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Old 30-03-2011, 19:10   #1
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Why Connect SSB Direct to House Battery?

Hello,
I am installing a ham radio on our sailboat. I am a new general class ham, which pretty much means I passed a test - I still don't feel like I know much of anything real-world.

I have read in many places that I should connect the power leads on the radio directly to the house battery, with a 30 amp fuse on both the + and the - leads.

My partner wants to have it explained, more clearly than I am able, why we are bypassing the main circuit panel. My simple understanding is that connecting the power leads directly to battery prevents RF noise from interfering with either the radio or other equipment. But I'm sure there is a more in-depth explanation. I'd also like to have some information that assures us that the radio won't run down the battery or damage it in some way if it's directly connected to it.

Can someone explain this in plain terms that a new ham (me) and a mechanical engineer (him) can understand in some depth?

BTW, the radio is a Yaesu FT600, and I will be installing a SWR meter inline on the coax cable coming from the SG-230 tuner, which will be connected via a short stretch of GTO-15 cable to the alternative backstay antennae. I will be constructing a ground from tuned radials (or maybe the KISS if I run out of time) and connecting it to the tuner.

Thanks in advance, all you radio gurus, and maybe others will learn from your answers to my question.
Cheers, Carla
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Old 30-03-2011, 20:04   #2
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Re: Why connect SSB direct to house battery?

im not a guru
pm btyfors who is
but most ssbs drew 150 watts,thats about 12-15 amps @ 12 volts.

lots of power when transmitting,will quickly draw batteris down,hence short cables and no breakers to fail/get hot......
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Old 30-03-2011, 20:07   #3
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Re: Why connect SSB direct to house battery?

The reason is simply to minimize voltage drop but there are other secondary advantages including no intermediate connectors which can also lead to voltage drop and less likelihood of stray RF loops.
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Old 30-03-2011, 20:19   #4
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Our SSB is connected directly to the battery. It does draw a lot (150 Watts= 12.5 Amps) when keyed. We use it primarily for weather nets & occasionally contacts- but short enough & mostly when underway so we don't run down the battery. We have a Xantex meter track our battery level and our house bank is 1300 amps & solar panels keep up their levels as well. We live onboard & cruise so we do have big battery bank.
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Old 30-03-2011, 20:36   #5
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Re: Why connect SSB direct to house battery?

We have a decently-sized battery bank, but are running out of lugs (they all have 3 terminals on them already). An additional question I have is this: if we run power from the battery to a bus bar near the nav station, which items can we connect to the bar in addition to the Ham? The VHF? SWR meter? SG-230 tuner? Sony stereo? Radar?

Seems like all those items could interfere w/each other if they are sharing the same bus bar and power lead to the battery, but maybe some of them play better togther than others... Any advice?
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Old 30-03-2011, 20:44   #6
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Re: Why connect SSB direct to house battery?

G'Day Carla,

The above answers nail it down ok: minimize voltage drop and reduce chances of unwanted interference being either generated by or received by your ham rig.

However, the issues of power usage miss one important and often overlooked consideration. There is seldom a reason to run your rig at it's full 100 or 150 watt power level, and there are several reasons NOT to. On Insatiable II my normal operating power for both voice communications and Pactor is between 20 and 50 watts. This level is essentially indistinguishable from full power at the receiving end, and has several good features: far less power consumption whilst transmitting, less chance of your RF getting into things on your boat, and less chance of interfering with other radio operations in nearby boats. It has become a common problem for one thoughtless operator in a crowded anchorage doing Pactor at full power and wiping out everyone else's reception. Running at reduced power reduces the area where receivers are overloaded and is not only good manners, but is mandated by the regs: you should run only the power needed to establish the contact.

Oh, if your worry was the radio running down the batteries whilst not being used, that is not an issue at all.

So, welcome to the interesting world of ham radio. Sounds like your installation will be just fine.

Cheers and 73/88 de N9GFT/VK4GFT

Jim and Ann s/v Insatiable II lying Morning Cove, NSW, Oz
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Old 30-03-2011, 21:15   #7
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Re: Why connect SSB direct to house battery?

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G'Day Carla,

The above answers nail it down ok: minimize voltage drop and reduce chances of unwanted interference being either generated by or received by your ham rig.

However, the issues of power usage miss one important and often overlooked consideration. There is seldom a reason to run your rig at it's full 100 or 150 watt power level, and there are several reasons NOT to. On Insatiable II my normal operating power for both voice communications and Pactor is between 20 and 50 watts. This level is essentially indistinguishable from full power at the receiving end, and has several good features: far less power consumption whilst transmitting, less chance of your RF getting into things on your boat, and less chance of interfering with other radio operations in nearby boats. It has become a common problem for one thoughtless operator in a crowded anchorage doing Pactor at full power and wiping out everyone else's reception. Running at reduced power reduces the area where receivers are overloaded and is not only good manners, but is mandated by the regs: you should run only the power needed to establish the contact.

Oh, if your worry was the radio running down the batteries whilst not being used, that is not an issue at all.

So, welcome to the interesting world of ham radio. Sounds like your installation will be just fine.

Cheers and 73/88 de N9GFT/VK4GFT

Jim and Ann s/v Insatiable II lying Morning Cove, NSW, Oz
hi jim thanks for your many great posts.

although we have been cruising the last 20 years and regularly listen to nets whilst on passage we never had a transmitter.

i now have an icom m700 and tuner that i will be fitting for our next adventure down to chile and argentina,from falmouth.

as far as i can see on the unit their is no power control how does one go about changing the output ? or is this somthing that the newer units are able to do?

best atoll
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Old 30-03-2011, 21:21   #8
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Re: Why connect SSB direct to house battery?

It is important to connect a SSB radio -- ham or marine -- directly to the house batteries because:

1. you thereby minimize voltage drop, using AWG6 cable for up to a 20' one-way run, or AWG4 cable for longer runs; and

2. you thereby minimize the chances of RFI getting into other instruments, and of noise from other equipment on the boat getting into the receiver. The house batteries act as a giant capacitor and help to attenuate unwanted signals.

In most installations, this is a much better solution than trying to tap off of the main breaker panel or other location.

BTW, a 150-watt marine SSB draws 30 amps on voice peaks; a 100-watt radio draws approximately 20 amps on voice peaks. However, this is only on those peaks, and only while transmitting. The average amperage used is much lower, something like 10-15 amps while actually transmitting, and 1-2 amps while receiving.

You'd have to talk a long long time to drain the average house bank.

Re: attaching other equipment to the "radio bus", I'd resist the temptation to hook up other things except: (1) the tuner; (2) a light for the SWR meter; and (3) a VHF radio.

Bill
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Old 30-03-2011, 21:31   #9
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Good comment. It is true to use the power needed for contact. We go long distance & usually alone so we use enough to get there. You also want to make sure your battery will cover you when you key up to get contact. For the connection, as a possibility, you could connect the radio direct & the rest to the bus bar. Ferrite &/or suppressors may help with reducing interference with other electronics.
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Old 30-03-2011, 21:43   #10
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I would also strongly recommend a battery voltage boost regulator to feed your ham radio a solid 14 volts even when batteries are not being charged or partially discharged. Ham radios typically do not transmit well at full power with much less than 12.5 volts, and you can get to that point pretty quickly with power cable voltage drop and a partially discharged battery. They will usually do fine at lower voltages if you run them well under their maximum power output.

"marine" radios usually do better at lower input voltages than ham gear however.
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Old 30-03-2011, 21:44   #11
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Re: Why connect SSB direct to house battery?

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Originally Posted by atoll View Post
hi jim thanks for your many great posts.

although we have been cruising the last 20 years and regularly listen to nets whilst on passage we never had a transmitter.

i now have an icom m700 and tuner that i will be fitting for our next adventure down to chile and argentina,from falmouth.

as far as i can see on the unit their is no power control how does one go about changing the output ? or is this somthing that the newer units are able to do?

best atoll
G'Day Atoll,

I'm not that familiar with the M-700, so I can't specifically answer your query. Yet, most marine SSB rigs do have at least some control over power output... perhaps "low, medium, high" sort of thing. I'd be surprised if the manual didn't say something about this.

One of the reasons I prefer ham radios on board is that they usually have much more accessible controls for such things as RF power, mike gain etc. Unfortunately, this degree of adjustability is also why they are not so easily type-accepted by regulatory bodies for Marine SSB usage!

Hope that you can find the right knob/button/whatever to easily reduce your power.

Cheers,

Jim
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Old 30-03-2011, 21:57   #12
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Re: Why connect SSB direct to house battery?

thanks for the reply jim just had a look at the manual,apart from the j3e etc and freq presets their is no gain control looks like it is a blaster..........but apparently a rock solid unit accarding to the reviews,mind you we will probably only use it as a reciever as have had good comms on the sat phone,and i guess their wont be too many cruisers following in our trail after west africa and back from cape horn till the azores on the way back
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Old 30-03-2011, 22:33   #13
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Re: Why connect SSB direct to house battery?

The Icom M700 is a very solid rig, and will serve you well. However, it does not have an adjustable output power,

Not all marine radios do. Here are some which DO NOT allow you to adjust the output power:

Icom M700
Icom M700Pro
Icom M800
Yaesu FT-600 (except you can set to half power via a switch inside the top cover)

Here are some which DO allow you to set the power out:

Icom M802
Icom M600
Icom M710
Kenwood TKM-707
Raytheon Ray-152
Furuno FS-1503

Bill
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Old 30-03-2011, 22:42   #14
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Re: Why connect SSB direct to house battery?

Quote:
Originally Posted by btrayfors View Post
The Icom M700 is a very solid rig, and will serve you well. However, it does not have an adjustable output power,

Not all marine radios do. Here are some which DO NOT allow you to adjust the output power:

Icom M700
Icom M700Pro
Icom M800
Yaesu FT-600 (except you can set to half power via a switch inside the top cover)

Here are some which DO allow you to set the power out:

Icom M802
Icom M600
Icom M710
Kenwood TKM-707
Raytheon Ray-152
Furuno FS-1503

Bill
Thanks, Bill,

Always good to hear from someone who actually knows something about the units in question!

But I wish that they did include some means of reducing power output...

73,
Jim
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Old 30-03-2011, 23:17   #15
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Re: Why connect SSB direct to house battery?

When transmitting on SSB, the RF power output is proportional to the modulation level.

Simply speaking softer or slightly away from the microphone will reduce the peak power output.

With a suppressed carrier, when there is no sound, there is no transmit power.
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