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Author Topic: Mobile hf linear amplifer power supply  (Read 270 times)

WB5OXQ

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Mobile hf linear amplifer power supply
« on: April 03, 2023, 10:04:17 AM »

I am using a RM Italy HLA 300+ amplifier mobile and it works well and I get great signal reports most of the time. This model does have filters for each band automatically switched. My question would a stiffening capacitor on the amplifier power input improve peak power.  The voltage at the amplifier would be 14.1 volts but drops to 13 volts on ssb voice peaks.  4 gage wire direct to the battery powers the Ft891 and the amplifier.  My antenna is a Tarheel 75A with a 30 inch rod and a capacity hat on top.  This works better and uses less of the coil on any band compared with the 6' whip.
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KD6VXI

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Re: Mobile hf linear amplifer power supply
« Reply #1 on: April 03, 2023, 10:11:40 AM »

I am using a RM Italy HLA 300+ amplifier mobile and it works well and I get great signal reports most of the time. This model does have filters for each band automatically switched. My question would a stiffening capacitor on the amplifier power input improve peak power.  The voltage at the amplifier would be 14.1 volts but drops to 13 volts on ssb voice peaks.  4 gage wire direct to the battery powers the Ft891 and the amplifier.  My antenna is a Tarheel 75A with a 30 inch rod and a capacity hat on top.  This works better and uses less of the coil on any band compared with the 6' whip.

Disclaimer:  I have, and can, operate legal limit mobile.  I've also set up mobiles bigger.

You need to find out what the voltage is at the alternator.

You need to find out what type of charging system your car has.  Depending on the vehicle charging system you may or may not want to run a beefed up alternator wire.

Case in point.  My old 77 GMC 4x4.  Had a #10 wire from the alternator to the battery.  I would drop serious voltage anything over 100 watts.

Changed that one wire out and added a wire from the negative terminal of the battery to the body and frame, and one to the alternator mount.

Solid 13.8 volts, keyed down.  14.4ish key up (it would run near 14 volts constant without the station running).  That was a 4 x 2879 amplifier and IIRC a 70A alternator (or 65 maybe????).

OTOH, 16 x 2879s, 2 x 165A leece neville alternators, a deep cycle and a standard car battery run just fine at 14.4 volts, key down.

My point is, if the voltage is dropping at the battery, then nothing you do at the amplifier is going to help.  If the vehicle electric system isn't up to the task of your amplifier (if it's doing 300 watts, it's pulling 600, that's 50ish amps peak, itself) and if the alternator isn't up to the task, if the wiring from the alternator to the battery group isn't good enough.... Etc.

Find the voltage drop at the car battery.  If it's dropping there, fix that problem first.  But make sure you have a charging system where you can just throw larger wire at it, because not every system is capable of doing that.

--Shane
WP2ASS / ex KD6VXI
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W9IQ

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Re: Mobile hf linear amplifer power supply
« Reply #2 on: April 03, 2023, 11:30:45 AM »

In addition to Shane's guidance, consider that a 1.1 volt drop with 40 amps of current only requires 27.5 milliohms of resistance. That isn't a lot of resistance! Fuse holders, butt connectors, lug connectors, wire resistance, etc. can all significantly contribute to this paltry resistance.

When I had to power gear in the back of my XL Yukon, I installed an SLA battery aside the gear and powered the battery off the 10 amp auxiliary power connector in the back of the Yukon. The battery very successfully supplied the current peaks yet it fully recharged from the 10 amp circuit due to my relatively low transmit duty cycle.

A bank of super-capacitors can also be used for peak shaving. But they require support circuitry to properly implement so it usually isn't a matter of simply paralleling them across the DC bus.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

WB5OXQ

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Re: Mobile hf linear amplifer power supply
« Reply #3 on: April 03, 2023, 01:18:21 PM »

I will check the voltage at the battery under full load.  I checked the current draw under full load and it was 50 amps for the radio and amplifier.  The factory alternator is rated at 140 amps since this car has the heated seats and heated rear window.  Of course that is a cold rating.  I know how to check the voltage drop on the wire, fuse holder etc.  My analog wattmeter pegs the 300 watt scale on peaks on most higher bands.  RM Italy says the amplifier has 4 transistors in the output.  I guess I should be happy and not try to get more since the antenna is rated for 250 watts.
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WA3SKN

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Re: Mobile hf linear amplifer power supply
« Reply #4 on: April 03, 2023, 04:41:30 PM »

I would get a DC clamp ammeter and check all the currents and voltages... there is no need to blow an electrical system just for a radio.  "better safe than sorry"!

-Mike.
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KC0W

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Re: Mobile hf linear amplifer power supply
« Reply #5 on: April 03, 2023, 06:06:56 PM »

 Using a Kenwood TS-480HX would be much simpler. The difference on the receiving end between 200 Watts & 300 Watts is nothing. In fact the difference between 100 Watts & 300 Watts is practically nothing as well. Running 300 Watts seems like a lot of work/expense for very limited gains to me...........Oh well, to each their own. 

                                                                               Tom KH0/KC0W
                                                                                   KH0W.com  
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W9IQ

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Re: Mobile hf linear amplifer power supply
« Reply #6 on: April 03, 2023, 06:58:35 PM »

The issue is SNR. Every dB counts when SNR is low.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KD6VXI

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Re: Mobile hf linear amplifer power supply
« Reply #7 on: Yesterday at 03:15:03 AM »

I think the issue is more the OP has this equipment, and not a 480.

Where I going to do it all over, I'd seriously look at the 480 myself.

--Shane
WP2ASS / ex KD6VXI
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