum!
And, have a seat....we're going to be here a while... LOL
As someone who has spent a good deal (45+ years) of my life dealing with
interference issues, in both my career in
communications and in amateur radio....whether microwave,
satellite, HF, and VHF/UHF....
And, as someone who has spent a good deal (50+ years) of my life on-the-water, cruising, sailing
offshore, etc...and dealing with radio
communications for decades (both marine and ham), at sea...
Further, as someone who has taught seminars about IMD, etc...
I'll gladly spend a couple minutes answering your question...
(hint: it's mostly about the poor IMD and a mic gain control)
(btw, IMD = Inter-Modulation Distortion....which in simple terms is how we measure / quantify level of non-linearity, which causes interference and inefficiencies....and, of course, cannot be "filtered out" by the transmitter, as poor IMD is just the result of poor transmitter design, and a little bit about those with mic gains cranked too high!)
1) Although the IC-7300 is a nice ham rig, neither it, nor any ham radio made in the past 40 some years, has ever been Part 80 Certified for use on anything other than the amateur radio frequencies (nor Certified by any other nation, nor ITU, etc. for maritime use, nor use on any other radio service) ....
Remember, in the amateur radio
service (ham radio) there are no specific in-band interference specs/standards, and it is up to the licensed amateur radio operator to adjust their radio properly so they do not cause interference to other stations (and must accept interference from other stations)...
So, it is illegal to use the IC-7300, or any ham radio, on the maritime bands, or on any band/frequency it was not designed/certified for....
Hands down, full stop, period.
Thhhhaaaattss all folks...
2) But, you asked for someone to tell you why....so...
The reason it is not certified for this use (other than Icom didn't design it for, nor did/would Icom submit it for certification) is that it (and all other ham radios made in the past 40 some years), does
not produce a clean signal....i.e. its transmit spectral purity is poor....
That's an unfortunate fact, but a fact none-the-less!
The transmit spectral purity / transmit IMD of the IC-7300 is significantly worse than what the Maritime Mobile
Service Part 80 (and ITU IMO) specification calls for...in the US, this is governed under US FCC Part 80 rules & regs...
Now, in comparison with other "modern" ham radios made today and in the past few years, the IC-7300 is about average....but worse than ham radios of the 1970's and early 80's...and significantly worse than the maritime specs...
This is commonly known as "splatter"...
And, these "specs" are measured with the radio operated as it is designed to / at its designed settings...and again, it doesn't come close to meeting these specs...
Of course, since the IC-7300 (and all other modern HF ham radios) has a "mic gain" control, and other transmitter controls / adjustments, the IC-7300 (and most other modern HF ham radios) can be adjusted to transmit an even worse signal, with even worse transmit spectral purity / worse transmit IMD....which would be very, very bad...
Understand that this IMD / poor transmit spectral purity is almost never noticed "on-frequency", meaning 99.9999% of the time, you can be talking with someone who says you "sound fine", but off-channel / off-frequency your transmit PA is producing splatter / IMD, and causing problems for others!
Also, let's not forget that Maritime, Aviation, and commercial/Fixed/land-mobile services are "channelized", and the channel usage and assignments are very specifically designed to not cause interference with adjacent users....and since ham radios (such as the IC-7300) are designed with a VFO, and not specifically designed for channeled use (yes, I know it has memories), it can be tuned off-frequency from the designated channels and cause significant interference...
{BTW, there are a few ham rigs made in the past 50 years (but, none in the past 30-35 years) that could pass the stringent transmit spectral purity and IMD specs for maritime operations, such as the old JRC JST-245 and the Drake TR-7....but, note that Drake made commercial versions of the TR-7, with synth digital vfo, to meet the frequency-stability spec, the TR-77 (for maritime use) and the TR-4310 (for commercial fixed/mobile use), which did of course pass....and JRC, used the same basic chassis and guts of the 245 for some of their marine radios of the day....so, it stands to reason that they also passed the spec...but, that's about it...}
3) The radio is designed to operate in the ham bands, and as such, even the relatively poor transmit specs get worse when operated significantly out-of-band....
Understand there is a big difference between operating a few khz outside of the ham bands, such as in MARS / CAP operating...versus operating several mhz outside of the designed band...
It might not seem to be "way out-of-band", but in terms of percentage and partial-octave, 8294khz and 6224khz, are quite aways away from 40 meters....as are 12359khz and 16528khz, way out-of-band of 20 meters....etc., etc...
This is a significant issue that many will never talk about....but it exists and is another reason you cannot operate an IC-7300 on the marine bands...
{BTW, MARS and CAP have fairly strict rules these days on what ham radios can be legally operated on their frequencies....and I'm not sure if they allow the 7300, but think not....as there are only a few HF ham rigs that do qualify, and its a darn easy spec to meet, so that should tell you something...just because you might find a mod on the internet that says you can do this (MARS mod), doesn't make it legal, nor acceptable...}
4) And, specific to our applications, on-board a boat...most ham radios suffer from issues when operated on "battery voltages" of 12.0 to 12.6vdc (at the radio), versus a regulated 13.8vdc....
Please note that to be Part 80 Certified, the radio needs to meet all of its specs, when operated over a wide range of voltages...(11.5 to 15.5vdc, for a 12-volt radio, I think)
And, most ham radios, even in the ham bands, have some transmit issues when voltages fall below 13vdc....and most / all modern hf ham radios (including the 7300) have serious transmit issues (increased transmit IMD, worsening spectral purity) when voltages fall to and below 12.5/12.6vdc....
And, when attempting to transmit in SSB mode, at these lower voltages many will start "fm'ing" (warbling) and cause serious harmful interference....
And, some/many ham rigs will just shut-down when transmit is attempted as voltages fall below these levels...
Oh, and btw, remember that while your
batteries might show 12.5vdc, when you figure even a slight 3% voltage drop to the rig, that becomes 12.1vdc at the radio....and that's bad....very bad...
(and, that doesn't take into account the possibility of having a fairly depleted
battery bank and/or a too-small
battery bank....which will be pulled further down in voltage, when attempting transmit...)
This is why so many hams trying to run HF mobile, need a "battery booster", which not only can cause RFI, but also add inefficiencies in the DC
power system (meaning you end up drawing more power from your
batteries, draining them quicker, there-by exasperating the problem...and so on and so on...)
5) Further, while you can modify your radio anyway you choose, it is
you the licensed ham operator, that is responsible for what you transmit with it....the good, the bad, and the ugly!
And,
no....even if you have a Maritime
License, you still cannot use a ham radio on the maritime bands, nor the aviation bands, etc. etc!!
6) On a side note, in the past 40 years, I have heard my share of illegally modified ham radios used on the marine bands, and with one or two exceptions, they
ALL were interfering off-channel / off-frequency....and many were causing many problems for others on-the-air...(most were oblivious)
As a quick example....recently (late 2018) I heard two sailors using ham radios on the 4mhz marine band....they weren't too strong, but the reason I heard them was that their transmit splatter was interfering with my comms....so, I spun around and found them...
They were yacking away on some non-channeled freq in the marine bands, oblivious to the interference they were causing....I listened for a couple minutes, trying to find a way to politely interrupt and let then know what their radios were doing....
During this time, one mentioned he was using an IC-706 and one was using an IC-718 (one was about 600 miles from me, and the other one was 250-300 miles from me...they were about 250-300 miles apart), and both were splattering...
I was about to say something when they decided to move up to 8mhz, 'cuz they were having trouble copying each other....and the frequency they said they were moving to was 1khz off from an HF Aviation channel used for North Atlantic
Route, trans-oceanic HF aviation!!
WHAT!!!
I thought, WTF....and quickly called them to warn them....to no avail....they'd already left for 8mhz band....and sure enough, I followed them up and there they were!
The good news is that while I could copy them both very well (much stronger here on 8mhz), they were a little too close to each other to have good comms on 8mhz, at that time....so, after a few "can't really hear you's", they signed off and disappeared...
Neither boat identified themselves with a callsign, just a boat name....so, while I spent a few evenings looking around the
internet trying to find how to get in touch with them, I was never able to do so...
And, I often wonder what they would think of some yahoo interfering with aviation (or maritime) comms, if they or one of their loved ones was on-board a plane or ship, reporting a position, or asking for assistance?
Sorry, for the digression...just wanted you to see that are real world consequences of ignoring simple-to-understand rules...
I do hope this helps answer your question?
And, since a used / discontinued Icom M-802 Marine Radio (IF-DSP-based Marine MF/HF-DSC-SSB Radiotelephone) is now about $700 to $1000....
And, the new Icom M-803 (a new SDR-based Marine MF/HF-DSC-SSB Radiotelephone) is about $2400....
https://www.icomamerica.com/en/products/marine/ssb/m803/default.aspx
http://docksideradio.com/
http://www.icomamerica.com/en/products/marine/ssb/M802/default.aspx
https://www.ebay.com/itm/40234716992...&ul_noapp=true
And, there are NO ham radios made, nor ever made, that have DSC....I think the whole discussion of the 7300 on the marine bands is kinda moot, isn't it?
Fair winds.
John
P.S. Btw, in recent years, the Temp-Comp-Cystal-Ocs (TCXO's) in most ham rigs are usually stable enough to maintain frequency within maritime spec, their actual freq accuracy is not usually within spec....way too large variations in production, and no reason to test/adjust for this...
Oh, and the marine radios have Oven-Controlled-Crystal-Osc (OCXO's), sometimes called Oven-Controlled-Master-Osc (OCMO's), and they are built and adjusted to be within spec...at all times...
I mention these in post script, because they are somewhat important to know, but these days are usually a minor issue...
P.P.S. Bob, while I always appreciate those that wish to learn and ask questions, I am a bit surprised that a fellow Extra is asking this question?