With all comments in mind I have gone and tested the m57719n at a low power
setting and it seem like it has to work harder at lower power setting. (as
stated below)
So I have decided to go with another power module.
Brent
----- Original Message -----
From: "Eric Lemmon" <[EMAIL PROTECTED]>
To: <Repeater-Builder@yahoogroups.com>
Sent: Wednesday, March 23, 2005 9:24 PM
Subject: Re: [Repeater-Builder] M57719N RF power module
>
> Brent,
>
> Typical RF power amplifier modules are most efficient and produce the
> least spurious output when operated at the rated output level. The
> M57719N is rated at 14 watts on a 12.5 VDC supply, over the 142-163 MHz
> range. When you start reducing the drive or lowering the supply voltage,
> you will very likely cause the module to become unstable and its
> efficiency will plummet.
>
> A case in point: My radio club has a packet node that uses a name-brand
> mobile transceiver on the 2m side of the system. In compliance with the
> Part 97 dictum to use the minimum power necessary for communications, we
> set the power level on the 2m radio to "low," thinking that it would
> dissipate much less power at the lowest level, thereby allowing its duty
> cycle to be high. After operating flawlessly for several months, the PA
> module burned up. A replacement module cost about 80% of the cost of a
> new radio, but we felt it was worth repairing the radio. I installed the
> new module carefully and ensured that all drive parameters were correct.
> I also ran some tests to determine the efficiency of the module at each
> of its four drive levels. Surprise! It was most efficient at the
> highest (50 watts) power setting, and the module ran hotter at lower
> power levels- verified with an infrared thermal scanner. I confirmed the
> amount of heat being generated within the PA module versus the power
> being transferred to the antenna, by noting the current draw. This was
> not what I expected; I really thought that the input current would be
> more or less proportional to the output power setting, but that was not
> the case. The radio current draw at the 5 watt setting was about half of
> the current draw at the 50 watt setting. That means that the input power
> that didn't go the antenna was being wasted in the PA module, and it
> couldn't handle the heat.
>
> This looks like a fertile ground for experimentation. Moreover, it may
> not be prudent to use a 14 watt module when all you need is, say, 5
> watts. If the 14 watt module does not lend itself to efficient power
> control, then it may be a good idea to install a 5 watt module. You
> might also contact Mitsubishi engineering for guidance on controlling the
> power of their products.
>
> 73, Eric Lemmon WB6FLY
>
> 73, Eric Lemmon WB6FLY
>
> Brent wrote:
>
> > Anybody have any suggestions on varing the power on the M57719N Power
> > Module?
> >
> > Would it be best to limit the rf input?
> >
> > Would it be ok to lower the vcc on the module?
> >
> > which would be the best approach?
> > Brent
> >
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