Modulation impact when amplifying a DSB signal?

Wilson Lamb infomet at EMBARQMAIL.COM
Mon Feb 16 10:45:51 EST 2009

Well, that's interesting.  Why the low voltage?  Batteries??  All these
> circuits will work better at higher voltage.  5W input is 40mA and 5W 
> output will take twice that, I expect.  If you are talking PEP, then much 
> more. That's a lot for the small tubes.
> The high level balanced modulator is the way to go for DSB, avoiding the 
> amplifier problem.  I remember the 7360 tube which was made for this, but 
> don't think it went to 5W...look it up.  There used to be lots of 7360 
> circuits in the Handbook and QST.  With the full QST archive on the ARRL 
> website, reference work has been facilitated dramatically!  If filament 
> power is not a big problem, any two RF  tubes would do.  6AQ5s are cheaper 
> than dirt and would do it easily.  Going farther back, a pair of 6AG7s 
> would be great, in octal sockets.
> I have circuitry froom the 30s doing it with a pair of 6V6s, probably fine 
> at least to 40 meters. You could keep the filaments of the TX off most of 
> the time, just turning on during contacts.
> To go fully retro, you could find an old Vibrapack for the HV, or build 
> your own.  Vibrators are available at many hamfests and on many websites. 
> Who knows, you might get to 10W, which would be a pretty useful SSB 
> signal!
> But I'd encourage you to bite the bullet and go SSB, maybe learn some 
> circuitry along the way.  When I was in grad school, I built a 50KHz 
> acoustic command link for use in the sea.  It was SSB, phasing method, and 
> worked great.  I could go thousands of feet in water, never got to max 
> range, and it worked fine as RF around the lab.  I tested it by running an 
> FM radio through it and casual listeners coming by the lab didn't notice I 
> wasn't listening to the usual radio.
> The phasing was done with the Dome network, as used by B&W in their 
> commercial product.  I simply copied their circuit and used opamps instead 
> of tubes.  My carrier phase shift was done with two ten cent transistors 
> and simple RC lead/lag elements.  I could give you the schematics for all 
> this. I may even have a set of the RC components for the network.  The 
> idea of produciing a nice SSB signal with a couple of 9V batteries is 
> pretty appealing!  So is the idea of a whole rig running on a little gel 
> cell or plugging into any car dashboard!  I'm about to embark on a qrp 
> project myself, but probably CW only for now...backpacking.
> Please tell us more about your objectives.
> 73,
> Wilson

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