Bob,
I am using the Freescale 300 W part. The part number is MRFE6VP6300H.
I will probably not build this into an amplifier. I have two home brew
solid state amplifiers, one at a kilowatt and one at 600 watts. You can
see details at http://www.tomthompson.com Both of those amps are
promoted by Communications Concepts and are Helge Granberg designs. The
transistors were so expensive that I did not feel comfortable really
playing around with them. When the LDMOS transistors came out, the
ruggedness and price were right for experimentation. I built a test jig
on a copper spreader and aluminum heat sink with a good fan. The traces
on the PC board are made with copper tape, so I can change the circuit
easily. I have thermistors mounted on the transistor flange, the copper
spreader and the heat sink so I can see what the thermal resistance is
between each interface. The bias is easily adjusted so I can easily
bias the transistors between Class B and Class A. My Vdd supply is also
adjustable so I can change the output impedance of the amp and look at
various efficiencies. You get the idea...it is just a learning platform.
73, Tom W0IVJ
On 5/5/2012 11:33 PM, Bob Henderson wrote:
> OK Tom. Thanks. It looks pretty good when operating at the 100W level.
>
> Out of interest, which Freescale device are you using and at what power
> level do you intend to operate the finished amp?
>
> 73 Bob, 5B4AGN
>
> On 5 May 2012 15:30, Tom Thompson<tlthompson@qwest.net> wrote:
>
>> Bob,
>>
>> Vdd was fed in at the U point on the brass tube, single turn, point. If I
>> switch back to that transformer, I'll try the bifilar choke feed and
>> report. I did some IMD measurements this morning. I fed the amp with two
>> Norcal 40 QRP transceivers on 40 m. The input IMD due to the combiner
>> isolation was -44 dBt where dBt means below one of the two tone peaks
>> instead of the carrier which if present would be 6 dB higher. The
>> contribution from the input IMD is given by B = 20Log(1+10^(-A/20)) where A
>> is difference in dB between the input IMD and the output IMD. I measured
>> an output IMD3 of -32 dBt at 100 watts on the amp under test. That makes A
>> = 12dB therefore B = 2dB which makes IMD3 = -34dBt. IMD5 was -60dBt and
>> IMD7 was -52dBt.
>>
>> 73 Tom W0IVJ
>>
>>
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