Hi Tom,
Yes, the broadcast 50 ohm load has a very low VSWR.
Harris claims that with the 75 % RF efficiency, and only 25 % heat
generation, it lets them to use air cooling.
Individual new power supply for each module.
I will have better information in a few weeks.
73
Bruce
> ----- Original Message -----
> From: "Tom W8JI" <w8ji@w8ji.com>
> To: "Bruce" <k1fz@myfairpoint.net>; <topband@contesting.com>
> Sent: Saturday, July 07, 2012 3:58 PM
> Subject: Re: Topband: New Linear amp
>
>
>> Hi Bruce,
>>
>>> The new Harris Flexiva 10 KW FM band (not pulse) stereo transmitter is
>>> not
>>> having a heat problem with air cooling, in a reasonably small package .
>>> It
>>> has individual modules that can be hot switched.
>>
>> I'm sure Harris did a great job. The modules can be swapped while the TX
>> is
>> on, even power supply modules, which is a nice feature. But hot or live
>> swapping does not mean the modules are "hot switched", as in allowed to
>> have
>> no load while amplifying. Generally a module is designed to remove power
>> first when pulled, and apply power last when plugged in, which is nothing
>> at
>> all like some ham transmitting with an arcing tuner, or without a
>> feedline.
>>
>> You will also note Harris protects the modules, which is what everyone
>> should do. VSWR ratings in data sheet are really useless marketing hype,
>> because near full power in longer duty cycle modes, as little as a 2:1
>> VSWR
>> can blow a device out.
>>
>> My point is about Ham gear use where people are thinking they do not need
>> to
>> watch SWR or other parameters. There is little worry in a commercial
>> transmitter that runs the device at 600 watts or less per device with
>> adequate protection for SWR and thermal issues, and most likely current
>> limiting.
>>
>> We should not translate what Harris did into something with no thermal
>> protection, no SWR protection, and twice the power on the device!!
>>
>>> The Harris Salesman, Engineer, Ham, said there was already a W2 using
>>> a
>>> pair, but had a small water cooled system.
>>
>> I played with a thick copper heatsink and air cooling, but concluded it
>> was
>> too expensive, and it would be a manufacturing PITA to get the surface
>> machining flat enough in production. With 1000 watts of heat in such a
>> small
>> footprint, the surface almost has to be polished flat. The copper
>> spreader
>> would have cost about $30-40, plus the aluminum heatsink would need to be
>> reasonably flat all across the surface. I'm not even sure that would work
>> without liquid cooling.
>>
>> It makes sense hearing the W2 used liquid cooling.
>>
>> At current costs for cooling and the devices, it is better to use more
>> lower
>> power devices and spread the heat around. Especially when the devices are
>> just as reliable, have a history of good SSB IM performance, and cost
>> less
>> per watt.
>>
>> My guess is the marketing blitz and creative specs are why we find a few
>> amateur "soon to be released" products without any final specifications.
>> They probably believed a single 1200 watt device would be linear at 1200
>> watts, and would actually handle high SWR without protection. Anyone who
>> has
>> actually worked with high power RF semiconductors knows the VSWR specs
>> are
>> meaningless marketing drivel.
>>
>> Like I said, I ran a pair of MRF150's in pulsed service, in deep class C,
>> and they were safe and reliable at a kilowatt without any SWR protection,
>> other than power supply limiting. Because they worked in pulse service
>> deep
>> class C in a low-Q system at 1000 watts without worry doesn't mean 2x
>> MRF150's would work on CW at that power, or be reliable at 200 watts CW
>> without SWR and thermal protection.
>>
>> Apples and oranges.
>>
>> When the device price comes down a bit, or if they make a smaller device
>> that allows spreading the heat around, you'll probably see the Freescale
>> device in Ham gear.
>>
>> 73 Tom
>>
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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