[hpsdr] Penny Whistle Bias

[Graham / KE9H]

Dave:

Yes.  If you are set up to watch the odd order (3rd, 5th, 7th) 
intermodulation products in real
time, feel free to play with the bias (Idq = quiescent drain current) 
levels.  A spectrum analyzer, or just a
Mercury looking at the output of the PennyWhistle through an attenuator 
works
well.

I found that the best IM performance came at around 350 to 425 mA Idq 
per device, at the expense
of giving up a little peak output power.

You can run the individual transistor Idq up to 1.5 amps and it won't 
hurt anything,
other than warm up the heat sink

You may also find other points where the transistors are highly 
unbalanced, you can
null one or more of the odd order products.

If you watch the heat sink temperature (say keep it below 60 degrees C.) 
and the
total drain currents below 3 Amps, you can't hurt the PA.  It has a lot 
of heat sink
for the power level.

In other words, feel free to experiment.

--- Graham / KE9H

==

On 12/23/2012 12:46 PM, David McQuate wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> If you do a two-tone test, you can fine-tune both R17 and R11 for 
> minimum third-order distortion products.  (Make only very small 
> adjustments!)
>
> 73,
> Dave
> WA8YWQ
>
> On 12/22/2012 4:25 PM, Graham / KE9H wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> John:
>>
>> I think you are fine.
>> You are plenty close enough.
>>
>> The quiescent PA currents will walk around about 10 percent
>> with heatsink temperature.
>>
>> --- Graham / KE9H
>>
>> ==
>>
>> On 12/22/2012 6:07 PM, John wrote:
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>>
>>> Powed my TAPR Penny Whistle kit up today for the first time. 
>>> According to the manual the PA bias should be about 20 mA. Mine is 
>>> only 8.23 mA.
>>>
>>> Is that in the normal range or should I begin looking for an 
>>> assembly error?  Both R11 and R17 adjust, but it is hard to set them 
>>> to an exact balance.
>>>
>>> My readings are:
>>>   Bias   8.23 mA
>>>   R17 set (only)  456.1 mA
>>>   R11 set 905.4 mA
>>>
>>> 73,
>>>
>>> John  WoGN
>>>
>>>
>>>
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