Radio WC6W wrote:
>
>Hi Everyone,
> I've had a breadboard of a digital (PIC microprocessor + a CD player
>DAC) low distortion Two-Tone Generator running for a while and I've
>gotten to the point of finishing it up and putting it in a box.
>
> I was wondering if anyone knows if there is any rationale to adding
>some extra frequencies beyond a couple of (FCC) standard two tone pairs;
>though "feature creeping" this device to the point of adding rotary
>digital encoders & LED readouts, or similar, is not part of the plan!
>
> Oh, and before anyone suggests FSK combinations, please note that
>their are some clock & software constraints that restrict the output
>frequencies to 100 Hz multiples.
>
That sounds like a great idea, especially for those of us who don't have
facilities for a two-signal test using separate CW transmitters.
A number of people have suggested "three-tone" testing, but I wonder if
that is totally appropriate to our needs.
For linearity testing we are really only interested in speech, and the
main question is how the power supplies (grid and screen voltages) hold
up under the pulsed conditions of speech modulation. A third tone of say
100Hz is hardly going to exercise the power supplies any more than a
two-tone test. The pulse rate needs to be a lot lower than that.
So, I'd suggest an option for envelope modulation of *both* tones
simultaneously, at a selectable rate from 1Hz (slow word speed) up to
say 100Hz. In the deluxe model this rate could even be sweepable, or
variable in steps.
The people who insist that testing should be done using two separate
transmitters are correct in principle, but here's an idea that might
suit everybody: if the modulated single tones are output separately from
the left and right stereo channels of the CD DAC, then they can each be
fed to a separate transmitter if available, or combined externally for
use with a single transmitter.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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