[600MRG] New transmitting rig for 630-meters

[Pat Bunn]

WSPR does not require a linear amplifier like many digital modes. A Class D amp works fine. You need to square up the signal to feed a Class F amp . W1VD has a nice doubler circuit on his website to use to drive a    x2 input on a Class D amp .

Pat Bunn
WG2XCT

Sent from my iPhone

> On Sep 22, 2014, at 4:30 PM, sbjohnston at aol.com wrote:
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> Today I used my Delta operating impedance bridge to check the match from the L-network to the linear amp.  I could easily adjust the network to 50-j0 ohms for a 1:1 match - excellent.  But I noticed that wasn't where I was getting max antenna current - that happened with a load of about 35-j0 ohms - interesting.  That should be OK - only a 1.4:1 SWR or so - the amp doesn't get hot after a long keydown so I think it is happy, maybe even happier than if it was working into 50 ohms.  
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> The question of linearity was next...  I got my two-tone generator out and rigged it to feed one of the audio inputs of the TS-990S.  I sampled the RF with oscilloscope and spectrum analyzer.  First I checked the basic rig performance on 75 meters to confirm my test setup was legit.  The scope waveform looked perfect, but I learned my spectrum analyzer was not good enough to resolve the two tones into separate pips.  But it did allow me to see whether or not mixing products were present, and to look for harmonics and spurious
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> Then I shifted to 630 meters and used the TS-990S to drive the linear amp into the inverted-L antenna.  I sampled the RF by draping a cliplead loop spaced around the antenna wire on its way outside.  The scope display of the two-tone RF looked as expected: some flat topping if I tried to crank the drive up too far for more power output, but very little at the point I had earlier decided on the bench was the right drive level.  The spectrum analyzer showed the harmonics were more than -50 dBc down and I saw no other spurious signals. 
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> I think this new setup should work for data modes.  Wonder what would be a good frequency to try WSPR on tonight?
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> Steve WD8DAS / WH2XHY
> 
> sbjohnston at aol.com
> http://www.wd8das.net/
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>        Posted by: sbjohnston at aol.com        
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