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maxtrac voltage drop

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airboss20

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I have a maxtrac 300, 32 ch, 60 watt vhf low band (42-50mhz). When I connect it to the power supply and tx-rx it seems to work fine. But while in tx the voltage on the power supply drops to 5v from 13.8v. When I connect a 40 watt uhf of the same make, there is no voltage drop. Do I have a bad supply or radio? Anyone have advice. Oh, the power lead to the low band is a motorola origional with a 15amp blade fuse. My power supply is an astron 20amp. Any help would be appreciated.
 

datainmotion

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Is the voltage actually dropping or is the needle on the meter being interfered with? Have you checked the voltage with a multimeter when in TX?

Is it possible the low frequency is interfering with the proper operation of the power supply?
 
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kb0nly

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Does the radio still actually transmit full power? Hook up a wattmeter and check. If so then its just the meter being messed with by RF, happens more often at lowband frequencies as the meters seem to be less susceptible to higher frequencies.

Also, if your using that lowband Maxtrac out of band, for example up into 6m, the power output goes wild on most that i have converted, and they can draw a lot of amperage, but you said it has a 15 amp fuse in the cord and that didn't blow so that must not be the case either.

Sounds like a good case of RF interference to the meter. If you have an RS-20M, Astron RS-20 with the builtin meters, its a common problem, you just need to add a bypass cap across the meter to keep the RF off.
 

airboss20

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The maxtrac is within its bandsplit, and I don't think it is rf interfearance because I hooked a small 12v fan to the astron to see if it was the rf or if it was actually dropping. Low and behold the fan is knoched out when in tx.
 

airboss20

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Forgot to mention that I. Turned the tx power down using the rss. Factory was at 103 on the scale, so I dropped it to 50 and the voltage drop was not as drastic, going from 13.8 to 8.4
 

K4IHS

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If you haven't done so... take a few minutes to check all the power supply connections and wiring to make sure everything is clean and tight. You may have already done this... but check it again looking for problems and don't take what's there for granted.
 

ramal121

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Something weird is going on here! A maxtrac will not run at that low a voltage. Typical scenario for a voltage drop problem: press PTT on mic, tx current will cause voltage drop, at 10.5V or less radio shuts off then resets and powers up again with the beep, sees that PTT is pressed and it all starts again.

I also think your test measurements are tainted by RF. How close is the antenna and what is the SWR/ ref power readings?
 
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kb0nly

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Something weird is going on here! A maxtrac will not run at that low a voltage. Typical scenario for a voltage drop problem: press PTT on mic, tx current will cause voltage drop, at 10.5V or less radio shuts off then resets and powers up again with the beep, sees that PTT is pressed and it all starts again.

I also think your test measurements are tainted by RF. How close is the antenna and what is the SWR/ ref power readings?
X2...

Sounds to me like turning down the power out on the radio lessened the RF amount getting into your measurements, hence the slightly higher voltage being read.

The Maxtrac as he said will NOT run at those voltages. I know this ALL too well. I have had them shut off at 11v, but anything below 11v they will for sure reset when you tap the PTT.

You didn't mention yet how your measuring the voltage.. Internal meter, Analog VOM, Digital VOM, what?
 
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kb0nly

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Another note, i was going to say the power supply must being having trouble providing the needed current, but i don't see a Maxtrac running at 8.5v so there is more at work here.

FYI... The Astron RS-20A/M is only good for 16 amps continuous, rated for 20 amp surge. The lowband radios i have played with pulled 15-20 amps depending on where they were programmed in the band. Pulling 15 amps off a 16 amp continuous rated power supply is pretty close to its limit, do you have anything else on the power supply other than the radio when testing? If you have anything else drawing an amp or two your probably pushing the power supply too hard.

In my opinion Astron's are overpriced and under current. I gave them up years ago and went to high amperage switching power supplies. I run an Iota 55a Continuous Duty power supply. Unline the Astrons they aren't sold by their Surge or ICS rating.
 
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