Output Power, Does it matter??

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mjthomas59

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I've been in search of a mid-tier mobile radio for several months now and came across what i felt was a good deal on a Midland Olympian radio. Its a 50watt VHF-Hi radio and overall looks like it should do the job for me as far as features go.

However, my question is how much does the output power really matter? In terms of simplex operation, how much further could I talk with a 110watt radio vs. a 50 watt radio?? I'm planning on using a "tuned" 5/8 wave VHF antenna on my car.

I'll be primarily using this radio for use on the repeater system, which has several remote receive locations, but our patrol cars use 110watt radios so I was curious if i'll have any issues not running that much juice.

Thanks for the help!
 

zz0468

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The difference between 50 and 100 watts is 3 db. Noticeable, but only in the fringe areas.
 

SLWilson

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Won't matter...

You say you have several remote receivers. 50 watts is good for most 2 meter Amateur radio systems.

You'll find that when running simplex, you probably won't even use the 50 watt setting. Remember, you just need enough power to complete your communications successfully. No need to run a billion watts if you only need five!!!!

Steve/KB8FAR :)
 

mjthomas59

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I may have put out a little more information than I needed to get a good answer. My concerns are primarily when i'm talking simplex car to car i.e. around the repeater. When it comes to talking through the repeater the radio system has pretty good coverage when talking on a portable, however there have been plenty of times where I wished I had an in-car repeater such as a pyramid or pac-rt due to static and/or interference. We never really attempt any car to car traffic at any great range, but I was curious how much more distance I could cover based on power output.

The county I work in is rather hilly, and I understand that to some extent there are going to be places where you just can't talk or receive from. But that being said it made me a little nervous to say that i've got a 50 watt radio instead of 110 watt radio. OF course i'm sure i'm just getting worked up for nothing, but I appreciate all the expert knowledge.
 

prcguy

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I find something that disagrees with physics and maybe wx4cbh meant to say something else. A 3dB increase in transmitter power will appear as a 3dB increase in receive level no matter what type of antenna is used at either end. 4 times the power as stated below will cause a 6dB increase in receive level with the omni antenna mentioned.
prcguy
With omni directional antennas, it takes 4 times the power to make a 3db difference on the receiving end because the radiation pattern is a circle, and the trigonometric functions of the area of a circle apply to the radiated power. Bottom line is that unless you're in a place where the remote receivers are 25 miles apart, a 25 watt radio would probably do the job, so 50 watts is not going to be a handicap. The 100 watters could make a difference on simplex, but only in the fringe areas and then under specific circumstances.
 

N4DES

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Other than putting a much higher demand on your car's electrical system you won't see much of a difference between the 50 watt and 110 watt radio, especially when on the repeater system that has remote receivers.

If you do go with the 110 watt radio you might want to look to upgrade your alternator to one with a higher current rating especially if you have any other communication electronics operational at the same time.
 

af5rn

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Good point. In most vehicles, you can actually see the headlights brown out when you key up a 110 watt transmitter! :lol:

But hey, if you are out on the plains or the high desert, trying to talk with stations a county or two away, then yeah, that extra power can come in handy. Not many people are in that situation though.
 

W4KRR

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Good point. In most vehicles, you can actually see the headlights brown out when you key up a 110 watt transmitter! :lol:
I used to drive an old four cylinder Dodge K Car where I work; it was equipped with a 100 watt VHF low band radio. When you keyed the mike, the car actually slowed down! :eek:
 

mjthomas59

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I've never had any problems in the P71 Vic's with keying up on a 110watt radio, but they do come with the upgraded alternator and electrical system. I think i'll stick with the 50 watt radio and see how it goes. I"m trying to locate a 9c3 Impala that I can make my daily-driver, although so far i'm having no luck. If I can find one I might consider upgrading my radio then, but I certainly don't want to fry the alternator on my current vehicle.

Thanks for all the advice. I'm also curious about that Dodge K Car. Did it slow down because the drain on the alternator, or was it the radio waves causing drag in the atmosphere?:D
 

RKG

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I read somewhere that everytime you double the output power you gain 1/3 the distance.
Horse exhaust.

First, no such "rule" could be valid, as there are too many other factors to be considered.

As others have noted, holding all else equal, increasing a given transmitter's power by a factor of two results in an increase in the signal strength at a given receiver by 3 dB. To put this in perspect, an "S" unit on most high end communications receivers is worth about 6 dB, and the "bars" on most consumer-grade receivers is worth between twice and four times that.
 

rescuecomm

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The Crown Vic and the Impala both have larger engines and police cars tend to have at least 85 amp alternators. For the last radio buy I made for our squad, I bought three 25 watt VHF CM300 radios. Two of these are run off of 1/4 wave antennas, but they can hit the repeaters with not problem. Since we have 90% coverage in our call area on HT's, I felt that the 25 watt mobiles would be fine (and they were). A 50 watt VHF radio on a 5/8 wave antenna should be real good on talk-a-round (simplex).

Bob
 
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