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Author Topic: Motorola shop question  (Read 1954 times)
K0BG
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« Reply #15 on: August 11, 2009, 03:13:29 PM »

Mark and I are on opposite ends of the spectrum here.

All manufacturers, without any exceptions, recommend direct connection to the battery for radio equipment. However, there is a case to be presented wherein direct connection could place a large load on the radio wiring itself. I personally have never seen the results of such a failure, but that in itself doesn't preclude it.

The other issue is one of current draw. The battery does have a DC return line for the accessories. It's typically inadequate for current draws in excess of that drawn by the accessories. One could argue that there isn't a case where everything in the vehicle is turned on at once, but the manufacturers know that too, so they size it accordingly. For example, the accessory ground in my Ridgeline is size #6, and the main harness fuse is 120 amps, which exceeds the wire's capability. If I were to add another 20 amps, the accessory ground could fail, and we'd have the scenario mentioned above.

To direct connect or not to direct connect is a matter of choice, except in cases where a high power amp is used. In any case, adequate wire size is essential. The rule of thumb is to keep the voltage drop below .5 volts, under full or peak load as the case may be (not average load). Quite obviously, the correct fuses need to selected as well.

For more information on selection, visit my web site.

Alan, KØBG
www.k0bg.com
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CERTNEAL
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« Reply #16 on: August 11, 2009, 05:16:08 PM »

I think I will go directly to the battery, using fuses on both lines at the battery.

Those powerpoles look nice but for now I think I will go a bit more simple in that area and upgrade as I get the cash.

Can you guys recommend any good meters I may need for a two meter setup like this? Budget being a concern, the very basics are what I can afford just now but I don't want anything blowing up on me if I can help it. Also anything I may need for my antenna?

Thanks again,
Neal
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K5LXP
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« Reply #17 on: August 11, 2009, 08:20:40 PM »

Odds are you can connect the negative lead to the battery and nothing bad will happen.  But your odds are even better than that if you don't.  I have seen the effects and it ranges from radios that get hot even when they're off, to wierdness during operation, to burned up circuit boards and damage beyond repair.  All for the sake of doing it "by the book".  So I move my negative connection 6" away and mitigate the risk.  The manufacturers are betting the fault current will blow the negative fuse.  I'm betting it won't.  My evidence is empirical.

What kind of meters are we talking about?  The meter I referred to was a basic voltmeter, $3 on sale at any Harbor Freight.  As far as SWR/power meters I would only worry about that when initially testing and tuning the antenna.  Nothing should change during normal operation to require you to monitor that.  You can borrow a meter or have another local ham help you check and tune the antenna.  You could also use an antenna analyzer, which makes the job quick and easy.  If your install is good the resonant points will be very close to the cutting chart.  The NMO 150 is a durable and reliable antenna, mine's been on my truck over 20 years now.


Mark K5LXP
Albuquerque, NM
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KF5BTI
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« Reply #18 on: August 12, 2009, 05:35:50 AM »

Got a question regarding the fusing of a ground.  Do you run the risk of blowing the ground fuse and the radio then pulling its ground through the shield of the coax?
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N8ESD
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« Reply #19 on: August 16, 2009, 07:16:21 PM »

I have worked in several Radio Shops including 7yrs at a Motorola Shop. Shops can be hit or miss when it comes to installations. Keep in mind that is where most techs start there career. If you find a good shop you will be fine.

A couple of suggestions-

#1 FUSE EVERYTHING AT THE ORIGINAL POINT OF POWER SOURCE.

#2 GROMMET ANY CABLES PASSING THRU THE FIREWALL.

#3 SOLDER EVERYTHING

#4 10ga power wire sould be fine , make sure they ground to the same point as the battery ground not the battery post, also take the power feed to the main lug of the under hood fuse block not the battery terminal. If you go to the battery terminals they WILL Corode. If your want the radio to turn off and on with the key add a bosch relay connected to a switched fuse in the internal fuse block. (Little trick- after making connections under hood, spray with clear Krylon spray paint. Connections will look new for a long time)

#5 DO NOT USE THHN wire, the insulation and coating WILL NOT hold up to automotive heat. A good source for wire is a car stereo install shop or www.partexpress.com

#6 Antenna use a Antenna Specialist ASPR-7495 for 2m (can also be cut to be 3DB gain on 440) This is a wide band 1/4 with a spring. These use an NMO mount and are 24mhz wide on VHF and 80mhz on UHF, they have an extremely heavy rod. I have used them for the last 20yrs and never had one fail.

#7 If you mount your antenna on a trunk lid make sure to add a heavy duty ground strap to the lid at the hidges.


Good Luck on your install
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CERTNEAL
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« Reply #20 on: August 16, 2009, 07:37:24 PM »

Thanks again for the advice, I just got my ticket today so kinda excited about getting my radio set. Hopefully by the time I have it set I will be in the fcc database.

I got 2 fuses for negative and positive by the battery, also some split loom to help protect the 10 gauge wire I got from advanced auto. I have a 10 amp fuse on the positive side by the radio, what size should I use for the ones by the battery? It's a 50 watt radio and that's all that will be on that line.

Thanks again!
Neal
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K0BG
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« Reply #21 on: August 17, 2009, 05:11:44 AM »

If you visit my web site, and read the two Wiring articles, you'll have all the info you need to do the job correctly.

Alan, KØBG
www.k0bg.com
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N8ESD
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« Reply #22 on: August 17, 2009, 03:04:59 PM »

Typically I use a fuse twice the amperage actually required. for a 50watt VHF radio I would use a 20A on both lines.
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W0FM
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« Reply #23 on: August 28, 2009, 12:43:18 PM »

Neal,

Most commercial shops (Motorola and otherwise) have signs posted keeping customers from service bay and installation areas for insurance reasons.  See if you can find a ham at that shop (hams are usually well-represented in these shops) that can get his manager's approval for you to view the installation.  Exceptions ARE made from time-to-time.  A ham tecnician or installer at the shop would be a good place to start.  Just a hint from an "insider".

73,

Terry, WØFM
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AF6IT
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« Reply #24 on: October 07, 2009, 04:29:38 PM »

What is the purpose of sizing a fuse at twice the typical load? Protecting the fuse? I thought the purpose was to protect the radio & car's wiring. I would use the same rating as what the manufacturer specified.
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K0BG
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« Reply #25 on: October 07, 2009, 06:00:20 PM »

Stu, twice is a little too much in some cases, but not all. The rule of thumb is not to exceed 60% of the fuse rating under sustained load, especially when it's ICAS.

If you stress a fuse by subjecting it to say 80% to 90% in an ICAS load, it will eventually fail even though the fuse never saw and overload above its rating.

Fuses aren't an art, they're a science, and specific factors play into what ever service they're subjected to. I suggest you read up on the Littelfuse site for more information.

http://www.littelfuse.com  (Note, the spelling is correct).

Alan, KØBG
www.k0bg.com
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W0HC
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« Reply #26 on: October 20, 2009, 09:59:57 AM »

I never ever ever use butt splices.  I learned that when working in a radio service shop.  Using them was grounds for immediate dismissal.
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