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Old 08-07-2020, 13:54   #1
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Use of ICOM M802 without Tuner for Listing watch only

Dear all,

I like to install a used M802 on my 55‘ Murray Peterson Schooner. Despite all the other „problems“ I am wondering
If it make sense to use the M802 without the AT140 powered for listing only ( to save power) and switch on the AT140 only when making transmissions or if you want to have the Antenna „tuned“ for better reception. For the DSC watch I am using an active antenna, wich have almost no power consumption
Up to my mind this could be done with a simple switch in the control cable.
I read about this in a german book about HAM vs Marine MF/HF on board. Unfortunately they only describe this with HAM radios. Up to my mind it should work out because It’s much worse to have an untuned antenna for transmitting as for receiving only. This should also make no damage to the transceiver, as long as you are not pushing the the PTT.
So any body has any experience with that?
Thank you folks!

PS:Anybody used the KISS SSB counterpoise on a woodenboat?
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Old 08-07-2020, 14:18   #2
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Re: Use of ICOM M802 without Tuner for Listing watch only

Why bother? The AT-140 really only uses a very small amount of power when tuning, which only takes a couple of seconds, less it you pre-program the tuner with your favorite frequencies. Saves you when you forget to turn the tunes on when you go and transmit.
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Old 08-07-2020, 15:11   #3
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Re: Use of ICOM M802 without Tuner for Listing watch only

Quote:
Originally Posted by greenschooner View Post
Dear all,

I like to install a used M802 on my 55‘ Murray Peterson Schooner. Despite all the other „problems“ I am wondering
If it make sense to use the M802 without the AT140 powered for listing only ( to save power) and switch on the AT140 only when making transmissions or if you want to have the Antenna „tuned“ for better reception. For the DSC watch I am using an active antenna, wich have almost no power consumption
Up to my mind this could be done with a simple switch in the control cable.
I read about this in a german book about HAM vs Marine MF/HF on board. Unfortunately they only describe this with HAM radios. Up to my mind it should work out because It’s much worse to have an untuned antenna for transmitting as for receiving only. This should also make no damage to the transceiver, as long as you are not pushing the the PTT.
So any body has any experience with that?
Thank you folks!

PS:Anybody used the KISS SSB counterpoise on a woodenboat?
You could

I don’t know the Icom but I have used an active antenna like Ramet for reception and it works well.

Naturally to transmit you would need a real ant plus tuner
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Old 08-07-2020, 15:15   #4
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Re: Use of ICOM M802 without Tuner for Listing watch only

I don’t believe it uses power except when tuning and that’s only when it first transmits, unless manually tuned?
But I also believe tuning is a transmit only function, meaning you can listen fine without tuning.
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Old 08-07-2020, 16:16   #5
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Re: Use of ICOM M802 without Tuner for Listing watch only

Quote:
Originally Posted by greenschooner View Post
If it make sense to use the M802 without the AT140 powered for listing only ( to save power) ...?
How much power do you think you might save?

Once you figure out that answer, it should be self-evident this is a frivolous concern.
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Old 09-07-2020, 06:14   #6
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Re: Use of ICOM M802 without Tuner for Listing watch only

greenschooner,

Of course, a "tuner" is not necessary for an HF receive antenna....(although technically they "can" be of some slight help, in some rare circumstances, but in the real world they are not necessary)
Bypassing a tuner to save some power is chasing your tail...and a waste of your time / effort....

BUT...
But, there are things in your post that do require some detailed answers...
So, please have a look here!




First a few facts that will help you some, and then some recommendations that will help a lot!

{Fyi, all of this is covered in the videos and in the stickies right at the top of the Marine Electronics page here...}


1) Fact: The Icom M-802 draws only 2.0 amps on receive when squelched or with volume turned down....and 2.1 amps unsquelched and with volume up....(these are actual measured current draws [at ~ 13vdc] from my three Icom M-802's and confirmed by others as well)

The AT-140 only draws measurable current when tuning....otherwise its power consumption is insignificant....and since actually tuning only takes seconds, the actual power used by the AT-140 overall is insignificant, and can be almost ignored.

So, that's about 48 A/H's per day (at 12vdc), using the M-802 24 hours a day...



2) Fact: The Icom M-802 has a built-in separate / dedicated DSC receiver that is constantly monitoring the six international GMDSS DSC Safety and Calling Frequencies (2187.5khz; 4207.5khz; 6312khz; 8414.5khz; 12577khz; 16804.5khz), for any "Safety", "Urgency", or "Distress" calls, all the time the M-802 is turned on....this is the receiver that is connected to the "DSC" antenna jack of the M-802, and as such requires its own receive-only antenna....
This is done all the time, in the background....and no indication that this is actually going on, until you receive a call!!
[assume you already know this]

An "active" antenna on-board is not usually recommended here....as all that is needed is a simple non-resonant wire antenna (vertical, horizontal, or sloping) of some significant length....approx 15' or longer....(usually longer is better....I use a 22' length of insulated rigging....some use a ~ 35' wire from a spreader....some use their whole uninsulated rig...etc. etc...)...

An "active" antenna is usually a short small, inefficient antenna with a pre-amplifier attached....and as such can increase your receiver's ambient noise levels from nearby and/or on-board RFI, and hence blocking all but the strongest radio signals from being received....

So, an "active" antenna is discouraged here....fyi, ironically "active" (although rare) can be used on commercial ships, where they usually have the room for more antennas, but as they must be GMDSS compliant they can place this antenna significantly far away from RFI sources on-board, and as such large ships can use a small "active" antenna for wefax, SITOR, or DSC receiving, but we on small boats usually cannot....



3) Fact: The M-802's main antenna (the one that the AT-140 matches to the transmitter) is used for all transmitting and receiving (except for the six international GMDSS DSC Safety and Calling Frequencies, which are only monitored on / received by the M-802's separate dedicated DSC receiver, and its own antenna)....so, whether you have the AT-140 connected or not, will have no effect on your ability to receiver any DSC "Safety", "Urgency", or "Distress" calls....




4) Fact: The M-802's "DSC Watch Mode" is misunderstood by most sailors (as this DSC Watch Mode was designed in the early 2000's, when much of the MF/HF-DSC was assumed to be used by ships calling shore stations and shore stations calling ships at sea, using duplex channels....mostly for "Routine" ship's business, to arrange for public correspondence / telephone calls, etc.)....and this is where "Routine" DSC calls were supposed to be sent, hence this is why the separate/dedicated DSC receiver only alerts you to "Safety", "Urgency", or "Distress" calls....{the "DSC Wact Mode" of course uses the "main antenna", the one that the AT-140 tunes....but all the Safety, Urgency, and Distress messages are received on the other separate, dedicated DSC receiver and its antenna...}


Although I (and some others) have reprogrammed our M-802's "DSC Watch" scanning frequencies to be simplex freqs 0.5khz up from the six int'l GMDSS DSC Safety and Calling freqs, 99.9% of all M-802's are still original / as programmed by Icom, and as such 5 of these 6 "DSC Watch" frequencies are duplex frequencies....and are all but useless to us sailors!!

So, for most sailors, the M-802's "DSC Watch" mode is useless (except that it allows access to the DSC memories, programming, etc.)


{FYI, there are many dedicated DSC frequencies set aside by the IMO/GMDSS....so I (and some others) reprogrammed our DSC Watch scanning freqs, as simplex freqs, one channel (0.5khz) above the six int'l GMDSS DSC Safety and Calling freqs....on the hopes that some would use them for some "Routine" DSC calling....but, since nobody ever wanted to run their HF radio 24 hours a day, this idea never took hold....but, if you want to play around with some friends, or if you're going to be sailing in an offshore rally, etc....you may want to do so?}


~~~~~~~~~~~~~~~~~~


Now, some recommendations:


5) Please watch these videos....and read the stickies....

HF-DSC comms
https://www.youtube.com/playlist?list=PLnN6ygtZ3h2n3z5nlv-ga2zYuPozhUXZX


Maritime HF Comms
https://www.youtube.com/playlist?list=PLnN6ygtZ3h2nPNdApNsZDo_Jk3NB_Bt1y


Offshore Weather

https://www.youtube.com/playlist?list=PLnN6ygtZ3h2mPZAx2vWzdjTJjHlChruyY


Icom M-802 Instruction Videos
https://www.youtube.com/playlist?list=PLnN6ygtZ3h2npivDjoFrC-8QKVyMb4tVr


Offshore Sailing
https://www.youtube.com/playlist?list=PLnN6ygtZ3h2nbwAGh5DKgTCj15iyl6qoY


VHF DSC
https://www.youtube.com/playlist?list=PLnN6ygtZ3h2m-IejYg7J6QugtO2epizxF


Marine SSB Stuff (how-to better use / properly-install SSB, & troubleshoot RFI, etc.)

https://www.cruisersforum.com/forums/f13/marine-ssb-stuff-how-to-better-use-properly-install-ssb-and-troubleshoot-rfi-etc-133496.html


HF-SSB Radio, Proper Installation Tips/Techniques, etc.

https://www.cruisersforum.com/forums/f13/hf-ssb-radio-proper-installation-tips-techniques-etc-198305.html




6) As for the KISS....this has been discussed way too often....and has been proven to be a waste of $$$ and does nothing that it is marketed to do!

Proven in the real world, and measured by antenna currents, as well as proven by calculation, etc....a direct sea water connection (a low-impedance direct sea water connection), is always better than any artificial counterpoise....

If that is not available, use of lifelines, toerails, pushpits, rub strakes, etc...are adequate alternatives....

If none of those are available, a low-impedance connection to an external lead keel, can also be acceptable...

If none of the above are available....then you can make your own artificial counterpoise (set of radials), for less than $5 USD (and most times, at no cost at all!) in less than 5 minutes....and this will significantly outperform the KISS!!

You can do a search here for more details....




I do hope this helps.

Fair winds.

John
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