[hpsdr] HPSDR finals

[Helmut, DC6NY]

HI,

 

Thanks Phil for clearing/rectification. At the present time the best
approach to better IMD is to use higher supply voltage (48V) and to quit
multi-stage-amp concepts. It's no problem to produce 300W PEP and more with
a single-stage push-pull configuration driven by Penny/Hermes using modern
LDMOS (gain 28 dB at HF+6m). I measured IMD -33dBc (equal -39 dB PEP, hi).

 

73, Helmut, DC6NY

 

 

Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von FRANCIS CARCIA
Gesendet: Freitag, 18. Januar 2013 02:34
An: hpsdr at lists.openhpsdr.org
Betreff: [hpsdr] HPSDR finals

 

Hi All,

I have been chasing the IMD monster for a while now. The first thing I
needed to do is adapt the MIL method of measuring IMD because that is what
you see in the RX. The 6dB gift method is a poor interface to the super
clean Penny / Hermes exciter.

Tiny transformers do not produce good IMD. Type 61 cores running at less
then 150g and 3 Oe is a good starting point.

TLT transformers work much better than the brass tube primary transformers.
I'm very close to -30dB IP3 at 300W PEP.

At 20 Watts I'm around -40dB IP3. I'm running 3 stages of push pull FETS,
MRE136, MRF148, MRF150. The first tuo stages are running class A. There is a
good chance I can eliminate the MRF136 stage because most of the time I have
15dB of pads between Hermes and the amplifier. I'm also working on a 1200
watt modified MRI amp with 4 SD2932s. The IMD still needs work but it is on
the air. Predistortion sounds very intereting. Frank WA1GFZ

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