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Thread: Astro Spectra 110W Trunk-mount power levels

  1. #1
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    Default Astro Spectra 110W Trunk-mount power levels

    Hello guys,

    I have received a 110W VHF trunk-mount Astro Spectra radio a few weeks ago. It was set to 120W (HI) and 95W (LO) by its previous user. I don't have a power supply to handle this, and this power level is just too much for me. I only need 10-20 watts to hit the local HAM repeaters and my HAM friends in simplex mode.

    I want to set the power levels back, but I am a little bit confused: I have read somewhere that the high power radios power level shouldn't be below cca. 80 watts. But why? I haven't found a logical and technical, fully understandable explanation about this issue.

    P.s.: I have heard that if a high power radio's power level is set too low, it can produce more heat compared to working higher power levels. Is is true? Why?

    Can you help me please?

    Thank you in advance!


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    Basic Service Manual. Page 90 details the power adjustment procedure.

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    Thank you I have the info about the HOW. I only wanted to know about the WHY? Why is it important to keep the minimum power levels above 54W in case of a 110W radio?

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    You could always start by reading the DETAILED Service Manual. Follow the forum links to get to the right download.

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    It's been noted that the PA can get flaky at lower levels. I've never encountered that issue but I keep hearing about it as well. I would think you should be safe dropping things down to the 40-50 watt levels.


    Quote Originally Posted by HA5BRG View Post
    Thank you I have the info about the HOW. I only wanted to know about the WHY? Why is it important to keep the minimum power levels above 54W in case of a 110W radio?

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    I was told by a Moto design engineer this is a general characteristic just about all Class "C" amplifiers. When you run the amp below about 1/2 it's rated power it becomes unstable and may start to "fly" or self-oscillate and produce spurious emissions. At least that was was I was told...

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    Thank you This seems legit. My trunk-mount HI PWR radio is operating at 15 watts without problems (monitored on a spectrum analyzer and a radio tester equipment).