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Old 07-23-2008, 06:24 AM
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Default Request for advice....


Ok, here's the story.
I have an old COBRA 139 which works excellantly on it's own. with a stock mic. or with my cheap power mic. Great radio for local xmit and rec.
Here's what I'm trying to accomplish.
I picked up a PALOMAR TX100 Broad Band 3-30MHz Bi-Linear Amp, hooked it up to a PYRAMD PS-3KX power supply (Fully Regulated, 115VAC, 60Hz, Output: 13.8VDC 2.5 AMP Constant, 3AMP Surge) for in house use. I also am using a Radio Shack SWR/Power Meter, going out to a home brew 8'8" dipole, built to spec. ("I've established 2:1 SWR) The Palomar, lights up and when I dead key, reads 150W PEP on the meter (AM) and of course fluctuates according to voice on SSB. So the boost is there at the meter, however, people receiving me say that my voice sounds muffled. So, I installed a PARA DYNAMICS PC1089 LOW PASS FILTER, thinking that would help but I still have a problem.
Does the AC vs DC situation cause the interfereance? Should I use an antenna tuner? Is the COBRA's output sufficient for the Bi-Linear to function properly? I have all heavy coax jumpers between the radio, the amp, the filter and the meter, with 50ohm going out to the antenna.
Here's the line-up: Radio>Amp.>Filter>Meter>Antenna.
I am not a formally trained tech., so if I seem a little dense with my knowledge or lack of it, you'll know why and perhaps be kind enough to assist me. I know that there are many variables when doing this sort of set-up.

Mike


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Old 07-23-2008, 07:27 AM
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I'd think your power supply is a little on the light side: 2.5 amps isn't going to do much for a 100 watt amplifier for very long.

Probably make your transmitted signal sound strange also - muffled, possibly FMing. Get a decent-sized power supply and try that.
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Old 07-23-2008, 07:55 AM
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Default Thanks,...any other input?

Hey, thanks! I thought that might be a factor, I'll give it a shot.

Mike

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Old 07-23-2008, 08:01 AM
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Would using a battery work for now?

Mike

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Old 07-23-2008, 08:56 AM
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If you're talking about an automotive battery, it'd probably work fine. Your power supply is grossly too small. Divide 100 watts by 12 volts and you get 8.3 amps. Since most solid state amplifiers are only about 50% efficient, double that 8.3 amps. A power supply for your 100 watt amplifier would require at least 16 - 18 amps to run normally and more would not be a bad idea. Call it something like 20 amps minimum.
Oh, keep that battery charged.
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Old 07-23-2008, 09:13 AM
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Another bit of excellent advice, thanks!

Mike

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Old 07-23-2008, 04:17 PM
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Hey, I think using the battery did it. I replaced the power supply with a good powerful battery from a Land Rover, eliminated the low pass filter and VIOLA! The problem seems to be cleared up.
Thanks again, I joined this website just to ask for that specific advice and I got my help pronto. I now have The Worldwide Radio Forum icon on my desktop.

Mike

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Old 07-23-2008, 04:39 PM
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Remember, if you're going to continue to use the battery, you're going to figure out how to keep it charged up, especially if you get long winded or you'll be right back to the same problem. Your best solution is to find a 20amp power supply and have it fixed for good.

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amplifier, cobra 139, linear, linear amplifier, palomar, power supply, pyramid
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