Re: Driving a linear with only 15 watts?

Posted by w2bvh on Mar 09, 2006; 3:32am
URL: http://elecraft.85.s1.nabble.com/Driving-a-linear-with-only-15-watts-tp387374p387376.html

Very interesting.

What IMD values would you consider "bad". "ok" and  "excellent"? As
examples, QST July '03 rates the ICOM 703 transmit 3rd order IMD at  24
db below PEP when running 10 watts. The March '06 QST shows the YAESU
FTDX9000 3rd order IMD at  35 db below PEP when running 200 watts.

24 db below 10 watts is 40 mW +/-, a small but still respectable qrp
signal that's rf "junk".
24 db below 200 watts would be 1 watt +/- !

Is there an FCC mandated 3rd order IMD requirement?

Inquiring minds (at least mine) want to know ;-)

73,
Lenny W2BVH

Charles Greene wrote:

> Darwin,
>
> I have a linear that has about 1000 watts output when driven with
> approx. 60 watts in class AB2 for CW and a little more when operating
> class AB1 for SSB.  It's an old Hallicrafter HT33A with a PL172
> pentode amplifier tube.  I tried it using my K2/100 on PSK31 with 20
> watts average power from the K2/100.  The amp put out 400 watts ave
> power.  The IMD coming out of the amp was identical to the IMD of the
> K2/100 without the amp, indicating no more distortion was added by the
> amp.  I don't expect you to hunt for a HT33A, but the principles are
> the same.  The efficiency is lower because of the idling power, but
> since it is all coming out of the power line, who cares?
>
> 73,  Chas W1CG
>
>
>
> At 11:13 AM 3/8/2006, Darwin, Keith wrote:
>
>> Since a linear amp is supposed to be "linear", is there any reason that
>> you have to run 65 to 100 watts into one?  What if you used a linear
>> designed for 65 watt drive and only gave it 15 watts?  Does the spectral
>> purity change?  Does the efficiency drop?  Does the linearity degrade?
>>
>> - Keith KD1E -
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