[hpsdr] PennyWhistle - Call for Comments

[Duncan Clark]

Hi Jens,

You said on the hpsdr forum:

>4. I made the G6ALU 20W PA with RD16HHF1 Fets and parts I found in my
>treasure hoard. I get 20 watts out, but it is difficult getting 
>anything
>out on 6m . I have tried with different core types and frequency
>compensation schemes with mixed luck.
>RD15VHF1 is probably worfth a try.
>
>jens - oz1gap


Having had exactly the same problem at 6m, try the following 
modification for Steve's board which I use in my STAR's:

Change the driver and the PA to the HVF1 transistors -RF Parts, off the 
shelf.

Using 14.5V,  increase bias on the RD06's to 250mA per transistor and 
the RD15's to 750mA per transistor. Worth a couple of dB extra output 
and should also be cleaner. Could probably take the driver to 400mA each 
for Class A

Use BN61-202 cores in place of the BN43-202's for the output 
transformer. May not need to, I just had them to hand.

Change the 330pf capacitor on the input to those transformers to 150pf 
(may need to play) - will need lower for 70MHz - makes a big difference 
in output above 30MHz so it must be adjusted

As per Steve's instructions adjust the ZTX300 bypass capacitor for best 
gain at 50MHz - mine went down to 100pf.

Don't use a large 500V SM capacitor for the 2n2 output capacitor. 
Sensitive to fingers nearby in that it will take off with no drive. 
Small 5mm 1kV ceramics give no problems. This was with an unboxed board 
with lots of leads around.

I can get a clean non-compressed 15W out on 50MHz with -22dBm input and 
easily 30W out on 160m with -30dBm. The ZTX300 pre-driver gain is the 
limiting step for 4m as it really drops off. Can still get 10W out on 
70MHz but with more playing in that area I am sure one can do a lot 
better.

Regards

Duncan
-- 
Duncan Clark (G4ELJ)