[hpsdr] More PS results on 6M with LDMOS

[Mike Seguin]

Howdy all,

I'm continuing to have a blast with the Pure Signal software. I finished 
off a driver amp to boost the output of my bare Hermes to be able to 
drive my LDMOS 6M kW amp harder.

The first issue I ran into was the less than desirable bias circuit in 
the amp. I ended up adding a regulated active circuit that performed 
much better.

Here is a shot of the Hermes into the driver amp without Pure Signal. 
Not as good as I'd like....

http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/driver_noPS.PNG

Clearly not the performance I had hoped for. (but what did I expect for 
a $35 kit...)

Here's it is with Pure Signal engaged:

http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/driver_withPS.PNG

Next, I drove it into the LDMOS amp and set it at the same 300 watt 
average level (600 PEP) that I used for the tests a few days ago.

Here it is without Pure Signal engaged:

http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/driver_amp300WnoPS.PNG

And finally with Pure Signal:

http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/driver_amp300WPS.PNG

Overall, results very similar to the tests without the driver. IMD 
levels were ~ -58 dBc (so do I use the ARRL method and add 6 dB for -64? 
<grin>)

I did a bit of testing utilizing the "amplifier delay" setting to see 
what effect it might have because I now had multiple stages cascaded. 
Nothing conclusive to report at this time. I did see changes as the 
delay approached 1000-1500 ns. It did seems to lower the products 
further out, but not significantly so. I need to do more testing.

At this point, I'd like to find a better/cleaner driver, but I'm not 
sure it will improve things much at this power level.

Next testing will be closer to the kW PEP level.

Finally for those that love messy benches, here's everything laid out 
for testing. From left to right, Hermes, Driver amp, LDMOS amp, 
Wattmeter, Bird sniffer. Next to the headset is the Cherokee 50 volt 
supply I use for testing all my LDMOS stuff.

http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/TheBench.JPG

Mike

-- 

73,
Mike, N1JEZ
"A closed mouth gathers no feet"


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