Oops. Well, at least some of the amps listed claim to be somewhat linear.
Thanks.
Safe way is to use a stronger transmitter with a power attenuator at the output.
That looks nice. The schematic is helpful.
Nice, Thanks. Opamps for everything, makes life easy.
George H.
try using this search term
"20 meter QRP"
mark
I just bought a couple of those from Farnel/Element14 last month to upgrade the crappy 3092I dual opamp version Feeltech had used in their cute little FY6600-60M AWG to cure the sine wave distortion when driving
50 ohm loads at the 20v p-p setting (10v p-p on load in this case) when close to the 20MHz limit before it limits the output to 5v p-p.In this signal generator application (DC to 60MHz), their outputs have a
50 ohm series resistor to create a standard 50 ohm generator impedance so the resulting rms output from a "20v p-p" output becomes a mere 250mW (5v amplitude half watt peak, thus 250mW rms). Obviously, the wasteful matching resistor can be eliminated using a transformer over a 10:1 frequency range, say 5 to 50 MHz. By using a pair in bridged output, they should comfortably generate the required 2 watts output using +/- 15v supply rails.Unless someone comes up with a hack to do away with the 5v p-p limit imposed above 20MHz, a pair of THS3491s are rather an overkill solution. A pair of THS3095s would have sufficed in this case but the 3491s didn't cost much more and I didn't want to miss out in the event of a hack materialising to let me use my investment at the full 60Mz sine wave output limit. :-)
But it's got a maximum current limit of 100mA. If you short circuit it for long enough it breaks itself.. or something? (just reading the spec sheet again.)
George H.
also there is a trick using current sense feedback to use a lower physical series resistance and have the feedback raise the effective output Z up to 50 Ohms.
mark
THS3491 ?
first page says 420mA current limit and thermal shutdown protection
Yeah, read absolute maximums (table 7.) note 3. (3) Long-term continuous current for electro-migration limits. Someone mentioned this part in a previous thread. (JL maybe?) And said the current limit was really a heat thing and if you kept the supply voltage low it wasn't a problem.... but I don't know.
It would be nice if they said what 'long term' is.
George H.
That's pathetic. Top-level chip metal (aluminum-copper alloy or just copper) is good for about 1E6 A/cm**2, a fact every baby chip designer knows. How did they get that one past the design review?
Cheers
Phil Hobbs
I've never used the THS3491.
Electromigration is a bit worse at high temps but it's not primarily a thermal thing. Electrons are just knocking metal out of the way. Running at lower voltage won't help much.
Sure.. sorry. I've never used it either. probably some other chip.
George H.
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